Structure and function of GluN1-3A NMDA receptor excitatory glycine receptor channel.

N-methyl-d-aspartate receptors (NMDARs) and other ionotropic glutamate receptors (iGluRs) mediate most of the excitatory signaling in the mammalian brains in response to the neurotransmitter glutamate. Uniquely, NMDARs composed of GluN1 and GluN3 are activated exclusively by glycine, the neurotransmitter conventionally mediating inhibitory signaling when it binds to pentameric glycine receptors. The GluN1-3 NMDARs are vital for regulating neuronal excitability, circuit function, and specific behaviors, yet our understanding of their functional mechanism at the molecular level has remained limited. Here, we present cryo-electron microscopy structures of GluN1-3A NMDARs bound to an antagonist, CNQX, and an agonist, glycine. The structures show a 1-3-1-3 subunit heterotetrameric arrangement and an unprecedented pattern of GluN3A subunit orientation shift between the glycine-bound and CNQX-bound structures. Site-directed disruption of the unique subunit interface in the glycine-bound structure mitigated desensitization. Our study provides a foundation for understanding the distinct structural dynamics of GluN3 that are linked to the unique function of GluN1-3 NMDARs.

Schisandrin B from Schisandra chinensis alleviated pain via glycine receptors, Nav1.7 channels and Cav2.2 channels.

ETHNOPHARMACOLOGICAL RELEVANCE: Schisandra chinensis, the dried and ripe fruit of the magnolia family plant Schisandra chinensis (Turcz.) Baill, was commonly used in traditional analgesic prescription. Studies have shown that the extract of Schisandra chinensis (SC) displayed analgesic activity. However, the analgesic active component and the exact mechanisms have yet to be revealed. AIM OF THE STUDY: The present study was to investigate the anti-nociceptive constituent of Schisandra chinensis, assess its analgesic effect, and explore the potential molecular mechanisms. MATERIALS AND METHODS: The effects of a series of well-recognized compounds from SC on glycine receptors were investigated. The analgesic effect of the identified compound was evaluated in three pain models. Mechanistic studies were performed using patch clamp technique on various targets expressed in recombinant cells. These targets included glycine receptors, Nav1.7 sodium channels, Cav2.2 calcium channels et al. Meanwhile, primary cultured spinal dorsal horn (SDH) neurons and dorsal root ganglion (DRG) neurons were also utilized. RESULTS: Schisandrin B (SchB) was a positive allosteric modulator of glycine receptors in spinal dorsal horn neurons. The EC50 of SchB on glycine receptors in spinal dorsal horn neurons was 2.94 ± 0.28 µM. In three pain models, the analgesic effect of SchB was comparable to that of indomethacin at the same dose. Besides, SchB rescued PGE2-induced suppression of α3 GlyR activity and alleviated persistent pain. Notably, SchB could also potently decrease the frequency of action potentials and inhibit sodium and calcium channels in DRG neurons. Consistent with the data from DRG neurons, SchB was also found to significantly block Nav1.7 sodium channels and Cav2.2 channels in recombinant cells. CONCLUSION: Our results demonstrated that, Schisandrin B, the primary lignan component of Schisandra chinensis, may exert its analgesic effect by acting on multiple ion channels, including glycine receptors, Nav1.7 channels, and Cav2.2 channels.

GPR39 regulated spinal glycinergic inhibition and mechanical inflammatory pain.

G protein-coupled receptor 39 (GPR39) senses the change of extracellular divalent zinc ion and signals through multiple G proteins to a broad spectrum of downstream effectors. Here, we found that GPR39 was prevalent at inhibitory synapses of spinal cord somatostatin-positive (SOM+) interneurons, a mechanosensitive subpopulation that is critical for the conveyance of mechanical pain. GPR39 complexed specifically with inhibitory glycine receptors (GlyRs) and helped maintain glycinergic transmission in a manner independent of G protein signalings. Targeted knockdown of GPR39 in SOM+ interneurons reduced the glycinergic inhibition and facilitated the excitatory output from SOM+ interneurons to spinoparabrachial neurons that engaged superspinal neural circuits encoding both the sensory discriminative and affective motivational domains of pain experience. Our data showed that pharmacological activation of GPR39 or augmenting GPR39 interaction with GlyRs at the spinal level effectively alleviated the sensory and affective pain induced by complete Freund's adjuvant and implicated GPR39 as a promising therapeutic target for the treatment of inflammatory mechanical pain.

