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Sharmin D, Mian MY, Marcotte M, Prevot TD, Sibille E, Witkin JM, Cook JM. Synthesis and Receptor Binding Studies of α5 GABA AR Selective Novel Imidazodiazepines Targeted for Psychiatric and Cognitive Disorders. Molecules 2023; 28:4771. [PMID: 37375326 DOI: 10.3390/molecules28124771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 06/09/2023] [Accepted: 06/12/2023] [Indexed: 06/29/2023] Open
Abstract
GABA mediates inhibitory actions through various GABAA receptor subtypes, including 19 subunits in human GABAAR. Dysregulation of GABAergic neurotransmission is associated with several psychiatric disorders, including depression, anxiety, and schizophrenia. Selective targeting of α2/3 GABAARs can treat mood and anxiety, while α5 GABAA-Rs can treat anxiety, depression, and cognitive performance. GL-II-73 and MP-III-022, α5-positive allosteric modulators have shown promising results in animal models of chronic stress, aging, and cognitive disorders, including MDD, schizophrenia, autism, and Alzheimer's disease. Described in this article is how small changes in the structure of imidazodiazepine substituents can greatly impact the subtype selectivity of benzodiazepine GABAAR. To investigate alternate and potentially more effective therapeutic compounds, modifications were made to the structure of imidazodiazepine 1 to synthesize different amide analogs. The novel ligands were screened at the NIMH PDSP against a panel of 47 receptors, ion channels, including hERG, and transporters to identify on- and off-target interactions. Any ligands with significant inhibition in primary binding were subjected to secondary binding assays to determine their Ki values. The newly synthesized imidazodiazepines were found to have variable affinities for the benzodiazepine site and negligible or no binding to any off-target profile receptors that could cause other physiological problems.
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Affiliation(s)
- Dishary Sharmin
- Department of Chemistry and Biochemistry, Milwaukee Institute of Drug Discovery, University of Wisconsin Milwaukee, Milwaukee, WI 53201, USA
| | - Md Yeunus Mian
- Department of Chemistry and Biochemistry, Milwaukee Institute of Drug Discovery, University of Wisconsin Milwaukee, Milwaukee, WI 53201, USA
| | - Michael Marcotte
- Campbell Family Mental Health Research Institute of CAMH, Toronto, ON M5S 2S1, Canada
| | - Thomas D Prevot
- Campbell Family Mental Health Research Institute of CAMH, Toronto, ON M5S 2S1, Canada
- Department of Psychiatry, University of Toronto, Toronto, ON M5T 1R8, Canada
| | - Etienne Sibille
- Campbell Family Mental Health Research Institute of CAMH, Toronto, ON M5S 2S1, Canada
- Department of Psychiatry, University of Toronto, Toronto, ON M5T 1R8, Canada
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5T 1R8, Canada
| | - Jeffrey M Witkin
- Department of Chemistry and Biochemistry, Milwaukee Institute of Drug Discovery, University of Wisconsin Milwaukee, Milwaukee, WI 53201, USA
- Laboratory of Antiepileptic Drug Discovery, Ascension, St. Vincent, Indianapolis, IN 46260, USA
| | - James M Cook
- Department of Chemistry and Biochemistry, Milwaukee Institute of Drug Discovery, University of Wisconsin Milwaukee, Milwaukee, WI 53201, USA
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Meanwell NA. The pyridazine heterocycle in molecular recognition and drug discovery. Med Chem Res 2023; 32:1-69. [PMID: 37362319 PMCID: PMC10015555 DOI: 10.1007/s00044-023-03035-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Accepted: 02/06/2023] [Indexed: 03/17/2023]
Abstract
The pyridazine ring is endowed with unique physicochemical properties, characterized by weak basicity, a high dipole moment that subtends π-π stacking interactions and robust, dual hydrogen-bonding capacity that can be of importance in drug-target interactions. These properties contribute to unique applications in molecular recognition while the inherent polarity, low cytochrome P450 inhibitory effects and potential to reduce interaction of a molecule with the cardiac hERG potassium channel add additional value in drug discovery and development. The recent approvals of the gonadotropin-releasing hormone receptor antagonist relugolix (24) and the allosteric tyrosine kinase 2 inhibitor deucravacitinib (25) represent the first examples of FDA-approved drugs that incorporate a pyridazine ring. In this review, the properties of the pyridazine ring are summarized in comparison to the other azines and its potential in drug discovery is illustrated through vignettes that explore applications that take advantage of the inherent physicochemical properties as an approach to solving challenges associated with candidate optimization. Graphical Abstract
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Ali AB, Islam A, Constanti A. The fate of interneurons, GABA A receptor sub-types and perineuronal nets in Alzheimer's disease. Brain Pathol 2022; 33:e13129. [PMID: 36409151 PMCID: PMC9836378 DOI: 10.1111/bpa.13129] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 10/12/2022] [Indexed: 11/23/2022] Open
Abstract
Alzheimer's disease (AD) is the most common neurological disease, which is associated with gradual memory loss and correlated with synaptic hyperactivity and abnormal oscillatory rhythmic brain activity that precedes phenotypic alterations and is partly responsible for the spread of the disease pathology. Synaptic hyperactivity is thought to be because of alteration in the homeostasis of phasic and tonic synaptic inhibition, which is orchestrated by the GABAA inhibitory system, encompassing subclasses of interneurons and GABAA receptors, which play a vital role in cognitive functions, including learning and memory. Furthermore, the extracellular matrix, the perineuronal nets (PNNs) which often go unnoticed in considerations of AD pathology, encapsulate the inhibitory cells and neurites in critical brain regions and have recently come under the light for their crucial role in synaptic stabilisation and excitatory-inhibitory balance and when disrupted, serve as a potential trigger for AD-associated synaptic imbalance. Therefore, in this review, we summarise the current understanding of the selective vulnerability of distinct interneuron subtypes, their synaptic and extrasynaptic GABAA R subtypes as well as the changes in PNNs in AD, detailing their contribution to the mechanisms of disease development. We aim to highlight how seemingly unique malfunction in each component of the interneuronal GABA inhibitory system can be tied together to result in critical circuit dysfunction, leading to the irreversible symptomatic damage observed in AD.
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Distinct sex-dependent behavioral responses induced by two positive allosteric modulators of alpha 5 subunit-containing GABAA receptors. Behav Brain Res 2022; 428:113832. [DOI: 10.1016/j.bbr.2022.113832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 02/24/2022] [Accepted: 03/03/2022] [Indexed: 11/18/2022]
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Santrač A, Batinić B, Stamenić TT, Aranđelović J, Sharmin D, Knutson DE, Cook JM, Savić MM. Positive modulation of α5GABAA receptors leads to dichotomous effects in rats on memory pattern and GABRA5 expression in prefrontal cortex and hippocampus. Behav Brain Res 2022; 416:113578. [PMID: 34508769 DOI: 10.1016/j.bbr.2021.113578] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Revised: 08/22/2021] [Accepted: 09/06/2021] [Indexed: 01/04/2023]
Abstract
Positive allosteric modulators (PAMs) of α5GABAA receptors (α5GABAARs) are emerging as potential therapeutics for a range of neuropsychiatric disorders. However, their role in memory processing of healthy animals is not sufficiently examined. We tested the effects of MP-III-022 (1 mg/kg, 2.5 mg/kg and 10 mg/kg), a PAM known to be selective for α5GABAARs and devoid of prominent side-effects, in different behavioral paradigms (Morris water maze, novel object recognition test and social novelty discrimination) and on GABRA5 expression in Wistar rats, 30 min and 24 h after intraperitoneal treatment administration. The lowest dose tested worsened short-term object memory. The same dose, administered two times in a span of 24 h, improved spatial and impaired object and, at a trend level, social memory. The highest dose had a detrimental effect on all types of long-term memory (object memory at a trend level) and short-term spatial memory, but improved short-term object and social memory. Distinct sets of expression changes were detected in both prefrontal cortex and two regions of the hippocampus, but the latter ones could be assessed as more consequential. An increase of GABRA5 mRNA in CA2 occurred in parallel with improvement of object and social, but impairment of spatial memory, while the opposite happened with a trend level change in CA1. Our study demonstrates the variability of the roles of the α5GABAAR based on its level of expression and localization, in dependence on the type and protocol of cognitive tasks, as well as the respective timing of pharmacological modulation and testing.
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Affiliation(s)
- Anja Santrač
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Bojan Batinić
- Department of Physiology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Tamara Timić Stamenić
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Jovana Aranđelović
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia
| | - Dishary Sharmin
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee and the Milwaukee Institute of Drug Discovery, P.O.Box 413, Milwaukee, WI 53201, USA
| | - Daniel E Knutson
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee and the Milwaukee Institute of Drug Discovery, P.O.Box 413, Milwaukee, WI 53201, USA
| | - James M Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee and the Milwaukee Institute of Drug Discovery, 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.
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Tonic GABA A Receptor-Mediated Currents of Human Cortical GABAergic Interneurons Vary Amongst Cell Types. J Neurosci 2021; 41:9702-9719. [PMID: 34667071 PMCID: PMC8612645 DOI: 10.1523/jneurosci.0175-21.2021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 09/08/2021] [Accepted: 09/10/2021] [Indexed: 12/03/2022] Open
Abstract
Persistent anion conductances through GABAA receptors (GABAARs) are important modulators of neuronal excitability. However, it is currently unknown how the amplitudes of these currents vary among different cell types in the human neocortex, particularly among diverse GABAergic interneurons. We have recorded 101 interneurons in and near layer 1 from cortical tissue surgically resected from both male and female patients, visualized 84 of them and measured tonic GABAAR currents in 48 cells with an intracellular [Cl–] of 65 mm and in the presence of 5 μm GABA. We compare these tonic currents among five groups of interneurons divided by firing properties and four types of interneuron defined by axonal distributions; rosehip, neurogliaform, stalked-bouton, layer 2–3 innervating and a pool of other cells. Interestingly, the rosehip cell, a type of interneuron only described thus far in human tissue, and layer 2–3 innervating cells exhibit larger tonic currents than other layer 1 interneurons, such as neurogliaform and stalked-bouton cells; the latter two groups showing no difference. The positive allosteric modulators of GABAARs allopregnanolone and DS2 also induced larger current shifts in the rosehip and layer 2–3 innervating cells, consistent with higher expression of the δ subunit of the GABAAR in these neurons. We have also examined how patient parameters, such as age, seizures, type of cancer and anticonvulsant treatment may alter tonic inhibitory currents in human neurons. The cell type-specific differences in tonic inhibitory currents could potentially be used to selectively modulate cortical circuitry. SIGNIFICANCE STATEMENT Tonic currents through GABAA receptors (GABAARs) are a potential therapeutic target for a number of neurologic and psychiatric conditions. Here, we show that these currents in human cerebral cortical GABAergic neurons display cell type-specific differences in their amplitudes which implies differential modulation of their excitability. Additionally, we examine whether the amplitudes of the tonic currents measured in our study show any differences between patient populations, finding some evidence that age, seizures, type of cancer, and anticonvulsant treatment may alter tonic inhibition in human tissue. These results advance our understanding of how pathology affects neuronal excitability and could potentially be used to selectively modulate cortical circuitry.
