1
|
Steinholtz L, Thörnblom E, Bodén R, Wall A, Axelson HW, Lubberink M, Fällmar D, Persson J. GABAA Receptor Availability in Relation to Cortical Excitability in Depressed and Healthy: A Positron Emission Tomography and Transcranial Magnetic Stimulation Study. Neuropsychobiology 2023; 83:17-27. [PMID: 38151012 PMCID: PMC10871686 DOI: 10.1159/000535512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 11/13/2023] [Indexed: 12/29/2023]
Abstract
INTRODUCTION Gamma-aminobutyric acid (GABA) deficiency is suggested in depressive disorders, along with alterations in cortical excitability. However, whether these excitability changes are related to GABAA receptor availability is largely unknown. Our aim was to assess the correlation between these measures in depressed patients and healthy controls. METHODS Twenty-eight patients with a major depressive episode, measured before and after participating in a clinical trial with repetitive transcranial magnetic stimulation (TMS), and 15 controls underwent [11C]flumazenil positron emission tomography to assess GABAA receptor availability and paired pulse TMS (ppTMS) to evaluate cortical excitability. Both whole-brain voxel-wise GABAA receptor availability and mean values from left hand motor cortex and left paracentral lobule were correlated to the ppTMS outcomes: short-interval intracortical inhibition reflecting GABAA receptor activity, long-interval intracortical inhibition representing GABAB receptor activity, intracortical facilitation reflecting glutamate N-methyl-D-aspartate-receptor activity, as well as the resting motor threshold (rMT), considered a global measure of corticospinal excitability. RESULTS No significant differences in baseline GABAA receptor availability or cortical excitability were found between patients and controls. Additionally, no correlations were observed between baseline measurements of GABAA receptor availability and TMS outcomes. Changes in GABAA receptor availability in the hand motor cortex, between pre- and post-assessments, were inversely related to pre-post changes in hand rMT. CONCLUSION We found that a change in GABAA receptor availability was inversely related to a change in rMT, suggesting a link between GABA deficiency and increased rMT previously observed in depressive episodes. The results highlight the complex mechanisms governing cortical excitability measures and offer new insight into their properties during the depressive state.
Collapse
Affiliation(s)
- Linda Steinholtz
- Department of Medical Sciences, Psychiatry, Uppsala University, Uppsala, Sweden
| | - Elin Thörnblom
- Department of Medical Sciences, Psychiatry, Uppsala University, Uppsala, Sweden
| | - Robert Bodén
- Department of Medical Sciences, Psychiatry, Uppsala University, Uppsala, Sweden
| | - Anders Wall
- PET-Centre, Uppsala University Hospital, Uppsala, Sweden
- Department of Surgical Sciences, Nuclear medicine and PET, Uppsala University, Uppsala, Sweden
| | - Hans W. Axelson
- Department of Medical Sciences, Clinical neurophysiology, Uppsala University, Uppsala, Sweden
| | - Mark Lubberink
- Department of Surgical Sciences, Nuclear medicine and PET, Uppsala University, Uppsala, Sweden
- Department of Medical Physics, Uppsala University Hospital, Uppsala, Sweden
| | - David Fällmar
- Department of Surgical Sciences, Neuroradiology, Uppsala University, Uppsala, Sweden
| | - Jonas Persson
- Department of Medical Sciences, Psychiatry, Uppsala University, Uppsala, Sweden
| |
Collapse
|
2
|
Kasaragod VB, Malinauskas T, Wahid AA, Lengyel J, Knoflach F, Hardwick SW, Jones CF, Chen WN, Lucas X, El Omari K, Chirgadze DY, Aricescu AR, Cecere G, Hernandez MC, Miller PS. The molecular basis of drug selectivity for α5 subunit-containing GABA A receptors. Nat Struct Mol Biol 2023; 30:1936-1946. [PMID: 37903907 PMCID: PMC10716045 DOI: 10.1038/s41594-023-01133-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 09/20/2023] [Indexed: 11/01/2023]
Abstract
α5 subunit-containing γ-aminobutyric acid type A (GABAA) receptors represent a promising drug target for neurological and neuropsychiatric disorders. Altered expression and function contributes to neurodevelopmental disorders such as Dup15q and Angelman syndromes, developmental epilepsy and autism. Effective drug action without side effects is dependent on both α5-subtype selectivity and the strength of the positive or negative allosteric modulation (PAM or NAM). Here we solve structures of drugs bound to the α5 subunit. These define the molecular basis of binding and α5 selectivity of the β-carboline, methyl 6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM), type II benzodiazepine NAMs, and a series of isoxazole NAMs and PAMs. For the isoxazole series, each molecule appears as an 'upper' and 'lower' moiety in the pocket. Structural data and radioligand binding data reveal a positional displacement of the upper moiety containing the isoxazole between the NAMs and PAMs. Using a hybrid molecule we directly measure the functional contribution of the upper moiety to NAM versus PAM activity. Overall, these structures provide a framework by which to understand distinct modulator binding modes and their basis of α5-subtype selectivity, appreciate structure-activity relationships, and empower future structure-based drug design campaigns.
Collapse
Affiliation(s)
- Vikram Babu Kasaragod
- Department of Pharmacology, University of Cambridge, Cambridge, UK
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
| | - Tomas Malinauskas
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Ayla A Wahid
- Department of Pharmacology, University of Cambridge, Cambridge, UK
| | - Judith Lengyel
- Roche Pharma Research and Early Development, Neuroscience and Rare Diseases, Roche Innovation Center, Basel, Switzerland
| | - Frederic Knoflach
- Roche Pharma Research and Early Development, Neuroscience and Rare Diseases, Roche Innovation Center, Basel, Switzerland
| | - Steven W Hardwick
- CryoEM Facility, Department of Biochemistry, University of Cambridge, Cambridge, UK
| | | | - Wan-Na Chen
- Department of Pharmacology, University of Cambridge, Cambridge, UK
| | - Xavier Lucas
- Roche Pharma Research and Early Development, Therapeutic Modalities, Roche Innovation Center, Basel, Switzerland
| | - Kamel El Omari
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK
| | - Dimitri Y Chirgadze
- CryoEM Facility, Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - A Radu Aricescu
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
| | - Giuseppe Cecere
- Roche Pharma Research and Early Development, Therapeutic Modalities, Roche Innovation Center, Basel, Switzerland
| | - Maria-Clemencia Hernandez
- Roche Pharma Research and Early Development, Neuroscience and Rare Diseases, Roche Innovation Center, Basel, Switzerland.
| | - Paul S Miller
- Department of Pharmacology, University of Cambridge, Cambridge, UK.
| |
Collapse
|
3
|
Handforth A, Singh RP, Treven M, Ernst M. Search for Novel Therapies for Essential Tremor Based on Positive Modulation of α6-Containing GABA A Receptors. Tremor Other Hyperkinet Mov (N Y) 2023; 13:39. [PMID: 37900009 PMCID: PMC10607569 DOI: 10.5334/tohm.796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Accepted: 10/10/2023] [Indexed: 10/31/2023] Open
Abstract
Background Prior work using GABAA receptor subunit knockouts and the harmaline model has indicated that low-dose alcohol, gaboxadol, and ganaxolone suppress tremor via α6βδ GABAA receptors. This suggests that drugs specifically enhancing the action of α6βδ or α6βγ2 GABAA receptors, both predominantly expressed on cerebellar granule cells, would be effective against tremor. We thus examined three drugs described by in vitro studies as selective α6βδ (ketamine) or α6βγ2 (Compound 6, flumazenil) receptor modulators. Methods In the first step of evaluation, the maximal dose was sought at which 6/6 mice pass straight wire testing, a sensitive test for psychomotor impairment. Only non-impairing doses were used to evaluate for anti-tremor efficacy in the harmaline model, which was assessed in wildtype and α6 subunit knockout littermates. Results Ketamine, in maximally tolerated doses of 2.0 and 3.5 mg/kg had minimal effect on harmaline tremor in both genotypes. Compound 6, at well-tolerated doses of 1-10 mg/kg, effectively suppressed tremor in both genotypes. Flumazenil suppressed tremor in wildtype mice at doses (0.015-0.05 mg/kg) far lower than those causing straight wire impairment, and did not suppress tremor in α6 knockout mice. Discussion Modulators of α6βδ and α6βγ2 GABAA receptors warrant attention for novel therapies as they are anticipated to be effective and well-tolerated. Ketamine likely failed to attain α6βδ-active levels. Compound 6 is an attractive candidate, but further study is needed to clarify its mechanism of action. The flumazenil results provide proof of principle that targeting α6βγ2 receptors represents a worthy strategy for developing essential tremor therapies. Highlights We tested for harmaline tremor suppression drugs previously described as in vitro α6βδ or α6βγ2 GABAA receptor-selective modulators. Well-tolerated flumazenil doses suppressed tremor in α6-wildtype but not α6-knockout mice. Compound 6 and ketamine failed to display this profile, likely from off-target effects. Selective α6 modulators hold promise as tremor therapy.
Collapse
Affiliation(s)
- Adrian Handforth
- Neurology Service, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
| | - Ram P. Singh
- Research Service, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
| | - Marco Treven
- Department of Neurology, Medical Neuroscience Cluster, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
4
|
Sun C, Zhu H, Clark S, Gouaux E. Cryo-EM structures reveal native GABA A receptor assemblies and pharmacology. Nature 2023; 622:195-201. [PMID: 37730991 PMCID: PMC10550821 DOI: 10.1038/s41586-023-06556-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Accepted: 08/21/2023] [Indexed: 09/22/2023]
Abstract
Type A γ-aminobutyric acid receptors (GABAARs) are the principal inhibitory receptors in the brain and the target of a wide range of clinical agents, including anaesthetics, sedatives, hypnotics and antidepressants1-3. However, our understanding of GABAAR pharmacology has been hindered by the vast number of pentameric assemblies that can be derived from 19 different subunits4 and the lack of structural knowledge of clinically relevant receptors. Here, we isolate native murine GABAAR assemblies containing the widely expressed α1 subunit and elucidate their structures in complex with drugs used to treat insomnia (zolpidem (ZOL) and flurazepam) and postpartum depression (the neurosteroid allopregnanolone (APG)). Using cryo-electron microscopy (cryo-EM) analysis and single-molecule photobleaching experiments, we uncover three major structural populations in the brain: the canonical α1β2γ2 receptor containing two α1 subunits, and two assemblies containing one α1 and either an α2 or α3 subunit, in which the single α1-containing receptors feature a more compact arrangement between the transmembrane and extracellular domains. Interestingly, APG is bound at the transmembrane α/β subunit interface, even when not added to the sample, revealing an important role for endogenous neurosteroids in modulating native GABAARs. Together with structurally engaged lipids, neurosteroids produce global conformational changes throughout the receptor that modify the ion channel pore and the binding sites for GABA and insomnia medications. Our data reveal the major α1-containing GABAAR assemblies, bound with endogenous neurosteroid, thus defining a structural landscape from which subtype-specific drugs can be developed.
Collapse
Affiliation(s)
- Chang Sun
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Hongtao Zhu
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Sarah Clark
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR, USA
| | - Eric Gouaux
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA.
