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Hleihil M, Benke D. Restoring GABA B receptor expression in the ventral tegmental area of methamphetamine addicted mice inhibits locomotor sensitization and drug seeking behavior. Front Mol Neurosci 2024; 17:1347228. [PMID: 38384279 PMCID: PMC10879384 DOI: 10.3389/fnmol.2024.1347228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Accepted: 01/15/2024] [Indexed: 02/23/2024] Open
Abstract
Repeated exposure to psychostimulants such as methamphetamine (METH) induces neuronal adaptations in the mesocorticolimbic dopamine system, including the ventral tegmental area (VTA). These changes lead to persistently enhanced neuronal activity causing increased dopamine release and addictive phenotypes. A factor contributing to increased dopaminergic activity in this system appears to be reduced GABAB receptor-mediated neuronal inhibition in the VTA. Dephosphorylation of serine 783 (Ser783) of the GABAB2 subunit by protein phosphatase 2A (PP2A) appears to trigger the downregulation GABAB receptors in psychostimulant-addicted rodents. Therefore, preventing the interaction of GABAB receptors with PP2A using an interfering peptide is a promising strategy to restore GABAB receptor-mediated neuronal inhibition. We have previously developed an interfering peptide (PP2A-Pep) that inhibits the GABAB receptors/PP2A interaction and thereby restores receptor expression under pathological conditions. Here, we tested the hypothesis that restoration of GABAB receptor expression in the VTA of METH addicted mice reduce addictive phenotypes. We found that the expression of GABAB receptors was significantly reduced in the VTA and nucleus accumbens but not in the hippocampus and somatosensory cortex of METH-addicted mice. Infusion of PP2A-Pep into the VTA of METH-addicted mice restored GABAB receptor expression in the VTA and inhibited METH-induced locomotor sensitization as assessed in the open field test. Moreover, administration of PP2A-Pep into the VTA also reduced drug seeking behavior in the conditioned place preference test. These observations underscore the importance of VTA GABAB receptors in controlling addictive phenotypes. Furthermore, this study illustrates the value of interfering peptides targeting diseases-related protein-protein interactions as an alternative approach for a potential development of selective therapeutic interventions.
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Affiliation(s)
- Mohammad Hleihil
- Institute of Pharmacology and Toxicology, University of Zurich, Zürich, Switzerland
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Zürich, Switzerland
- Neuroscience Center Zurich, University and ETH Zurich, Zürich, Switzerland
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2
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Opretzka LCF, Viana MDM, de Lima AA, de Souza TA, Scotti MT, Tavares JF, da Silva MS, Soares MBP, Villarreal CF. Cleomin Exerts Acute Antinociceptive Effects in Mice via GABA B and Muscarinic Receptors. Pharmaceuticals (Basel) 2023; 16:1547. [PMID: 38004413 PMCID: PMC10675606 DOI: 10.3390/ph16111547] [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: 09/11/2023] [Revised: 10/21/2023] [Accepted: 10/27/2023] [Indexed: 11/26/2023] Open
Abstract
Cleomin, a 1,3-oxazolidine-2-thione, was recently isolated from Neocalyptrocalyx longifolium, a species traditionally used for treating painful conditions. Reports about the pharmacological activities of cleomin are lacking. Here, the antinociceptive effects of cleomin were investigated using mice models of pain, namely the formalin, the cold plate, and the tail flick tests. Motor integrity was assessed in the rota-rod test. Antagonism assays and in silico docking analyses were performed to investigate the putative mechanisms of action. Cleomin (12.5-25 mg/kg), at doses that did not induce motor impairment, induced dose-dependent antinociception in both early and late phases of the formalin test and reduced nociceptive behaviors in both the cold plate and tail flick tests. Pretreatments with phaclofen and atropine attenuated the antinociceptive effects of cleomin, implicating the involvement of GABAB and muscarinic receptors. In silico docking studies suggested satisfactory coupling between cleomin and GABAB and M2 receptors, hence corroborating their role in cleomin's activity. Pretreatments with naloxone, yohimbine, bicuculline, and methysergide did not affect the antinociception of cleomin. In silico pharmacokinetics prediction showed a good drug ability profile of cleomin. In conclusion, cleomin promoted antinociception mediated by GABAB and muscarinic receptors. These findings support further investigation of the analgesic potential of cleomin.
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Affiliation(s)
| | | | - Alyne Almeida de Lima
- Gonçalo Moniz Institute, FIOCRUZ, Salvador 40296710, BA, Brazil; (A.A.d.L.); (M.B.P.S.)
| | - Thalisson Amorim de Souza
- Institute for Research on Drugs and Medicines, Federal University of Paraíba, João Pessoa 58059900, PB, Brazil; (T.A.d.S.); (M.T.S.); (J.F.T.); (M.S.d.S.)
| | - Marcus Tullius Scotti
- Institute for Research on Drugs and Medicines, Federal University of Paraíba, João Pessoa 58059900, PB, Brazil; (T.A.d.S.); (M.T.S.); (J.F.T.); (M.S.d.S.)
| | - Josean Fechine Tavares
- Institute for Research on Drugs and Medicines, Federal University of Paraíba, João Pessoa 58059900, PB, Brazil; (T.A.d.S.); (M.T.S.); (J.F.T.); (M.S.d.S.)
| | - Marcelo Sobral da Silva
- Institute for Research on Drugs and Medicines, Federal University of Paraíba, João Pessoa 58059900, PB, Brazil; (T.A.d.S.); (M.T.S.); (J.F.T.); (M.S.d.S.)
| | - Milena Botelho Pereira Soares
- Gonçalo Moniz Institute, FIOCRUZ, Salvador 40296710, BA, Brazil; (A.A.d.L.); (M.B.P.S.)
- Institute for Research on Drugs and Medicines, Federal University of Paraíba, João Pessoa 58059900, PB, Brazil; (T.A.d.S.); (M.T.S.); (J.F.T.); (M.S.d.S.)
- Institute of Advanced Systems in Health, SENAI CIMATEC, Salvador 41650010, BA, Brazil
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3
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Bhat MA, Grampp T, Benke D. ERK1/2-Dependent Phosphorylation of GABA B1(S867/T872), Controlled by CaMKIIβ, Is Required for GABA B Receptor Degradation under Physiological and Pathological Conditions. Int J Mol Sci 2023; 24:13436. [PMID: 37686242 PMCID: PMC10488028 DOI: 10.3390/ijms241713436] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 08/28/2023] [Accepted: 08/29/2023] [Indexed: 09/10/2023] Open
Abstract
GABAB receptor-mediated inhibition is indispensable for maintaining a healthy neuronal excitation/inhibition balance. Many neurological diseases are associated with a disturbed excitation/inhibition balance and downregulation of GABAB receptors due to enhanced sorting of the receptors to lysosomal degradation. A key event triggering the downregulation of the receptors is the phosphorylation of S867 in the GABAB1 subunit mediated by CaMKIIβ. Interestingly, close to S867 in GABAB1 exists another phosphorylation site, T872. Therefore, the question arose as to whether phosphorylation of T872 is involved in downregulating the receptors and whether phosphorylation of this site is also mediated by CaMKIIβ or by another protein kinase. Here, we show that mutational inactivation of T872 in GABAB1 prevented the degradation of the receptors in cultured neurons. We found that, in addition to CaMKIIβ, also ERK1/2 is involved in the degradation pathway of GABAB receptors under physiological and ischemic conditions. In contrast to our previous view, CaMKIIβ does not appear to directly phosphorylate S867. Instead, the data support a mechanism in which CaMKIIβ activates ERK1/2, which then phosphorylates S867 and T872 in GABAB1. Blocking ERK activity after subjecting neurons to ischemic stress completely restored downregulated GABAB receptor expression to normal levels. Thus, preventing ERK1/2-mediated phosphorylation of S867/T872 in GABAB1 is an opportunity to inhibit the pathological downregulation of the receptors after ischemic stress and is expected to restore a healthy neuronal excitation/inhibition balance.
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Affiliation(s)
- Musadiq A. Bhat
- Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; (M.A.B.); (T.G.)
| | - Thomas Grampp
- Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; (M.A.B.); (T.G.)
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, 8057 Zurich, Switzerland; (M.A.B.); (T.G.)
- Neuroscience Center Zurich, University of Zurich and ETH Zurich, 8057 Zurich, Switzerland
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4
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Hleihil M, Balakrishnan K, Benke D. Protein phosphatase 2A regulation of GABAB receptors normalizes ischemia-induced aberrant receptor trafficking and provides neuroprotection. Front Mol Neurosci 2022; 15:1015906. [PMID: 36311027 PMCID: PMC9607930 DOI: 10.3389/fnmol.2022.1015906] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Accepted: 09/26/2022] [Indexed: 11/13/2022] Open
Abstract
One major factor regulating the strength of GABAB receptor signaling and thereby neuronal excitability is the dynamic control of their cell surface expression. GABAB receptors are constitutively internalized and recycled back to the plasma membrane to maintain a stable number of receptors at cell surface for appropriate signaling. Protein phosphatase 2A (PP2A) dependent dephosphorylation of serine 783 (S783) in the GABAB2 subunit is a key event for downregulating GABAB receptor cell surface expression particularly under conditions associated with excitotoxicity. Here, we investigated the role of PP2A in regulating GABAB receptor cell surface expression under physiological and excitotoxic conditions. For this purpose, we developed an interfering peptide (PP2A-Pep) that inhibits the interaction of GABAB receptors with PP2A. Using cultured cortical neurons, we found that PP2A downregulates GABAB receptor cell surface expression by inhibiting recycling of the receptors and thereby promoting degradation of the receptors. Inhibition of the GABAB receptor/PP2A interaction by PP2A-Pep in cultured cortical neurons restored GABAB receptor cell surface expression after excitotoxic stress and inhibited progressing neuronal death even when added 48 h after the insult. To explore the therapeutic potential of PP2A-Pep, we further analyzed effect of PP2A-Pep in the middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia. Incubation of brain slices prepared from MCAO-treated mice with PP2A-Pep restored normal GABAB receptor expression and GABAB receptor-mediated inhibition, reduced ischemic-induced overexcitability of neurons, and prevented neuronal death in the ischemic penumbra. This data illustrates the crucial role of regulating GABAB receptor phosphorylation by PP2A for controlling neuronal inhibition and excitability. The results further suggest that interfering with the GABAB receptor/PP2A interaction is a promising strategy for the development of specific therapeutic interventions to treat neurological diseases associated with a disturbed excitation/inhibition balance and downregulation of GABAB receptors.