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McGinnity CJ, Riaño Barros DA, Hinz R, Myers JF, Yaakub SN, Thyssen C, Heckemann RA, de Tisi J, Duncan JS, Sander JW, Lingford-Hughes A, Koepp MJ, Hammers A. Αlpha 5 subunit-containing GABA A receptors in temporal lobe epilepsy with normal MRI. Brain Commun 2021; 3:fcaa190. [PMID: 33501420 PMCID: PMC7811756 DOI: 10.1093/braincomms/fcaa190] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Revised: 09/06/2020] [Accepted: 09/24/2020] [Indexed: 01/08/2023] Open
Abstract
GABAA receptors containing the α5 subunit mediate tonic inhibition and are widely expressed in the limbic system. In animals, activation of α5-containing receptors impairs hippocampus-dependent memory. Temporal lobe epilepsy is associated with memory impairments related to neuron loss and other changes. The less selective PET ligand [11C]flumazenil has revealed reductions in GABAA receptors. The hypothesis that α5 subunit receptor alterations are present in temporal lobe epilepsy and could contribute to impaired memory is untested. We compared α5 subunit availability between individuals with temporal lobe epilepsy and normal structural MRI ('MRI-negative') and healthy controls, and interrogated the relationship between α5 subunit availability and episodic memory performance, in a cross-sectional study. Twenty-three healthy male controls (median ± interquartile age 49 ± 13 years) and 11 individuals with MRI-negative temporal lobe epilepsy (seven males; 40 ± 8) had a 90-min PET scan after bolus injection of [11C]Ro15-4513, with arterial blood sampling and metabolite correction. All those with epilepsy and six controls completed the Adult Memory and Information Processing Battery on the scanning day. 'Bandpass' exponential spectral analyses were used to calculate volumes of distribution separately for the fast component [V F; dominated by signal from α1 (α2, α3)-containing receptors] and the slow component (V S; dominated by signal from α5-containing receptors). We made voxel-by-voxel comparisons between: the epilepsy and control groups; each individual case versus the controls. We obtained parametric maps of V F and V S measures from a single bolus injection of [11C]Ro15-4513. The epilepsy group had higher V S in anterior medial and lateral aspects of the temporal lobes, the anterior cingulate gyri, the presumed area tempestas (piriform cortex) and the insulae, in addition to increases of ∼24% and ∼26% in the ipsilateral and contralateral hippocampal areas (P < 0.004). This was associated with reduced V F:V S ratios within the same areas (P < 0.009). Comparisons of V S for each individual with epilepsy versus controls did not consistently lateralize the epileptogenic lobe. Memory scores were significantly lower in the epilepsy group than in controls (mean ± standard deviation -0.4 ± 1.0 versus 0.7 ± 0.3; P = 0.02). In individuals with epilepsy, hippocampal V S did not correlate with memory performance on the Adult Memory and Information Processing Battery. They had reduced V F in the hippocampal area, which was significant ipsilaterally (P = 0.03), as expected from [11C]flumazenil studies. We found increased tonic inhibitory neurotransmission in our cohort of MRI-negative temporal lobe epilepsy who also had co-morbid memory impairments. Our findings are consistent with a subunit shift from α1/2/3 to α5 in MRI-negative temporal lobe epilepsy.
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Affiliation(s)
- Colm J McGinnity
- Centre for Neuroscience, Department of Medicine, Imperial College London, London W12 0NN, UK
- MRC Clinical Sciences Centre, Hammersmith Hospital, London W12 0NN, UK
- King's College London & Guy's and St Thomas' PET Centre, School of Biomedical Engineering & Imaging Sciences, King’s College London, London SE1 7EH, UK
| | - Daniela A Riaño Barros
- Centre for Neuroscience, Department of Medicine, Imperial College London, London W12 0NN, UK
- MRC Clinical Sciences Centre, Hammersmith Hospital, London W12 0NN, UK
| | - Rainer Hinz
- Wolfson Molecular Imaging Centre, University of Manchester, Manchester M20 3LJ, UK
| | - James F Myers
- Centre for Neuroscience, Department of Medicine, Imperial College London, London W12 0NN, UK
| | - Siti N Yaakub
- King's College London & Guy's and St Thomas' PET Centre, School of Biomedical Engineering & Imaging Sciences, King’s College London, London SE1 7EH, UK
| | - Charlotte Thyssen
- Medical Image and Signal Processing (MEDISIP), Department of Electronics and Information Systems, Faculty of Engineering and Architecture, Ghent University, 9000 Ghent, Belgium
| | - Rolf A Heckemann
- Department of Medical Radiation Sciences, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden
| | - Jane de Tisi
- NIHR University College London Hospitals Biomedical Research Centre, UCL Queen Square Institute of Neurology, London WC1N 3BG, UK, and Chalfont Centre for Epilepsy, Chalfont St Peter SL9 0RJ, UK
| | - John S Duncan
- NIHR University College London Hospitals Biomedical Research Centre, UCL Queen Square Institute of Neurology, London WC1N 3BG, UK, and Chalfont Centre for Epilepsy, Chalfont St Peter SL9 0RJ, UK
| | - Josemir W Sander
- NIHR University College London Hospitals Biomedical Research Centre, UCL Queen Square Institute of Neurology, London WC1N 3BG, UK, and Chalfont Centre for Epilepsy, Chalfont St Peter SL9 0RJ, UK
- Stichting Epilepsie Instellingen Nederland (SEIN), Heemstede 2103SW, The Netherlands
| | - Anne Lingford-Hughes
- Neuropsychopharmacology Unit, Centre for Psychiatry, Department of Brain Sciences, Faculty of Medicine, Imperial College London, London W12 0NN, UK
| | - Matthias J Koepp
- NIHR University College London Hospitals Biomedical Research Centre, UCL Queen Square Institute of Neurology, London WC1N 3BG, UK, and Chalfont Centre for Epilepsy, Chalfont St Peter SL9 0RJ, UK
| | - Alexander Hammers
- Centre for Neuroscience, Department of Medicine, Imperial College London, London W12 0NN, UK
- MRC Clinical Sciences Centre, Hammersmith Hospital, London W12 0NN, UK
- King's College London & Guy's and St Thomas' PET Centre, School of Biomedical Engineering & Imaging Sciences, King’s College London, London SE1 7EH, UK
- Neurodis Foundation, CERMEP, Imagerie du Vivant, 69003 Lyon, France
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Impaired Expression of GABA Signaling Components in the Alzheimer's Disease Middle Temporal Gyrus. Int J Mol Sci 2020; 21:ijms21228704. [PMID: 33218044 PMCID: PMC7698927 DOI: 10.3390/ijms21228704] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 11/13/2020] [Accepted: 11/16/2020] [Indexed: 12/26/2022] Open
Abstract
γ-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter, playing a central role in the regulation of cortical excitability and the maintenance of the excitatory/inhibitory (E/I) balance. Several lines of evidence point to a remodeling of the cerebral GABAergic system in Alzheimer’s disease (AD), with past studies demonstrating alterations in GABA receptor and transporter expression, GABA synthesizing enzyme activity and focal GABA concentrations in post-mortem tissue. AD is a chronic neurodegenerative disorder with a poorly understood etiology and the temporal cortex is one of the earliest regions in the brain to be affected by AD neurodegeneration. Utilizing NanoString nCounter analysis, we demonstrate here the transcriptional downregulation of several GABA signaling components in the post-mortem human middle temporal gyrus (MTG) in AD, including the GABAA receptor α1, α2, α3, α5, β1, β2, β3, δ, γ2, γ3, and θ subunits and the GABAB receptor 2 (GABABR2) subunit. In addition to this, we note the transcriptional upregulation of the betaine-GABA transporter (BGT1) and GABA transporter 2 (GAT2), and the downregulation of the 67 kDa isoform of glutamate decarboxylase (GAD67), the primary GABA synthesizing enzyme. The functional consequences of these changes require further investigation, but such alterations may underlie disruptions to the E/I balance that are believed to contribute to cognitive decline in AD.
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Vinnakota C, Govindpani K, Tate WP, Peppercorn K, Anekal PV, Waldvogel HJ, Faull RLM, Kwakowsky A. An 5 GABAA Receptor Inverse Agonist, 5IA, Attenuates Amyloid Beta-Induced Neuronal Death in Mouse Hippocampal Cultures. Int J Mol Sci 2020; 21:ijms21093284. [PMID: 32384683 PMCID: PMC7247548 DOI: 10.3390/ijms21093284] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 04/28/2020] [Accepted: 04/29/2020] [Indexed: 12/30/2022] Open
Abstract
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder for which no cognition-restoring therapies exist. Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the brain. Increasing evidence suggests a remodeling of the GABAergic system in AD, which might represent an important therapeutic target. An inverse agonist of α5 subunit-containing GABAA receptors (α5GABAARs), 3-(5-Methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-yl)methyloxy]-1,2,4-triazolo[3–a]phthalazine (α5IA) has cognition-enhancing properties. This study aimed to characterize the effects of α5IA on amyloid beta (Aβ1–42)-induced molecular and cellular changes. Mouse primary hippocampal cultures were exposed to either Aβ1-42 alone, or α5IA alone, α5IA with Aβ1–42 or vehicle alone, and changes in cell viability and mRNA expression of several GABAergic signaling components were assessed. Treatment with 100 nM of α5IA reduced Aβ1–42-induced cell loss by 23.8% (p < 0.0001) after 6 h and by 17.3% after 5 days of treatment (p < 0.0001). Furthermore, we observed an Aβ1-42-induced increase in ambient GABA levels, as well as upregulated mRNA expression of the GABAAR α2,α5,β2/3 subunits and the GABABR R1 and R2 subunits. Such changes in GABARs expression could potentially disrupt inhibitory neurotransmission and normal network activity. Treatment with α5IA restored Aβ1-42-induced changes in the expression of α5GABAARs. In summary, this compound might hold neuroprotective potential and represent a new therapeutic avenue for AD.
