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Werynska K, Neumann E, Cramer T, Ganley RP, Gingras J, Zeilhofer HU. A phospho-deficient α3 glycine receptor mutation alters synaptic glycine and GABA release in mouse spinal dorsal horn neurons. J Physiol 2023; 601:4121-4133. [PMID: 37598301 DOI: 10.1113/jp284589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2023] [Accepted: 08/03/2023] [Indexed: 08/21/2023] Open
Abstract
Glycine receptors (GlyRs), together with GABAA receptors, mediate postsynaptic inhibition in most spinal cord and hindbrain neurons. In several CNS regions, GlyRs are also expressed in presynaptic terminals. Here, we analysed the effects of a phospho-deficient mutation (S346A) in GlyR α3 subunits on inhibitory synaptic transmission in superficial spinal dorsal horn neurons, where this subunit is abundantly expressed. Unexpectedly, we found that not only were the amplitudes of evoked glycinergic inhibitory postsynaptic currents (IPSCs) significantly larger in GlyRα3(S346A) mice than in mice expressing wild-type α3GlyRs (GlyRα3(WT) mice), but so were those of GABAergic IPSCs. Decreased frequencies of spontaneously occurring glycinergic and GABAergic miniature IPSCs (mIPSCs) with no accompanying change in mIPSC amplitudes suggested a change in presynaptic transmitter release. Paired-pulse experiments on glycinergic IPSCs revealed an increased paired-pulse ratio and a smaller coefficient of variation in GlyRα3(S346A) mice, which together indicate a reduction in transmitter release probability and an increase in the number of releasable vesicles. Paired-pulse ratios of GABAergic IPSCs recorded in the presence of strychnine were not different between genotypes, while the coefficient of variation was smaller in GlyRα3(S346A) mice, demonstrating that the decrease in release probability was readily reversible by GlyR blockade, while the difference in the size of the pool of releasable vesicles remained. Taken together, our results suggest that presynaptic α3 GlyRs regulate synaptic glycine and GABA release in superficial dorsal horn neurons, and that this effect is potentially regulated by their phosphorylation status. KEY POINTS: A serine-to-alanine point mutation was introduced into the glycine receptor α3 subunit of mice. This point mutation renders α3 glycine receptors resistant to protein kinase A mediated phosphorylation but has otherwise only small effects on receptor function. Patch-clamp recordings from neurons in mouse spinal cord slices revealed an unexpected increase in the amplitudes of both glycinergic and GABAergic evoked inhibitory postsynaptic currents (IPSCs). Miniature IPSCs, paired-pulse ratios and synaptic variation analyses indicate a change in synaptic glycine and GABA release. The results strongly suggest that α3 subunit-containing glycine receptors are expressed on presynaptic terminals of inhibitory dorsal horn neurons where they regulate transmitter release.
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Affiliation(s)
- Karolina Werynska
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Drug Discovery Network Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland
| | - Elena Neumann
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Teresa Cramer
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Robert P Ganley
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | | | - Hanns Ulrich Zeilhofer
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Drug Discovery Network Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland
- Institute of Pharmaceutical Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Zurich, Switzerland
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Sheipouri D, Gallagher CI, Shimmon S, Rawling T, Vandenberg RJ. A System for Assessing Dual Action Modulators of Glycine Transporters and Glycine Receptors. Biomolecules 2020; 10:biom10121618. [PMID: 33266066 PMCID: PMC7760315 DOI: 10.3390/biom10121618] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 11/23/2020] [Accepted: 11/25/2020] [Indexed: 12/13/2022] Open
Abstract
Reduced inhibitory glycinergic neurotransmission is implicated in a number of neurological conditions such as neuropathic pain, schizophrenia, epilepsy and hyperekplexia. Restoring glycinergic signalling may be an effective method of treating these pathologies. Glycine transporters (GlyTs) control synaptic and extra-synaptic glycine concentrations and slowing the reuptake of glycine using specific GlyT inhibitors will increase glycine extracellular concentrations and increase glycine receptor (GlyR) activation. Glycinergic neurotransmission can also be improved through positive allosteric modulation (PAM) of GlyRs. Despite efforts to manipulate this synapse, no therapeutics currently target it. We propose that dual action modulators of both GlyTs and GlyRs may show greater therapeutic potential than those targeting individual proteins. To show this, we have characterized a co-expression system in Xenopus laevis oocytes consisting of GlyT1 or GlyT2 co-expressed with GlyRα1. We use two electrode voltage clamp recording techniques to measure the impact of GlyTs on GlyRs and the effects of modulators of these proteins. We show that increases in GlyT density in close proximity to GlyRs diminish receptor currents. Reductions in GlyR mediated currents are not observed when non-transportable GlyR agonists are applied or when Na+ is not available. GlyTs reduce glycine concentrations across different concentration ranges, corresponding with their ion-coupling stoichiometry, and full receptor currents can be restored when GlyTs are blocked with selective inhibitors. We show that partial inhibition of GlyT2 and modest GlyRα1 potentiation using a dual action compound, is as useful in restoring GlyR currents as a full and potent single target GlyT2 inhibitor or single target GlyRα1 PAM. The co-expression system developed in this study will provide a robust means for assessing the likely impact of GlyR PAMs and GlyT inhibitors on glycine neurotransmission.