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Affiliation(s)
- Mohammad Hleihil
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Neuroscience Center Zurich, University of Zurich and ETH Zürich, Zurich, Switzerland
| | - Karthik Balakrishnan
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Neuroscience Center Zurich, University of Zurich and ETH Zürich, Zurich, Switzerland
- Drug Discovery Network Zurich, Zurich, Switzerland
- *Correspondence: Dietmar Benke,
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5
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Balakrishnan K, Hleihil M, Bhat MA, Ganley RP, Vaas M, Klohs J, Zeilhofer HU, Benke D. Targeting the interaction of GABA B receptors with CaMKII with an interfering peptide restores receptor expression after cerebral ischemia and inhibits progressive neuronal death in mouse brain cells and slices. Brain Pathol 2022; 33:e13099. [PMID: 35698024 PMCID: PMC9836377 DOI: 10.1111/bpa.13099] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 05/29/2022] [Indexed: 01/21/2023] Open
Abstract
Cerebral ischemia is the leading cause for long-term disability and mortality in adults due to massive neuronal death. Currently, there is no pharmacological treatment available to limit progressive neuronal death after stroke. A major mechanism causing ischemia-induced neuronal death is the excessive release of glutamate and the associated overexcitation of neurons (excitotoxicity). Normally, GABAB receptors control neuronal excitability in the brain via prolonged inhibition. However, excitotoxic conditions rapidly downregulate GABAB receptors via a CaMKII-mediated mechanism and thereby diminish adequate inhibition that could counteract neuronal overexcitation and neuronal death. To prevent the deleterious downregulation of GABAB receptors, we developed a cell-penetrating synthetic peptide (R1-Pep) that inhibits the interaction of GABAB receptors with CaMKII. Administration of this peptide to cultured cortical neurons exposed to excitotoxic conditions restored cell surface expression and function of GABAB receptors. R1-Pep did not affect CaMKII expression or activity but prevented its T286 autophosphorylation that renders it autonomously and persistently active. Moreover, R1-Pep counteracted the aberrant downregulation of G protein-coupled inwardly rectifying K+ channels and the upregulation of N-type voltage-gated Ca2+ channels, the main effectors of GABAB receptors. The restoration of GABAB receptors activated the Akt survival pathway and inhibited excitotoxic neuronal death with a wide time window in cultured neurons. Restoration of GABAB receptors and neuroprotective activity of R1-Pep was verified by using brain slices prepared from mice after middle cerebral artery occlusion (MCAO). Treatment with R1-Pep restored normal GABAB receptor expression and GABA receptor-mediated K+ channel currents. This reduced MCAO-induced neuronal excitability and inhibited neuronal death. These results support the hypothesis that restoration of GABAB receptor expression under excitatory conditions provides neuroprotection and might be the basis for the development of a selective intervention to inhibit progressive neuronal death after ischemic stroke.
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Affiliation(s)
- Karthik Balakrishnan
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland,Neuroscience Center ZurichUniversity of Zurich and ETH ZurichZurichSwitzerland,Present address:
Dewpoint Therapeutics GMBHDresdenGermany
| | - Mohammad Hleihil
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland,Neuroscience Center ZurichUniversity of Zurich and ETH ZurichZurichSwitzerland
| | - Musadiq A. Bhat
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland
| | - Robert P. Ganley
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland
| | - Markus Vaas
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland,Present address:
Clinical Trial Center ZurichUniversity Hospital of ZurichZurichSwitzerland
| | - Jan Klohs
- Neuroscience Center ZurichUniversity of Zurich and ETH ZurichZurichSwitzerland,Institute for Biomedical Engineering, University of Zurich and ETH ZurichZurichSwitzerland
| | - Hanns Ulrich Zeilhofer
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland,Neuroscience Center ZurichUniversity of Zurich and ETH ZurichZurichSwitzerland,Drug Discovery Network ZurichZurichSwitzerland,Institute of Pharmaceutical Sciences, ETH ZurichZurichSwitzerland
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of ZurichZurichSwitzerland,Neuroscience Center ZurichUniversity of Zurich and ETH ZurichZurichSwitzerland,Drug Discovery Network ZurichZurichSwitzerland
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6
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Bhat MA, Esmaeili A, Neumann E, Balakrishnan K, Benke D. Targeting the Interaction of GABA B Receptors With CHOP After an Ischemic Insult Restores Receptor Expression and Inhibits Progressive Neuronal Death. Front Pharmacol 2022; 13:870861. [PMID: 35422706 PMCID: PMC9002115 DOI: 10.3389/fphar.2022.870861] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Accepted: 03/14/2022] [Indexed: 01/01/2023] Open
Abstract
GABAB receptors control neuronal excitability via slow and prolonged inhibition in the central nervous system. One important function of GABAB receptors under physiological condition is to prevent neurons from shifting into an overexcitation state which can lead to excitotoxic death. However, under ischemic conditions, GABAB receptors are downregulated, fostering over-excitation and excitotoxicity. One mechanism downregulating GABAB receptors is mediated via the interaction with the endoplasmic reticulum (ER) stress-induced transcription factor CHOP. In this study, we investigated the hypothesis that preventing the interaction of CHOP with GABAB receptors after an ischemic insult restores normal expression of GABAB receptors and reduces neuronal death. For this, we designed an interfering peptide (R2-Pep) that restored the CHOP-induced downregulation of cell surface GABAB receptors in cultured cortical neurons subjected to oxygen and glucose deprivation (OGD). Administration of R2-Pep after OGD restored normal cell surface expression of GABAB receptors as well as GABAB receptor-mediated inhibition. As a result, R2-Pep reduced enhanced neuronal activity and inhibited progressive neuronal death in OGD stressed cultures. Thus, targeting diseases relevant protein-protein interactions might be a promising strategy for developing highly specific novel therapeutics.
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Affiliation(s)
- Musadiq A Bhat
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Abolghasem Esmaeili
- Department of Cell and Molecular Biology & Microbiology, Faculty of Biological Science and Technology, University of Isfahan, Isfahan, Iran
| | - Elena Neumann
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Karthik Balakrishnan
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland.,Drug Discovery Network Zurich (DDNZ), Zurich, Switzerland
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7
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Lee R, McGee A, Fernandez FX. Systematic review of drugs that modify the circadian system's phase-shifting responses to light exposure. Neuropsychopharmacology 2022; 47:866-879. [PMID: 34961774 PMCID: PMC8882192 DOI: 10.1038/s41386-021-01251-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 11/08/2021] [Accepted: 11/30/2021] [Indexed: 11/09/2022]
Abstract
We searched PubMed for primary research quantifying drug modification of light-induced circadian phase-shifting in rodents. This search, conducted for work published between 1960 and 2018, yielded a total of 146 papers reporting results from 901 studies. Relevant articles were those with any extractable data on phase resetting in wildtype (non-trait selected) rodents administered a drug, alongside a vehicle/control group, near or at the time of exposure. Most circadian pharmacology experiments were done using drugs thought to act directly on either the brain's central pacemaker, the suprachiasmatic nucleus (SCN), the SCN's primary relay, the retinohypothalamic tract, secondary pathways originating from the medial/dorsal raphe nuclei and intergeniculate leaflet, or the brain's sleep-arousal centers. While the neurotransmitter systems underlying these circuits were of particular interest, including those involving glutamate, gamma-aminobutyric acid, serotonin, and acetylcholine, other signaling modalities have also been assessed, including agonists and antagonists of receptors linked to dopamine, histamine, endocannabinoids, adenosine, opioids, and second-messenger pathways downstream of glutamate receptor activation. In an effort to identify drugs that unduly influence circadian responses to light, we quantified the net effects of each drug class by ratioing the size of the phase-shift observed after administration to that observed with vehicle in a given experiment. This allowed us to organize data across the literature, compare the relative efficacy of one mechanism versus another, and clarify which drugs might best suppress or potentiate phase resetting. Aggregation of the available data in this manner suggested that several candidates might be clinically relevant as auxiliary treatments to suppress ectopic light responses during shiftwork or amplify the circadian effects of timed bright light therapy. Future empirical research will be necessary to validate these possibilities.
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Affiliation(s)
- Robert Lee
- Department of Psychology, University of Arizona, Tucson, AZ, USA
| | - Austin McGee
- Department of Psychology, University of Arizona, Tucson, AZ, USA
| | - Fabian-Xosé Fernandez
- Department of Psychology, University of Arizona, Tucson, AZ, USA.
- Department of Neurology, University of Arizona, Tucson, AZ, USA.
- BIO5 and McKnight Brain Research Institutes, Tucson, AZ, USA.
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Abstract
A substantial fraction of the human population suffers from chronic pain states, which often cannot be sufficiently treated with existing drugs. This calls for alternative targets and strategies for the development of novel analgesics. There is substantial evidence that the G protein-coupled GABAB receptor is involved in the processing of pain signals and thus has long been considered a valuable target for the generation of analgesics to treat chronic pain. In this review, the contribution of GABAB receptors to the generation and modulation of pain signals, their involvement in chronic pain states as well as their target suitability for the development of novel analgesics is discussed.
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Affiliation(s)
- Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
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9
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Ozsvár A, Komlósi G, Oláh G, Baka J, Molnár G, Tamás G. Predominantly linear summation of metabotropic postsynaptic potentials follows coactivation of neurogliaform interneurons. eLife 2021; 10:65634. [PMID: 34308838 PMCID: PMC8360660 DOI: 10.7554/elife.65634] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 07/14/2021] [Indexed: 01/13/2023] Open
Abstract
Summation of ionotropic receptor-mediated responses is critical in neuronal computation by shaping input-output characteristics of neurons. However, arithmetics of summation for metabotropic signals are not known. We characterized the combined ionotropic and metabotropic output of neocortical neurogliaform cells (NGFCs) using electrophysiological and anatomical methods in the rat cerebral cortex. These experiments revealed that GABA receptors are activated outside release sites and confirmed coactivation of putative NGFCs in superficial cortical layers in vivo. Triple recordings from presynaptic NGFCs converging to a postsynaptic neuron revealed sublinear summation of ionotropic GABAA responses and linear summation of metabotropic GABAB responses. Based on a model combining properties of volume transmission and distributions of all NGFC axon terminals, we predict that in 83% of cases one or two NGFCs can provide input to a point in the neuropil. We suggest that interactions of metabotropic GABAergic responses remain linear even if most superficial layer interneurons specialized to recruit GABAB receptors are simultaneously active.