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Affiliation(s)
- Chitra Vinnakota
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health, Sciences, University of Auckland, Auckland 1023, New Zealand; (C.V.); (K.G.); (H.J.W.); (R.L.M.F.)
| | - Karan Govindpani
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health, Sciences, University of Auckland, Auckland 1023, New Zealand; (C.V.); (K.G.); (H.J.W.); (R.L.M.F.)
| | - Warren Perry Tate
- Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand; (W.P.T.); (K.P.)
| | - Katie Peppercorn
- Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand; (W.P.T.); (K.P.)
| | - Praju Vikas Anekal
- Biomedical Imaging Research Unit, Faculty of Medical and Health Sciences, University of Auckland, Auckland 1023, New Zealand;
| | - Henry John Waldvogel
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health, Sciences, University of Auckland, Auckland 1023, New Zealand; (C.V.); (K.G.); (H.J.W.); (R.L.M.F.)
| | - Richard Lewis Maxwell Faull
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health, Sciences, University of Auckland, Auckland 1023, New Zealand; (C.V.); (K.G.); (H.J.W.); (R.L.M.F.)
| | - Andrea Kwakowsky
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health, Sciences, University of Auckland, Auckland 1023, New Zealand; (C.V.); (K.G.); (H.J.W.); (R.L.M.F.)
- Correspondence: ; Tel.: +64-9923-9346
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10
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Nguyen AQ, Koeppen J, Woodruff S, Mina K, Figueroa Z, Ethell IM. Astrocytic Ephrin-B1 Controls Synapse Formation in the Hippocampus During Learning and Memory. Front Synaptic Neurosci 2020; 12:10. [PMID: 32256333 PMCID: PMC7092624 DOI: 10.3389/fnsyn.2020.00010] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 02/24/2020] [Indexed: 01/20/2023] Open
Abstract
Astrocytes play a fundamental role in synapse formation, pruning, and plasticity, which are associated with learning and memory. However, the role of astrocytes in learning and memory is still largely unknown. Our previous study showed that astrocyte-specific ephrin-B1 knock-out (KO) enhanced but ephrin-B1 overexpression (OE) in hippocampal astrocytes impaired contextual memory recall following fear conditioning. The goal of this study was to understand the mechanism by which astrocytic ephrin-B1 influences learning; specifically, learning-induced remodeling of synapses and dendritic spines in CA1 hippocampus using fear-conditioning paradigm. While we found a higher dendritic spine density and clustering on c-Fos-positive (+) neurons activated during contextual memory recall in both wild-type (WT) and KO mice, overall spine density and mEPSC amplitude were increased in CA1 neurons of KO compared to WT. In contrast, ephrin-B1 OE in hippocampal astrocytes impaired dendritic spine formation and clustering, specifically on c-Fos(+) neurons, coinciding with an overall decrease in vGlut1/PSD95 co-localization. Although astrocytic ephrin-B1 influenced learning-induced spine formation, the changes in astrocytic ephrin-B1 levels did not affect spine enlargement as no genotype differences in spine volume were observed between trained WT, KO, and OE groups. Our results suggest that a reduced formation of new spines rather than spine maturation in activated CA1 hippocampal neurons is most likely responsible for impaired contextual learning in OE mice due to abundantly high ephrin-B1 levels in astrocytes. The ability of astrocytic ephrin-B1 to negatively influence new spine formation during learning can potentially regulate new synapse formation at specific dendritic domains and underlie memory encoding.
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Affiliation(s)
- Amanda Q. Nguyen
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
- Neuroscience Graduate Program, University of California, Riverside, Riverside, CA, United States
| | - Jordan Koeppen
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
- Cell, Molecular, and Developmental Biology Graduate Program, University of California, Riverside, Riverside, CA, United States
| | - Simone Woodruff
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
| | - Karen Mina
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
| | - Zoe Figueroa
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
| | - Iryna M. Ethell
- Division of Biomedical Sciences, University of California Riverside School of Medicine, Riverside, CA, United States
- Neuroscience Graduate Program, University of California, Riverside, Riverside, CA, United States
- Cell, Molecular, and Developmental Biology Graduate Program, University of California, Riverside, Riverside, CA, United States
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Vega Alanis BA, Iorio MT, Silva LL, Bampali K, Ernst M, Schnürch M, Mihovilovic MD. Allosteric GABA A Receptor Modulators-A Review on the Most Recent Heterocyclic Chemotypes and Their Synthetic Accessibility. Molecules 2020; 25:E999. [PMID: 32102309 PMCID: PMC7070463 DOI: 10.3390/molecules25040999] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 02/18/2020] [Accepted: 02/19/2020] [Indexed: 11/17/2022] Open
Abstract
GABAA receptor modulators are structurally almost as diverse as their target protein. A plethora of heterocyclic scaffolds has been described as modulating this extremely important receptor family. Some made it into clinical trials and, even on the market, some were dismissed. This review focuses on the synthetic accessibility and potential for library synthesis of GABAA receptor modulators containing at least one heterocyclic scaffold, which were disclosed within the last 10 years.
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Affiliation(s)
- Blanca Angelica Vega Alanis
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Maria Teresa Iorio
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Luca L. Silva
- Department of Anesthesiology and Intensive Care Medicine, Charité–Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany;
| | - Konstantina Bampali
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria;
| | - Margot Ernst
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria;
| | - Michael Schnürch
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
| | - Marko D. Mihovilovic
- Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/193, 1060 Vienna, Austria; (B.A.V.A.); (M.T.I.); (M.D.M.)
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GABA A Receptors Are Well Preserved in the Hippocampus of Aged Mice. eNeuro 2019; 6:ENEURO.0496-18.2019. [PMID: 31340951 PMCID: PMC6709233 DOI: 10.1523/eneuro.0496-18.2019] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 07/02/2019] [Accepted: 07/15/2019] [Indexed: 01/04/2023] Open
Abstract
GABA is the primary inhibitory neurotransmitter in the nervous system. GABAA receptors (GABAARs) are pentameric ionotropic channels. Subunit composition of the receptors is associated with the affinity of GABA binding and its downstream inhibitory actions. Fluctuations in subunit expression levels with increasing age have been demonstrated in animal and human studies. However, our knowledge regarding the age-related hippocampal GABAAR expression changes is limited and based on rat studies. This study is the first analysis of the aging-related changes of the GABAAR subunit expression in the CA1, CA2/3, and dentate gyrus regions of the mouse hippocampus. Using Western blotting and immunohistochemistry we found that the GABAergic system is robust, with no significant age-related differences in GABAAR α1, α2, α3, α5, β3, and γ2 subunit expression level differences found between the young (6 months) and old (21 months) age groups in any of the hippocampal regions examined. However, we detected a localized decrease of α2 subunit expression around the soma, proximal dendrites, and in the axon initial segment of pyramidal cells in the CA1 and CA3 regions that is accompanied by a pronounced upregulation of the α2 subunit immunoreactivity in the neuropil of aged mice. In summary, GABAARs are well preserved in the mouse hippocampus during normal aging although GABAARs in the hippocampus are severely affected in age-related neurological disorders, including Alzheimer’s disease.
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Solomon VR, Tallapragada VJ, Chebib M, Johnston G, Hanrahan JR. GABA allosteric modulators: An overview of recent developments in non-benzodiazepine modulators. Eur J Med Chem 2019; 171:434-461. [DOI: 10.1016/j.ejmech.2019.03.043] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Revised: 02/17/2019] [Accepted: 03/17/2019] [Indexed: 01/13/2023]
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Kwakowsky A, Calvo-Flores Guzmán B, Pandya M, Turner C, Waldvogel HJ, Faull RL. GABA A receptor subunit expression changes in the human Alzheimer's disease hippocampus, subiculum, entorhinal cortex and superior temporal gyrus. J Neurochem 2019; 145:374-392. [PMID: 29485232 DOI: 10.1111/jnc.14325] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 01/17/2018] [Accepted: 02/12/2018] [Indexed: 12/14/2022]
Abstract
Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABA type A receptors (GABAA Rs) are severely affected in Alzheimer's disease (AD). However, the distribution and subunit composition of GABAA Rs in the AD brain are not well understood. This is the first comprehensive study to show brain region- and cell layer-specific alterations in the expression of the GABAA R subunits α1-3, α5, β1-3 and γ2 in the human AD hippocampus, entorhinal cortex and superior temporal gyrus. In late-stage AD tissue samples using immunohistochemistry we found significant alteration of all investigated GABAA Rs subunits except for α3 and β1 that were well preserved. The most prominent changes include an increase in GABAA R α1 expression associated with AD in all layers of the CA3 region, in the stratum (str.) granulare and hilus of the dentate gyrus. We found a significant increase in GABAA R α2 expression in the str. oriens of the CA1-3, str. radiatum of the CA2,3 and decrease in the str. pyramidale of the CA1 region in AD cases. In AD there was a significant increase in GABAA R α5 subunit expression in str. pyramidale, str. oriens of the CA1 region and decrease in the superior temporal gyrus. We also found a significant decrease in the GABAA R β3 subunit immunoreactivity in the str. oriens of the CA2, str. granulare and str. moleculare of the dentate gyrus. In conclusion, these findings indicate that the expression of the GABAA R subunits shows brain region- and layer-specific alterations in AD, and these changes could significantly influence and alter GABAA R function in the disease. Cover Image for this issue: doi: 10.1111/jnc.14179.
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Affiliation(s)
- Andrea Kwakowsky
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Beatriz Calvo-Flores Guzmán
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Madhavi Pandya
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Clinton Turner
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.,Department of Anatomical Pathology, LabPlus, Auckland City Hospital, Auckland, New Zealand
| | - Henry J Waldvogel
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Richard L Faull
- Centre for Brain Research, Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
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Eimerbrink M, Pendry R, Hodges S, Wiles J, Peterman J, White J, Hayes H, Chumley M, Boehm G. The α5-GABAAR inverse agonist MRK-016 upregulates hippocampal BDNF expression and prevents cognitive deficits in LPS-treated mice, despite elevations in hippocampal Aβ. Behav Brain Res 2019; 359:871-877. [DOI: 10.1016/j.bbr.2018.07.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 07/03/2018] [Accepted: 07/19/2018] [Indexed: 12/18/2022]
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Chagraoui A, Skiba M, Thuillez C, Thibaut F. To what extent is it possible to dissociate the anxiolytic and sedative/hypnotic properties of GABAA receptors modulators? Prog Neuropsychopharmacol Biol Psychiatry 2016; 71:189-202. [PMID: 27495357 DOI: 10.1016/j.pnpbp.2016.08.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 07/21/2016] [Accepted: 08/01/2016] [Indexed: 01/16/2023]
Abstract
The relatively common view indicates a possible dissociation between the anxiolytic and sedative/hypnotic properties of benzodiazepines (BZs). Indeed, GABAA receptor (GABAAR) subtypes have specific cerebral distribution in distinct neural circuits. Thus, GABAAR subtype-selective drugs may be expected to perform distinct functions. However, standard behavioral test assays provide limited direction towards highlighting new action mechanisms of ligands targeting GABAARs. Automated behavioral tests, lack sensitivity as some behavioral characteristics or subtle behavioral changes of drug effects or that are not considered in the overall analysis (Ohl et al., 2001) and observation-based analyses are not always performed. In addition, despite the use of genetically engineered mice, any possible dissociation between the anxiolytic and sedative properties of BZs remains controversial. Moreover, the involvement the different subtypes of GABAAR subtypes in the anxious behavior and the mechanism of action of anxiolytic agents remains unclear since there has been little success in the pharmacological investigations so far. This raises the question of the involvement of the different subunits in anxiolytic-like and/or sedative effects; and the actual implication of these subunits, particularly, α-subunits in the modulation of sedation and/or anxiety-related disorders. This present review was prompted by several conflicting studies on the degree of involvement of these subunits in anxiolytic-like and/or sedative effects. To this end, we explored the GABAergic system, particularly, the role of different subunits containing synaptic GABAARs. We report herein the targeting gene encoding the different subunits and their contribution in anxiolytic-like and/or sedative actions, as well as, the mechanism underlying tolerance to BZs.