Successful Autologous Hematopoietic Stem Cell Transplant in Glycine Receptor Antibody-Positive Stiff Person Syndrome: A Case Report

BACKGROUND AND OBJECTIVES: To describe a case of glycine receptor (GlyR) antibody-positive stiff person syndrome (SPS) treated with autologous hematopoietic stem cell transplant (aHSCT). METHODS: This was a multicenter collaboration for the treatment of a single patient who underwent aHSCT as part of a clinical trial (NCT00716066). To objectively assess the response to transplantation, several clinical outcome measures were evaluated pretransplant and up to 18 months post-transplant, including modified Rankin Score (mRS), stiffness index, Hauser Ambulation Score (HAS), hypersensitivity index, timed 25-foot walk, and Montreal Cognitive Assessment. RESULTS: After transplant, the patient achieved sustained clinical improvement evidenced across various clinical scales, including mRS, stiffness index, HAS, and 25-foot walk time. DISCUSSION: aHSCT represents a promising treatment option for SPS, including for GlyR-positive patients. In addition, this case represents the need to validate and standardize best clinical outcome measures for patients with SPS. CLASSIFICATION OF EVIDENCE: Class IV; this is a single observational study without controls.

Synthesis and preclinical evaluation of [11C]uPSEM792 for PSAM4-GlyR based chemogenetics.

Chemogenetic tools are designed to control neuronal signaling. These tools have the potential to contribute to the understanding of neuropsychiatric disorders and to the development of new treatments. One such chemogenetic technology comprises modified Pharmacologically Selective Actuator Modules (PSAMs) paired with Pharmacologically Selective Effector Molecules (PSEMs). PSAMs are receptors with ligand-binding domains that have been modified to interact only with a specific small-molecule agonist, designated a PSEM. PSAM4 is a triple mutant PSAM derived from the α7 nicotinic receptor (α7L131G,Q139L,Y217F). Although having no constitutive activity as a ligand-gated ion channel, PSAM4 has been coupled to the serotonin 5-HT3 receptor (5-HT3R) and to the glycine receptor (GlyR). Treatment with the partner PSEM to activate PSAM4-5-HT3 or PSAM4-GlyR, causes neuronal activation or silencing, respectively. A suitably designed radioligand may enable selective visualization of the expression and location of PSAMs with positron emission tomography (PET). Here, we evaluated uPSEM792, an ultrapotent PSEM for PSAM4-GlyR, as a possible lead for PET radioligand development. We labeled uPSEM792 with the positron-emitter, carbon-11 (t1/2 = 20.4 min), in high radiochemical yield by treating a protected precursor with [11C]iodomethane followed by base deprotection. PET experiments with [11C]uPSEM792 in rodents and in a monkey transduced with PSAM4-GlyR showed low peak radioactivity uptake in brain. This low uptake was probably due to high polarity of the radioligand, as evidenced by physicochemical measurements, and to the vulnerability of the radioligand to efflux transport at the blood-brain barrier. These findings can inform the design of a more effective PSAM4 based PET radioligand, based on the uPSEM792 chemotype.

Glycine Receptor ß-Targeting Autoantibodies Contribute to the Pathology of Autoimmune Diseases.