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Affiliation(s)
- Attila Ozsvár
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
| | - Gergely Komlósi
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
| | - Gáspár Oláh
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
| | - Judith Baka
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
| | - Gábor Molnár
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
| | - Gábor Tamás
- MTA-SZTE Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences,, Department of Physiology, Anatomy and Neuroscience, University of Szeged, Szeged, Hungary
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10
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Moldavan M, Cravetchi O, Allen CN. Diurnal properties of tonic and synaptic GABA A receptor-mediated currents in suprachiasmatic nucleus neurons. J Neurophysiol 2021; 126:637-652. [PMID: 34259044 DOI: 10.1152/jn.00556.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Synaptic and extrasynaptic GABAA receptor (GABAAR)-mediated neurotransmission is a critical component of the suprachiasmatic nucleus (SCN) neuronal network. However, the properties of the GABAA tonic current (Itonic) and its origin remain unexplored. Spontaneous GABAA postsynaptic currents (sGPSCs) and Itonic were recorded from SCN neurons with the whole cell voltage-clamp technique at different times of the day. GABAAR antagonists (bicuculline, gabazine, and picrotoxin) inhibited sGPSC and induced an outward shift of the holding current, which defined the Itonic amplitude. The sGPSC frequency, synaptic charge transfer, and Itonic amplitude all demonstrated significant diurnal rhythms, with peaks in the middle of the day [zeitgeber time (ZT)7-8] and nadirs at night (ZT19-20). The Itonic amplitude increased proportionally with the sGPSC frequency and synaptic charge transfer during the day and required action potential-mediated GABA release, which was confirmed by TTX application. The activation of presynaptic GABAB receptors by baclofen did not significantly alter the Itonic of neurons with low-frequency sGPSC. The equilibrium potential (Eq) for Itonic was similar to the Eq for chloride and GABAA receptor-activated currents. Itonic showed outward rectification at membrane potentials over the range of -70 to -10 mV and then was linear at voltages greater than -10 mV. GABAAR containing α4-, α5-, and δ-subunits were expressed in SCN, and their contribution to Itonic was confirmed by application of the GABAAR agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and the GABAAR inverse agonist 11,12,13,13a-tetrahydro-7-methoxy-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-c][1,4]benzodiazepine-1-carboxylic acid ethyl ester (L655,708). Thus, the Itonic was mediated by extrasynaptic GABAARs activated predominantly by GABA diffusing out of GABAergic synapses.NEW & NOTEWORTHY A tonic current (Itonic) mediated by GABAA receptors (GABAARs) containing α4-, α5- and δ-subunits was observed in the suprachiasmatic nucleus. The Itonic amplitude strongly depended on the action potential-mediated synaptic release of GABA. The equilibrium potential for Itonic corresponds to that for GABAA currents. The frequency of GABAA postsynaptic currents and Itonic amplitude increased during the day, with peak in the middle of the day, and then gradually declined with a nadir at night, thus showing a diurnal rhythm.
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Affiliation(s)
- Michael Moldavan
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon
| | - Olga Cravetchi
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon
| | - Charles N Allen
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon.,Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon
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11
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Ammari R, Broberger C. Pre- and post-synaptic modulation by GABA B receptors of rat neuroendocrine dopamine neurones. J Neuroendocrinol 2020; 32:e12881. [PMID: 32803906 DOI: 10.1111/jne.12881] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 05/22/2020] [Accepted: 06/05/2020] [Indexed: 12/17/2022]
Abstract
The secretion of prolactin from the pituitary is negatively controlled by tuberoinfundibular dopamine (TIDA) neurones. The electrical properties of TIDA cells have recently been identified as a modulatory target of neurotransmitters and hormones in the lactotrophic axis. The role of the GABAB receptor in this control has received little attention, yet is of particular interest because it may act as a TIDA neurone autoreceptor. Here, this issue was explored in a spontaneously active rat TIDA in vitro slice preparation using whole-cell recordings. Application of the GABAB receptor agonist, baclofen, dose-dependently slowed down or abolished the network oscillations typical of this preparation. Pharmacological manipulations identify the underlying mechanism as an outward current mediated by G-protein-coupled inwardly rectifying K+ -like channels. In addition to this postsynaptic modulation, we describe a presynaptic modulation where GABAB receptors restrain the release of glutamate and GABA onto TIDA neurones. Our data identify both pre- and postsynaptic modulation of TIDA neurones by GABAB receptors that may play a role in the neuronal network control of pituitary prolactin secretion and lactation.
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Affiliation(s)
- Rachida Ammari
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Christian Broberger
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
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12
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McNally BA, Plante AE, Meredith AL. Diurnal properties of voltage-gated Ca 2+ currents in suprachiasmatic nucleus and roles in action potential firing. J Physiol 2019; 598:1775-1790. [PMID: 31177540 DOI: 10.1113/jp278327] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 06/06/2019] [Indexed: 02/04/2023] Open
Abstract
KEY POINTS Circadian oscillations in spontaneous action potential firing in the suprachiasmatic nucleus (SCN) translate time-of-day throughout the mammalian brain. The ion channels that regulate the circadian pattern of SCN firing have not been comprehensively identified. Ca2+ channels regulate action potential activity across many types of excitable cells, and the activity of L-, N-, P/Q- and R-type channels are required for normal daytime firing frequency in SCN neurons and circuit rhythms. Only the L-type Ca2+ current exhibits a day versus night difference in current magnitude, providing insight into the mechanism that produces rhythmic action potential firing in SCN. ABSTRACT The mammalian circadian clock encodes time via rhythmic action potential activity in the suprachiasmatic nucleus (SCN) of the hypothalamus, which governs daily rhythms in physiology and behaviour. SCN neurons exhibit 24 h oscillations in spontaneous firing, with higher firing during day compared to night. Several ionic currents have been identified that regulate SCN firing, including voltage-gated Ca2+ currents, but the circadian regulation of distinct voltage-gated Ca2+ channel (VGCC) components has not been comprehensively addressed. In this study, whole-cell L- (nimodipine-sensitive), N- and P/Q- (ω-agatoxin IVA, ω-conotoxin GVIA, ω-conotoxin MVIIC-sensitive), R- (Ni2+ -sensitive) and T-type (TTA-P2-sensitive) currents were recorded from day and night SCN slices. Using standard voltage protocols, Ni2+ -sensitive currents comprised the largest proportion of total VGCC current, followed by nimodipine-, ω-agatoxin IVA-, ω-conotoxin GVIA- and TTA-P2-sensitive currents. Only the nimodipine-sensitive current exhibited a diurnal difference in magnitude, with daytime current larger than night. No diurnal variation was observed for the other Ca2+ current subtypes. The difference in nimodipine-sensitive current was due to larger peak current activated during the day, not differences in inactivation, and was eliminated by Bay K8644. Blocking L-type channels decreased firing selectively during the day, consistent with higher current magnitudes, and reduced SCN circuit rhythmicity recorded by multi-electrode arrays. Yet blocking N-, P/Q- and R-type channels also decreased daytime firing, with little effect at night, and decreased circuit rhythmicity. These data identify a unique diurnal regulation of L-type current among the major VGCC subtypes in SCN neurons, but also reveal that diurnal modulation is not required for time-of-day-specific effects on firing and circuit rhythmicity.
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Affiliation(s)
- Beth A McNally
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA
| | - Amber E Plante
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA
| | - Andrea L Meredith
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA
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13
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Jurčić N, Er-Raoui G, Airault C, Trouslard J, Wanaverbecq N, Seddik R. GABA B receptors modulate Ca 2+ but not G protein-gated inwardly rectifying K + channels in cerebrospinal-fluid contacting neurones of mouse brainstem. J Physiol 2018; 597:631-651. [PMID: 30418666 DOI: 10.1113/jp277172] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 11/08/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Medullo-spinal CSF contacting neurones (CSF-cNs) located around the central canal are conserved in all vertebrates and suggested to be a novel sensory system intrinsic to the CNS. CSF-cNs receive GABAergic inhibitory synaptic inputs involving ionotropic GABAA receptors, but the contribution of metabotropic GABAB receptors (GABAB -Rs) has not yet been studied. Here, we indicate that CSF-cNs express functional GABAB -Rs that inhibit postsynaptic calcium channels but fail to activate inhibitory potassium channel of the Kir3-type. We further show that GABAB -Rs localise presynaptically on GABAergic and glutamatergic synaptic inputs contacting CSF-cNs, where they inhibit the release of GABA and glutamate. Our data are the first to address the function of GABAB -Rs in CSF-cNs and show that on the presynaptic side they exert a classical synaptic modulation whereas at the postsynaptic level they have an atypical action by modulating calcium signalling without inducing potassium-dependent inhibition. ABSTRACT Medullo-spinal neurones that contact the cerebrospinal fluid (CSF-cNs) are a population of evolutionary conserved cells located around the central canal. CSF-cN activity has been shown to be regulated by inhibitory synaptic inputs involving ionotropic GABAA receptors, but the contribution of the G-protein coupled GABAB receptors has not yet been studied. Here, we used a combination of immunofluorescence, electrophysiology and calcium imaging to investigate the expression and function of GABAB -Rs in CSF-cNs of the mouse brainstem. We found that CSF-cNs express GABAB -Rs, but their selective activation failed to induce G protein-coupled inwardly rectifying potassium (GIRK) currents. Instead, CSF-cNs express primarily N-type voltage-gated calcium (CaV 2.2) channels, and GABAB -Rs recruit Gβγ subunits to inhibit CaV channel activity induced by membrane voltage steps or under physiological conditions by action potentials. Moreover, using electrical stimulation, we indicate that GABAergic inhibitory (IPSCs) and excitatory glutamatergic (EPSCs) synaptic currents can be evoked in CSF-cNs showing that mammalian CSF-cNs are also under excitatory control by glutamatergic synaptic inputs. We further demonstrate that baclofen reversibly reduced the amplitudes of both IPSCs and EPSCs evoked in CSF-cNs through a presynaptic mechanism of regulation. In summary, these results are the first to demonstrate the existence of functional postsynaptic GABAB -Rs in medullar CSF-cNs, as well as presynaptic GABAB auto- and heteroreceptors regulating the release of GABA and glutamate. Remarkably, postsynaptic GABAB -Rs associate with CaV but not GIRK channels, indicating that GABAB -Rs function as a calcium signalling modulator without GIRK-dependent inhibition in CSF-cNs.