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Affiliation(s)
- A Chagraoui
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, Institute for Research and Innovation in Biomedecine, Normandy University, France; Department of Medical Biochemistry, Rouen University Hospital, Rouen, France.
| | - M Skiba
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, Institute for Research and Innovation in Biomedecine, Normandy University, France
| | - C Thuillez
- Department of Pharmacology, Rouen University Hospital, Rouen, and INSERM U1096, Laboratory of New Pharmacological Targets for Endothelial Protection and Heart Failure, Institute for Research and Innovation in Biomedicine, Normandy University, France
| | - F Thibaut
- Department of Psychiatry, University Hospital Cochin (site Tarnier), University of Paris-Descartes and INSERM U 894 Laboratory of Psychiatry and Neurosciences, Paris, France
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Hamid K, Ng I, Tallapragada VJ, Váradi L, Hibbs DE, Hanrahan J, Groundwater PW. An Investigation of the Differential Effects of Ursane Triterpenoids fromCentella asiatica, and Their Semisynthetic Analogues, on GABAAReceptors. Chem Biol Drug Des 2016; 88:386-97. [DOI: 10.1111/cbdd.12766] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 02/29/2016] [Accepted: 03/28/2016] [Indexed: 11/27/2022]
Affiliation(s)
- Kaiser Hamid
- Faculty of Pharmacy; The University of Sydney; Sydney NSW 2006 Australia
| | - Irene Ng
- Faculty of Pharmacy; The University of Sydney; Sydney NSW 2006 Australia
| | | | - Linda Váradi
- Faculty of Pharmacy; The University of Sydney; Sydney NSW 2006 Australia
| | - David E. Hibbs
- Faculty of Pharmacy; The University of Sydney; Sydney NSW 2006 Australia
| | - Jane Hanrahan
- Faculty of Pharmacy; The University of Sydney; Sydney NSW 2006 Australia
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Formation of GABA A receptor complexes containing α1 and α5 subunits is paralleling a multiple T-maze learning task in mice. Brain Struct Funct 2016; 222:549-561. [PMID: 27155990 DOI: 10.1007/s00429-016-1233-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 04/28/2016] [Indexed: 10/21/2022]
Abstract
There is limited information on the role of GABA type A receptors (GABAARs) containing α1, α5 and γ2 subunits in learning and memory. Here, we assessed the possible role of such receptors in spatial learning using the multiple T-maze (MTM) paradigm. C57BL/6J mice were trained in the MTM which induced elevated levels of α1 and α5 subunit-containing hippocampal GABAAR complexes. Moreover, spatial learning evoked a significant increase in the colocalization of α1 and α5 subunits in both, CA1 and dentate gyrus regions of the hippocampus suggesting the formation of complexes containing both subunits. Additionally, the presence of α1, α5 and γ2 subunits in high molecular weight GABAARs was detected and significant correlation in the level of α1-containing complexes with those containing α5 and γ2 subunits was demonstrated. Accordingly, α1 deficiency led to decreased levels of γ2 subunit-containing complexes, however, had no effect on α5-containing ones. On the other hand, α1 knockout mice showed impaired performance in the MTM correlating with increased levels of α5 subunit-containing GABAARs in comparison to trained floxed control animals which quickly learned the task. Taken together, these results suggest that α1, α5 and γ2-containing hippocampal GABAAR complexes play an essential role in spatial learning and memory in which targeted disruption of the α1 subunit produces profound deficits.
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Hoestgaard-Jensen K, O'Connor RM, Dalby NO, Simonsen C, Finger BC, Golubeva A, Hammer H, Bergmann ML, Kristiansen U, Krogsgaard-Larsen P, Bräuner-Osborne H, Ebert B, Frølund B, Cryan JF, Jensen AA. The orthosteric GABAA receptor ligand Thio-4-PIOL displays distinctly different functional properties at synaptic and extrasynaptic receptors. Br J Pharmacol 2014; 170:919-32. [PMID: 23957253 DOI: 10.1111/bph.12340] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/06/2013] [Accepted: 08/11/2013] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Explorations into the heterogeneous population of native GABA type A receptors (GABAA Rs) and the physiological functions governed by the multiple GABAA R subtypes have for decades been hampered by the lack of subtype-selective ligands. EXPERIMENTAL APPROACH The functional properties of the orthosteric GABAA receptor ligand 5-(4-piperidyl)-3-isothiazolol (Thio-4-PIOL) have been investigated in vitro, ex vivo and in vivo. KEY RESULTS Thio-4-PIOL displayed substantial partial agonist activity at the human extrasynaptic GABAA R subtypes expressed in Xenopus oocytes, eliciting maximal responses of up to ∼30% of that of GABA at α5 β3 γ2S , α4 β3 δ and α6 β3 δ and somewhat lower efficacies at the corresponding α5 β2 γ2S , α4 β2 δ and α6 β2 δ subtypes (maximal responses of 4-12%). In contrast, it was an extremely low efficacious agonist at the α1 β3 γ2S , α1 β2 γ2S , α2 β2 γ2S , α2 β3 γ2S , α3 β2 γ2S and α3 β3 γ2S GABAA Rs (maximal responses of 0-4%). In concordance with its agonism at extrasynaptic GABAA Rs and its de facto antagonism at the synaptic receptors, Thio-4-PIOL elicited robust tonic currents in electrophysiological recordings on slices from rat CA1 hippocampus and ventrobasal thalamus and antagonized phasic currents in hippocampal neurons. Finally, the observed effects of Thio-4-PIOL in rat tests of anxiety, locomotion, nociception and spatial memory were overall in good agreement with its in vitro and ex vivo properties. CONCLUSION AND IMPLICATIONS The diverse signalling characteristics of Thio-4-PIOL at GABAA Rs represent one of the few examples of a functionally subtype-selective orthosteric GABAA R ligand reported to date. We propose that Thio-4-PIOL could be a useful pharmacological tool in future studies exploring the physiological roles of native synaptic and extrasynaptic GABAA Rs.
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Affiliation(s)
- K Hoestgaard-Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Effects of an α5GABAA inverse agonist on MK-801-induced learning deficits in an incremental repeated acquisition task. Behav Pharmacol 2014; 25:331-5. [PMID: 25006978 DOI: 10.1097/fbp.0000000000000053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
N-methyl-D-aspartate receptors (NMDARs) are essential for several kinds of synaptic plasticity and play a critical role in learning and memory. Deficits in NMDAR functioning may be partially responsible for the learning and memory deficits associated with aging and numerous diseases. Administration of MK-801, a noncompetitive NMDAR antagonist, is commonly used as a preclinical model of NMDAR dysfunction. The objective of this study was to assess the effects of α5GABAA receptor inhibition on learning deficits in the incremental repeated acquisition (IRA) task induced by acute MK-801 administration. The IRA task, commonly used to examine factors that affect learning, begins with a single response and increments to progressively longer chains throughout a single session as behavior meets preset criteria. MK-801 (0.03-0.5 mg/kg, intraperitoneally), administered 10 min pretesting, produced a significant dose-dependent decrease in measures of IRA performance at doses greater than or equal to 0.25 mg/kg. The MK-801-induced deficit was attenuated after treatment with an α5GABAA receptor inverse agonist, L-655,708 (1 mg/kg, intraperitoneally). The present study provides the focus for, and supports the feasibility of, further in-depth definitive studies examining α5GABAA receptor inhibition as a suitable candidate for the attenuation of NMDAR-related deficits.
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Martínez-Cué C, Delatour B, Potier MC. Treating enhanced GABAergic inhibition in Down syndrome: use of GABA α5-selective inverse agonists. Neurosci Biobehav Rev 2014; 46 Pt 2:218-27. [PMID: 24412222 DOI: 10.1016/j.neubiorev.2013.12.008] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 11/27/2013] [Accepted: 12/16/2013] [Indexed: 11/27/2022]
Abstract
Excess inhibition in the brain of individuals carrying an extra copy of chromosome 21 could be responsible for cognitive deficits observed throughout their lives. A change in the excitatory/inhibitory balance in adulthood would alter synaptic plasticity, potentially triggering learning and memory deficits. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mature central nervous system and binds to GABAA receptors, opens a chloride channel, and reduces neuronal excitability. In this review we discuss methods to alleviate neuronal inhibition in a mouse model of Down syndrome, the Ts65Dn mouse, using either an antagonist (pentylenetetrazol) or two different inverse agonists selective for the α5-subunit containing receptor. Both inverse agonists, which reduce inhibitory GABAergic transmission, could rescue learning and memory deficits in Ts65Dn mice. We also discuss safety issues since modulation of the excitatory-inhibitory balance to improve cognition without inducing seizures remains particularly difficult when using GABA antagonists.
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Affiliation(s)
- Carmen Martínez-Cué
- Department of Physiology and Pharmacology, Faculty of Medicine, University of Cantabria, Santander, Spain
| | - Benoît Delatour
- Institut du Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM U1127, UPMC, IHUA-ICM, Hôpital Pitié-Salpêtrière, Paris, France
| | - Marie-Claude Potier
- Institut du Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM U1127, UPMC, IHUA-ICM, Hôpital Pitié-Salpêtrière, Paris, France.