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Affiliation(s)
- Diba Sheipouri
- School of Medical Sciences, University of Sydney, Sydney, NSW 2006, Australia; (D.S.); (C.I.G.)
| | - Casey I. Gallagher
- School of Medical Sciences, University of Sydney, Sydney, NSW 2006, Australia; (D.S.); (C.I.G.)
| | - Susan Shimmon
- School of Mathematical and Physical Sciences, University of Technology Sydney, Sydney, NSW 2007, Australia; (S.S.); (T.R.)
| | - Tristan Rawling
- School of Mathematical and Physical Sciences, University of Technology Sydney, Sydney, NSW 2007, Australia; (S.S.); (T.R.)
| | - Robert J. Vandenberg
- School of Medical Sciences, University of Sydney, Sydney, NSW 2006, Australia; (D.S.); (C.I.G.)
- Correspondence:
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Glycine receptor α3 and α2 subunits mediate tonic and exogenous agonist-induced currents in forebrain. Proc Natl Acad Sci U S A 2017; 114:E7179-E7186. [PMID: 28784756 DOI: 10.1073/pnas.1703839114] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Neuronal inhibition can occur via synaptic mechanisms or through tonic activation of extrasynaptic receptors. In spinal cord, glycine mediates synaptic inhibition through the activation of heteromeric glycine receptors (GlyRs) composed primarily of α1 and β subunits. Inhibitory GlyRs are also found throughout the brain, where GlyR α2 and α3 subunit expression exceeds that of α1, particularly in forebrain structures, and coassembly of these α subunits with the β subunit appears to occur to a lesser extent than in spinal cord. Here, we analyzed GlyR currents in several regions of the adolescent mouse forebrain (striatum, prefrontal cortex, hippocampus, amygdala, and bed nucleus of the stria terminalis). Our results show ubiquitous expression of GlyRs that mediate large-amplitude currents in response to exogenously applied glycine in these forebrain structures. Additionally, tonic inward currents were also detected, but only in the striatum, hippocampus, and prefrontal cortex (PFC). These tonic currents were sensitive to both strychnine and picrotoxin, indicating that they are mediated by extrasynaptic homomeric GlyRs. Recordings from mice deficient in the GlyR α3 subunit (Glra3-/-) revealed a lack of tonic GlyR currents in the striatum and the PFC. In Glra2-/Y animals, GlyR tonic currents were preserved; however, the amplitudes of current responses to exogenous glycine were significantly reduced. We conclude that functional α2 and α3 GlyRs are present in various regions of the forebrain and that α3 GlyRs specifically participate in tonic inhibition in the striatum and PFC. Our findings suggest roles for glycine in regulating neuronal excitability in the forebrain.