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Affiliation(s)
- Nina Jurčić
- Aix Marseille Univ, CNRS, INT, Inst Neurosci Timone, Marseille, France
| | - Ghizlane Er-Raoui
- Aix Marseille Univ, CNRS, INT, Inst Neurosci Timone, Marseille, France.,Université Sultan Moulay Slimane, Laboratoire de Génie Biologique, Béni Mellal, Morocco
| | | | - Jérôme Trouslard
- Aix Marseille Univ, CNRS, INT, Inst Neurosci Timone, Marseille, France
| | | | - Riad Seddik
- Aix Marseille Univ, CNRS, INT, Inst Neurosci Timone, Marseille, France
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14
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Brewer CL, Baccei ML. Enhanced Postsynaptic GABA B Receptor Signaling in Adult Spinal Projection Neurons after Neonatal Injury. Neuroscience 2018; 384:329-339. [PMID: 29885525 PMCID: PMC6053268 DOI: 10.1016/j.neuroscience.2018.05.046] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 04/28/2018] [Accepted: 05/30/2018] [Indexed: 12/19/2022]
Abstract
Clinical and basic science research have revealed persistent effects of early-life injury on nociceptive processing and resulting pain sensitivity. While recent work has identified clear deficits in fast GABAA- and glycine receptor-mediated inhibition in the adult spinal dorsal horn after neonatal tissue damage, the effects of early injury on slow, metabotropic inhibition within spinal pain circuits are poorly understood. Here we provide evidence that neonatal surgical incision significantly enhances postsynaptic GABAB receptor signaling within the mature superficial dorsal horn (SDH) in a cell type-dependent manner. In vitro patch-clamp recordings were obtained from identified lamina I projection neurons and GABAergic interneurons in the SDH of adult female mice following hindpaw incision at postnatal day (P)3. Early tissue damage increased the density of the outward current evoked by baclofen, a selective GABAB receptor agonist, in projection neurons but not inhibitory interneurons. This could reflect enhanced postsynaptic expression of downstream G protein-coupled inward-rectifying potassium channels (GIRKs), as the response to the GIRK agonist ML297 was greater in projection neurons from neonatally incised mice compared to naive littermate controls. Meanwhile, presynaptic GABAB receptor-mediated reduction of spontaneous neurotransmitter release onto both neuronal populations was unaffected by early-life injury. Collectively, our findings suggest that ascending nociceptive transmission to the adult brain is under stronger control by spinal metabotropic inhibition in the aftermath of neonatal tissue damage.
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Affiliation(s)
- Chelsie L Brewer
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
| | - Mark L Baccei
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA.
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15
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Rolland B, Simon N, Franchitto N. Safety Challenges of Using High Dose Baclofen for Alcohol Use Disorder: A Focused Review. Front Psychiatry 2018; 9:367. [PMID: 30186187 PMCID: PMC6113385 DOI: 10.3389/fpsyt.2018.00367] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Accepted: 07/24/2018] [Indexed: 01/13/2023] Open
Abstract
Since the early 2000s, the gamma-aminobutyric acid type B (GABA-B) receptor agonist baclofen has been extensively used for treating alcohol use disorder (AUD). In some countries, like France, Australia, or Germany, baclofen has been used at patient-tailored dose regimens, which can reach 300 mgpd or even more in some patients. The GABA-B-related pharmacology of baclofen expose patients to a specific profile of neuropsychiatric adverse drug reactions (ADRs), primarily some frequent sedative symptoms whose risk of occurrence and severity are both related to the absolute baclofen dosing and the kinetics of dose variations. Other frequent neuropsychiatric ADRs can occur, i.e., tinnitus, insomnia, or dizziness. More rarely, other serious ADRs have been reported, like seizures, manic symptoms, or sleep apnea. However, real-life AUD patients are also exposed to other sedative drugs, like alcohol of course, but also benzodiazepines, other drugs of abuse, or other sedative medications. Consequently, the occurrence of neuropsychiatric safety issues in these patients is essentially the result of a complex multifactorial exposure, in which baclofen causality is rarely obvious by itself. As a result, the decision of initiating baclofen, as well as the daily dose management should be patient-tailored, according the medical history but also the immediate clinical situation of the patient. The overall safety profile of baclofen, as well as the clinical context in which baclofen is used, have many similarities with the use of opiate substitution medications for opiate use disorder. This empirical statement has many implications on how baclofen should be managed and dosing should be adjusted. Moreover, this constant patient-tailored adjustment can be difficult to adapt in the design of clinical trials, which may explain inconsistent findings in baclofen-related literature on AUD.
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Affiliation(s)
- Benjamin Rolland
- Service Universitaire d'Addictologie de Lyon (SUAL), Pôle MOPHA, CH Le Vinatier, Bron, France.,Univ Lyon, Inserm U1028, CNRS UMR5292, UCBL, CRNL, Lyon, France
| | - Nicolas Simon
- APHM, INSERM, IRD, SESSTIM, Hop Sainte Marguerite, Service de Pharmacologie Clinique, CAP-TV, Aix Marseille Univ, Marseille, France
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16
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Shen W, Nan C, Nelson PT, Ripps H, Slaughter MM. GABA B receptor attenuation of GABA A currents in neurons of the mammalian central nervous system. Physiol Rep 2017; 5:5/6/e13129. [PMID: 28348006 PMCID: PMC5371550 DOI: 10.14814/phy2.13129] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2016] [Accepted: 11/18/2016] [Indexed: 11/24/2022] Open
Abstract
Ionotropic receptors are tightly regulated by second messenger systems and are often present along with their metabotropic counterparts on a neuron's plasma membrane. This leads to the hypothesis that the two receptor subtypes can interact, and indeed this has been observed in excitatory glutamate and inhibitory GABA receptors. In both systems the metabotropic pathway augments the ionotropic receptor response. However, we have found that the metabotropic GABAB receptor can suppress the ionotropic GABAA receptor current, in both the in vitro mouse retina and in human amygdala membrane fractions. Expression of amygdala membrane microdomains in Xenopus oocytes by microtransplantation produced functional ionotropic and metabotropic GABA receptors. Most GABAA receptors had properties of α‐subunit containing receptors, with ~5% having ρ‐subunit properties. Only GABAA receptors with α‐subunit‐like properties were regulated by GABAB receptors. In mouse retinal ganglion cells, where only α‐subunit‐containing GABAA receptors are expressed, GABAB receptors suppressed GABAA receptor currents. This suppression was blocked by GABAB receptor antagonists, G‐protein inhibitors, and GABAB receptor antibodies. Based on the kinetic differences between metabotropic and ionotropic receptors, their interaction would suppress repeated, rapid GABAergic inhibition.
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Affiliation(s)
- Wen Shen
- Department of Biomedical Science, Charles E. Schmidt College of Medicine Florida Atlantic University, Boca Raton, Florida
| | - Changlong Nan
- Department of Biomedical Science, Charles E. Schmidt College of Medicine Florida Atlantic University, Boca Raton, Florida
| | - Peter T Nelson
- Division of Neuropathology, Department of Pathology, University of Kentucky, Lexington, Kentucky.,Sanders-Brown Centre on Aging, University of Kentucky, Lexington, Kentucky
| | - Harris Ripps
- Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, Chicago, Illinois.,Whitman Investigator, Marine Biological Laboratory, Woods Hole, Massachusetts
| | - Malcolm M Slaughter
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York
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17
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Moldavan M, Cravetchi O, Allen CN. GABA transporters regulate tonic and synaptic GABA A receptor-mediated currents in the suprachiasmatic nucleus neurons. J Neurophysiol 2017; 118:3092-3106. [PMID: 28855287 PMCID: PMC5814714 DOI: 10.1152/jn.00194.2017] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 08/23/2017] [Accepted: 08/24/2017] [Indexed: 11/22/2022] Open
Abstract
GABA is a principal neurotransmitter in the hypothalamic suprachiasmatic nucleus (SCN) that contributes to intercellular communication between individual circadian oscillators within the SCN network and the stability and precision of the circadian rhythms. GABA transporters (GAT) regulate the extracellular GABA concentration and modulate GABAA receptor (GABAAR)-mediated currents. GABA transport inhibitors were applied to study how GABAAR-mediated currents depend on the expression and function of GAT. Nipecotic acid inhibits GABA transport and induced an inward tonic current in concentration-dependent manner during whole cell patch-clamp recordings from SCN neurons. Application of either the selective GABA transporter 1 (GAT1) inhibitors NNC-711 or SKF-89976A, or the GABA transporter 3 (GAT3) inhibitor SNAP-5114, produced only small changes of the baseline current. Coapplication of GAT1 and GAT3 inhibitors induced a significant GABAAR-mediated tonic current that was blocked by gabazine. GAT inhibitors decreased the amplitude and decay time constant and increased the rise time of spontaneous GABAAR-mediated postsynaptic currents. However, inhibition of GAT did not alter the expression of either GAT1 or GAT3 in the hypothalamus. Thus GAT1 and GAT3 functionally complement each other to regulate the extracellular GABA concentration and GABAAR-mediated synaptic and tonic currents in the SCN. Coapplication of SKF-89976A and SNAP-5114 (50 µM each) significantly reduced the circadian period of Per1 expression in the SCN by 1.4 h. Our studies demonstrate that GAT are important regulators of GABAAR-mediated currents and the circadian clock in the SCN.NEW & NOTEWORTHY In the suprachiasmatic nucleus (SCN), the GABA transporters GAT1 and GAT3 are expressed in astrocytes. Inhibition of these GABA transporters increased a tonic GABA current and reduced the circadian period of Per1 expression in SCN neurons. GAT1 and GAT3 showed functional cooperativity: inhibition of one GAT increased the activity but not the expression of the other. Our data demonstrate that GABA transporters are important regulators of GABAA receptor-mediated currents and the circadian clock.
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Affiliation(s)
- Michael Moldavan
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon; and
| | - Olga Cravetchi
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon; and
| | - Charles N Allen
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon; and
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon
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18
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Albers HE, Walton JC, Gamble KL, McNeill JK, Hummer DL. The dynamics of GABA signaling: Revelations from the circadian pacemaker in the suprachiasmatic nucleus. Front Neuroendocrinol 2017; 44:35-82. [PMID: 27894927 PMCID: PMC5225159 DOI: 10.1016/j.yfrne.2016.11.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 10/16/2016] [Accepted: 11/22/2016] [Indexed: 12/31/2022]
Abstract
Virtually every neuron within the suprachiasmatic nucleus (SCN) communicates via GABAergic signaling. The extracellular levels of GABA within the SCN are determined by a complex interaction of synthesis and transport, as well as synaptic and non-synaptic release. The response to GABA is mediated by GABAA receptors that respond to both phasic and tonic GABA release and that can produce excitatory as well as inhibitory cellular responses. GABA also influences circadian control through the exclusively inhibitory effects of GABAB receptors. Both GABA and neuropeptide signaling occur within the SCN, although the functional consequences of the interactions of these signals are not well understood. This review considers the role of GABA in the circadian pacemaker, in the mechanisms responsible for the generation of circadian rhythms, in the ability of non-photic stimuli to reset the phase of the pacemaker, and in the ability of the day-night cycle to entrain the pacemaker.