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Rudolph U, Möhler H. GABAA receptor subtypes: Therapeutic potential in Down syndrome, affective disorders, schizophrenia, and autism. Annu Rev Pharmacol Toxicol 2013; 54:483-507. [PMID: 24160694 DOI: 10.1146/annurev-pharmtox-011613-135947] [Citation(s) in RCA: 231] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The γ-aminobutyric acid (GABA) system plays a pivotal role in orchestrating the synchronicity of local networks and the functional coupling of different brain regions. Here we review the impact of the GABAA receptor subtypes on cognitive and emotional behavior, paying particular attention to five disease states: cognitive dysfunction and Down syndrome, anxiety disorders, depression, schizophrenia, and autism. Through the bidirectional modulation of tonic inhibition, α5-subunit-containing GABAA receptors permit the bidirectional modulation of cognitive processes, and a partial inverse agonist acting at the α5-subunit-containing GABAA receptor is in a clinical trial in individuals with Down syndrome. With regard to anxiety disorders, the viability of nonsedative anxiolytics based on the modulation of α2- and α3-subunit-containing GABAA receptors has been established in clinical proof-of-concept trials. Regarding the remaining three disease states, the GABA hypothesis of depression offers new options for antidepressant drug development; cognitive symptoms in schizophrenia are attributed to a cortical GABAergic deficit, and dysfunctional GABAergic inhibition is increasingly understood to contribute to the pathophysiology of autism spectrum disorders.
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Affiliation(s)
- Uwe Rudolph
- Laboratory of Genetic Neuropharmacology, McLean Hospital and Department of Psychiatry, Harvard Medical School, Belmont, Massachusetts 02478;
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Allosteric modulation of GABA(A) receptor subtypes:effects on visual recognition and visuospatial working memory in rhesus monkeys [corrected]. Neuropsychopharmacology 2013; 38:2315-25. [PMID: 23722241 PMCID: PMC3773684 DOI: 10.1038/npp.2013.137] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 05/21/2013] [Accepted: 05/21/2013] [Indexed: 11/08/2022]
Abstract
Non-selective positive allosteric modulators (PAMs) of GABAA receptors (GABAARs) are known to impair anterograde memory. The role of the various GABAAR subtypes in the memory-impairing effects of non-selective GABAAR PAMs has not been fully elucidated. The current study assessed, in rhesus monkeys, effects of modulation of α1, α2/3, and α5GABAARs on visual recognition and spatial working memory using delayed matching-to-sample (DMTS) and self-ordered spatial search (SOSS) procedures, respectively. The DMTS procedure (n=8) involved selecting a previously presented 'sample' image from a set of multiple images presented after a delay. The SOSS procedure (n=6) involved touching a number of boxes without repeats. The non-selective GABAAR PAM triazolam and the α1GABAA preferential PAMS zolpidem and zaleplon reduced accuracy in both procedures, whereas the α5GABAA preferential PAMs SH-053-2'F-R-CH3 and SH-053-2'F-S-CH3, and the α2/3GABAA preferential PAM TPA023B were without effects on accuracy or trial completion. The low-efficacy α5GABAAR negative allosteric modulator (NAM) PWZ-029 slightly increased only DMTS accuracy, whereas the high-efficacy α5GABAAR NAMs RY-23 and RY-24 did not affect accuracy under either procedure. Finally, the slopes of the accuracy dose-effect curves for triazolam, zolpidem, and zaleplon increased with box number in the SOSS procedure, but were equivalent across DMTS delays. The present results suggest that (1) α1GABAARs, compared with α2/3 and α5GABAARs, are primarily involved in the impairment, by non-selective GABAAR PAMs, of visual recognition and visuospatial working memory in nonhuman primates; and (2) relative cognitive impairment produced by positive modulation of GABAARs increases with number of locations to be remembered, but not with the delay for remembering.
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Lecker I, Yin Y, Wang DS, Orser BA. Potentiation of GABAA receptor activity by volatile anaesthetics is reduced by α5GABAA receptor-preferring inverse agonists. Br J Anaesth 2013; 110 Suppl 1:i73-81. [PMID: 23535829 DOI: 10.1093/bja/aet038] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Animal studies have shown that memory deficits in the early post-anaesthetic period can be prevented by pre-treatment with an inverse agonist that preferentially inhibits α5 subunit-containing γ-aminobutyric acid type A (α5GABA(A)) receptors. The goal of this in vitro study was to determine whether inverse agonists that inhibit α5GABA(A) receptors reduce anaesthetic potentiation of GABAA receptor activity. METHODS Cultures of hippocampal neurones were prepared from Swiss white mice, wild-type mice (genetic background C57BL/6J and Sv129Ev) and α5GABA(A)receptor null mutant (Gabra5-/-) mice. Whole-cell voltage clamp techniques were used to study the effects of the α5GABA(A) receptor-preferring inverse agonists L-655,708 and MRK-016 on anaesthetic potentiation of GABA-evoked currents. RESULTS L-655,708 (50 nM) reduced sevoflurane potentiation of GABA-evoked current in wild-type neurones but not Gabra5-/- neurones, and produced a rightward shift in the sevoflurane concentration-response plot [sevoflurane EC50: 1.9 (0.1) mM; sevoflurane+L-655,708 EC(50): 2.4 (0.2) mM, P<0.05]. Similarly, L-655,708 (50 nM) reduced isoflurane potentiation of GABA-evoked current [isoflurane: 4.0 (0.6) pA pF(-1); isoflurane+L-655,708: 3.1 (0.5) pA pF(-1), P<0.01]. MRK-016 also reduced sevoflurane and isoflurane enhancement of GABA-evoked current [sevoflurane: 1.5 (0.1) pA pF(-1); sevoflurane+MRK-016 (10 nM): 1.2 (0.1) pA pF(-1), P<0.05; isoflurane: 3.5 (0.3) pA pF(-1); isoflurane+MRK-016 (1 nM): 2.9 (0.2) pA pF(-1), P<0.05]. CONCLUSIONS L-655,708 and MRK-016 reduced the potentiation by inhaled anaesthetics of GABAA receptor activated by a low concentration of GABA. Future studies are required to determine whether this effect contributes to the memory preserving properties of inverse agonists after anaesthesia.
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Affiliation(s)
- I Lecker
- Department of Physiology, University of Toronto, Toronto, ON, Canada M5S 1A8
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Guerrini G, Ciciani G, Costanzo A, Daniele S, Martini C, Ghelardini C, Di Cesare Mannelli L, Ciattini S. Synthesis of novel cognition enhancers with pyrazolo[5,1-c][1,2,4]benzotriazine core acting at γ-aminobutyric acid type A (GABA(A)) receptor. Bioorg Med Chem 2013; 21:2186-2198. [PMID: 23490154 DOI: 10.1016/j.bmc.2013.02.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 01/16/2013] [Accepted: 02/14/2013] [Indexed: 01/13/2023]
Abstract
Memory dysfunction associated with aging, neurodegenerative and psychiatric disorders represents an increasing medical need. Advances in research exploring the biological mechanisms underlying learning and memory have opened new potential approaches for development of memory-enhancing therapies addressed to selective neuronal targets. In this work, we synthesized some derivatives with a pyrazolo[5,1-c][1,2,4]benzotriazine core to identify ligands on GABAA receptors subtype (benzodiazepine site on GABAA-receptor) endowed with the potential of enhancing cognition activity without the side effects usually associated with non-selective GABAA modulators. In fact, there is much evidence that GABAA-R (γ-aminobutyric acid, type A receptor) subtype ligands have relevance in learning and memory. In vitro and in vivo tests have been performed. Pharmacological data indicate that compounds 7, 13, 14 and 22 act as dual functional modulators of GABAA-Rs (promnemonic and anxiolytic agents) while only compounds 3 and 10 stand out as selectively displaying good antiamnesic and procognitive activity (1 and 3 mg/kg, respectively).
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Affiliation(s)
- Gabriella Guerrini
- Dipartimento di Scienze Farmaceutiche, Laboratorio di Progettazione, Sintesi e Studio di Eterocicli Biologicamente attivi (HeteroBioLab) Università degli Studi di Firenze, Via U. Schiff, 6, 50019 Polo Scientifico, Sesto Fiorentino, Firenze, Italy.
| | - Giovanna Ciciani
- Dipartimento di Scienze Farmaceutiche, Laboratorio di Progettazione, Sintesi e Studio di Eterocicli Biologicamente attivi (HeteroBioLab) Università degli Studi di Firenze, Via U. Schiff, 6, 50019 Polo Scientifico, Sesto Fiorentino, Firenze, Italy
| | - Annarella Costanzo
- Dipartimento di Scienze Farmaceutiche, Laboratorio di Progettazione, Sintesi e Studio di Eterocicli Biologicamente attivi (HeteroBioLab) Università degli Studi di Firenze, Via U. Schiff, 6, 50019 Polo Scientifico, Sesto Fiorentino, Firenze, Italy
| | - Simona Daniele
- Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Università degli Studi di Pisa, via Bonanno, 6, 56126 Pisa, Italy
| | - Claudia Martini
- Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Università degli Studi di Pisa, via Bonanno, 6, 56126 Pisa, Italy
| | - Carla Ghelardini
- Dipartimento di Farmacologia Preclinica e Clinica Aiazzi-Mancini, Università degli Studi di Firenze, Viale Pieraccini, 6, 50139 Firenze, Italy
| | - Lorenzo Di Cesare Mannelli
- Dipartimento di Farmacologia Preclinica e Clinica Aiazzi-Mancini, Università degli Studi di Firenze, Viale Pieraccini, 6, 50139 Firenze, Italy
| | - Samuele Ciattini
- Centro di Cristallografia, Università degli Studi di Firenze, Via della Lastruccia, 3, 50019 Polo Scientifico, Sesto Fiorentino, Firenze, Italy
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Silverman JL, Oliver CF, Karras MN, Gastrell PT, Crawley JN. AMPAKINE enhancement of social interaction in the BTBR mouse model of autism. Neuropharmacology 2013; 64:268-82. [PMID: 22801296 PMCID: PMC3445667 DOI: 10.1016/j.neuropharm.2012.07.013] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 07/05/2012] [Accepted: 07/06/2012] [Indexed: 12/16/2022]
Abstract
Autism is a neurodevelopmental disorder in which the first diagnostic symptom is unusual reciprocal social interactions. Approximately half of the children diagnosed with an autism spectrum disorder also have intellectual impairments. General cognitive abilities may be fundamental to many aspects of social cognition. Cognitive enhancers could conceivably be of significant benefit to children and adults with autism. AMPAKINE compounds are a novel class of pharmacological agents that act as positive modulators of AMPA receptors to enhance excitatory glutamatergic neurotransmission. This class of compounds was reported to improve learning and memory in several rodent and non-human primate tasks, and to normalize respiratory abnormalities in a mouse model of Rett syndrome. Here we evaluate the actions of AMPA compounds in adult male and female BTBR mice, a well characterized mouse model of autism. Acute treatment with CX1837 and CX1739 reversed the deficit in sociability in BTBR mice on the most sensitive parameter, time spent sniffing a novel mouse as compared to time spent sniffing a novel object. The less sensitive parameter, time in the chamber containing the novel mouse versus time in the chamber containing the novel object, was not rescued by CX1837 or CX1739 treatment. Preliminary data with CX546, in which β-cyclodextrin was the vehicle, revealed behavioral effects of the acute intraperitoneal and oral administration of vehicle alone. To circumvent the artifacts introduced by the vehicle administration, we employed a novel treatment regimen using pellets of peanut butter for drug delivery. Absence of vehicle treatment effects when CX1837 and CX1739 were given in the peanut butter pellets, to multiple cohorts of BTBR and B6 control mice, confirmed that the pharmacologically-induced improvements in sociability in BTBR were not confounded by the administration procedures. The highest dose of CX1837 improved the cognitive deficit in novel object recognition in BTBR. No drug effects were detected on the high levels of repetitive self-grooming in BTBR. In open field tests, CX1837 and CX1739 did not induce hyperactivity or sedation in either strain. It is interesting to speculate that the ability of CX1837 and CX1739 to restore aspects of sociability in BTBR mice could utilize synaptic mechanisms regulating social cognition, suggesting a potential pharmacological target for interventions to treat symptoms of autism. This article is part of a Special Issue entitled 'Cognitive Enhancers'.