- Howard Hughes Medical Institute, Oregon Health and Science University, Portland, OR, USA.
| |
Collapse
|
5
|
Sun C, Zhu H, Clark S, Gouaux E. Regulated assembly and neurosteroid modulation constrain GABA A receptor pharmacology in vivo. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.16.528867. [PMID: 36824901 PMCID: PMC9949137 DOI: 10.1101/2023.02.16.528867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Type A GABA receptors (GABA A Rs) are the principal inhibitory receptors in the brain and the target of a wide range of clinical agents, including anesthetics, sedatives, hypnotics, and antidepressants. However, our understanding of GABA A R pharmacology has been hindered by the vast number of pentameric assemblies that can be derived from a total 19 different subunits and the lack of structural knowledge of clinically relevant receptors. Here, we isolate native murine GABA A R assemblies containing the widely expressed α 1 subunit, and elucidate their structures in complex with drugs used to treat insomnia (zolpidem and flurazepam) and postpartum depression (the neurosteroid allopregnanolone). Using cryo-EM analysis and single-molecule photobleaching experiments, we uncover only three structural populations in the brain: the canonical α 1 β2γ 2 receptor containing two α 1 subunits and two unanticipated assemblies containing one α 1 and either an α 2 , α 3 or α 5 subunit. Both of the noncanonical assemblies feature a more compact arrangement between the transmembrane and extracellular domains. Interestingly, allopregnanolone is bound at the transmembrane α/β subunit interface, even when not added to the sample, revealing an important role for endogenous neurosteroids in modulating native GABA A Rs. Together with structurally engaged lipids, neurosteroids produce global conformational changes throughout the receptor that modify both the pore diameter and binding environments for GABA and insomnia medications. Together, our data reveal that GABA A R assembly is a strictly regulated process that yields a small number of structurally distinct complexes, defining a structural landscape from which subtype-specific drugs can be developed.
Collapse
|
6
|
Sieghart W, Chiou LC, Ernst M, Fabjan J, M Savić M, Lee MT. α6-Containing GABA A Receptors: Functional Roles and Therapeutic Potentials. Pharmacol Rev 2022; 74:238-270. [PMID: 35017178 DOI: 10.1124/pharmrev.121.000293] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 09/08/2021] [Indexed: 12/11/2022] Open
Abstract
GABAA receptors containing the α6 subunit are highly expressed in cerebellar granule cells and less abundantly in many other neuronal and peripheral tissues. Here, we for the first time summarize their importance for the functions of the cerebellum and the nervous system. The cerebellum is not only involved in motor control but also in cognitive, emotional, and social behaviors. α6βγ2 GABAA receptors located at cerebellar Golgi cell/granule cell synapses enhance the precision of inputs required for cerebellar timing of motor activity and are thus involved in cognitive processing and adequate responses to our environment. Extrasynaptic α6βδ GABAA receptors regulate the amount of information entering the cerebellum by their tonic inhibition of granule cells, and their optimal functioning enhances input filtering or contrast. The complex roles of the cerebellum in multiple brain functions can be compromised by genetic or neurodevelopmental causes that lead to a hypofunction of cerebellar α6-containing GABAA receptors. Animal models mimicking neuropsychiatric phenotypes suggest that compounds selectively activating or positively modulating cerebellar α6-containing GABAA receptors can alleviate essential tremor and motor disturbances in Angelman and Down syndrome as well as impaired prepulse inhibition in neuropsychiatric disorders and reduce migraine and trigeminal-related pain via α6-containing GABAA receptors in trigeminal ganglia. Genetic studies in humans suggest an association of the human GABAA receptor α6 subunit gene with stress-associated disorders. Animal studies support this conclusion. Neuroimaging and post-mortem studies in humans further support an involvement of α6-containing GABAA receptors in various neuropsychiatric disorders, pointing to a broad therapeutic potential of drugs modulating α6-containing GABAA receptors. SIGNIFICANCE STATEMENT: α6-Containing GABAA receptors are abundantly expressed in cerebellar granule cells, but their pathophysiological roles are widely unknown, and they are thus out of the mainstream of GABAA receptor research. Anatomical and electrophysiological evidence indicates that these receptors have a crucial function in neuronal circuits of the cerebellum and the nervous system, and experimental, genetic, post-mortem, and pharmacological studies indicate that selective modulation of these receptors offers therapeutic prospects for a variety of neuropsychiatric disorders and for stress and its consequences.
Collapse
Affiliation(s)
- Werner Sieghart
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Lih-Chu Chiou
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Margot Ernst
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Jure Fabjan
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Miroslav M Savić
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| | - Ming Tatt Lee
- Center for Brain Research, Department of Molecular Neurosciences (W.S.), and Center for Brain Research, Department of Pathobiology of the Nervous System (M.E., J.F.), Medical University Vienna, Vienna, Austria; Graduate Institute of Pharmacology (L.-C.C., M.T.L.), and Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan (L.-C.C., M.T.L.); Faculty of Pharmacy, Department of Pharmacology, University of Belgrade, Belgrade, Serbia (M.M.S.); Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, Malaysia (M.T.L.); and Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan (L.-C.C.)
| |
Collapse
|
7
|
Manzo MA, Wang DS, Li WW, Pinguelo A, Popa MO, Khodaei S, Atack JR, Ross RA, Orser BA. Inhibition of a tonic inhibitory conductance in mouse hippocampal neurones by negative allosteric modulators of α5 subunit-containing γ-aminobutyric acid type A receptors: implications for treating cognitive deficits. Br J Anaesth 2020; 126:674-683. [PMID: 33388140 DOI: 10.1016/j.bja.2020.11.032] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Revised: 10/30/2020] [Accepted: 11/16/2020] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Multiple cognitive and psychiatric disorders are associated with an increased tonic inhibitory conductance that is generated by α5 subunit-containing γ-aminobutyric acid type A (α5 GABAA) receptors. Negative allosteric modulators that inhibit α5 GABAA receptors (α5-NAMs) are being developed as treatments for these disorders. The effects of α5-NAMs have been studied on recombinant GABAA receptors expressed in non-neuronal cells; however, no study has compared drug effects on the tonic conductance generated by native GABAA receptors in neurones, which was the goal of this study. METHODS The effects of five α5-NAMs (basmisanil, Ono-160, L-655,708, α5IA, and MRK-016) on tonic current evoked by a low concentration of GABA were studied using whole-cell recordings in cultured mouse hippocampal neurones. Drug effects on current evoked by a saturating concentration of GABA and on miniature inhibitory postsynaptic currents (mIPSCs) were also examined. RESULTS The α5-NAMs caused a concentration-dependent decrease in tonic current. The potencies varied as the inhibitory concentration for 50% inhibition (IC50) of basmisanil (127 nM) was significantly higher than those of the other compounds (0.4-0.8 nM). In contrast, the maximal efficacies of the drugs were similar (35.5-51.3% inhibition). The α5-NAMs did not modify current evoked by a saturating GABA concentration or mIPSCs. CONCLUSIONS Basmisanil was markedly less potent than the other α5-NAMs, an unexpected result based on studies of recombinant α5 GABAA receptors. Studying the effects of α5 GABAA receptor-selective drugs on the tonic inhibitory current in neurones could inform the selection of compounds for future clinical trials.
Collapse
Affiliation(s)
- Marc A Manzo
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Dian-Shi Wang
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Winston W Li
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Arsène Pinguelo
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Mariana O Popa
- Medicines Discovery Institute, Cardiff University, Cardiff, Wales
| | - Shahin Khodaei
- Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - John R Atack
- Medicines Discovery Institute, Cardiff University, Cardiff, Wales
| | - Ruth A Ross
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, Canada
| | - Beverley A Orser
- Department of Physiology, University of Toronto, Toronto, ON, Canada; Department of Anesthesiology and Pain Medicine, University of Toronto, Toronto, ON, Canada; Department of Anesthesia, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
| |
Collapse
|
8
|
Richter G, Liao VWY, Ahring PK, Chebib M. The Z-Drugs Zolpidem, Zaleplon, and Eszopiclone Have Varying Actions on Human GABA A Receptors Containing γ1, γ2, and γ3 Subunits. Front Neurosci 2020; 14:599812. [PMID: 33328871 PMCID: PMC7710685 DOI: 10.3389/fnins.2020.599812] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 10/26/2020] [Indexed: 11/13/2022] Open
Abstract
γ-Aminobutyric-acid type A (GABA A ) receptors expressing the γ1 or γ3 subunit are only found within a few regions of the brain, some of which are involved in sleep. No known compounds have been reported to selectively target γ1- or γ3-containing GABA A receptors. Pharmacological assessments of this are conflicting, possibly due to differences in experimental models, conditions, and exact protocols when reporting efficacies and potencies. In this study, we evaluated the modulatory properties of five non-benzodiazepine Z-drugs (zaleplon, indiplon, eszopiclone, zolpidem, and alpidem) used in sleep management and the benzodiazepine, diazepam on human α1β2γ receptors using all three γ subtypes. This was accomplished using concatenated GABA A pentamers expressed in Xenopus laevis oocytes and measured via two-electrode voltage clamp. This approach removes the potential for single subunits to form erroneous receptors that could contribute to the pharmacological assessment of these compounds. No compound tested had significant effects on γ1-containing receptors below 10 μM. Interestingly, zaleplon and indiplon were found to modulate γ3-containing receptors equally as efficacious as γ2-containing receptors. Furthermore, zaleplon had a higher potency for γ3- than for γ2-containing receptors, indicating certain therapeutic effects could occur via these γ3-containing receptors. Eszopiclone modulated γ3-containing receptors with reduced efficacy but no reduction in potency. These data demonstrate that the imidazopyridines zaleplon and indiplon are well suited to further investigate potential γ3 effects on sleep in vivo.
Collapse
Affiliation(s)
- Grant Richter
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
| | | | | | - Mary Chebib
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
| |
Collapse
|
9
|
Tonon MC, Vaudry H, Chuquet J, Guillebaud F, Fan J, Masmoudi-Kouki O, Vaudry D, Lanfray D, Morin F, Prevot V, Papadopoulos V, Troadec JD, Leprince J. Endozepines and their receptors: Structure, functions and pathophysiological significance. Pharmacol Ther 2020; 208:107386. [DOI: 10.1016/j.pharmthera.2019.06.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Accepted: 06/20/2019] [Indexed: 02/06/2023]
|
10
|
Sieghart W, Savić MM. International Union of Basic and Clinical Pharmacology. CVI: GABAA Receptor Subtype- and Function-selective Ligands: Key Issues in Translation to Humans. Pharmacol Rev 2018; 70:836-878. [DOI: 10.1124/pr.117.014449] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
|
11
|
Siebert DCB, Bampali K, Puthenkalam R, Varagic Z, Sarto-Jackson I, Scholze P, Sieghart W, Mihovilovic MD, Schnürch M, Ernst M. Engineered Flumazenil Recognition Site Provides Mechanistic Insight Governing Benzodiazepine Modulation in GABA A Receptors. ACS Chem Biol 2018; 13:2040-2047. [PMID: 29989390 DOI: 10.1021/acschembio.8b00145] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The anxiolytic, anticonvulsant, muscle-relaxant, and sedative-hypnotic effects of benzodiazepine site ligands are mainly elicited by allosteric modulation of GABAA receptors via their extracellular αx+/γ2- ( x = 1, 2, 3, 5) interfaces. In addition, a low affinity binding site at the homologous α+/β- interfaces was reported for some benzodiazepine site ligands. Classical benzodiazepines and pyrazoloquinolinones have been used as molecular probes to develop structure-activity relationship models for benzodiazepine site activity. Considering all possible α+/β- and α+/γ- interfaces, such ligands potentially interact with as many as 36 interfaces, giving rise to undesired side effects. Understanding the binding modes at their binding sites will enable rational strategies to design ligands with desired selectivity profiles. Here, we compared benzodiazepine site ligand interactions in the high affinity α1+/γ2- site with the homologous α1+/β3- site using a successive mutational approach. We incorporated key amino acids known to contribute to high affinity benzodiazepine binding of the γ2- subunit into the β3- subunit, resulting in a quadruple mutant β3(4mut) with high affinity flumazenil (Ro 15-1788) binding properties. Intriguingly, some benzodiazepine site ligands displayed positive allosteric modulation in the tested recombinant α1β3(4mut) constructs while diazepam remained inactive. Consequently, we performed in silico molecular docking in the wildtype receptor and the quadruple mutant. The results led to the conclusion that different benzodiazepine site ligands seem to use distinct binding modes, rather than a common binding mode. These findings provide structural hypotheses for the future optimization of both benzodiazepine site ligands, and ligands that interact with the homologous α+/β- sites.