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Affiliation(s)
- H Elliott Albers
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States.
| | - James C Walton
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Karen L Gamble
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, United States
| | - John K McNeill
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Daniel L Hummer
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Department of Psychology, Morehouse College, Atlanta, GA 30314, United States
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19
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Dias QM, Prado WA. The lesion of dorsolateral funiculus changes the antiallodynic effect of the intrathecal muscimol and baclofen in distinct phases of neuropathic pain induced by spinal nerve ligation in rats. Brain Res Bull 2016; 124:103-15. [DOI: 10.1016/j.brainresbull.2016.04.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 03/31/2016] [Accepted: 04/04/2016] [Indexed: 12/20/2022]
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20
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Ambient GABA modulates septo-hippocampal inhibitory terminals via presynaptic GABAb receptors. Neuropharmacology 2015; 88:55-62. [PMID: 25446671 DOI: 10.1016/j.neuropharm.2014.10.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 10/03/2014] [Accepted: 10/05/2014] [Indexed: 12/17/2022]
Abstract
The septo-hippocampal GABAergic pathway connects inhibitory neurons in the medial septum with hippocampal interneurons. Phasic release of GABA from septo-hippocampal terminals is thought to play an important role in shaping hippocampal network activity during behavior. Here, we found that GABA release from septo-hippocampal terminals is under negative feedback from the hippocampal local inhibitory network. We found that the strength of septo-hippocampal GABAergic inhibition is constrained by presynaptic GABAb receptors that are activated by ambient GABA during states of increased hippocampal network activity.
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21
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Huang Y, Thathiah A. Regulation of neuronal communication by G protein-coupled receptors. FEBS Lett 2015; 589:1607-19. [PMID: 25980603 DOI: 10.1016/j.febslet.2015.05.007] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/05/2015] [Accepted: 05/05/2015] [Indexed: 02/06/2023]
Abstract
Neuronal communication plays an essential role in the propagation of information in the brain and requires a precisely orchestrated connectivity between neurons. Synaptic transmission is the mechanism through which neurons communicate with each other. It is a strictly regulated process which involves membrane depolarization, the cellular exocytosis machinery, neurotransmitter release from synaptic vesicles into the synaptic cleft, and the interaction between ion channels, G protein-coupled receptors (GPCRs), and downstream effector molecules. The focus of this review is to explore the role of GPCRs and G protein-signaling in neurotransmission, to highlight the function of GPCRs, which are localized in both presynaptic and postsynaptic membrane terminals, in regulation of intrasynaptic and intersynaptic communication, and to discuss the involvement of astrocytic GPCRs in the regulation of neuronal communication.
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Affiliation(s)
- Yunhong Huang
- VIB Center for the Biology of Disease, Leuven, Belgium; Center for Human Genetics (CME) and Leuven Institute for Neurodegenerative Diseases (LIND), University of Leuven (KUL), Leuven, Belgium.
| | - Amantha Thathiah
- VIB Center for the Biology of Disease, Leuven, Belgium; Center for Human Genetics (CME) and Leuven Institute for Neurodegenerative Diseases (LIND), University of Leuven (KUL), Leuven, Belgium.
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22
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Benke D, Balakrishnan K, Zemoura K. Regulation of Cell Surface GABAB Receptors. DIVERSITY AND FUNCTIONS OF GABA RECEPTORS: A TRIBUTE TO HANNS MÖHLER, PART B 2015; 73:41-70. [DOI: 10.1016/bs.apha.2014.11.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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23
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Blankenburg S, Balfanz S, Hayashi Y, Shigenobu S, Miura T, Baumann O, Baumann A, Blenau W. Cockroach GABAB receptor subtypes: molecular characterization, pharmacological properties and tissue distribution. Neuropharmacology 2014; 88:134-44. [PMID: 25242738 DOI: 10.1016/j.neuropharm.2014.08.022] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 08/10/2014] [Accepted: 08/23/2014] [Indexed: 11/29/2022]
Abstract
γ-aminobutyric acid (GABA) is the predominant inhibitory neurotransmitter in the central nervous system (CNS). Its effects are mediated by either ionotropic GABAA receptors or metabotropic GABAB receptors. GABAB receptors regulate, via Gi/o G-proteins, ion channels, and adenylyl cyclases. In humans, GABAB receptor subtypes are involved in the etiology of neurologic and psychiatric disorders. In arthropods, however, these members of the G-protein-coupled receptor family are only inadequately characterized. Interestingly, physiological data have revealed important functions of GABAB receptors in the American cockroach, Periplaneta americana. We have cloned cDNAs coding for putative GABAB receptor subtypes 1 and 2 of P. americana (PeaGB1 and PeaGB2). When both receptor proteins are co-expressed in mammalian cells, activation of the receptor heteromer with GABA leads to a dose-dependent decrease in cAMP production. The pharmacological profile differs from that of mammalian and Drosophila GABAB receptors. Western blot analyses with polyclonal antibodies have revealed the expression of PeaGB1 and PeaGB2 in the CNS of the American cockroach. In addition to the widespread distribution in the brain, PeaGB1 is expressed in salivary glands and male accessory glands. Notably, PeaGB1-like immunoreactivity has been detected in the GABAergic salivary neuron 2, suggesting that GABAB receptors act as autoreceptors in this neuron.
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Affiliation(s)
- S Blankenburg
- Institute of Biochemistry and Biology, Department of Animal Physiology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany.
| | - S Balfanz
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Research Center Jülich, Forschungszentrum Jülich, 52425, Jülich, Germany.
| | - Y Hayashi
- Laboratory of Ecological Genetics, Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido, 060-0810, Japan.
| | - S Shigenobu
- NIBB Core Research Facilities, National Institute for Basic Biology, National Institutes of Natural Sciences, Okazaki, 444-8585, Japan.
| | - T Miura
- Laboratory of Ecological Genetics, Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido, 060-0810, Japan.
| | - O Baumann
- Institute of Biochemistry and Biology, Department of Animal Physiology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany.
| | - A Baumann
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Research Center Jülich, Forschungszentrum Jülich, 52425, Jülich, Germany.
| | - W Blenau
- Institut für Bienenkunde, Polytechnische Gesellschaft, Goethe-Universität Frankfurt am Main, FB Biowissenschaften, Karl-von-Frisch-Weg 2, 61440, Oberursel, Germany.
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24
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Dlouhá K, Kagan D, Roubalová L, Ujčíková H, Svoboda P. Plasma membrane density of GABA(B)-R1a, GABA(B)-R1b, GABA-R2 and trimeric G-proteins in the course of postnatal development of rat brain cortex. Physiol Res 2013; 62:547-59. [PMID: 24020808 DOI: 10.33549/physiolres.932552] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
With the aim to understand the onset of expression and developmental profile of plasma membrane (PM) content /density of crucial components of GABA(B)-R signaling cascade, GABA(B)-R1a, GABA(B)-R1b, GABA(B)-R2, G(i)1/G(i)2alpha, G(i)3alpha, G(o)alpha, G(z)alpha and Gbeta subunit proteins were determined by quantitative immunoblotting and compared in PM isolated from brain cortex of rats of different ages: between postnatal-day-1 (PD1) and 90 (PD90). PM density of GABA(B)-R1a, GABA(B)-R2, G(i)1/G(i)2alpha, G(i)3alpha, G(o)alpha, G(z)alpha and Gbeta was high already at birth and further development was reflected in parallel decrease of both GABA(B)-R1a and GABA(B)-R2 subunits. The major decrease of GABA(B)-R1a and GABA(B)-R2 occurred between the birth and PD15: to 55 % (R1a, **) and 51 % (R2, **), respectively. Contrarily, PM level of the cognate G-proteins G(i)1/G(i)2alpha, G(i)3alpha, G(o)alpha, G(z)alpha and Gbeta was unchanged in the course of the whole postnatal period of brain cortex development. Maturation of GABA(B)-R cascade was substantially different from ontogenetic profile of prototypical plasma membrane marker, Na, K-ATPase, which was low at birth and further development was reflected in continuous increase of PM density of this enzyme. Major change occurred between the birth and PD25. In adult rats, membrane content of Na, K-ATPase was 3-times higher than around the birth.
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Affiliation(s)
- K Dlouhá
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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25
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Han C, Salyer AE, Kim EH, Jiang X, Jarrard RE, Powers MS, Kirchhoff AM, Salvador TK, Chester JA, Hockerman GH, Colby DA. Evaluation of difluoromethyl ketones as agonists of the γ-aminobutyric acid type B (GABAB) receptor. J Med Chem 2013; 56:2456-65. [PMID: 23428109 DOI: 10.1021/jm301805e] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The design, synthesis, biological evaluation, and in vivo studies of difluoromethyl ketones as GABAB agonists that are not structurally analogous to known GABAB agonists, such as baclofen or 3-aminopropyl phosphinic acid, are presented. The difluoromethyl ketones were assembled in three synthetic steps using a trifluoroacetate-release aldol reaction. Following evaluation at clinically relevant GABA receptors, we have identified a difluoromethyl ketone that is a potent GABAB agonist, obtained its X-ray structure, and presented preliminary in vivo data in alcohol-preferring mice. The behavioral studies in mice demonstrated that this compound tended to reduce the acoustic startle response, which is consistent with an anxiolytic profile. Structure-activity investigations determined that replacing the fluorines of the difluoromethyl ketone with hydrogens resulted in an inactive analogue. Resolution of the individual enantiomers of the difluoromethyl ketone provided a compound with full biological activity at concentrations less than an order of magnitude greater than the pharmaceutical, baclofen.
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Affiliation(s)
- Changho Han
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA
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Moldavan MG, Allen CN. GABAB receptor-mediated frequency-dependent and circadian changes in synaptic plasticity modulate retinal input to the suprachiasmatic nucleus. J Physiol 2013; 591:2475-90. [PMID: 23401614 DOI: 10.1113/jphysiol.2012.248047] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Light is the most important environmental signal that entrains the circadian clock located in the hypothalamic suprachiasmatic nucleus (SCN). The retinohypothalamic tract (RHT) was stimulated to simulate the light intensity-dependent discharges of intrinsically photosensitive retinal ganglion cells projecting axons to the hypothalamus. EPSCs were evoked by paired-pulse stimulation or by application of stimulus trains, and recorded from SCN neurons in rat brain slices. Initial release probability (Pr) and synaptic plasticity changes depended on the strength of GABAB receptor (GABABR)-mediated presynaptic inhibition and could be different at the same GABABR agonist concentration. Facilitation caused by frequency-dependent relief of GABABR-mediated inhibition was observed when the initial Pr was decreased to less than 15% of control during strong activation of presynaptic GABAB receptors by (±)baclofen (10 μm), GABA (2 mm) or by GABA uptake inhibitor nipecotic acid (5 mm). In contrast, short-term synaptic depression appeared during baclofen (10 μm) application when initial Pr was greater than 30% of control. Block of 4-aminopyridine-sensitive K(+) currents increased the amplitude and time constant of decay of evoked EPSCs (eEPSCs), and decreased the GABABR-mediated presynaptic inhibition. The GABAB receptor antagonist CGP55845 (3 μm) increased the eEPSCs amplitude 30% throughout the light-dark cycle. During light and dark phases the RHT inputs to 55% and 33% of recorded neurons, respectively, were under GABAB inhibitory control indicating that the tonic inhibition induced by local changes of endogenous GABA concentration contributes to the circadian variation of RHT transmitter release. We conclude that GABABR-mediated presynaptic inhibition decreased with increasing frequency and broadening of presynaptic action potentials, and depended on the sensitivity of RHT terminals to GABABR agonists, and diurnal changes of the extracellular GABA concentration around RHT axon terminals in the SCN.