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MESH Headings
- Animals
- Autistic Disorder/drug therapy
- Autistic Disorder/physiopathology
- Behavior, Animal/drug effects
- Cognition Disorders/etiology
- Cognition Disorders/prevention & control
- Dioxoles/administration & dosage
- Dioxoles/adverse effects
- Dioxoles/therapeutic use
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Drugs, Investigational/administration & dosage
- Drugs, Investigational/adverse effects
- Drugs, Investigational/therapeutic use
- Excitatory Amino Acid Agonists/administration & dosage
- Excitatory Amino Acid Agonists/adverse effects
- Excitatory Amino Acid Agonists/therapeutic use
- Female
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Inbred Strains
- Molecular Targeted Therapy
- Nootropic Agents/administration & dosage
- Nootropic Agents/adverse effects
- Nootropic Agents/therapeutic use
- Piperidines/administration & dosage
- Piperidines/adverse effects
- Piperidines/therapeutic use
- Random Allocation
- Receptors, AMPA/agonists
- Recognition, Psychology/drug effects
- Social Behavior
- Social Behavior Disorders/etiology
- Social Behavior Disorders/prevention & control
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Affiliation(s)
- J L Silverman
- Laboratory of Behavioral Neuroscience, National Institute of Mental Health, Bethesda, MD 20892-3730, USA.
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27
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PWZ-029, an inverse agonist selective for α₅ GABAA receptors, improves object recognition, but not water-maze memory in normal and scopolamine-treated rats. Behav Brain Res 2012; 241:206-13. [PMID: 23261875 DOI: 10.1016/j.bbr.2012.12.016] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 12/07/2012] [Accepted: 12/10/2012] [Indexed: 01/03/2023]
Abstract
Inverse agonism at the benzodiazepine site of α(5) subunit-containing GABA(A) receptors is an attractive approach for the development of putative cognition-enhancing compounds, which are still far from clinical application. Several ligands with binding and/or functional selectivity for α(5) GABA(A) receptors have been synthesized and tested in a few animal models. PWZ-029 is an α(5) GABA(A) selective inverse agonist whose memory enhancing effects were demonstrated in the passive avoidance task in rats and in Pavlovian fear conditioning in mice. In the present study we investigated the effects of PWZ-029 administration in novel object recognition test and Morris water maze, in normal and scopolamine-treated rats. All the three doses of PWZ-029 (2, 5 and 10 mg/kg) improved object recognition after the 24-h delay period, as shown by significant differences between the exploration times of the novel and old object, and the respective discrimination indices. PWZ-029 (2 mg/kg) also successfully reversed the 0.3 mg/kg scopolamine-induced deficit in recognition memory after the 1-h delay. In the Morris water maze test, PWZ-029 (5, 10 and 15 mg/kg) did not significantly influence swim patterns, either during five acquisition days or during the treatment-free probe trial. PWZ-029 (2, 5 and 10 mg/kg) also proved to be ineffective in the reversal of the 1mg/kg scopolamine-induced memory impairment in the water maze. The present mixed results encourage use of a variety of tests and experimental conditions in order to increase the predictability of preclinical testing of selective α(5) GABA(A) inverse agonists.
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28
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Wang L, Li WG, Huang C, Zhu MX, Xu TL, Wu DZ, Li Y. Subunit-specific inhibition of glycine receptors by curcumol. J Pharmacol Exp Ther 2012; 343:371-9. [PMID: 22892339 DOI: 10.1124/jpet.112.195669] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Emerging evidence has suggested that inhibitory glycine receptors (GlyRs) are an important molecular target in the treatment of numerous neurological disorders. Rhizoma curcumae is a medicinal plant with positive neurological effects. In this study, we showed that curcumol, a major bioactive component of R. curcumae, reversibly and concentration-dependently inhibited the glycine-activated current (IGly) in cultured rat hippocampal neurons. The inhibitory effect was neither voltage- nor agonist concentration-dependent. Moreover, curcumol selectively inhibited homomeric α2-containing, but not α1- or α3-containing, GlyRs. The addition of β subunit conferred the curcumol sensitivity of α3-containing, but not α1-containing, GlyRs. Site-directed mutagenesis analysis revealed that a threonine at position 59 of the α2 subunit is critical for the susceptibility of GlyRs to curcumol-mediated inhibition. Furthermore, paralleling a decline of α2 subunit expression during spinal cord development, the degree of IGly inhibition by curcumol decreased with prolonged culture of rat spinal dorsal horn neurons. Taken together, our results suggest that the GlyRs are novel molecular targets of curcumol, which may underlie its pharmaceutical effects in the central nervous system.
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Affiliation(s)
- Li Wang
- Institute of Chinese Materia Medica, Shanghai Key Laboratory of Complex Prescription, Shanghai University of Traditional Chinese Medicine, Shanghai, China
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29
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Möhler H. Cognitive enhancement by pharmacological and behavioral interventions: the murine Down syndrome model. Biochem Pharmacol 2012; 84:994-9. [PMID: 22898099 DOI: 10.1016/j.bcp.2012.06.028] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Revised: 06/29/2012] [Accepted: 06/29/2012] [Indexed: 12/26/2022]
Abstract
The cognitive deficits in Down syndrome (DS) are attributed to an excessive hippocampal inhibition, which obstructs neuronal plasticity and normal learning and memory, a view which is largely based on studies of Ts65Dn mice, the best characterized mouse model of DS. The cognitive behavioral deficits of Ts65Dn mice can be rescued by reducing GABAergic inhibition, most selectively by partial inverse agonists acting on α(5) GABA-A receptors, of which one compound has recently entered clinical trials in DS. Most remarkably, the improved cognitive performance of Ts65Dn can persist for weeks and months after cessation of drug treatment, as demonstrated for the non-specific GABA antagonist pentylenetetrazole. The Alzheimer drugs, memantine and donepezil largely fail to show any benefit. Finally, repeated non-invasive sensory stimulation such as over-training or enriching the environment, are able to enhance the learning performance which underlines the reversibility of an obstructed neuronal plasticity in Ts65Dn mice.
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Affiliation(s)
- Hanns Möhler
- Institute of Pharmacology, University of Zurich and, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.
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30
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Brickley SG, Mody I. Extrasynaptic GABA(A) receptors: their function in the CNS and implications for disease. Neuron 2012; 73:23-34. [PMID: 22243744 DOI: 10.1016/j.neuron.2011.12.012] [Citation(s) in RCA: 486] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/18/2011] [Indexed: 12/30/2022]
Abstract
Over the past two decades, research has identified extrasynaptic GABA(A) receptor populations that enable neurons to sense the low ambient GABA concentrations present in the extracellular space in order to generate a form of tonic inhibition not previously considered in studies of neuronal excitability. The importance of this tonic inhibition in regulating states of consciousness is highlighted by the fact that extrasynaptic GABA(A) receptors (GABA(A)Rs) are believed to be key targets for anesthetics, sleep-promoting drugs, neurosteroids, and alcohol. The neurosteroid sensitivity of these extrasynaptic GABA(A)Rs may explain their importance in stress-, ovarian cycle-, and pregnancy-related mood disorders. Moreover, disruptions in network dynamics associated with schizophrenia, epilepsy, and Parkinson's disease may well involve alterations in the tonic GABA(A)R-mediated conductance. Extrasynaptic GABA(A)Rs may therefore present a therapeutic target for treatment of these diseases, with the potential to enhance cognition and aid poststroke functional recovery.
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Affiliation(s)
- Stephen G Brickley
- Division of Cell & Molecular Biology, South Kensington Campus, Imperial College, London SW7 2AZ, UK.
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31
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Improved cognitive performance following supplementation with a mixed-grain diet in high school students: A randomized controlled trial. Nutrition 2012; 28:165-72. [DOI: 10.1016/j.nut.2011.05.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Revised: 01/21/2011] [Accepted: 05/28/2011] [Indexed: 11/19/2022]
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32
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The GABA system in anxiety and depression and its therapeutic potential. Neuropharmacology 2012; 62:42-53. [DOI: 10.1016/j.neuropharm.2011.08.040] [Citation(s) in RCA: 348] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Accepted: 08/23/2011] [Indexed: 01/01/2023]
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33
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Chronic Treatment with a Promnesiant GABA-A α5-Selective Inverse Agonist Increases Immediate Early Genes Expression during Memory Processing in Mice and Rectifies Their Expression Levels in a Down Syndrome Mouse Model. Adv Pharmacol Sci 2011; 2011:153218. [PMID: 22028705 PMCID: PMC3199058 DOI: 10.1155/2011/153218] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 07/27/2011] [Accepted: 07/31/2011] [Indexed: 12/20/2022] Open
Abstract
Decrease of GABAergic transmission has been proposed to improve memory functions. Indeed, inverse agonists selective for α5 GABA-A-benzodiazepine receptors (α5IA) have promnesiant activity. Interestingly, we have recently shown that α5IA can rescue cognitive deficits in Ts65Dn mice, a Down syndrome mouse model with altered GABAergic transmission. Here, we studied the impact of chronic treatment with α5IA on gene expression in the hippocampus of Ts65Dn and control euploid mice after being trained in the Morris water maze task. In euploid mice, chronic treatment with α5IA increased IEGs expression, particularly of c-Fos and Arc genes. In Ts65Dn mice, deficits of IEGs activation were completely rescued after treatment with α5IA. In addition, normalization of Sod1 overexpression in Ts65Dn mice after α5IA treatment was observed. IEG expression regulation after α5IA treatment following behavioral stimulation could be a contributing factor for both the general promnesiant activity of α5IA and its rescuing effect in Ts65Dn mice alongside signaling cascades that are critical for memory consolidation and cognition.