BACKGROUND AND OBJECTIVES: Stiff-person syndrome (SPS) and progressive encephalomyelitis with rigidity and myoclonus (PERM) are rare neurologic disorders of the CNS. Until now, exclusive GlyRα subunit-binding autoantibodies with subsequent changes in function and surface numbers were reported. GlyR autoantibodies have also been described in patients with focal epilepsy. Autoimmune reactivity against the GlyRß subunits has not yet been shown. Autoantibodies against GlyRα1 target the large extracellular N-terminal domain. This domain shares a high degree of sequence homology with GlyRß making it not unlikely that GlyRß-specific autoantibody (aAb) exist and contribute to the disease pathology. METHODS: In this study, we investigated serum samples from 58 patients for aAb specifically detecting GlyRß. Studies in microarray format, cell-based assays, and primary spinal cord neurons and spinal cord tissue immunohistochemistry were performed to determine specific GlyRß binding and define aAb binding to distinct protein regions. Preadsorption approaches of aAbs using living cells and the purified extracellular receptor domain were further used. Finally, functional consequences for inhibitory neurotransmission upon GlyRß aAb binding were resolved by whole-cell patch-clamp recordings. RESULTS: Among 58 samples investigated, cell-based assays, tissue analysis, and preadsorption approaches revealed 2 patients with high specificity for GlyRß aAb. Quantitative protein cluster analysis demonstrated aAb binding to synaptic GlyRß colocalized with the scaffold protein gephyrin independent of the presence of GlyRα1. At the functional level, binding of GlyRß aAb from both patients to its target impair glycine efficacy. DISCUSSION: Our study establishes GlyRß as novel target of aAb in patients with SPS/PERM. In contrast to exclusively GlyRα1-positive sera, which alter glycine potency, aAbs against GlyRß impair receptor efficacy for the neurotransmitter glycine. Imaging and functional analyses showed that GlyRß aAbs antagonize inhibitory neurotransmission by affecting receptor function rather than localization.

Role of the Glycine Receptor ß Subunit in Synaptic Localization and Pathogenicity in Severe Startle Disease.

Startle disease is due to the disruption of recurrent inhibition in the spinal cord. Most common causes are genetic variants in genes (GLRA1, GLRB) encoding inhibitory glycine receptor (GlyR) subunits. The adult GlyR is a heteropentameric complex composed of α1 and ß subunits that localizes at postsynaptic sites and replaces embryonically expressed GlyRα2 homomers. The human GlyR variants of GLRA1 and GLRB, dominant and recessive, have been intensively studied in vitro. However, the role of unaffected GlyRß, essential for synaptic GlyR localization, in the presence of mutated GlyRα1 in vivo is not fully understood. Here, we used knock-in mice expressing endogenous mEos4b-tagged GlyRß that were crossed with mouse Glra1 startle disease mutants. We explored the role of GlyRß under disease conditions in mice carrying a missense mutation (shaky) or resulting from the loss of GlyRα1 (oscillator). Interestingly, synaptic targeting of GlyRß was largely unaffected in both mouse mutants. While synaptic morphology appears unaltered in shaky animals, synapses were notably smaller in homozygous oscillator animals. Hence, GlyRß enables transport of functionally impaired GlyRα1 missense variants to synaptic sites in shaky animals, which has an impact on the efficacy of possible compensatory mechanisms. The observed enhanced GlyRα2 expression in oscillator animals points to a compensation by other GlyRα subunits. However, trafficking of GlyRα2ß complexes to synaptic sites remains functionally insufficient, and homozygous oscillator mice still die at 3 weeks after birth. Thus, both functional and structural deficits can affect glycinergic neurotransmission in severe startle disease, eliciting different compensatory mechanisms in vivo.

The GlyT1-inhibitor Org 24598 facilitates the alcohol deprivation abolishing and dopamine elevating effects of bupropion + varenicline in rats.