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Affiliation(s)
- Mykhaylo G Moldavan
- CROET, L606, Oregon Health & Science University, Portland, OR 97239-3098, USA.
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Ribeiro AF, Correia D, Torres AA, Boas GRV, Rueda AVL, Camarini R, Chiavegatto S, Boerngen-Lacerda R, Brunialti-Godard AL. A transcriptional study in mice with different ethanol-drinking profiles: possible involvement of the GABA(B) receptor. Pharmacol Biochem Behav 2012; 102:224-32. [PMID: 22579910 DOI: 10.1016/j.pbb.2012.04.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 04/24/2012] [Accepted: 04/29/2012] [Indexed: 12/15/2022]
Abstract
Previous studies have suggested that γ-aminobutyric acid-B (GABA(B)) receptor agonists effectively reduce ethanol intake. The quantification using real-time polymerase chain reaction of Gabbr1 and Gabbr2 mRNA from the prefrontal cortex, hypothalamus, hippocampus, and striatum in mice exposed to an animal model of the addiction developed in our laboratory was performed to evaluate the involvement of the GABA(B) receptor in ethanol consumption. We used outbred, Swiss mice exposed to a three-bottle free-choice model (water, 5% v/v ethanol, and 10% v/v ethanol) that consisted of four phases: acquisition (AC), withdrawal (W), reexposure (RE), and quinine-adulteration (AD). Based on individual ethanol intake, the mice were classified into three groups: "addicted" (A group; preference for ethanol and persistent consumption during all phases), "heavy" (H group; preference for ethanol and a reduction in ethanol intake in the AD phase compared to AC phase), and "light" (L group; preference for water during all phases). In the prefrontal cortex in the A group, we found high Gabbr1 and Gabbr2 transcription levels, with significantly higher Gabbr1 transcription levels compared with the C (ethanol-naive control mice), L, and H groups. In the hippocampus in the A group, Gabbr2 mRNA levels were significantly lower compared with the C, L, and H groups. In the striatum, we found a significant increase in Gabbr1 transcription levels compared with the C, L, and H groups. No differences in Gabbr1 or Gabbr2 transcription levels were observed in the hypothalamus among groups. In summary, Gabbr1 and Gabbr2 transcription levels were altered in cerebral areas related to drug taking only in mice behaviorally classified as "addicted" drinkers, suggesting that these genes may contribute to high and persistent ethanol consumption.
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Affiliation(s)
- Andrea Frozino Ribeiro
- Department of General Biology, Universidade Federal de Minas Gerais, Pampulha, Belo Horizonte, MG, CEP 31270-901, Brazil
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Meijer JH, Colwell CS, Rohling JHT, Houben T, Michel S. Dynamic neuronal network organization of the circadian clock and possible deterioration in disease. PROGRESS IN BRAIN RESEARCH 2012; 199:143-162. [PMID: 22877664 DOI: 10.1016/b978-0-444-59427-3.00009-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In mammals, the suprachiasmatic nuclei (SCNs) function as a circadian pacemaker that drives 24-h rhythms in physiology and behavior. The SCN is a multicellular clock in which the constituent oscillators show dynamics in their functional organization and phase coherence. Evidence has emerged that plasticity in phase synchrony among SCN neurons determines (i) the amplitude of the rhythm, (ii) the response to continuous light, (iii) the capacity to respond to seasonal changes, and (iv) the phase-resetting capacity. A decrease in circadian amplitude and phase-resetting capacity is characteristic during aging and can be a result of disease processes. Whether the decrease in amplitude is caused by a loss of synchronization or by a loss of single-cell rhythmicity remains to be determined and is important for the development of strategies to ameliorate circadian disorders.
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Affiliation(s)
- Johanna H Meijer
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands.
| | - Christopher S Colwell
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands; Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Jos H T Rohling
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Thijs Houben
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Stephan Michel
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
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Gannon RL, Millan MJ. Positive allosteric modulators at GABAB receptors exert intrinsic actions and enhance the influence of baclofen on light-induced phase shifts of hamster circadian activity rhythms. Pharmacol Biochem Behav 2011; 99:712-7. [DOI: 10.1016/j.pbb.2011.06.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Revised: 06/20/2011] [Accepted: 06/24/2011] [Indexed: 11/28/2022]
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Abstract
Neurons in the suprachiasmatic nucleus (SCN) function as part of a central timing circuit that drives daily changes in our behaviour and underlying physiology. A hallmark feature of SCN neuronal populations is that they are mostly electrically silent during the night, start to fire action potentials near dawn and then continue to generate action potentials with a slow and steady pace all day long. Sets of currents are responsible for this daily rhythm, with the strongest evidence for persistent Na(+) currents, L-type Ca(2+) currents, hyperpolarization-activated currents (I(H)), large-conductance Ca(2+) activated K(+) (BK) currents and fast delayed rectifier (FDR) K(+) currents. These rhythms in electrical activity are crucial for the function of the circadian timing system, including the expression of clock genes, and decline with ageing and disease. This article reviews our current understanding of the ionic and molecular mechanisms that drive the rhythmic firing patterns in the SCN.
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Affiliation(s)
- Christopher S Colwell
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, California 90024, USA.
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Padgett CL, Slesinger PA. GABAB receptor coupling to G-proteins and ion channels. ADVANCES IN PHARMACOLOGY 2010; 58:123-47. [PMID: 20655481 DOI: 10.1016/s1054-3589(10)58006-2] [Citation(s) in RCA: 161] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
GABA(B) receptors have been found to play a key role in regulating membrane excitability and synaptic transmission in the brain. The GABA(B) receptor is a G-protein coupled receptor (GPCR) that associates with a subset of G-proteins (pertussis toxin sensitive Gi/o family), that in turn regulate specific ion channels and trigger cAMP cascades. In this review, we describe the relationships between the GABA(B) receptor, its effectors and associated proteins that mediate GABA(B) receptor function within the brain. We discuss a unique feature of the GABA(B) receptor, the requirement for heterodimerization to produce functional receptors, as well as an increasing body of evidence that suggests GABA(B) receptors comprise a macromolecular signaling heterocomplex, critical for efficient targeting and function of the receptors. Within this complex, GABA(B) receptors associate specifically with Gi/o G-proteins that regulate voltage-gated Ca(2+) (Ca(V)) channels, G-protein activated inwardly rectifying K(+) (GIRK) channels, and adenylyl cyclase. Numerous studies have revealed that lipid rafts, scaffold proteins, targeting motifs in the receptor, and regulators of G-protein signaling (RGS) proteins also contribute to the function of GABA(B) receptors and affect cellular processes such as receptor trafficking and activity-dependent desensitization. This complex regulation of GABA(B) receptors in the brain may provide opportunities for new ways to regulate GABA-dependent inhibition in normal and diseased states of the nervous system.
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Affiliation(s)
- Claire L Padgett
- Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA, USA
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32
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Sun J, Moenter SM. Progesterone treatment inhibits and dihydrotestosterone (DHT) treatment potentiates voltage-gated calcium currents in gonadotropin-releasing hormone (GnRH) neurons. Endocrinology 2010; 151:5349-58. [PMID: 20739401 PMCID: PMC2954728 DOI: 10.1210/en.2010-0385] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
GnRH neurons are central regulators of fertility, and their activity is modulated by steroid feedback. In normal females, GnRH secretion is regulated by estradiol and progesterone (P). Excess androgens present in hyperandrogenemic fertility disorders may disrupt communication of negative feedback signals from P and/or independently stimulate GnRH release. Voltage-gated calcium channels (VGCCs) are important in regulating excitability and hormone release. Estradiol alters VGCCs in a time-of-day-dependent manner. To further elucidate ovarian steroid modulation of GnRH neuron VGCCs, we studied the effects of dihydrotestosterone (DHT) and P. Adult mice were ovariectomized (OVX) or OVX and treated with implants containing DHT (OVXD), estradiol (OVXE), estradiol and DHT (OVXED), estradiol and P (OVXEP), or estradiol, DHT, and P (OVXEDP). Macroscopic calcium current (I(Ca)) was recorded in the morning or afternoon 8-12 d after surgery using whole-cell voltage-clamp. I(Ca) was increased in afternoon vs. morning in GnRH neurons from OVXE mice but this increase was abolished in cells from OVXEP mice. I(Ca) in cells from OVXD mice was increased regardless of time of day; there was no additional effect in OVXED mice. P reduced N-type and DHT potentiated N- and R-type VGCCs; P blocked the DHT potentiation of N-type-mediated current. These data suggest P and DHT have opposing actions on VGCCs in GnRH neurons, but in the presence of both steroids, P dominates. VGCCs are targets of ovarian steroid feedback modulation of GnRH neuron activity and, more specifically, a potential mechanism whereby androgens could activate GnRH neuronal function.
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Affiliation(s)
- Jianli Sun
- Department of Medicine, University of Virginia, Charlottesville, Virginia 22908, USA
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Abstract
Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of approximately 24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber ("time giver") signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.
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Affiliation(s)
- Diego A Golombek
- Laboratory of Chronobiology, Department of Science and Technology, University of Quilmes/Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Quilmes, Argentina.
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Kushnir IG, Kokoshchouk GI. Modulation of the Circadian Rhythm of the Renal Function upon the Action of a GABAA Receptor Agonist and Melatonin. NEUROPHYSIOLOGY+ 2010. [DOI: 10.1007/s11062-010-9108-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Bowery N. Historical Perspective and Emergence of the GABAB Receptor. GABABRECEPTOR PHARMACOLOGY - A TRIBUTE TO NORMAN BOWERY 2010; 58:1-18. [DOI: 10.1016/s1054-3589(10)58001-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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GABAB receptors: physiological functions and mechanisms of diversity. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 58:231-55. [PMID: 20655485 DOI: 10.1016/s1054-3589(10)58010-4] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
GABA(B) receptors are the G-protein-coupled receptors (GPCRs) for gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the central nervous system. GABA(B) receptors are implicated in the etiology of a variety of psychiatric disorders and are considered attractive drug targets. With the cloning of GABA(B) receptor subunits 13 years ago, substantial progress was made in the understanding of the molecular structure, physiology, and pharmacology of these receptors. However, it remained puzzling that native studies demonstrated a heterogeneity of GABA(B) responses that contrasted with a very limited diversity of cloned GABA(B) receptor subunits. Until recently, the only firmly established molecular diversity consisted of two GABA(B1) subunit isoforms, GABA(B1a) and GABA(B1b), which assemble with GABA(B2) subunits to generate heterodimeric GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Using genetic, ultrastructural, biochemical, and electrophysiological approaches, it has been possible to identify functional properties that segregate with these two receptors. Moreover, receptor modifications and factors that can alter the receptor response have been identified. Most importantly, recent data reveal the existence of a family of auxiliary GABA(B) receptor subunits that assemble as tetramers with the C-terminal domain of GABA(B2) subunits and drastically alter pharmacology and kinetics of the receptor response. The data are most consistent with native GABA(B) receptors minimally forming dimeric assemblies of units composed of GABA(B1), GABA(B2), and a tetramer of auxiliary subunits. This represents a substantial departure from current structural concepts for GPCRs.