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34
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Barak S, Weiner I. Putative cognitive enhancers in preclinical models related to schizophrenia: The search for an elusive target. Pharmacol Biochem Behav 2011; 99:164-89. [DOI: 10.1016/j.pbb.2011.03.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 02/27/2011] [Accepted: 03/12/2011] [Indexed: 12/12/2022]
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35
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Möhler H. The rise of a new GABA pharmacology. Neuropharmacology 2011; 60:1042-9. [DOI: 10.1016/j.neuropharm.2010.10.020] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Revised: 10/13/2010] [Accepted: 10/21/2010] [Indexed: 10/18/2022]
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36
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Atack JR, Wafford KA, Street LJ, Dawson GR, Tye S, Van Laere K, Bormans G, Sanabria-Bohórquez SM, De Lepeleire I, de Hoon JN, Van Hecken A, Burns HD, McKernan RM, Murphy MG, Hargreaves RJ. MRK-409 (MK-0343), a GABAA receptor subtype-selective partial agonist, is a non-sedating anxiolytic in preclinical species but causes sedation in humans. J Psychopharmacol 2011; 25:314-28. [PMID: 20147571 DOI: 10.1177/0269881109354927] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
MRK-409 binds to α1-, α2-, α3- and α5-containing human recombinant GABA(A) receptors with comparable high affinity (0.21-0.40 nM). However, MRK-409 has greater agonist efficacy at the α3 compared with α1 subtypes (respective efficacies relative to the full agonist chlordiazepoxide of 0.45 and 0.18). This compound readily penetrates the brain in rats and occupies the benzodiazepine site of GABA(A) receptors, measured using an in vivo [(3)H]flumazenil binding assay, with an Occ(50) of 2.2 mg/kg p.o. and a corresponding plasma EC(50) of 115 ng/mL. Behaviourally, the α3-preferring agonist efficacy profile of MRK-409 produced anxiolytic-like activity in rodent and primate unconditioned and conditioned models of anxiety with minimum effective doses corresponding to occupancies, depending on the particular model, ranging from ∼35% to 65% yet there were minimal overt signs of sedation at occupancies greater than 90%. In humans, however, safety and tolerability studies showed that there was pronounced sedation at a dose of 2 mg, resulting in a maximal tolerated dose of 1 mg. This 2 mg dose corresponded to a C(max) plasma concentration of 28 ng/mL, which, based on the rodent plasma EC(50) for occupancy of 115 ng/mL, suggested that sedation in humans occurs at low levels of occupancy. This was confirmed in human positron emission tomography studies, in which [(11)C]flumazenil uptake following a single dose of 1 mg MRK-409 was comparable to that of placebo, indicating that occupancy of GABA(A) receptor benzodiazepine binding sites by MRK-409 was below the limits of detection (i.e. <10%). Taken together, these data show that MRK-409 causes sedation in humans at a dose (2 mg) corresponding to levels of occupancy considerably less than those predicted from rodent models to be required for anxiolytic efficacy (∼35-65%). Thus, the preclinical non-sedating anxiolytic profile of MRK-409 did not translate into humans and further development of this compound was halted.
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Affiliation(s)
- J R Atack
- Neuroscience Research Centre, Merck Sharp & Dohme Research Laboratories, Harlow, UK.
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Vinkers CH, Mirza NR, Olivier B, Kahn RS. The inhibitory GABA system as a therapeutic target for cognitive symptoms in schizophrenia: investigational agents in the pipeline. Expert Opin Investig Drugs 2011; 19:1217-33. [PMID: 20812877 DOI: 10.1517/13543784.2010.513382] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
IMPORTANCE OF THE FIELD Cognitive impairments associated with schizophrenia include neuropsychological deficits in attention, working memory, learning and executive function. Because these cognitive deficits precede the onset of psychosis, are present in non-affected relatives and constitute the best predictor of functional outcome, they are a cardinal clinical feature in schizophrenia. Currently, no effective treatment for the cognitive symptoms in schizophrenia exists. AREAS COVERED IN THIS REVIEW There is evidence that the inhibitory GABA system is affected in schizophrenia, suggesting that cognitive impairments associated with schizophrenia may be effectively treated by drugs that modulate the GABA(A) receptor. However, classical benzodiazepines produce cognitive impairments and are associated with numerous side effects. The recent development of compounds with selective efficacy for different α subunits at the benzodiazepine site of the GABA(A) receptor has renewed interest for the therapeutic potential of GABAergic drugs. WHAT THE READER WILL GAIN This review summarizes the involvement of the inhibitory GABA system in the cognitive abnormalities of schizophrenia and discusses putative (selective) GABAergic cognition-enhancing drugs for schizophrenia. TAKE HOME MESSAGE If cognitive abnormalities in schizophrenic individuals are the result of GABAergic dysfunction, selectively modulating the GABA system could comprise a promising therapeutic intervention for cognitive symptoms in schizophrenia.
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Affiliation(s)
- Christiaan H Vinkers
- Department of Psychiatry, University Medical Center Utrecht, Rudolf Magnus Institute of Neuroscience, Utrecht, The Netherlands
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38
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Makkar SR, Zhang SQ, Cranney J. Behavioral and neural analysis of GABA in the acquisition, consolidation, reconsolidation, and extinction of fear memory. Neuropsychopharmacology 2010; 35:1625-52. [PMID: 20410874 PMCID: PMC3055480 DOI: 10.1038/npp.2010.53] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 03/17/2010] [Accepted: 03/22/2010] [Indexed: 11/09/2022]
Abstract
The current review systematically documents the role of gamma-amino-butyric acid (GABA) in different aspects of fear memory-acquisition and consolidation, reconsolidation, and extinction, and attempts to resolve apparent contradictions in the data in order to identify the function of GABA(A) receptors in fear memory. First, numerous studies have shown that pre- and post-training administration of drugs that facilitate GABAergic transmission disrupt the initial formation of fear memories, indicating a role for GABA(A) receptors, possibly within the amygdala and hippocampus, in the acquisition and consolidation of fear memories. Similarly, recent evidence indicates that these drugs are also detrimental to the restorage of fear memories after their reactivation. This suggests a role for GABA(A) receptors in the reconsolidation of fear memories, although the precise neural circuits are yet to be identified. Finally, research regarding the role of GABA in extinction has shown that GABAergic transmission is also disruptive to the formation of newly acquired extinction memories. We argue that contradictions to these patterns are the result of variations in (a) the location of drug infusion, (b) the dosage of the drug and/or (c) the time point of drug administration. The question of whether these GABA-induced memory deficits reflect deficits in retrieval is discussed. Overall, the evidence implies that the processes mediating memory stability consequent to initial fear learning, memory reactivation, and extinction training are dependent on a common mechanism of reduced GABAergic neurotransmission.
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Affiliation(s)
- Steve R Makkar
- School of Psychology, University of New South Wales, Sydney, NSW, Australia
| | - Shirley Q Zhang
- School of Psychology, University of New South Wales, Sydney, NSW, Australia
| | - Jacquelyn Cranney
- School of Psychology, University of New South Wales, Sydney, NSW, Australia
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39
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Thomson AM, Jovanovic JN. Mechanisms underlying synapse-specific clustering of GABA(A) receptors. Eur J Neurosci 2010; 31:2193-203. [PMID: 20550567 DOI: 10.1111/j.1460-9568.2010.07252.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A principle that arises from a body of previous work is that each presynaptic terminal recognises its postsynaptic partner and that each postsynaptic site recognises the origin of the synaptic bouton innervating it. In response, the presynaptic terminal sequesters the proteins whose interactions result in the dynamic transmitter release pattern and chemical modulation appropriate for that connection. In parallel, the postsynaptic site sequesters, inserts or captures the receptors and postsynaptic density proteins appropriate for that type of synapse. The focus of this review is the selective clustering of GABA(A) receptors (GABA(A)R) at synapses made by each class of inhibitory interneurone. This provides a system in which the mechanisms underlying transynaptic recognition can be explored. There are many synaptic proteins, often with several isoforms created by post-translational modifications. Complex cascades of interactions between these proteins, on either side of the synaptic cleft, are essential for normal function, normal transmitter release and postsynaptic responsiveness. Interactions between presynaptic and postsynaptic proteins that have binding domains in the synaptic cleft are proposed here to result in a local cleft structure that captures and stabilises only the appropriate subtype of GABA(A)Rs, allowing others to drift away from that synapse, either to be captured by another synapse, or internalised.
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Affiliation(s)
- Alex M Thomson
- The School of Pharmacy, London University, 29-39 Brunswick Square, London WC1N 1AX, UK.
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40
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Alpha5GABAA receptor activity sets the threshold for long-term potentiation and constrains hippocampus-dependent memory. J Neurosci 2010; 30:5269-82. [PMID: 20392949 DOI: 10.1523/jneurosci.4209-09.2010] [Citation(s) in RCA: 133] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Synaptic plasticity, which is the neuronal substrate for many forms of hippocampus-dependent learning, is attenuated by GABA type A receptor (GABA(A)R)-mediated inhibition. The prevailing notion is that a synaptic or phasic form of GABAergic inhibition regulates synaptic plasticity; however, little is known about the role of GABA(A)R subtypes that generate a tonic or persistent inhibitory conductance. We studied the regulation of synaptic plasticity by alpha5 subunit-containing GABA(A)Rs (alpha5GABA(A)Rs), which generate a tonic inhibitory conductance in CA1 pyramidal neurons using electrophysiological recordings of field and whole-cell potentials in hippocampal slices from both wild-type and null mutant mice for the alpha5 subunit of the GABA(A)R (Gabra5(-/-) mice). In addition, the strength of fear-associated memory was studied. The results showed that alpha5GABA(A)R activity raises the threshold for induction of long-term potentiation in a highly specific band of stimulation frequencies (10-20 Hz) through mechanisms that are predominantly independent of inhibitory synaptic transmission. The deletion or pharmacological inhibition of alpha5GABA(A)Rs caused no change in baseline membrane potential or input resistance but increased depolarization during 10 Hz stimulation. The encoding of hippocampus-dependent memory was regulated by alpha5GABA(A)Rs but only under specific conditions that generate moderate but not robust forms of fear-associated learning. Thus, under specific conditions, alpha5GABA(A)R activity predominates over synaptic inhibition in modifying the strength of both synaptic plasticity in vitro and certain forms of memory in vivo.