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Islam R, Zhang Y, Xu L, Sah P, Lynch JW. A Chemogenetic Receptor That Enhances the Magnitude and Frequency of Glycinergic Inhibitory Postsynaptic Currents without Inducing a Tonic Chloride Flux. ACS Chem Neurosci 2017; 8:460-467. [PMID: 27958714 DOI: 10.1021/acschemneuro.6b00382] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The gene transfer-mediated expression of inhibitory ion channels in nociceptive neurons holds promise for treating intractable pain. Chemogenetics, which involves expressing constructs activated by biologically inert molecules, is of particular interest as it permits tunable neuromodulation. However, current chloride-permeable chemogenetic constructs are problematic as they mediate a tonic chloride influx which over time would deplete the chloride electrochemical gradient and reduce inhibitory efficacy. Inflammatory pain sensitization can be caused by prostaglandin E2-mediated inhibition of glycinergic inhibitory postsynaptic currents in spinal nociceptive neurons. We developed a highly conducting (100 pS) inhibitory chemogenetic construct based on a human glycine receptor (α1Y279F,A288G) with high ivermectin sensitivity. When virally infected into spinal neurons, 10 nM ivermectin increased the magnitude and frequency of glycinergic postsynaptic currents without activating a tonic chloride flux. The construct should thus produce analgesia. Its human origin and the well-established biocompatibility of its ligand suggest it may be suited to human use.
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Affiliation(s)
- Robiul Islam
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yan Zhang
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Li Xu
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Pankaj Sah
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Joseph W. Lynch
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
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Xie Z, Li G, Ye JH. Acute effects of ethanol on GABA A and glycine currents in the lateral habenula neurons of young rats. ACTA ACUST UNITED AC 2013; 3. [PMID: 28066680 PMCID: PMC5218823 DOI: 10.13055/ojns_3_1_5.130821] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Compelling evidence has shown a pivotal role of dopaminergic function in drug addiction. Recently, the lateral habenula (LHb) has attracted a great deal of attention as another target for abused drugs in the brain because its role in regulating dopaminergic system, among others. GABA and glycine are major inhibitory neurotransmitters. Their corresponding receptors are key targets of ethanol. The properties of these receptors in LHb neurons and their responses to ethanol in particular however, remain unknown. Using the patch clamp techniques, we examined the effects of ethanol on the chloride currents elicited by GABA and glycine in LHb neurons acutely dissociated from 10-20 day-old Sprague-Dawley rats. We show that GABA concentration-dependently elicited a bicuculline sensitive inward current in 96% (130/140) of the neurons tested. Ethanol (43.2 mM) suppressed current elicited by a wide range of concentrations (1-300 μM) of GABA in 74% (35/47) cells tested. Ethanol suppression is dependent on its concentrations but not on membrane potentials of the neurons. Moreover, glycine concentration-dependently elicited an inward current in 94% (112/120) of the neurons tested. Both strychnine and picrotoxin concentration dependently suppressed glycine current with IC50 of 220 nM and 813 μM, respectively. Ethanol (43.2 mM) potentiated current elicited by unsaturated but not saturated concentrations of glycine. Thus, the LHb neurons of young rats contain both functional GABAA and glycine receptors which are sensitive to ethanol at pharmacologically relevant concentrations. These effects of ethanol might be important in the control of the activity and output of LHb neurons.
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Affiliation(s)
- Zijing Xie
- Department of Anesthesiology, Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey.,Department of Neurology Dong-Zhi-Men Hospital, Beijing University of Chinese Medicine. Key laboratory for internal Chinese Medicine of Ministry of Education, China
| | - Guohui Li
- Department of Anesthesiology, Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey
| | - Jiang-Hong Ye
- Department of Anesthesiology, Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey
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Lu Y, Ye JH. Glycine-activated chloride currents of neurons freshly isolated from the prefrontal cortex of young rats. Brain Res 2011; 1393:17-22. [PMID: 21524730 DOI: 10.1016/j.brainres.2011.03.073] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 03/09/2011] [Accepted: 03/29/2011] [Indexed: 02/02/2023]
Abstract
Strychnine-sensitive glycine receptors (GlyR) play a major role in the excitability of CNS neurons and are also a major target of many drugs including some general anesthetics and ethanol. The prefrontal cortex (PFC) is an important substrate responsible for cognitive function and for sedation, as well as hypnosis (unconsciousness) which is induced by general anesthetics and ethanol. However, the functions and the physiological and pharmacological properties of GlyRs in mature PFC neurons have not been well studied. In this study, whole-cell currents induced by glycine (I(Gly)) were recorded from freshly isolated PFC neurons of Sprague-Dawley rats aged 5 to 39 postnatal days (neonatal, P5-12; weanling, P17-21 and peri-adolescent, P30-39). We found that most of the neurons examined were responsive to glycine and the response was concentration dependent. With the increase of age, the sensitivity to glycine was significantly decreased and the sensitivity to picrotoxin was significantly increased. Conversely, the changes in sensitivity to strychnine were not significant. Interestingly, I(Gly) of all age groups was suppressed (to different scope) by low concentrations of picrotoxin (≤ 30 μM), which selectively blocked α homomeric GlyRs. Conversely, about 20-65% of I(Gly) remained in the presence of 300 μM picrotoxin, suggesting the picrotoxin-resistant subtype the αβ heteromeric GlyR, was also present. These data provide the first evidence that there are at least two subtypes of functional GlyRs in the PFC neurons of young rats, and their physiological and pharmacological properties change substantially during maturation.