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Leal K, Klein M. Direct enhancement of presynaptic calcium influx in presynaptic facilitation at Aplysia sensorimotor synapses. Mol Cell Neurosci 2009; 41:247-57. [PMID: 19344767 DOI: 10.1016/j.mcn.2009.03.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Revised: 03/01/2009] [Accepted: 03/23/2009] [Indexed: 01/20/2023] Open
Abstract
Regulation of synaptic transmission by modulation of the calcium influx that triggers transmitter release underlies different forms of synaptic plasticity, and thus could contribute to learning. In the mollusk Aplysia, the neuromodulator serotonin (5-HT) increases evoked transmitter release from sensory neurons and thereby contributes to dishabituation and sensitization of defensive reflexes. We combined electrophysiological recording with fluorescence measurements of intracellular calcium in sensory neuron synapses in culture to test whether direct up-modulation by 5-HT of calcium influx triggered by single action potentials contributes to facilitation of transmitter release. We observe increases in a previously undescribed calcium influx that are strongly correlated with increases in the amplitude of the evoked postsynaptic potentials and which cannot be accounted for by action potential prolongation. Our results suggest that direct modulation of a presynaptic calcium conductance that controls neurotransmitter release contributes to the presynaptic facilitation that underlies a simple form of learning.
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Affiliation(s)
- Karina Leal
- Department of Physiological Science and Brain Research Institute, University of California at Los Angeles, 621 Charles Young Drive South, Los Angeles, CA 90095, USA.
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38
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van Oosterhout F, Michel S, Deboer T, Houben T, van de Ven RCG, Albus H, Westerhout J, Vansteensel MJ, Ferrari MD, van den Maagdenberg AMJM, Meijer JH. Enhanced circadian phase resetting in R192Q Cav2.1 calcium channel migraine mice. Ann Neurol 2008; 64:315-24. [DOI: 10.1002/ana.21418] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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39
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Choi IS, Cho JH, Jeong SG, Hong JS, Kim SJ, Kim J, Lee MG, Choi BJ, Jang IS. GABAB receptor-mediated presynaptic inhibition of glycinergic transmission onto substantia gelatinosa neurons in the rat spinal cord. Pain 2008; 138:330-342. [DOI: 10.1016/j.pain.2008.01.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 12/17/2007] [Accepted: 01/08/2008] [Indexed: 12/01/2022]
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40
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Spary EJ, Maqbool A, Saha S, Batten TFC. Increased GABA B receptor subtype expression in the nucleus of the solitary tract of the spontaneously hypertensive rat. J Mol Neurosci 2008; 35:211-24. [PMID: 18338268 DOI: 10.1007/s12031-008-9055-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Accepted: 02/14/2008] [Indexed: 02/07/2023]
Abstract
Expression of GABA(B) receptor messenger RNA (mRNA) in the central nervous system was compared between the spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rat. Polymerase chain reaction (PCR) revealed all the isoforms except B1e in cortex, hypothalamus, and medulla oblongata. In the nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM), the B1a-c and 1 g isoforms were present as well as B2. Real-time PCR detected significantly higher levels of B1a (p < 0.01) and B2 (p < 0.05) mRNA in the NTS of SHR compared to WKY. A significant increase in B1a expression (p < 0.05) was detected in VLM. Immunolabeling suggested presynaptic and postsynaptic expression of B1a, B1b, and B2 subtypes throughout the NTS, with significant differences in distribution patterns and labeling between subtypes and between SHR and WKY. These findings suggest that GABA(B) receptors expressed by neurones in NTS may be involved in cardiovascular regulation and that changes in GABA(B) mRNA expression levels may contribute to the hypertensive state in SHR.
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Affiliation(s)
- Emma J Spary
- Division of Cardiovascular and Neuronal Remodelling, LIGHT Institute, Faculty of Medicine & Health, University of Leeds, Worsley Building, Leeds, LS2 9JT, UK.
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41
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Belenky MA, Yarom Y, Pickard GE. Heterogeneous expression of gamma-aminobutyric acid and gamma-aminobutyric acid-associated receptors and transporters in the rat suprachiasmatic nucleus. J Comp Neurol 2008; 506:708-32. [PMID: 18067149 DOI: 10.1002/cne.21553] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The hypothalamic suprachiasmatic nucleus (SCN) is the primary mammalian circadian clock that regulates rhythmic physiology and behavior. The SCN is composed of a diverse set of neurons arranged in a tight intrinsic network. In the rat, vasoactive intestinal peptide (VIP)- and gastrin-releasing peptide (GRP)-containing neurons are the dominant cell phenotypes of the ventral SCN, and these cells receive photic information from the retina and the intergeniculate leaflet. Neurons expressing vasopressin (VP) are concentrated in the dorsal and medial aspects of the SCN. Although the VIP/GRP and VP cell groups are concentrated in different regions of the SCN, the separation of these cell groups is not absolute. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is expressed in most SCN neurons irrespective of their location or peptidergic phenotype. In the present study, immunoperoxidase labeling, immunofluorescence confocal microscopy, and ultrastructural immunocytochemistry were used to examine the spatial distribution of several markers associated with SCN GABAergic neurons. Glutamate decarboxylase, a marker of GABA synthesis, and vesicular GABA transporter were more prominently observed in the ventral SCN. KCC2, a K(+)/Cl(-) cotransporter, was highly expressed in the ventral SCN in association with VIP- and GRP-producing neurons, whereas VP neurons in the dorsal SCN were devoid of KCC2. On the other hand, GABA(B) receptors were observed predominantly in VPergic neurons dorsally, whereas, in the ventral SCN, GABA(B) receptors were associated almost exclusively with retinal afferent fibers and terminals. The differential expression of GABAergic markers within the SCN suggests that GABA may play dissimilar roles in different SCN neuronal phenotypes.
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Affiliation(s)
- Michael A Belenky
- Department of Cell/Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
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Castro A, Aguilar J, Elias D, Felix R, Delgado-Lezama R. G-protein-coupled GABAB receptors inhibit Ca2+ channels and modulate transmitter release in descending turtle spinal cord terminal synapsing motoneurons. J Comp Neurol 2007; 503:642-54. [PMID: 17559099 DOI: 10.1002/cne.21421] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Presynaptic gamma-aminobutyric acid type B receptors (GABA(B)Rs) regulate transmitter release at many central synapses by inhibiting Ca(2+) channels. However, the mechanisms by which GABA(B)Rs modulate neurotransmission at descending terminals synapsing on motoneurons in the spinal cord remain unexplored. To address this issue, we characterized the effects of baclofen, an agonist of GABA(B)Rs, on the monosynaptic excitatory postsynaptic potentials (EPSPs) evoked in motoneurons by stimulation of the dorsolateral funiculus (DLF) terminals in a slice preparation from the turtle spinal cord. We found that baclofen depressed neurotransmission in a dose-dependent manner (IC(50) of approximately 2 microM). The membrane time constant of the motoneurons did not change, whereas the amplitude ratio of the evoked EPSPs in response to a paired pulse was altered in the presence of the drug, suggesting a presynaptic mechanism. Likewise, the use of N- and P/Q-type Ca(2+) channel antagonists (omega-conotoxin GVIA and omega-agatoxin IVA, respectively) also depressed EPSPs significantly. Therefore, these channels are likely involved in the Ca(2+) influx that triggers transmitter release from DLF terminals. To determine whether the N and P/Q channels were regulated by GABA(B)R activation, we analyzed the action of the toxins in the presence of baclofen. Interestingly, baclofen occluded omega-conotoxin GVIA action by approximately 50% without affecting omega-agatoxin IVA inhibition, indicating that the N-type channels are the target of GABA(B)Rs. Lastly, the mechanism underlying this effect was further assessed by inhibiting G-proteins with N-ethylmaleimide (NEM). Our data show that EPSP depression caused by baclofen was prevented by NEM, suggesting that GABA(B)Rs inhibit N-type channels via G-protein activation.
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Affiliation(s)
- Alberto Castro
- Department of Physiology, Biophysics, and Neuroscience, Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav-IPN), Mexico City, CP 07300, Mexico
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Brown TM, Piggins HD. Electrophysiology of the suprachiasmatic circadian clock. Prog Neurobiol 2007; 82:229-55. [PMID: 17646042 DOI: 10.1016/j.pneurobio.2007.05.002] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Revised: 03/29/2007] [Accepted: 05/30/2007] [Indexed: 01/28/2023]
Abstract
In mammals, an internal timekeeping mechanism located in the suprachiasmatic nuclei (SCN) orchestrates a diverse array of neuroendocrine and physiological parameters to anticipate the cyclical environmental fluctuations that occur every solar day. Electrophysiological recording techniques have proved invaluable in shaping our understanding of how this endogenous clock becomes synchronized to salient environmental cues and appropriately coordinates the timing of a multitude of physiological rhythms in other areas of the brain and body. In this review we discuss the pioneering studies that have shaped our understanding of how this biological pacemaker functions, from input to output. Further, we highlight insights from new studies indicating that, more than just reflecting its oscillatory output, electrical activity within individual clock cells is a vital part of SCN clockwork itself.
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Affiliation(s)
- Timothy M Brown
- Faculty of Life Sciences, Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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44
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Marshall FH. The role of GABA(B) receptors in the regulation of excitatory neurotransmission. Results Probl Cell Differ 2007; 44:87-98. [PMID: 17549439 DOI: 10.1007/400_2007_038] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
GABA(B) receptors are the metabotrophic receptors for GABA. They are members of the G-protein coupled superfamily of receptors but are highly unusual as they are made up of a dimer of 7-transmembrane spanning subunits. The receptors are widely distributed throughout the central nervous system where they act post-synaptically to cause a long-lasting hyperpolarisation through the activation of a potassium conductance. They are also present pre-synaptically where they act as auto and heteroreceptors to inhibit neurotransmitter release. GABA(B) receptors play a complex role in the regulation of excitatory transmission and their activation can have both inhibitory and dis-inhibitory effects. This has profound physiological and behavioural consequences including modification of LTP and memory, regulation of seizure activity and nociception.