Collapse
Affiliation(s)
- David C. B. Siebert
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Konstantina Bampali
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Roshan Puthenkalam
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Zdravko Varagic
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | | | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Marko D. Mihovilovic
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Michael Schnürch
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163, 1060 Vienna, Austria
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| |
Collapse
|
12
|
Courtney CD, Christian CA. Subregion-Specific Impacts of Genetic Loss of Diazepam Binding Inhibitor on Synaptic Inhibition in the Murine Hippocampus. Neuroscience 2018; 388:128-138. [PMID: 30031126 DOI: 10.1016/j.neuroscience.2018.07.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Revised: 06/27/2018] [Accepted: 07/09/2018] [Indexed: 11/16/2022]
Abstract
Benzodiazepines are commonly prescribed to treat neurological conditions including epilepsy, insomnia, and anxiety. The discovery of benzodiazepine-specific binding sites on γ-aminobutyric acid type-A receptors (GABAARs) led to the hypothesis that the brain may produce endogenous benzodiazepine-binding site ligands. An endogenous peptide, diazepam binding inhibitor (DBI), which can bind these sites, is thought to be capable of both enhancing and attenuating GABAergic transmission in different brain regions. However, the role that DBI plays in modulating GABAARs in the hippocampus remains unclear. Here, we investigated the role of DBI in modulating synaptic inhibition in the hippocampus using a constitutive DBI knockout mouse. Miniature and evoked inhibitory postsynaptic currents (mIPSCs, eIPSCs) were recorded from CA1 pyramidal cells and dentate gyrus (DG) granule cells. Loss of DBI signaling increased mIPSC frequency and amplitude in CA1 pyramidal cells from DBI knockout mice compared to wild-types. In DG granule cells, conversely, the loss of DBI decreased mIPSC amplitude and increased mIPSC decay time, indicating bidirectional modulation of GABAAR-mediated transmission in specific subregions of the hippocampus. eIPSC paired-pulse ratios were consistent across genotypes, suggesting that alterations in mIPSC frequency were not due to changes in presynaptic release probability. Furthermore, cells from DBI knockout mice did not display altered responsiveness to pharmacological applications of diazepam, a benzodiazepine, nor flumazenil, a benzodiazepine-binding site antagonist. These results provide evidence that genetic loss of DBI alters synaptic inhibition in the adult hippocampus, and that the direction of DBI-mediated modulation can vary discretely between specific subregions of the same brain structure.
Collapse
Affiliation(s)
- Connor D Courtney
- Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Catherine A Christian
- Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL, United States; Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, United States.
| |
Collapse
|
13
|
Knutson DE, Kodali R, Divović B, Treven M, Stephen MR, Zahn NM, Dobričić V, Huber AT, Meirelles MA, Verma RS, Wimmer L, Witzigmann C, Arnold LA, Chiou LC, Ernst M, Mihovilovic MD, Savić MM, Sieghart W, Cook JM. Design and Synthesis of Novel Deuterated Ligands Functionally Selective for the γ-Aminobutyric Acid Type A Receptor (GABA AR) α6 Subtype with Improved Metabolic Stability and Enhanced Bioavailability. J Med Chem 2018; 61:2422-2446. [PMID: 29481759 DOI: 10.1021/acs.jmedchem.7b01664] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Recent reports indicate that α6β2/3γ2 GABAAR selective ligands may be important for the treatment of trigeminal activation-related pain and neuropsychiatric disorders with sensori-motor gating deficits. Based on 3 functionally α6β2/3γ2 GABAAR selective pyrazoloquinolinones, 42 novel analogs were synthesized, and their in vitro metabolic stability and cytotoxicity as well as their in vivo pharmacokinetics, basic behavioral pharmacology, and effects on locomotion were investigated. Incorporation of deuterium into the methoxy substituents of the ligands increased their duration of action via improved metabolic stability and bioavailability, while their selectivity for the GABAAR α6 subtype was retained. 8b was identified as the lead compound with a substantially improved pharmacokinetic profile. The ligands allosterically modulated diazepam insensitive α6β2/3γ2 GABAARs and were functionally silent at diazepam sensitive α1β2/3γ2 GABAARs, thus no sedation was detected. In addition, these analogs were not cytotoxic, which render them interesting candidates for treatment of CNS disorders mediated by GABAAR α6β2/3γ2 subtypes.
Collapse
Affiliation(s)
- Daniel E Knutson
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Revathi Kodali
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Branka Divović
- Department of Pharmacology, Faculty of Pharmacy , University of Belgrade , Vojvode Stepe 450 , 11221 Belgrade , Serbia
| | - Marco Treven
- Department of Molecular Neurosciences, Center for Brain Research , Medical University of Vienna , Spitalgasse 4 , A-1090 Vienna , Austria
| | - Michael R Stephen
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Nicolas M Zahn
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Vladimir Dobričić
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy , University of Belgrade , Vojvode Stepe 450 , 11221 Belgrade , Serbia
| | - Alec T Huber
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Matheus A Meirelles
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Ranjit S Verma
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Laurin Wimmer
- TU Wien-Institute of Applied Synthetic Chemistry , Getreidemarkt 9/163 , A-1060 Vienna , Austria
| | - Christopher Witzigmann
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| | - Lih-Chu Chiou
- Graduate Institute of Acupuncture Science , China Medical University , Taichung 40402 , Taiwan
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research , Medical University of Vienna , Spitalgasse 4 , A-1090 Vienna , Austria
| | - Marko D Mihovilovic
- TU Wien-Institute of Applied Synthetic Chemistry , Getreidemarkt 9/163 , A-1060 Vienna , Austria
| | - Miroslav M Savić
- Department of Pharmacology, Faculty of Pharmacy , University of Belgrade , Vojvode Stepe 450 , 11221 Belgrade , Serbia
| | - Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research , Medical University of Vienna , Spitalgasse 4 , A-1090 Vienna , Austria
| | - James M Cook
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery , University of Wisconsin-Milwaukee , 3210 N. Cramer St. , Milwaukee , Wisconsin 53211 , United States
| |
Collapse
|
14
|
Blum K, Modestino EJ, Gondre-Lewis M, Chapman EJ, Neary J, Siwicki D, Baron D, Hauser M, Smith DE, Roy AK, Thanos PK, Steinberg B, McLaughlin T, Fried L, Barh D, Dunston GA, Badgaiyan RD. The Benefits of Genetic Addiction Risk Score (GARS ™) Testing in Substance Use Disorder (SUD). INTERNATIONAL JOURNAL OF GENOMICS AND DATA MINING 2018; 2018. [PMID: 30198022 DOI: 10.29014/ijgd-115.000015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Following 25 years of extensive research by many scientists worldwide, a panel of ten reward gene risk variants, called the Genetic Addiction Risk Score (GARS), has been developed. In unpublished work, when GARS was compared to the Addiction Severity Index (ASI), which has been used in many clinical settings, GARS significantly predicted the severity of both alcohol and drug dependency. In support of early testing for addiction and other RDS subtypes, parents caught up in the current demographic of 127 people, both young and old, dying daily from opiate/opioid overdose, need help. In the past, families would have never guessed that their loved ones would die or could be in real danger due to opiate addiction. Author, Bill Moyers, in Parade Magazine, reported that as he traveled around the United States, he found many children with ADHD and other spectrum disorders like Autism, and noted that many of these children had related conditions like substance abuse. He called for better ways to identify these children and treat them with approaches other than addictive pharmaceuticals. To our knowledge, GARS is the only panel of genes with established polymorphisms reflecting the Brain Reward Cascade (BRC), which has been correlated with the ASI-MV alcohol and drug risk severity score. While other studies are required to confirm and extend the GARS test to include other genes and polymorphisms that associate with an hypodopaminergic trait, these results provide clinicians with a non-invasive genetic test. Genomic testing, such as GARS, can improve clinical interactions and decision-making. Knowledge of precise polymorphic associations can help in the attenuation of guilt and denial, corroboration of family gene-o-grams; assistance in risk-severity-based decisions about appropriate therapies, including pain medications and risk for addiction; choice of the appropriate level of care placement (i.e., inpatient, outpatient, intensive outpatient, residential); determination of the length of stay in treatment; determination of genetic severity-based relapse and recovery liability and vulnerability; determination of pharmacogenetic medical monitoring for better clinical outcomes (e.g., the A1 allele of the DRD2 gene reduces the binding to opioid delta receptors in the brain, thus, reducing Naltrexone's clinical effectiveness); and supporting medical necessity for insurance scrutiny.