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Affiliation(s)
- Yongli Lu
- Department of Anesthesiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, NJ 07103, USA
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Abstract
Glycine and GABA are the two main inhibitory neurotransmitters in the central nervous system (CNS). While GABA receptors in the hippocampus have been studied in great detail, the role of glycine receptors (GlyRs) in the hippocampus is less understood. Here we examine recent evidence suggesting that GlyRs are present and active throughout the hippocampus. Extracellular glycine levels are controlled through a combination of release and transport mechanisms, both of which, along with the GlyRs themselves, can be modulated by a number of factors. We discuss the role of GlyRs in suppressing excitation by decreasing postsynaptic membrane resistance in the hippocampus, as well as the contribution of GlyRs to both short- and long-term plasticity.
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Affiliation(s)
- Tara Keck
- Department of Cellular and Systems Neurobiology, Max Planck-Institute of Neurobiology, Martinsried, Germany.
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Mangin JM, Guyon A, Eugène D, Paupardin-Tritsch D, Legendre P. Functional glycine receptor maturation in the absence of glycinergic input in dopaminergic neurones of the rat substantia nigra. J Physiol 2002; 542:685-97. [PMID: 12154171 PMCID: PMC2290440 DOI: 10.1113/jphysiol.2002.018978] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The postnatal maturation pattern of glycine receptor channels (GlyRs) expressed by dopaminergic (DA) neurones of the rat substantia nigra pars compacta (SNc) was investigated using single-channel and whole-cell patch-clamp recordings in brain slices from rats aged 7-21 postnatal days (P). In neonatal rats (P7-P10), GlyRs exhibited a main conductance state of 100-110 pS with a mean open time of 16 ms. In juvenile rats (P19-P22), both the GlyR main conductance state (46-55 pS) and the mean open time (6.8 ms) were decreased. In neonatal rats, application of 30 microM picrotoxin, which is known to block homomeric GlyRs, strongly reduced glycine-evoked responses, while it was much less effective in juvenile rats. These results suggest that these GlyRs correspond functionally to alpha(2) homomeric GlyRs in neonatal rats and alpha(1)/beta heteromeric GlyRs in juvenile rats. A drastic but transient decrease in the glycine responsiveness of DA neurones occurred around P17 concomitant to the functional switch from the homomeric state to the heteromeric state. This age corresponds to a maturation phase for DA neurones. The application of 1 microM gabazine blocked spontaneous or evoked inhibitory synaptic current, while the addition of 1 microM strychnine had no effect, suggesting a lack of functional glycinergic synapses on DA neurones. Although it has been proposed that taurine is co-released with GABA at GABAergic synapses on DA neurones, in the present study the stimulation of GABAergic fibres failed to activate GlyRs. Blockade of taurine transporters and applications of high K(+) and hyposmotic solutions were also unable to induce any strychnine-sensitive current. We conclude that functional maturation of GlyRs can occur in the absence of any detectable GlyR activation in DA neurones of the SNc.
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Affiliation(s)
- J M Mangin
- UMR CNRS 7102 Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie, 9 Quai St Bernard, 75252 Paris cedex 05, France.
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