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Affiliation(s)
- Fiona H Marshall
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK.
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Barbaresi P. Cellular and subcellular localization of the GABAB receptor 1a/b subunit in the rat periaqueductal gray matter. J Comp Neurol 2007; 505:478-92. [DOI: 10.1002/cne.21509] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Aton SJ, Huettner JE, Straume M, Herzog ED. GABA and Gi/o differentially control circadian rhythms and synchrony in clock neurons. Proc Natl Acad Sci U S A 2006; 103:19188-93. [PMID: 17138670 PMCID: PMC1748197 DOI: 10.1073/pnas.0607466103] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2006] [Indexed: 11/18/2022] Open
Abstract
Neurons in the mammalian suprachiasmatic nuclei (SCN) generate daily rhythms in physiology and behavior, but it is unclear how they maintain and synchronize these rhythms in vivo. We hypothesized that parallel signaling pathways in the SCN are required to synchronize rhythms in these neurons for coherent output. We recorded firing and clock-gene expression patterns while blocking candidate signaling pathways for at least 8 days. GABA(A) and GABA(B) antagonism increased circadian peak firing rates and rhythm precision of cultured SCN neurons, but G(i/o) did not impair synchrony or rhythmicity. In contrast, inhibiting G(i/o) with pertussis toxin abolished rhythms in most neurons and desynchronized the population, phenocopying the loss of vasoactive intestinal polypeptide (VIP). Daily VIP receptor agonist treatment restored synchrony and rhythmicity to VIP(-/-) SCN cultures during continuous GABA receptor antagonism but not during G(i/o) blockade. Pertussis toxin did not affect circadian cycling of the liver, suggesting that G(i/o) plays a specialized role in maintaining SCN rhythmicity. We conclude that endogenous GABA controls the amplitude of SCN neuronal rhythms by reducing daytime firing, whereas G(i/o) signaling suppresses nighttime firing, and it is necessary for synchrony among SCN neurons. We propose that G(i/o), not GABA activity, converges with VIP signaling to maintain and coordinate rhythms among SCN neurons.
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Affiliation(s)
| | - James E. Huettner
- Cell Biology and Physiology, Washington University, St. Louis, MO 63130; and
| | - Martin Straume
- Customized Online Biomathematical Research Applications, Charlottesville, VA 22901
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Moldavan MG, Irwin RP, Allen CN. Presynaptic GABABReceptors Regulate Retinohypothalamic Tract Synaptic Transmission by Inhibiting Voltage-Gated Ca2+Channels. J Neurophysiol 2006; 95:3727-41. [PMID: 16709723 DOI: 10.1152/jn.00909.2005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Presynaptic GABABreceptor activation inhibits glutamate release from retinohypothalamic tract (RHT) terminals in the suprachiasmatic nucleus (SCN). Voltage-clamp whole cell recordings from rat SCN neurons and optical recordings of Ca2+-sensitive fluorescent probes within RHT terminals were used to examine GABAB-receptor modulation of RHT transmission. Baclofen inhibited evoked excitatory postsynaptic currents (EPSCs) in a concentration-dependent manner equally during the day and night. Blockers of N-, P/Q-, T-, and R-type voltage-dependent Ca2+channels, but not L-type, reduced the EPSC amplitude by 66, 36, 32, and 18% of control, respectively. Joint application of multiple Ca2+channel blockers inhibited the EPSCs less than that predicted, consistent with a model in which multiple Ca2+channels overlap in the regulation of transmitter release. Presynaptic inhibition of EPSCs by baclofen was occluded by ω-conotoxin GVIA (≤72%), mibefradil (≤52%), and ω-agatoxin TK (≤15%), but not by SNX-482 or nimodipine. Baclofen reduced both evoked presynaptic Ca2+influx and resting Ca2+concentration in RHT terminals. Tertiapin did not alter the evoked EPSC and baclofen-induced inhibition, indicating that baclofen does not inhibit glutamate release by activation of Kir3 channels. Neither Ba2+nor high extracellular K+modified the baclofen-induced inhibition. 4-Aminopyridine (4-AP) significantly increased the EPSC amplitude and the charge transfer, and dramatically reduced the baclofen effect. These data indicate that baclofen inhibits glutamate release from RHT terminals by blocking N-, T-, and P/Q-type Ca2+channels, and possibly by activation of 4-AP–sensitive K+channels, but not by inhibition of R- and L-type Ca2+channels or by Kir3 channel activation.
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Affiliation(s)
- Mykhaylo G Moldavan
- Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, Portland 97239-30, USA
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Vacher CM, Gassmann M, Desrayaud S, Challet E, Bradaia A, Hoyer D, Waldmeier P, Kaupmann K, Pévet P, Bettler B. Hyperdopaminergia and altered locomotor activity in GABAB1-deficient mice. J Neurochem 2006; 97:979-91. [PMID: 16606363 DOI: 10.1111/j.1471-4159.2006.03806.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GABAB1-/- mice, which are devoid of functional GABAB receptors, consistently exhibit marked hyperlocomotion when exposed to a novel environment. Telemetry recordings now revealed that, in a familiar environment, GABAB1-/- mice display an altered pattern of circadian activity but no hyperlocomotion. This indicates that hyperlocomotion is only triggered when GABAB1-/- mice are aroused by novelty. In microdialysis experiments, GABAB1-/- mice exhibited a 2-fold increased extracellular level of dopamine in the striatum. Following D-amphetamine administration, GABAB1-/- mice released less dopamine than wild-type mice, indicative of a reduced cytoplasmic dopamine pool. The hyperdopaminergic state of GABAB1-/- mice is accompanied by molecular changes, including reduced levels of tyrosine hydroxylase mRNA, D1 receptor binding-sites and Ser40 phosphorylation of tyrosine hydroxylase. Tyrosine hydroxylase activity, tissue dopamine content and dopamine metabolism do not appear to be measurably altered. Pharmacological and electrophysiological experiments support that the hyperdopaminergic state of GABAB1-/- mice is not severe enough to inactivate dopamine D2 receptors and to disrupt D2-mediated feedback inhibition of tyrosine hydroxylase activity. The data support that loss of GABAB activity results in a sustained moderate hyperdopaminergic state, which is phenotypically revealed by contextual hyperlocomotor activity. Importantly, the presence of an inhibitory GABA tone on the dopaminergic system mediated by GABAB receptors provides an opportunity for therapeutic intervention.
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Affiliation(s)
- Claire-Marie Vacher
- Institute of Physiology, Department of Clinical Biological Sciences, University of Basel, Basel, Switzerland
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Hamasaka Y, Wegener C, Nässel DR. GABA modulates Drosophila circadian clock neurons via GABAB receptors and decreases in calcium. ACTA ACUST UNITED AC 2006; 65:225-40. [PMID: 16118795 DOI: 10.1002/neu.20184] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Circadian clocks play vital roles in the control of daily rhythms in physiology and behavior of animals. In Drosophila, analysis of the molecular and behavioral rhythm has shown that the master clock neurons are entrained by sensory inputs and are synchronized with other clock neurons. However, little is known about the neuronal circuits of the Drosophila circadian system and the neurotransmitters that act on the clock neurons. Here, we provide evidence for a new neuronal input pathway to the master clock neurons, s-LN(v)s, in Drosophila that utilizes GABA as a slow inhibitory neurotransmitter. We monitored intracellular calcium levels in dissociated larval s-LN(v)s with the calcium-sensitive dye Fura-2. GABA decreased intracellular calcium in the s-LN(v)s and blocked spontaneous oscillations in calcium levels. The duration of this response was dose-dependent between 1 nM and 100 microM. The response to GABA was blocked by a metabotropic GABA(B) receptor (GABA(B)-R) antagonist, CGP54626, but not by an ionotropic receptor antagonist, picrotoxin. The GABA(B)-R agonist, 3-APMPA, produced a response similar to GABA. An antiserum against one of the Drosophila GABA(B)-Rs (GABA(B)-R2) labeled the dendritic regions of the s-LN(v)s in both adults and larvae, as well as the dissociated s-LN(v)s. We found that some GABAergic processes terminate at the dendrites of the LN(v)s, as revealed by GABA immunostaining and a GABA-specific GAL4 line (GAD1-gal4). Our results suggest that the s-LN(v)s receive slow inhibitory GABAergic inputs that decrease intracellular calcium of these clock neurons and block their calcium cycling. This response is mediated by postsynaptic GABA(B) receptors.
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Liu X, Tribollet E, Raggenbass M. GABA(B) receptor-activation inhibits GABAergic synaptic transmission in parvocellular neurones of rat hypothalamic paraventricular nucleus. J Neuroendocrinol 2006; 18:177-86. [PMID: 16454801 DOI: 10.1111/j.1365-2826.2005.01402.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The paraventricular nucleus of the hypothalamus contains three classes of neurones: (i) magnocellular and (ii) parvocellular neurosecretory neurones and (iii) nonendocrine projection neurones. The present study aimed to determine whether functional GABA(B) receptors are present on axon terminals that synapse with parvocellular neurosecretory and nonendocrine paraventricular neurones and to determine how activation of GABA(B) receptors control GABAergic input to these neurones. Whole-cell recordings were performed in coronal hypothalamic slices of the rat containing the paraventricular nucleus. GABA(A) receptor-mediated inhibitory postsynaptic currents (i.p.s.c.) were isolated pharmacologically in the presence of antagonists of glutamatergic ionotropic receptors. We found that baclofen, an agonist of GABA(B) receptors, decreased the frequency of spontaneous and miniature i.p.s.c. It also decreased the amplitude of evoked i.p.s.c. These effects were suppressed by CGP55845A, a competitive antagonist of GABA(B) receptors. CGP55845A also increased the frequency of miniature i.p.s.c. and the amplitude of evoked i.p.s.c., suggesting that, in physiological conditions, presynaptic GABA(B) receptors exert a tonic inhibition on GABA release. Baclofen had no effect on GABA-evoked postsynaptic currents, suggesting that the baclofen-dependent suppression of GABAergic i.p.s.c. was exclusively due to a presynaptic action of the agonist. Our data indicate that GABA(B) receptors are present on axon terminals of GABAergic presynaptic neurones contacting parvocellular neurosecretory and nonendocrine paraventricular neurones, and suggest that GABA(B) receptors exert a tonic inhibition of GABA release from GABAergic terminals. Activation of these receptors causes disinhibition of parvocellular neurosecretory and nonendocrine paraventricular neurones.
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Affiliation(s)
- X Liu
- Department of Basic Neuroscience, University Medical Centre, Geneva, Switzerland
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