Collapse
Affiliation(s)
- Kenneth Blum
- Department of Psychiatry & McKnight Brain Institute, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Psychiatry and Behavioral Sciences, Keck Medicine University of Southern California, Los Angeles, CA, USA.,Division of Applied Clinical Research & Education, Dominion Diagnostics, LLC, North Kingstown, RI, USA.,Department of Neurogenetics, Igene, LLC, Austin, TX, USA.,Division of Neuroscience Based Addiction Therapy, The Shores Treatment & Recovery Center, Port Saint Lucie, FL, USA.,Eötvös Loránd University, Institute of Psychology, Budapest, Hungary.,Department of Psychiatry, Wright State University Boonshoft School of Medicine and Dayton VA Medical Center, Dayton, OH (IE), USA.,Division of Precision Medicine, Geneus Health, LLC, USA.,Department of Psychiatry, Human Integrated Services Unit University of Vermont Center for Clinical & Translational Science, College of Medicine, Burlington, VT, USA.,Center for Genomics and Applied Gene Technology, Institute of Integrative Omics and applied Biotechnology (IIOAB), Nonakuri, Purbe Medinpur, West Bengal, India.,NeuroPsychoSocial Genomics Core, National Human Genome Center, Howard University, Washington, DC, USA
| | | | - Marjorie Gondre-Lewis
- NeuroPsychoSocial Genomics Core, National Human Genome Center, Howard University, Washington, DC, USA.,Developmental Neuropsychopharmacology Laboratory, Department of Anatomy, Howard University College of Medicine, Washington, DC, USA.,Department of Psychiatry and Behavioral Sciences, Howard University College of Medicine, Washington, DC, USA
| | - Edwin J Chapman
- Department of Medicine, Howard University College of Medicine, Washington, DC, USA
| | | | - David Siwicki
- Division of Precision Medicine, Geneus Health, LLC, USA
| | - David Baron
- Department of Psychiatry and Behavioral Sciences, Keck Medicine University of Southern California, Los Angeles, CA, USA
| | - Mary Hauser
- Division of Applied Clinical Research & Education, Dominion Diagnostics, LLC, North Kingstown, RI, USA
| | - David E Smith
- David E. Smith Associates, San Francisco, CA, & Institute of Health & Aging University of California, San Francisco, CA, USA
| | | | - Panayotis K Thanos
- Behavioral Neuropharmacology and Neuroimaging Laboratory on Addictions, Research Institute on Addictions, University at Buffalo, Buffalo, NY, USA
| | | | | | - Lyle Fried
- Division of Neuroscience Based Addiction Therapy, The Shores Treatment & Recovery Center, Port Saint Lucie, FL, USA
| | - Debmalya Barh
- Center for Genomics and Applied Gene Technology, Institute of Integrative Omics and applied Biotechnology (IIOAB), Nonakuri, Purbe Medinpur, West Bengal, India
| | - Georgia A Dunston
- NeuroPsychoSocial Genomics Core, National Human Genome Center, Howard University, Washington, DC, USA
| | - Rajendra D Badgaiyan
- Department of Psychiatry & McKnight Brain Institute, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Psychiatry and Behavioral Sciences, Keck Medicine University of Southern California, Los Angeles, CA, USA.,Division of Applied Clinical Research & Education, Dominion Diagnostics, LLC, North Kingstown, RI, USA.,Department of Neurogenetics, Igene, LLC, Austin, TX, USA.,Division of Neuroscience Based Addiction Therapy, The Shores Treatment & Recovery Center, Port Saint Lucie, FL, USA.,Eötvös Loránd University, Institute of Psychology, Budapest, Hungary.,Department of Psychiatry, Wright State University Boonshoft School of Medicine and Dayton VA Medical Center, Dayton, OH (IE), USA.,Division of Precision Medicine, Geneus Health, LLC, USA.,Department of Psychiatry, Human Integrated Services Unit University of Vermont Center for Clinical & Translational Science, College of Medicine, Burlington, VT, USA.,Center for Genomics and Applied Gene Technology, Institute of Integrative Omics and applied Biotechnology (IIOAB), Nonakuri, Purbe Medinpur, West Bengal, India.,Department of Psychology, Curry College, Milton, MA, USA.,NeuroPsychoSocial Genomics Core, National Human Genome Center, Howard University, Washington, DC, USA.,Developmental Neuropsychopharmacology Laboratory, Department of Anatomy, Howard University College of Medicine, Washington, DC, USA.,Department of Psychiatry and Behavioral Sciences, Howard University College of Medicine, Washington, DC, USA.,Department of Medicine, Howard University College of Medicine, Washington, DC, USA.,David E. Smith Associates, San Francisco, CA, & Institute of Health & Aging University of California, San Francisco, CA, USA.,Addiction Recovery Resources, Inc. New Orleans, LA, USA.,Behavioral Neuropharmacology and Neuroimaging Laboratory on Addictions, Research Institute on Addictions, University at Buffalo, Buffalo, NY, USA.,Center for Psychiatric Medicine Lawrence, MA, USA
| |
Collapse
|
15
|
Molecular tools for GABA A receptors: High affinity ligands for β1-containing subtypes. Sci Rep 2017; 7:5674. [PMID: 28720884 PMCID: PMC5516028 DOI: 10.1038/s41598-017-05757-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 06/05/2017] [Indexed: 12/15/2022] Open
Abstract
γ-Aminobutyric acid type A (GABAA) receptors are pentameric GABA-gated chloride channels that are, in mammalians, drawn from a repertoire of 19 different genes, namely α1-6, β1-3, γ1-3, δ, ε, θ, π and ρ1-3. The existence of this wide variety of subunits as well as their diverse assembly into different subunit compositions result in miscellaneous receptor subtypes. In combination with the large number of known and putative allosteric binding sites, this leads to a highly complex pharmacology. Recently, a novel binding site at extracellular α+/β- interfaces was described as the site of modulatory action of several pyrazoloquinolinones. In this study we report a highly potent ligand from this class of compounds with pronounced β1-selectivity that mainly lacks α-subunit selectivity. It constitutes the most potent β1-selective positive allosteric modulatory ligand with known binding site. In addition, a proof of concept pyrazoloquinolinone ligand lacking the additional high affinity interaction with the benzodiazepine binding site is presented. Ultimately, such ligands can be used as invaluable molecular tools for the detection of β1-containing receptor subtypes and the investigation of their abundance and distribution.
Collapse
|
16
|
Poe MM, Methuku KR, Li G, Verma AR, Teske KA, Stafford DC, Arnold LA, Cramer JW, Jones TM, Cerne R, Krambis MJ, Witkin JM, Jambrina E, Rehman S, Ernst M, Cook JM, Schkeryantz JM. Synthesis and Characterization of a Novel γ-Aminobutyric Acid Type A (GABA A) Receptor Ligand That Combines Outstanding Metabolic Stability, Pharmacokinetics, and Anxiolytic Efficacy. J Med Chem 2016; 59:10800-10806. [PMID: 27933953 DOI: 10.1021/acs.jmedchem.6b01332] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
1,4-Benzodiazepines are used in the treatment of anxiety disorders but have limited long-term use due to adverse effects. HZ-166 (2) has been shown to have anxiolytic-like effects with reduced sedative/ataxic liabilities. A 1,3-oxazole KRM-II-81 (9) was discovered from a series of six bioisosteres with significantly improved pharmacokinetic and pharmacodynamic properties as compared to 2. Oxazole 9 was further characterized and exhibited improved anxiolytic-like effects in a mouse marble burying assay and a rat Vogel conflict test.
Collapse
Affiliation(s)
- Michael M Poe
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Kashi Reddy Methuku
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Guanguan Li
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Ashwini R Verma
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Kelly A Teske
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Douglas C Stafford
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Jeffrey W Cramer
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| | - Timothy M Jones
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| | - Rok Cerne
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| | - Michael J Krambis
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| | - Jeffrey M Witkin
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| | - Enrique Jambrina
- Lilly Research Laboratories, Eli Lilly and Company , 28108 Alcobendas, Spain
| | - Sabah Rehman
- Department for Molecular Neurosciences, Medical University of Vienna , 1090 Vienna, Austria
| | - Margot Ernst
- Department for Molecular Neurosciences, Medical University of Vienna , 1090 Vienna, Austria
| | - James M Cook
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Jeffrey M Schkeryantz
- Lilly Research Laboratories, Eli Lilly and Company , Indianapolis, Indiana 42685, United States
| |
Collapse
|
17
|
Jahan R, Stephen MR, Forkuo GS, Kodali R, Guthrie ML, Nieman AN, Yuan NY, Zahn NM, Poe MM, Li G, Yu OB, Yocum GT, Emala CW, Stafford DC, Cook JM, Arnold LA. Optimization of substituted imidazobenzodiazepines as novel asthma treatments. Eur J Med Chem 2016; 126:550-560. [PMID: 27915170 DOI: 10.1016/j.ejmech.2016.11.045] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Revised: 11/19/2016] [Accepted: 11/21/2016] [Indexed: 12/14/2022]
Abstract
We describe the synthesis of analogs of XHE-III-74, a selective α4β3γ2 GABAAR ligand, shown to relax airway smooth muscle ex vivo and reduce airway hyperresponsiveness in a murine asthma model. To improve properties of this compound as an asthma therapeutic, a series of analogs with a deuterated methoxy group in place of methoxy group at C-8 position was evaluated for isotope effects in preclinical assays; including microsomal stability, cytotoxicity, and sensorimotor impairment. The deuterated compounds were equally or more metabolically stable than the corresponding non-deuterated analogs and increased sensorimotor impairment was observed for some deuterated compounds. Thioesters were more cytotoxic in comparison to other carboxylic acid derivatives of this compound series. The most promising compound 16 identified from the in vitro screens also strongly inhibited smooth muscle constriction in ex vivo guinea pig tracheal rings. Smooth muscle relaxation, determined by reduction of airway hyperresponsiveness with a murine ovalbumin sensitized and challenged model, showed that 16 was efficacious at low methacholine concentrations. However, this effect was limited due to suboptimal pharmacokinetics of 16. Based on these findings, further analogs of XHE-III-74 will be investigated to improve in vivo metabolic stability while retaining the efficacy at lung tissues involved in asthma pathology.
Collapse
Affiliation(s)
- Rajwana Jahan
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Michael Rajesh Stephen
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Gloria S Forkuo
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Revathi Kodali
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Margaret L Guthrie
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Amanda N Nieman
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Nina Y Yuan
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Nicolas M Zahn
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Michael M Poe
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Guanguan Li
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Olivia B Yu
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - Gene T Yocum
- Department of Anesthesiology, Columbia University, New York, NY, 10032, United States
| | - Charles W Emala
- Department of Anesthesiology, Columbia University, New York, NY, 10032, United States
| | - Douglas C Stafford
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States
| | - James M Cook
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States.
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry, Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, United States.
| |
Collapse
|
18
|
Synthesis and pharmacological evaluation of functionalized isoindolinones on GABA-activated chloride currents in rat cerebellum granule cells in culture. Bioorg Med Chem Lett 2016; 26:5284-5289. [DOI: 10.1016/j.bmcl.2016.09.042] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 09/14/2016] [Accepted: 09/15/2016] [Indexed: 01/17/2023]
|
19
|
Stamenić TT, Poe MM, Rehman S, Santrač A, Divović B, Scholze P, Ernst M, Cook JM, Savić MM. Ester to amide substitution improves selectivity, efficacy and kinetic behavior of a benzodiazepine positive modulator of GABA A receptors containing the α5 subunit. Eur J Pharmacol 2016; 791:433-443. [PMID: 27639297 DOI: 10.1016/j.ejphar.2016.09.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Revised: 09/07/2016] [Accepted: 09/07/2016] [Indexed: 12/22/2022]
Abstract
We have synthesized and characterized MP-III-022 ((R)-8-ethynyl-6-(2-fluorophenyl)-N,4-dimethyl-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxamide) in vitro and in vivo as a binding- and efficacy-selective positive allosteric modulator of GABAA receptors containing the α5 subunit (α5GABAARs). By approximation of the electrophysiological responses which the estimated free rat brain concentrations can induce, we demonstrated that convenient systemic administration of MP-III-022 in the dose range 1-10mg/kg may result in a selective potentiation, over a wide range from mild to moderate to strong, of α5βγ2 GABAA receptors. For eliciting a comparable range of potentiation, the widely studied parent ligand SH-053-2'F-R-CH3 containing an ester moiety needs to be administered over a much wider dose range (10-200mg/kg), but at the price of activating non-α5 GABAARs as well as the desired α5GABAARs at the highest dose. At the dose of 10mg/kg, which elicits a strong positive modulation of α5GABAARs, MP-III-022 caused mild, but significant muscle relaxation, while at doses 1-10mg/kg was devoid of ataxia, sedation or an influence on the anxiety level, characteristic for non-selective benzodiazepines. As an amide compound with improved stability and kinetic properties, MP-III-022 may represent an optimized tool to study the influence of α5GABAARs on the neuronal pathways related to CNS disorders such as schizophrenia, Alzheimer's disease, Down syndrome or autism.