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Probing compulsive and impulsive behaviors, from animal models to endophenotypes: a narrative review. Neuropsychopharmacology 2010; 35:591-604. [PMID: 19940844 PMCID: PMC3055606 DOI: 10.1038/npp.2009.185] [Citation(s) in RCA: 521] [Impact Index Per Article: 37.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Failures in cortical control of fronto-striatal neural circuits may underpin impulsive and compulsive acts. In this narrative review, we explore these behaviors from the perspective of neural processes and consider how these behaviors and neural processes contribute to mental disorders such as obsessive-compulsive disorder (OCD), obsessive-compulsive personality disorder, and impulse-control disorders such as trichotillomania and pathological gambling. We present findings from a broad range of data, comprising translational and human endophenotypes research and clinical treatment trials, focussing on the parallel, functionally segregated, cortico-striatal neural projections, from orbitofrontal cortex (OFC) to medial striatum (caudate nucleus), proposed to drive compulsive activity, and from the anterior cingulate/ventromedial prefrontal cortex to the ventral striatum (nucleus accumbens shell), proposed to drive impulsive activity, and the interaction between them. We suggest that impulsivity and compulsivity each seem to be multidimensional. Impulsive or compulsive behaviors are mediated by overlapping as well as distinct neural substrates. Trichotillomania may stand apart as a disorder of motor-impulse control, whereas pathological gambling involves abnormal ventral reward circuitry that identifies it more closely with substance addiction. OCD shows motor impulsivity and compulsivity, probably mediated through disruption of OFC-caudate circuitry, as well as other frontal, cingulate, and parietal connections. Serotonin and dopamine interact across these circuits to modulate aspects of both impulsive and compulsive responding and as yet unidentified brain-based systems may also have important functions. Targeted application of neurocognitive tasks, receptor-specific neurochemical probes, and brain systems neuroimaging techniques have potential for future research in this field.
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Preclinical and clinical pharmacology of the GABAA receptor α5 subtype-selective inverse agonist α5IA. Pharmacol Ther 2010; 125:11-26. [DOI: 10.1016/j.pharmthera.2009.09.001] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Accepted: 09/01/2009] [Indexed: 11/17/2022]
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43
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γ-Aminobutyric Acid Type A (GABAA) Receptor Subtype Inverse Agonists as Therapeutic Agents in Cognition. Methods Enzymol 2010; 485:197-211. [DOI: 10.1016/b978-0-12-381296-4.00011-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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44
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Abstract
Complex brains have developed specialized mechanisms for the grouping of principal cells into temporal coalitions of local or distant networks: the inhibitory interneuron ‘clocking’ networks. They consist of GABAergic (where GABA is γ-aminobutyric acid) interneurons of a rich diversity. In cortical circuits, these neurons control spike timing of the principal cells, sculpt neuronal rhythms, select cell assemblies and implement brain states. On the basis of these considerations, the deficits in cognition, emotion and perception in psychiatric disorders such as anxiety, depression or schizophrenia are considered to manifest themselves through a dysregulation of the inhibitory interneuron ‘clocking’ network as a final common denominator, irrespective of the diverse underlying disease pathologies. The diversity of GABAergic interneurons is paralleled by a corresponding diversity of GABAA receptors in network regulation. The region-, cell- and domain-specific location of these receptor subtypes offers the possibility to gain functional insights into the role of behaviourally relevant neuronal circuits. Using genetic manipulation, the regulation of anxiety behaviour was attributed to neuronal circuits characterized by the expression of α2-GABAA receptors. Neurons expressing α3-GABAA receptors, located mainly in aminergic and basal forebrain cholinergic neurons, were related to a hyperdopaminergic phenotype, typical of schizophrenic symptoms. Temporal and spatial memory were selectively modulated by extrasynaptic α5-GABAA receptors. Chronic pathological pain was under the regulation of spinal and cortical α2- (and α3-) GABAA receptors. Thus the relevance of the diversity of inhibitory GABAA receptor subtypes for the regulation of cognition, emotion and memory is increasingly being recognized. The clinical proof-of-concept of a subtype-specific pharmacology is most advanced for the alleviation of cognitive dysfunctions in schizophrenia, based on the treatment of patients with an α2/α3-GABAA receptor ligand.
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Discovery of the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine scaffold as a novel, potent and selective GABAA α5 inverse agonist series. Bioorg Med Chem Lett 2009; 19:5746-52. [DOI: 10.1016/j.bmcl.2009.07.153] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Revised: 07/30/2009] [Accepted: 07/31/2009] [Indexed: 01/16/2023]
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Atack JR, Maubach KA, Wafford KA, O'Connor D, Rodrigues AD, Evans DC, Tattersall FD, Chambers MS, MacLeod AM, Eng WS, Ryan C, Hostetler E, Sanabria SM, Gibson RE, Krause S, Burns HD, Hargreaves RJ, Agrawal NGB, McKernan RM, Murphy MG, Gingrich K, Dawson GR, Musson DG, Petty KJ. In Vitro and in Vivo Properties of 3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d]-[1,2,4]triazine (MRK-016), a GABAA Receptor α5 Subtype-Selective Inverse Agonist. J Pharmacol Exp Ther 2009; 331:470-84. [DOI: 10.1124/jpet.109.157636] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Charych EI, Liu F, Moss SJ, Brandon NJ. GABA(A) receptors and their associated proteins: implications in the etiology and treatment of schizophrenia and related disorders. Neuropharmacology 2009; 57:481-95. [PMID: 19631671 DOI: 10.1016/j.neuropharm.2009.07.027] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Revised: 07/02/2009] [Accepted: 07/13/2009] [Indexed: 02/05/2023]
Abstract
Gamma-aminobutyric acid type A (GABA(A)) receptors play an important role in mediating fast synaptic inhibition in the brain. They are ubiquitously expressed in the CNS and also represent a major site of action for clinically relevant drugs. Recent technological advances have greatly clarified the molecular and cellular roles played by distinct GABA(A) receptor subunit classes and isoforms in normal brain function. At the same time, postmortem and genetic studies have linked neuropsychiatric disorders including schizophrenia and bipolar disorder with GABAergic neurotransmission and various specific GABA(A) receptor subunits, while evidence implicating GABA(A)R-associated proteins is beginning to emerge. In this review we discuss the mounting genetic, molecular, and cellular evidence pointing toward a role for GABA(A) receptor heterogeneity in both schizophrenia etiology and therapeutic development. Finally, we speculate on the relationship between schizophrenia-related disorders and selected GABA(A) receptor associated proteins, key regulators of GABA(A) receptor trafficking, targeting, clustering, and anchoring that often carry out these functions in a subtype-specific manner.
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Affiliation(s)
- Erik I Charych
- Wyeth Research, Neuroscience Discovery, Princeton NJ 08852, USA.
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Powell SB, Zhou X, Geyer MA. Prepulse inhibition and genetic mouse models of schizophrenia. Behav Brain Res 2009; 204:282-94. [PMID: 19397931 DOI: 10.1016/j.bbr.2009.04.021] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2008] [Revised: 04/15/2009] [Accepted: 04/19/2009] [Indexed: 12/26/2022]
Abstract
Mutant mouse models related to schizophrenia have been based primarily on the pathophysiology of schizophrenia, the known effects of antipsychotic drugs, and candidate genes for schizophrenia. Sensorimotor gating deficits in schizophrenia patients, as indexed by measures of prepulse inhibition of startle (PPI), have been well characterized and suggested to meet the criteria as a useful endophenotype in human genetic studies. PPI refers to the ability of a non-startling "prepulse" to inhibit responding to the subsequent startling stimulus or "pulse." Because of the cross-species nature of PPI, it has been used primarily in pharmacological animal models to screen putative antipsychotic medications. As techniques in molecular genetics have progressed over the past 15 years, PPI has emerged as a phenotype used in assessing genetic mouse models of relevance to schizophrenia. In this review, we provide a selected overview of the use of PPI in mouse models of schizophrenia and discuss the contribution and usefulness of PPI as a phenotype in the context of genetic mouse models. To that end, we discuss mutant mice generated to address hypotheses regarding the pathophysiology of schizophrenia and candidate genes (i.e., hypothesis driven). We also briefly discuss the usefulness of PPI in phenotype-driven approaches in which a PPI phenotype could lead to "bottom up" approaches of identifying novel genes of relevance to PPI (i.e., hypothesis generating).
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Affiliation(s)
- Susan B Powell
- Department of Psychiatry, University of California San Diego, 9500 Gilman Dr. MC0804, La Jolla, CA 92093, United States.
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Zhou L, Liu YW, Peoples RW, Yang M, Tian X, Ai YX, Pang YP, Li ZW, Han YF, Li CY. Mechanism of bis(7)-tacrine inhibition of GABA-activated current in cultured rat hippocampal neurons. Neuropharmacology 2009; 57:33-40. [PMID: 19393253 DOI: 10.1016/j.neuropharm.2009.04.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 04/09/2009] [Indexed: 11/17/2022]
Abstract
Bis(7)-tacrine is a novel dimeric acetylcholinesterase inhibitor derived from tacrine that shows promise for the treatment of Alzheimer's disease. We have previously reported that bis(7)-tacrine inhibits GABA(A) receptors. In the present study we investigated the mechanism of bis(7)-tacrine inhibition of GABA(A) receptor function using whole-cell patch-clamp recording in cultured rat hippocampal neurons. Bis(7)-tacrine produced a gradual decline of GABA-activated current to a steady-state, but this was not an indication of use-dependence, as the gradually declining component could be eliminated by exposure to bis(7)-tacrine prior to GABA application. In addition, bis(7)-tacrine inhibition did not require the presence of agonist, and GABA-activated current recovered completely from inhibition by bis(7)-tacrine in the absence of agonist. The slow onset of inhibition by bis(7)-tacrine was not apparently due to an action at an intracellular site, as inclusion of 25 microM bis(7)-tacrine in the recording pipette did not alter inhibition by bis(7)-tacrine applied externally. Bis(7)-tacrine shifted the GABA concentration-response curve to the right in a parallel manner and the pA(2) value estimated from a Schild plot was 5.7. Bis(7)-tacrine increased the time constant of activation of GABA-gated ion channels without affecting the time constants of deactivation or desensitization. These results suggest that bis(7)-tacrine is a competitive GABA(A) receptor antagonist with slow onset and offset kinetics. The competitive inhibition of GABA receptors by bis(7)-tacrine could contribute to its ability to enhance memory.
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Affiliation(s)
- Li Zhou
- Department of Neurobiology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
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