Collapse
Affiliation(s)
- Tamara Timić Stamenić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Michael M Poe
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, USA
| | - Sabah Rehman
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Anja Santrač
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Branka Divović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, USA
| | - Miroslav M Savić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
| |
Collapse
|
20
|
Yocum GT, Gallos G, Zhang Y, Jahan R, Stephen MR, Varagic Z, Puthenkalam R, Ernst M, Cook JM, Emala CW. Targeting the γ-Aminobutyric Acid A Receptor α4 Subunit in Airway Smooth Muscle to Alleviate Bronchoconstriction. Am J Respir Cell Mol Biol 2016; 54:546-53. [PMID: 26405827 DOI: 10.1165/rcmb.2015-0176oc] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
We previously demonstrated that airway smooth muscle (ASM) cells express γ-aminobutyric acid A receptors (GABA(A)Rs), and that GABA(A)R agonists acutely relax ASM. Among the GABA(A)R α subunits, human ASM cells express only α4 and α5, providing the opportunity for selective pharmacologic targeting. Novel GABA(A)R-positive allosteric modulators designed for enhanced α4/α6 subunit selectivity were synthesized using iterative computational analyses (CMD-45 and XHe-III-74). Studies using oocyte heterologous expression systems confirmed that CMD-45 and XHe-III-74 led to significantly greater augmentation of currents induced by a 3% maximal effective concentration (EC3) of GABA [EC3]-induced currents in oocytes expressing α4 or α6 subunits (along with β3 and γ2) compared with other α subunits. CMD-45 and XHe-III-74 also led to greater ex vivo relaxation of contracted wild-type mouse tracheal rings compared with tracheal rings from GABA(A)R α4 subunit (Gabra4) knockout mice. Furthermore, CMD-45 and XHe-III-74 significantly relaxed precontracted human ASM ex vivo, and, at a low concentration, both ligands led to a significant leftward shift in albuterol-mediated ASM relaxation. In vivo, inhaled XHe-III-74 reduced respiratory system resistance in an asthmatic mouse model. Pretreatment of human ASM cells with CMD-45 and XHe-III-74 inhibited histamine-induced increases in intracellular calcium concentrations in vitro, an effect that was lost when calcium was omitted from the extracellular buffer, suggesting that inhibition of calcium influx due to alterations in plasma membrane potential may play a role in the mechanism of ASM relaxation. Selective targeting of the GABA(A)R α4 subunit with inhaled ligands may be a novel therapeutic pathway to treat bronchoconstriction, while avoiding sedative central nervous system effects, which are largely mediated by α1-3 subunit-containing GABA(A)Rs in the brain.
Collapse
Affiliation(s)
- Gene T Yocum
- 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
| | - George Gallos
- 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
| | - Yi Zhang
- 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
| | - Rajwana Jahan
- 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and
| | - Michael Rajesh Stephen
- 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and
| | - Zdravko Varagic
- 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Roshan Puthenkalam
- 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - James M Cook
- 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and
| | - Charles W Emala
- 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
| |
Collapse
|
21
|
Zolpidem is a potent stoichiometry-selective modulator of α1β3 GABAA receptors: evidence of a novel benzodiazepine site in the α1-α1 interface. Sci Rep 2016; 6:28674. [PMID: 27346730 PMCID: PMC4921915 DOI: 10.1038/srep28674] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 06/06/2016] [Indexed: 12/16/2022] Open
Abstract
Zolpidem is not a typical GABAA receptor hypnotic. Unlike benzodiazepines, zolpidem modulates tonic GABA currents in the rat dorsal motor nucleus of the vagus, exhibits residual effects in mice lacking the benzodiazepine binding site, and improves speech, cognitive and motor function in human patients with severe brain injury. The receptor by which zolpidem mediates these effects is not known. In this study we evaluated binary α1β3 GABAA receptors in either the 3α1:2β3 or 2α1:3β3 subunit stoichiometry, which differ by the existence of either an α1-α1 interface, or a β3-β3 interface, respectively. Both receptor stoichiometries are readily expressed in Xenopus oocytes, distinguished from each other by using GABA, zolpidem, diazepam and Zn2+. At the 3α1:2β3 receptor, clinically relevant concentrations of zolpidem enhanced GABA in a flumazenil-sensitive manner. The efficacy of diazepam was significantly lower compared to zolpidem. No modulation by either zolpidem or diazepam was detected at the 2α1:3β3 receptor, indicating that the binding site for zolpidem is at the α1-α1 interface, a site mimicking the classical α1-γ2 benzodiazepine site. Activating α1β3 (3α1:2β3) receptors may, in part, mediate the physiological effects of zolpidem observed under distinct physiological and clinical conditions, constituting a potentially attractive drug target.
Collapse
|
22
|
Forkuo GS, Guthrie ML, Yuan NY, Nieman AN, Kodali R, Jahan R, Stephen MR, Yocum GT, Treven M, Poe MM, Li G, Yu OB, Hartzler BD, Zahn NM, Ernst M, Emala CW, Stafford DC, Cook JM, Arnold LA. Development of GABAA Receptor Subtype-Selective Imidazobenzodiazepines as Novel Asthma Treatments. Mol Pharm 2016; 13:2026-38. [PMID: 27120014 DOI: 10.1021/acs.molpharmaceut.6b00159] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recent studies have demonstrated that subtype-selective GABAA receptor modulators are able to relax precontracted human airway smooth muscle ex vivo and reduce airway hyper-responsiveness in mice upon aerosol administration. Our goal in this study was to investigate systemic administration of subtype-selective GABAA receptor modulators to alleviate bronchoconstriction in a mouse model of asthma. Expression of GABAA receptor subunits was identified in mouse lungs, and the effects of α4-subunit-selective GABAAR modulators, XHE-III-74EE and its metabolite XHE-III-74A, were investigated in a murine model of asthma (ovalbumin sensitized and challenged BALB/c mice). We observed that chronic treatment with XHE-III-74EE significantly reduced airway hyper-responsiveness. In addition, acute treatment with XHE-III-74A but not XHE-III-74EE decreased airway eosinophilia. Immune suppressive activity was also shown in activated human T-cells with a reduction in IL-2 expression and intracellular calcium concentrations [Ca(2+)]i in the presence of GABA or XHE-III-74A, whereas XHE-III-74EE showed only partial reduction of [Ca(2+)]i and no inhibition of IL-2 secretion. However, both compounds significantly relaxed precontracted tracheal rings ex vivo. Overall, we conclude that the systemic delivery of a α4-subunit-selective GABAAR modulator shows good potential for a novel asthma therapy; however, the pharmacokinetic properties of this class of drug candidates have to be improved to enable better beneficial systemic pharmacodynamic effects.
Collapse
Affiliation(s)
- Gloria S Forkuo
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Margaret L Guthrie
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Nina Y Yuan
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Amanda N Nieman
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Revathi Kodali
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Rajwana Jahan
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Michael R Stephen
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Gene T Yocum
- Department of Anesthesiology, Columbia University , New York, New York 10032, United States
| | - Marco Treven
- Department of Molecular Neurosciences, Medical University of Vienna , 1090 Vienna, Austria
| | - Michael M Poe
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Guanguan Li
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Olivia B Yu
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Benjamin D Hartzler
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Nicolas M Zahn
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Margot Ernst
- Department of Molecular Neurosciences, Medical University of Vienna , 1090 Vienna, Austria
| | - Charles W Emala
- Department of Anesthesiology, Columbia University , New York, New York 10032, United States
| | - Douglas C Stafford
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - James M Cook
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| | - Leggy A Arnold
- Department of Chemistry and Biochemistry and the Milwaukee Institute for Drug Discovery, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53201, United States
| |
Collapse
|
23
|
Afroz S, Parato J, Shen H, Smith SS. Synaptic pruning in the female hippocampus is triggered at puberty by extrasynaptic GABAA receptors on dendritic spines. eLife 2016; 5. [PMID: 27136678 PMCID: PMC4871702 DOI: 10.7554/elife.15106] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 04/29/2016] [Indexed: 01/24/2023] Open
Abstract
Adolescent synaptic pruning is thought to enable optimal cognition because it is disrupted in certain neuropathologies, yet the initiator of this process is unknown. One factor not yet considered is the α4βδ GABAA receptor (GABAR), an extrasynaptic inhibitory receptor which first emerges on dendritic spines at puberty in female mice. Here we show that α4βδ GABARs trigger adolescent pruning. Spine density of CA1 hippocampal pyramidal cells decreased by half post-pubertally in female wild-type but not α4 KO mice. This effect was associated with decreased expression of kalirin-7 (Kal7), a spine protein which controls actin cytoskeleton remodeling. Kal7 decreased at puberty as a result of reduced NMDAR activation due to α4βδ-mediated inhibition. In the absence of this inhibition, Kal7 expression was unchanged at puberty. In the unpruned condition, spatial re-learning was impaired. These data suggest that pubertal pruning requires α4βδ GABARs. In their absence, pruning is prevented and cognition is not optimal. DOI:http://dx.doi.org/10.7554/eLife.15106.001 Memories are formed at structures in the brain known as dendritic spines. These structures receive connections from other brain cells through regions called synapses. In humans, the number of these brain connections increases dramatically from birth to childhood, reflecting a period of rapid learning. However, the number of these brain connections halves after puberty, a dramatic reduction shown in many brain areas and for many species, including humans and rodents. This process is referred to as adolescent synaptic pruning and is thought to be important for optimal learning in adulthood because it is disrupted in autism and schizophrenia. Synaptic pruning is believed to remove unnecessary brain connections to make room for new relevant memories. However, the process that triggers synaptic pruning is not known. Within the brain, proteins called inhibitory GABA receptors are targets for chemicals that reduce the activity of nerve cells. As brain connections must be kept active to survive, inhibitory receptors could help to trigger synaptic pruning. Afroz, Parato et al. now show that, at puberty, the number of a particular type of GABAA receptor increases in the brain of female mice. This triggers synaptic pruning in the hippocampus, a key brain area necessary for learning and memory. By reducing brain activity, these inhibitory receptors also reduce the levels of a protein in the dendritic spine that stabilizes the scaffolding of the spine to maintain its structure. Mice that do not have these GABAA receptors maintain a constant high level of brain connections throughout adolescence, and synaptic pruning does not occur in their brains. These mice were initially able to learn to avoid a specific location that provided a mild shock to their foot. However, when this location changed the mice were unable to re-learn where to avoid, suggesting that too many brain connections limits learning potential. Brain connections are regulated by many factors, including the environment and stress. Future studies will test how these additional factors alter synaptic pruning in adolescence, and will test drugs that target these inhibitory receptors to manipulate adolescent pruning. These findings may suggest new treatments for “normalizing” synaptic pruning in conditions where this process occurs abnormally, such as autism and schizophrenia. DOI:http://dx.doi.org/10.7554/eLife.15106.002
Collapse
Affiliation(s)
- Sonia Afroz
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, Brooklyn, United States.,Program in Neural and Behavioral Science, SUNY Downstate Medical Center, Brooklyn, United States
| | - Julie Parato
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, Brooklyn, United States.,Program in Neural and Behavioral Science, SUNY Downstate Medical Center, Brooklyn, United States
| | - Hui Shen
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, Brooklyn, United States.,School of Biomedical Engineering, Tianjin Medical University, Tianjin, China
| | - Sheryl Sue Smith
- Department of Physiology and Pharmacology, SUNY Downstate Medical Center, Brooklyn, United States.,The Robert F. Furchgott Center for Neural and Behavioral Science, SUNY Downstate Medical Center, Brooklyn, United States
| |
Collapse
|
24
|
Stamenić TT, Joksimović S, Biawat P, Stanković T, Marković B, Cook JM, Savić MM. Negative modulation of α₅ GABAA receptors in rats may partially prevent memory impairment induced by MK-801, but not amphetamine- or MK-801-elicited hyperlocomotion. J Psychopharmacol 2015; 29:1013-24. [PMID: 26105958 PMCID: PMC4861997 DOI: 10.1177/0269881115590601] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Reportedly, negative modulation of α5 GABAA receptors may improve cognition in normal and pharmacologically-impaired animals, and such modulation has been proposed as an avenue for treatment of cognitive symptoms in schizophrenia. This study assessed the actions of PWZ-029, administered at doses (2, 5, and 10 mg/kg) at which it reached micromolar concentrations in brain tissue with estimated free concentrations adequate for selective modulation of α5 GABAA receptors, in three cognitive tasks in male Wistar rats acutely treated with the noncompetitive N-methyl-d-aspartate receptor antagonist, MK-801 (0.1 mg/kg), as well in tests of locomotor activity potentiated by MK-801 (0.2 mg/kg) or amphetamine (0.5 mg/kg). In a hormetic-like manner, only 5 mg/kg PWZ-029 reversed MK-801-induced deficits in novel object recognition test (visual recognition memory), whereas in the Morris water maze, the 2 mg/kg dose of PWZ-029 exerted partial beneficial effects on spatial learning impairment. PWZ-029 did not affect recognition memory deficits in social novelty discrimination procedure. Motor hyperactivity induced with MK-801 or amphetamine was not preventable by PWZ-029. Our results show that certain MK-801-induced memory deficits can be ameliorated by negative modulation of α5 GABAA receptors, and point to the need for further elucidation of their translational relevance to cognitive deterioration in schizophrenia.
Collapse
Affiliation(s)
| | - Srdjan Joksimović
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
| | - Poonam Biawat
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Tamara Stanković
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
| | - Bojan Marković
- Department of Pharmaceutical Chemistry, University of Belgrade, Belgrade, Serbia
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Miroslav M Savić
- Department of Pharmacology, University of Belgrade, Belgrade, Serbia
| |
Collapse
|
25
|
Abstract
Since their introduction in the 1960s, benzodiazepines (BZs) remain one of the most commonly prescribed medications, acting as potent sedatives, hypnotics, anxiolytics, anticonvulsants, and muscle relaxants. The primary neural action of BZs and related compounds is augmentation of inhibitory transmission, which occurs through allosteric modulation of the gamma-aminobutyric acid (GABA)-induced current at the gamma-aminobutyric acid receptor (GABAAR). The discovery of the BZ-binding site on GABAARs encouraged many to speculate that the brain produces its own endogenous ligands to this site (Costa & Guidotti, 1985). The romanticized quest for endozepines, endogenous ligands to the BZ-binding site, has uncovered a variety of ligands that might fulfill this role, including oleamides (Cravatt et al., 1995), nonpeptidic endozepines (Rothstein et al., 1992), and the protein diazepam-binding inhibitor (DBI) (Costa & Guidotti, 1985). Of these ligands, DBI, and affiliated peptide fragments, is the most extensively studied endozepine. The quest for the "brain's Valium" over the decades has been elusive as mainly negative allosteric modulatory effects have been observed (Alfonso, Le Magueresse, Zuccotti, Khodosevich, & Monyer, 2012; Costa & Guidotti, 1985), but recent evidence is accumulating that DBI displays regionally discrete endogenous positive modulation of GABA transmission through activation of the BZ receptor (Christian et al., 2013). Herein, we review the literature on this topic, focusing on identification of the endogenous molecule and its region-specific expression and function.
Collapse
|
26
|
Sieghart W. Allosteric modulation of GABAA receptors via multiple drug-binding sites. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2014; 72:53-96. [PMID: 25600367 DOI: 10.1016/bs.apha.2014.10.002] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
GABAA receptors are ligand-gated ion channels composed of five subunits that can be opened by GABA and be modulated by multiple pharmacologically and clinically important drugs. Over the time, hundreds of compounds from different structural classes have been demonstrated to modulate, directly activate, or inhibit GABAA receptors, and most of these compounds interact with more than one binding site at these receptors. Crystal structures of proteins and receptors homologous to GABAA receptors as well as homology modeling studies have provided insights into the possible location of ligand interaction sites. Some of these sites have been identified by mutagenesis, photolabeling, and docking studies. For most of these ligands, however, binding sites are not known. Due to the high flexibility of GABAA receptors and the existence of multiple drug-binding sites, the unequivocal identification of interaction sites for individual drugs is extremely difficult. The existence of multiple GABAA receptor subtypes with distinct subunit composition, the contribution of distinct subunit sequences to binding sites of different receptor subtypes, as well as the observation that even subunits not directly contributing to a binding site are able to influence affinity and efficacy of drugs, contribute to a unique pharmacology of each GABAA receptor subtype. Thus, each receptor subtype has to be investigated to identify a possible subtype selectivity of a compound. Although multiple binding sites make GABAA receptor pharmacology even more complicated, the exploitation of ligand interaction with novel-binding sites also offers additional possibilities for a subtype-selective modulation of GABAA receptors.
Collapse
Affiliation(s)
- Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University Vienna, Vienna, Austria.
| |
Collapse
|
27
|
Varagic Z, Ramerstorfer J, Huang S, Rallapalli S, Sarto-Jackson I, Cook J, Sieghart W, Ernst M. Subtype selectivity of α+β- site ligands of GABAA receptors: identification of the first highly specific positive modulators at α6β2/3γ2 receptors. Br J Pharmacol 2014; 169:384-99. [PMID: 23472935 DOI: 10.1111/bph.12153] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Revised: 12/21/2012] [Accepted: 01/31/2013] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND AND PURPOSE GABAA receptors are the major inhibitory neurotransmitter receptors in the mammalian brain and the target of many clinically important drugs interacting with different binding sites. Recently, we demonstrated that CGS 9895 (2-(4-methoxyphenyl)-2H-pyrazolo[4,3-c]quinolin-3(5H)-one) elicits a strong and subtype-dependent enhancement of GABA-induced currents via a novel drug-binding site at extracellular αx+βy- (x = 1-6, y = 1-3) interfaces. Here, we investigated 16 structural analogues of CGS 9895 for their ability to modulate GABA-induced currents of various GABAA receptor subtypes. EXPERIMENTAL APPROACH Recombinant GABAA receptor subtypes were expressed in Xenopus laevis oocytes and investigated by the two-electrode voltage clamp method. KEY RESULTS Most of the compounds investigated were able to modulate GABA-induced currents of αβ and αβγ receptors to a comparable extent, suggesting that the effect of these drugs is not dependent on the benzodiazepine site of GABAA receptors. Steric hindrance experiments demonstrated that these compounds exert their action predominantly via the αx+βy- (x = 1-6, y = 1-3) interfaces. Whereas some compounds are unselectively modulating a broad range of receptor subtypes, other compounds feature remarkable functional selectivity for the α6β3γ2 receptor, or behave as null modulators at some receptor subtypes investigated. CONCLUSION AND IMPLICATIONS Pyrazoloquinolinones and pyrazolopyridinones represent the first prototypes of drugs exerting benzodiazepine-like modulatory effects via the α+β- interface of GABAA receptors. The discovery of modulators with functional subtype selectivity at this class of binding sites provides a highly useful tool for the investigation of α6β2/3γ2 receptor function, and may lead to novel therapeutic principles.
Collapse
Affiliation(s)
- Zdravko Varagic
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | | | | | | | | | | | | | | |
Collapse
|
28
|
Varagic Z, Wimmer L, Schnürch M, Mihovilovic MD, Huang S, Rallapalli S, Cook JM, Mirheydari P, Ecker GF, Sieghart W, Ernst M. Identification of novel positive allosteric modulators and null modulators at the GABAA receptor α+β- interface. Br J Pharmacol 2014; 169:371-83. [PMID: 23472852 DOI: 10.1111/bph.12151] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Revised: 12/21/2012] [Accepted: 01/31/2013] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND AND PURPOSE GABAA receptors are the major inhibitory neurotransmitter receptors in the mammalian brain and the target of many clinically important drugs interacting with different binding sites. Recently, we demonstrated that CGS 9895 (2-(4-methoxyphenyl)-2H-pyrazolo[4,3-c]quinolin-3(5H)-one) acts as a null modulator (antagonist) at the high affinity benzodiazepine binding site, but in addition elicits a strong enhancement of GABA-induced currents via a novel drug binding site at the extracellular α+β- interface. Here, we investigated 32 structural analogues of CGS 9895 for their ability to mediate their effects via the α1+β3- interface of GABAA receptors. EXPERIMENTAL APPROACH GABAA receptors were expressed in Xenopus laevis oocytes and investigated by the two-electrode voltage clamp method. KEY RESULTS We not only identified compounds with higher efficacy/potency than CGS 9895 for stimulating GABA-induced currents via the α1+β3-binding site, but also discovered compounds acting as null modulators at this site. Most of the compounds also acted as null modulators via the benzodiazepine binding site of GABAA receptors. But some of the positive allosteric modulators or null modulators exclusively exerted their action via the α+β- binding site. CONCLUSION AND IMPLICATIONS Pyrazoloquinolinones and pyrazolopyridinones represent the first prototype of drug candidates mediating benzodiazepine like modulatory effects via the α+β-interface of GABAA receptors. The discovery of null modulators acting as inhibitors of the plus modulators provides a highly useful tool for the discovery of additional classes of compounds that can modulate GABAA receptors via this site, which may lead to novel therapeutic principles.
Collapse
Affiliation(s)
- Zdravko Varagic
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, Vienna, Austria
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Abstract
Rapid activation of postsynaptic GABAA receptors (GABAARs) is crucial in many neuronal functions, including the synchronization of neuronal ensembles and controlling the precise timing of action potentials. Although the γ2 subunit is believed to be essential for the postsynaptic clustering of GABAARs, synaptic currents have been detected in neurons obtained from γ2(-/-) mice. To determine the role of the γ2 subunit in synaptic GABAAR enrichment, we performed a spatially and temporally controlled γ2 subunit deletion by injecting Cre-expressing viral vectors into the neocortex of GABAARγ2(77I)lox mice. Whole-cell recordings revealed the presence of miniature IPSCs in Cre(+) layer 2/3 pyramidal cells (PCs) with unchanged amplitudes and rise times, but significantly prolonged decays. Such slowly decaying currents could be evoked in PCs by action potentials in presynaptic fast-spiking interneurons. Freeze-fracture replica immunogold labeling revealed the presence of the α1 and β3 subunits in perisomatic synapses of cells that lack the γ2 subunit. Miniature IPSCs in Cre(+) PCs were insensitive to low concentrations of flurazepam, providing a pharmacological confirmation of the lack of the γ2 subunit. Receptors assembled from only αβ subunits were unlikely because Zn(2+) did not block the synaptic currents. Pharmacological experiments indicated that the αβγ3 receptor, rather than the αβδ, αβε, or αβγ1 receptors, was responsible for the slowly decaying IPSCs. Our data demonstrate the presence of IPSCs and the synaptic enrichment of the α1 and β3 subunits and suggest that the γ3 subunit is the most likely candidate for clustering GABAARs at synapses in the absence of the γ2 subunit.
Collapse
|
30
|
Beltrán González AN, Pomata PE, Goutman JD, Gasulla J, Chebib M, Calvo DJ. Benzodiazepine modulation of homomeric GABAAρ1 receptors: differential effects of diazepam and 4'-chlorodiazepam. Eur J Pharmacol 2014; 743:24-30. [PMID: 25246015 DOI: 10.1016/j.ejphar.2014.09.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 09/09/2014] [Accepted: 09/10/2014] [Indexed: 11/26/2022]
Abstract
GABA(A) receptors (GABA(A)Rs) are ligand-gated ion channels that mediate inhibitory neurotransmission in the central nervous system (CNS). They are members of the Cys-loop receptor family and display marked structural and functional heterogeneity. Many GABA(A)Rs receptor subtypes are allosterically modulated by benzodiazepines (BDZs), which are drugs extensively used as anxiolytics, sedative-hypnotics and anticonvulsants. One high-affinity site and at least three additional low-affinity sites for BDZ recognition have been identified in several heteromeric and homomeric variants of the GABA(A)Rs (e.g.: α1β2γ2, α1β2/3, β3, etc.). However, the modulation of homomeric GABA(A)ρRs by BDZs was not previously revealed, and these receptors, for a long a time, were assumed to be fully insensitive to the actions of these drugs. In the present study, human homomeric GABA(A)ρ1 receptors were expressed in Xenopus oocytes and GABA-evoked responses electrophysiologically recorded in the presence or absence of BDZs. GABA(A)ρ1 receptor-mediated responses were modulated by diazepam and 4'-chlorodiazepam in the micromolar range, in a concentration-dependent, voltage-independent and reversible manner. Diazepam produced potentiating effects on GABA-evoked Cl(-) currents and 4'-Cl diazepam induced biphasic effects depending on the GABA concentration, whereas Ro15-4513 and alprazolam were negative modulators. BDZ actions were insensitive to flumazenil. Other BDZs showed negligible activity at equivalent experimental conditions. Our results suggest that GABA(A)ρ1 receptor function can be selectively and differentially modulated by BDZs.
Collapse
Affiliation(s)
- Andrea N Beltrán González
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Pablo E Pomata
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Juan D Goutman
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Javier Gasulla
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Mary Chebib
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina
| | - Daniel J Calvo
- Laboratorio de Neurobiología Celular y Molecular, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Vuelta de Obligado 2490, Ciudad Autónoma de Buenos Aires CP 1428, Argentina.
| |
Collapse
|
31
|
May AC, Fleischer W, Kletke O, Haas HL, Sergeeva OA. Benzodiazepine-site pharmacology on GABAA receptors in histaminergic neurons. Br J Pharmacol 2014; 170:222-32. [PMID: 23799902 DOI: 10.1111/bph.12280] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2012] [Revised: 06/13/2013] [Accepted: 06/18/2013] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND AND PURPOSE The histaminergic tuberomamillary nucleus (TMN) of the posterior hypothalamus controls the cognitive aspects of vigilance which is reduced by common sedatives and anxiolytics. The receptors targeted by these drugs in histaminergic neurons are unknown. TMN neurons express nine different subunits of the GABAA receptor (GABAA R) with three α- (α1, α2 and α5) and two γ- (γ1, γ 2) subunits, which confer different pharmacologies of the benzodiazepine-binding site. EXPERIMENTAL APPROACH We investigated the actions of zolpidem, midazolam, diazepam, chlordiazepoxide, flumazenil (Ro15-1788) and methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) in TMN neurons using mouse genetics, electrophysiological and molecular biological methods. KEY RESULTS We find the sensitivity of GABAA R to zolpidem, midazolam and DMCM significantly reduced in TMN neurons from γ2F77I mice, but modulatory activities of diazepam, chlordiazepoxide and flumazenil not affected. Potencies and efficacies of these compounds are in line with the dominance of α2- and α1-subunit containing receptors associated with γ2- or γ1-subunits. Functional expression of the γ1-subunit is supported by siRNA-based knock-down experiments in γ2F77I mice. CONCLUSIONS AND IMPLICATIONS GABAA R of TMN neurons respond to a variety of common sedatives with a high affinity binding site (γ2F77I) involved. The γ1-subunit likely contributes to the action of common sedatives in TMN neurons. This study is relevant for understanding the role of neuronal histamine and benzodiazepines in disorders of sleep and metabolism.
Collapse
Affiliation(s)
- A C May
- Department of Neurophysiology, Medical Faculty, Heinrich-Heine-Universität, Düsseldorf, Germany
| | | | | | | | | |
Collapse
|
32
|
Evidence for the participation of peripheral α5 subunit-containing GABAA receptors in GABAA agonists-induced nociception in rats. Eur J Pharmacol 2014; 734:91-7. [DOI: 10.1016/j.ejphar.2014.03.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 03/11/2014] [Accepted: 03/22/2014] [Indexed: 11/17/2022]
|
33
|
Obradović AL, Joksimović S, Poe MM, Ramerstorfer J, Varagic Z, Namjoshi O, Batinić B, Radulović T, Marković B, Roth BL, Sieghart W, Cook JM, Savić MM. Sh-I-048A, an in vitro non-selective super-agonist at the benzodiazepine site of GABAA receptors: the approximated activation of receptor subtypes may explain behavioral effects. Brain Res 2014; 1554:36-48. [PMID: 24472579 DOI: 10.1016/j.brainres.2014.01.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 12/19/2013] [Accepted: 01/20/2014] [Indexed: 12/24/2022]
Abstract
Enormous progress in understanding the role of four populations of benzodiazepine-sensitive GABAA receptors was paralleled by the puzzling findings suggesting that substantial separation of behavioral effects may be accomplished by apparently non-selective modulators. We report on SH-I-048A, a newly synthesized chiral positive modulator of GABAA receptors characterized by exceptional subnanomolar affinity, high efficacy and non-selectivity. Its influence on behavior was assessed in Wistar rats and contrasted to that obtained with 2mg/kg diazepam. SH-I-048A reached micromolar concentrations in brain tissue, while the unbound fraction in brain homogenate was around 1.5%. The approximated electrophysiological responses, which estimated free concentrations of SH-I-048A or diazepam are able to elicit, suggested a similarity between the 10mg/kg dose of the novel ligand and 2mg/kg diazepam; however, SH-I-048A was relatively more active at α1- and α5-containing GABAA receptors. Behaviorally, SH-I-048A induced sedative, muscle relaxant and ataxic effects, reversed mechanical hyperalgesia 24h after injury, while it was devoid of clear anxiolytic actions and did not affect water-maze performance. While lack of clear anxiolytic actions may be connected with an enhanced potentiation at α1-containing GABAA receptors, the observed behavior in the rotarod, water maze and peripheral nerve injury tests was possibly affected by its prominent action at receptors containing the α5 subunit. The current results encourage further innovative approaches aimed at linking in vitro and in vivo data in order to help define fine-tuning mechanisms at four sensitive receptor populations that underlie subtle differences in behavioral profiles of benzodiazepine site ligands.
Collapse
Affiliation(s)
- Aleksandar Lj Obradović
- Department of Physiology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Srđan Joksimović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Michael M Poe
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Joachim Ramerstorfer
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Zdravko Varagic
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Ojas Namjoshi
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Bojan Batinić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Tamara Radulović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Bojan Marković
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Brian L Roth
- Department of Pharmacology, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA; Division of Chemical Biology and Medicinal Chemistry, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA
| | - Werner Sieghart
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA
| | - Miroslav M Savić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
| |
Collapse
|
34
|
Insights into functional pharmacology of α₁ GABA(A) receptors: how much does partial activation at the benzodiazepine site matter? Psychopharmacology (Berl) 2013; 230:113-23. [PMID: 23685860 PMCID: PMC3795825 DOI: 10.1007/s00213-013-3143-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 04/29/2013] [Indexed: 01/09/2023]
Abstract
RATIONALE Synthesis of ligands inactive or with low activity at α₁ GABA(A) receptors has become the key concept for development of novel, more tolerable benzodiazepine (BZ)-like drugs. WYS8, a remarkably (105 times) α₁-subtype selective partial positive modulator, may serve as a pharmacological tool for refining the role of α₁ GABA(A) receptors in mediation of BZs' effects. OBJECTIVES Here, the effects of WYS8 on GABA-induced currents and on diazepam-induced potentiation of recombinant BZ-sensitive GABA(A) receptors were studied in more detail. In addition, the behavioral profile of WYS8 (0.2, 1, and 10 mg/kg i.p.), on its own and in combination with diazepam, was tested in the spontaneous locomotor activity, elevated plus maze, grip strength, rotarod, and pentylenetetrazole tests. RESULTS WYS8, applied at an in vivo attainable concentration of 100 nM, reduced the stimulation of GABA currents by 1 μM diazepam by 57 % at α₁β₃γ₂, but not at α₂β₃γ₂, α₃β₃γ₂, or α₅β₃γ₂ GABA(A) receptors. The administration of WYS8 alone induced negligible behavioral consequences. When combined with diazepam, WYS8 caused a reduction in sedation, muscle relaxation, and anticonvulsant activity, as compared with this BZ alone, whereas ataxia was preserved, and the anxiolytic effect of 2 mg/kg diazepam was unmasked. CONCLUSIONS Hence, a partial instead of full activation at α₁ GABA(A) receptors did not necessarily result in the attenuation of the effects assumed to be mediated by activation of these receptors, or in the full preservation of the effects mediated by activation of other GABA(A) receptors. Thus, the role of α₁ GABA(A) receptors appears more complex than that proposed by genetic studies.
Collapse
|
35
|
Dopamine D2 receptors regulate collateral inhibition between striatal medium spiny neurons. J Neurosci 2013; 33:14075-86. [PMID: 23986243 DOI: 10.1523/jneurosci.0692-13.2013] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The principle neurons of the striatum are GABAergic medium spiny neurons (MSNs), whose collateral synapses onto neighboring neurons play critical roles in striatal function. MSNs can be divided by dopamine receptor expression into D1-class and D2-class MSNs, and alterations in D2 MSNs are associated with various pathological states. Despite overwhelming evidence for D2 receptors (D2Rs) in maintaining proper striatal function, it remains unclear how MSN collaterals are specifically altered by D2R activation. Here, we report that chronic D2R stimulation regulates MSN collaterals in vitro by presynaptic and postsynaptic mechanisms. We used corticostriatal cultures from mice in which MSN subtypes were distinguished by fluorophore expression. Quinpirole, an agonist for D2/3 receptors, was used to chronically activate D2Rs. Quinpirole increased the rate and strength of collateral formation onto D2R-containing MSNs as measured by dual whole-cell patch-clamp recordings. Additionally, these neurons were more sensitive to low concentrations of GABA and exhibited an increase in gephyrin puncta density, suggesting increased postsynaptic GABAA receptors. Last, quinpirole treatment increased presynaptic GABA release sites, as shown by increased frequency of sIPSCs and mIPSCs, correlating with increased VGAT (vesicular GABA transporter) puncta. Combined with the observation that there were no detectable differences in sensitivity to specific GABAA receptor modulators, we provide evidence that D2R activation powerfully transforms MSN collaterals via coordinated presynaptic and postsynaptic alterations. As the D2 class of MSNs is highly implicated in Parkinson's disease and other neurological disorders, our findings may contribute to understanding and treating the changes that occur in these pathological states.
Collapse
|
36
|
Mirheydari P, Ramerstorfer J, Varagic Z, Scholze P, Wimmer L, Mihovilovic MM, Sieghart W, Ernst M. Unexpected Properties of δ-Containing GABAA Receptors in Response to Ligands Interacting with the α+ β- Site. Neurochem Res 2013; 39:1057-1067. [PMID: 24072672 DOI: 10.1007/s11064-013-1156-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 09/11/2013] [Accepted: 09/17/2013] [Indexed: 10/26/2022]
Abstract
GABAA receptors are the major inhibitory neurotransmitter receptors in the central nervous system and are the targets of many clinically important drugs, which modulate GABA induced chloride flux by interacting with separate and distinct allosteric binding sites. Recently, we described an allosteric modulation occurring upon binding of pyrazoloquinolinones to a novel binding site at the extracellular α+ β- interface. Here, we investigated the effect of 4-(8-methoxy-3-oxo-3,5-dihydro-2H-pyrazolo[4,3-c]quinolin-2-yl)benzonitrile (the pyrazoloquinolinone LAU 177) at several αβ, αβγ and αβδ receptor subtypes. LAU 177 enhanced GABA-induced currents at all receptors investigated, and the extent of modulation depended on the type of α and β subunits present within the receptors. Whereas the presence of a γ2 subunit within αβγ2 receptors did not dramatically change LAU 177 induced modulation of GABA currents compared to αβ receptors, we observed an unexpected threefold increase in modulatory efficacy of this compound at α1β2,3δ receptors. Steric hindrance experiments as well as inhibition by the functional α+ β- site antagonist LAU 157 indicated that the effects of LAU 177 at all receptors investigated were mediated via the α+ β- interface. The stronger enhancement of GABA-induced currents by LAU 177 at α1β3δ receptors was not observed at α4,6β3δ receptors. Other experiments indicated that this enhancement of modulatory efficacy at α1β3δ receptors was not observed with another α+ β- modulator, and that the efficacy of modulation by α+ β- ligands is influenced by all subunits present in the receptor complex and by structural details of the respective ligand.
Collapse
Affiliation(s)
- Pantea Mirheydari
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Joachim Ramerstorfer
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Zdravko Varagic
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Laurin Wimmer
- Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 6/163, 1060 Vienna, Austria
| | - Marko M Mihovilovic
- Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 6/163, 1060 Vienna, Austria
| | - Werner Sieghart
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
| | - Margot Ernst
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria.
| |
Collapse
|
37
|
Christian CA, Herbert AG, Holt RL, Peng K, Sherwood KD, Pangratz-Fuehrer S, Rudolph U, Huguenard JR. Endogenous positive allosteric modulation of GABA(A) receptors by diazepam binding inhibitor. Neuron 2013; 78:1063-74. [PMID: 23727119 DOI: 10.1016/j.neuron.2013.04.026] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2013] [Indexed: 11/30/2022]
Abstract
Benzodiazepines (BZs) allosterically modulate γ-aminobutyric acid type-A receptors (GABAARs) to increase inhibitory synaptic strength. Diazepam binding inhibitor (DBI) protein is a BZ site ligand expressed endogenously in the brain, but functional evidence for BZ-mimicking positive modulatory actions has been elusive. We demonstrate an endogenous potentiation of GABAergic synaptic transmission and responses to GABA uncaging in the thalamic reticular nucleus (nRT) that is absent in both nm1054 mice, in which the Dbi gene is deleted, and mice in which BZ binding to α3 subunit-containing GABAARs is disrupted. Viral transduction of DBI into nRT is sufficient to rescue the endogenous potentiation of GABAergic transmission in nm1054 mice. Both mutations enhance thalamocortical spike-and-wave discharges characteristic of absence epilepsy. Together, these results indicate that DBI mediates endogenous nucleus-specific BZ-mimicking ("endozepine") roles to modulate nRT function and suppress thalamocortical oscillations. Enhanced DBI signaling might serve as a therapy for epilepsy and other neurological disorders.
Collapse
Affiliation(s)
- Catherine A Christian
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | | | | | | | | | | | | | | |
Collapse
|
38
|
Benzodiazepine-induced spatial learning deficits in rats are regulated by the degree of modulation of α1 GABA(A) receptors. Eur Neuropsychopharmacol 2013; 23:390-9. [PMID: 22633616 PMCID: PMC3448846 DOI: 10.1016/j.euroneuro.2012.05.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 02/25/2012] [Accepted: 05/05/2012] [Indexed: 11/21/2022]
Abstract
Despite significant advances in understanding the role of benzodiazepine (BZ)-sensitive populations of GABAA receptors, containing the α1, α2, α3 or α5 subunit, factual substrates of BZ-induced learning and memory deficits are not yet fully elucidated. It was shown that α1-subunit affinity-selective antagonist β-CCt almost completely abolished spatial learning deficits induced by diazepam (DZP) in the Morris water maze. We examined a novel, highly (105 fold) α1-subunit selective ligand-WYS8 (0.2, 1 and 10 mg/kg), on its own and in combination with the non-selective agonist DZP (2 mg/kg) or β-CCt (5 mg/kg) in the water maze in rats. The in vitro efficacy study revealed that WYS8 acts as α1-subtype selective weak partial positive modulator (40% potentiation at 100nM). Measurement of concentrations of WYS8 and DZP in rat serum and brain tissues suggested that they did not substantially cross-influence the respective disposition. In the water maze, DZP impaired spatial learning (acquisition trials) and memory (probe trial). WYS8 caused no effect per se, did not affect the overall influence of DZP on the water-maze performance and was devoid of any activity in this task when combined with β-CCt. Nonetheless, an additional analysis of the latency to reach the platform and the total distance swam suggested that WYS8 addition attenuated the run-down of the spatial impairment induced by DZP at the end of acquisition trials. These results demonstrate a clear difference in the influence of an α1 subtype-selective antagonist and a partial agonist on the effects of DZP on the water-maze acquisition.
Collapse
|
39
|
Sieghart W. Unravelling the role of GABAA receptor subtypes in distinct neurons and behaviour. J Physiol 2012; 590:2181-2. [PMID: 22589205 DOI: 10.1113/jphysiol.2012.231100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Werner Sieghart
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Austria.
| |
Collapse
|
40
|
Jo JY, Jeong JA, Pandit S, Stern JE, Lee SK, Ryu PD, Lee SY, Han SK, Cho CH, Kim HW, Jeon BH, Park JB. Neurosteroid modulation of benzodiazepine-sensitive GABAA tonic inhibition in supraoptic magnocellular neurons. Am J Physiol Regul Integr Comp Physiol 2011; 300:R1578-87. [PMID: 21451144 DOI: 10.1152/ajpregu.00627.2010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Interactions between neurosteroids and GABA receptors have attracted particular attention in the supraoptic nucleus (SON). Although GABA(A) receptors (GABA(A)R) mediate a sustained tonic inhibitory current (I(tonic)), as well as conventional phasic inhibitory postsynaptic currents (IPSCs, I(phasic)) in the SON, whether the steroid modulation on I(tonic) is present in SON magnocelluar neurosecretory cells (MNCs) is unknown. Here, we addressed this question and gained insights into the potential molecular configuration of GABA(A) receptors mediating I(tonic) and conferring its neurosteroids sensitivity in SON MNCs. 4,5,6,7-tetrahydroisoxazolo[5,4-c]-pyridin-3-ol (THIP) (1 μM), a relatively selective extrasynaptic GABA(A)R agonist, facilitated I(tonic) without affecting the main characteristics of IPSCs, while DS-2, a relatively selective modulator of GABA(A)R δ-subunits, caused minimal changes in I(tonic) of SON MNCs. l-655,708, a relatively selective GABA(A)R α(5)-subunit inverse agonist, blocked ∼35% of the total I(tonic) both under basal and elevated ambient GABA concentration (3 μM). Facilitation of I(tonic) by benzodiazepines further supported the role of GABA(A)R γ(2)-subunit in I(tonic) of SON MNCs. Quantitative RT-PCR analysis showed much lesser expression of GABA(A)R δ-subunit than the α(5) or γ(2)-subunit in the SON. Allopregnanolone and 3α,5α-tetrahydrodeoxycorticosterone increased both I(tonic) and I(phasic) in SON MNCs, respectively, although more than 90% of the current increase was mediated by I(tonic) during the neurosteroid facilitation. Finally, l-655,708 attenuated the neurosteroid facilitation of I(tonic) but not of I(phasic). Altogether, our results suggest that I(tonic), mediated mainly by benzodiazepine-sensitive GABA(A)Rs containing α(5)-, β-, and γ(2)-, and to a lesser extent, δ-subunits, is a potential target of neurosteroid modulation in SON neurons.
Collapse
Affiliation(s)
- Ji Yoon Jo
- Department of Physiology, School of Medicine, Chungnam National University, Daejeon, Korea
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
41
|
Abstract
GABA(A) receptors mediate the action of many clinically important drugs interacting with different binding sites. For some potential binding sites, no interacting drugs have yet been identified. Here, we established a steric hindrance procedure for the identification of drugs acting at the extracellular α1+β3- interface, which is homologous to the benzodiazepine binding site at the α1+γ2- interface. On screening of >100 benzodiazepine site ligands, the anxiolytic pyrazoloquinoline 2-p-methoxyphenylpyrazolo[4,3-c]quinolin-3(5H)-one (CGS 9895) was able to enhance GABA-induced currents at α1β3 receptors from rat. CGS 9895 acts as an antagonist at the benzodiazepine binding site at nanomolar concentrations, but enhances GABA-induced currents via a different site present at α1β3γ2 and α1β3 receptors. By mutating pocket-forming amino acid residues at the α1+ and the β3- side to cysteines, we demonstrated that covalent labeling of these cysteines by the methanethiosulfonate ethylamine reagent MTSEA-biotin was able to inhibit the effect of CGS 9895. The inhibition was not caused by a general inactivation of GABA(A) receptors, because the GABA-enhancing effect of ROD 188 or the steroid α-tetrahydrodeoxycorticosterone was not influenced by MTSEA-biotin. Other experiments indicated that the CGS 9895 effect was dependent on the α and β subunit types forming the interface. CGS 9895 thus represents the first prototype of drugs mediating benzodiazepine-like modulatory effects via the α+β- interface of GABA(A) receptors. Since such binding sites are present at αβ, αβγ, and αβδ receptors, such drugs will have a much broader action than benzodiazepines and might become clinical important for the treatment of epilepsy.
Collapse
|
42
|
Gross A, Sims RE, Swinny JD, Sieghart W, Bolam JP, Stanford IM. Differential localization of GABA(A) receptor subunits in relation to rat striatopallidal and pallidopallidal synapses. Eur J Neurosci 2011; 33:868-78. [PMID: 21219474 DOI: 10.1111/j.1460-9568.2010.07552.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
As a central integrator of basal ganglia function, the external segment of the globus pallidus (GP) plays a critical role in the control of voluntary movement. The GP is composed of a network of inhibitory GABA-containing projection neurons which receive GABAergic input from axons of the striatum (Str) and local collaterals of GP neurons. Here, using electrophysiological techniques and immunofluorescent labeling we have investigated the differential cellular distribution of α1, α2 and α3 GABA(A) receptor subunits in relation to striatopallidal (Str-GP) and pallidopallidal (GP-GP) synapses. Electrophysiological investigations showed that zolpidem (100 nm; selective for the α1 subunit) increased the amplitude and the decay time of both Str-GP and GP-GP IPSCs, indicating the presence of the α1 subunits at both synapses. However, the application of drugs selective for the α2, α3 and α5 subunits (zolpidem at 400 nm, L-838,417 and TP003) revealed differential effects on amplitude and decay time of IPSCs, suggesting the nonuniform distribution of non-α1 subunits. Immunofluorescence revealed widespread distribution of the α1 subunit at both soma and dendrites, while double- and triple-immunofluorescent labeling for parvalbumin, enkephalin, gephyrin and the γ2 subunit indicated strong immunoreactivity for GABA(A) α3 subunits in perisomatic synapses, a region mainly targeted by local axon collaterals. In contrast, immunoreactivity for synaptic GABA(A) α2 subunits was observed in dendritic compartments where striatal synapses are preferentially located. Due to the kinetic properties which each GABA(A) α subunit confers, this distribution is likely to contribute differentially to both physiological and pathological patterns of activity.
Collapse
Affiliation(s)
- A Gross
- Aston University, School of Life and Health Sciences, Birmingham, UK
| | | | | | | | | | | |
Collapse
|