Alcohol Use Disorder (AUD) is a relapsing brain disorder that involves perturbations of brain dopamine (DA) systems, and combined treatment with varenicline + bupropion produces additive effects on accumbal DA output and abolishes the alcohol deprivation effect (ADE) in rats. Also, direct and indirect glycine receptor (GlyR) agonists raise basal DA, attenuate alcohol-induced DA release in the nucleus Accumbens (nAc) and reduce alcohol consumption in rats. This study in rats examines whether the GlyT1-inhibitor Org 24598, an indirect GlyR agonist, enhances the ADE-reducing and DA elevating action of the combined administration of varenicline + bupropion in lower doses than previously applied. Effects on voluntary alcohol consumption, the ADE and extracellular levels of glycine and DA in nAc were examined following treatment with Org 24598 6 and 9 mg/kg i.p., bupropion 3.75 mg/kg i.p. and varenicline 1.5 mg/kg s.c., in monotherapy or combined, using a two-bottle, free-choice alcohol consumption paradigm with an ADE paradigm, and in vivo microdialysis in male Wistar rats. Notably, all treatment regimens appeared to abolish the ADE but only the effect produced by the triple combination (Org24598 + varenicline + bupropion) was significant compared to vehicle. Hence, addition of Org 24598 may enhance the ADE-reducing action of varenicline + bupropion and appears to allow for a dose reduction of bupropion. Treatment with Org 24598 raised accumbal glycine levels but did not significantly alter DA output in monotherapy. Varenicline + bupropion produced a substantial elevation in accumbal DA output that was slightly enhanced following addition of Org 24598. Conceivably, the blockade of the ADE is achieved by the triple combination enhancing accumbal DA transmission in complementary ways, thereby alleviating a hypothesized hypodopaminergia and negative reinforcement to drink. Ultimately, combining an indirect or direct GlyR agonist with varenicline + bupropion may constitute a new pharmacological treatment principle for AUD, although further refinement in dosing and evaluation of other glycinergic compounds are warranted.

Schisandrin B, a dual positive allosteric modulator of GABAA and glycine receptors, alleviates seizures in multiple mouse models.

Epilepsy is a prevalent and severe neurological disorder and approximately 30% of patients are resistant to existing medications. It is of utmost importance to develop alternative therapies to treat epilepsy. Schisandrin B (SchB) is a major bioactive constituent of Schisandra chinensis (Turcz.) Baill and has multiple neuroprotective effects, sedative and hypnotic activities. In this study, we investigated the antiseizure effect of SchB in various mouse models of seizure and explored the underlying mechanisms. Pentylenetetrazole (PTZ), strychnine (STR), and pilocarpine-induced mouse seizure models were established. We showed that injection of SchB (10, 30, 60 mg/kg, i.p.) dose-dependently delayed the onset of generalized tonic-clonic seizures (GTCS), reduced the incidence of GTCS and mortality in PTZ and STR models. Meanwhile, injection of SchB (30 mg/kg, i.p.) exhibited therapeutic potential in pilocarpine-induced status epilepticus model, which was considered as a drug-resistant model. In whole-cell recording from CHO/HEK-239 cells stably expressing recombinant human GABAA receptors (GABAARs) and glycine receptors (GlyRs) and cultured hippocampal neurons, co-application of SchB dose-dependently enhanced GABA or glycine-induced current with EC50 values at around 5 µM, and application of SchB (10 µM) alone did not activate the channels in the absence of GABA or glycine. Furthermore, SchB (10 µM) eliminated both PTZ-induced inhibition on GABA-induced current (IGABA) and strychnine (STR)-induced inhibition on glycine-induced current (Iglycine). Moreover, SchB (10 µM) efficiently rescued the impaired GABAARs associated with genetic epilepsies. In addition, the homologous mutants in both GlyRs-α1(S267Q) and GABAARs-α1(S297Q)ß2(N289S)γ2L receptors by site-directed mutagenesis tests abolished SchB-induced potentiation of IGABA and Iglycine. In conclusion, we have identified SchB as a natural positive allosteric modulator of GABAARs and GlyRs, supporting its potential as alternative therapies for epilepsy.

Streptozotocin-Induced Diabetic Rats Showed a Differential Glycine Receptor Expression in the Spinal Cord: A GlyR Role in Diabetic Neuropathy.

In the spinal cord, attenuation of the inhibitory action of glycine is related to an increase in both inflammatory and diabetic neuropathic pain; however, the glycine receptor involvement in diabetic neuropathy has not been reported. We determined the expression of the glycine receptor subunits (α1-α3 and ß) in streptozotocin-induced diabetic Long-Evans rats by qPCR and Western blot. The total mRNA and protein expression (whole spinal cord homogenate) of the α1, α3, and ß subunits did not change during diabetes; however, the α2 subunit mRNA, but not the protein, was overexpressed 45 days after diabetes induction. By contrast, the synaptic expression of the α1 and α2 subunits decreased in all the studied stages of diabetes, but that of the α3 subunit increased on day 45 after diabetes induction. Intradermal capsaicin produced higher paw-licking behavior in the streptozotocin-induced diabetic rats than in the control animals. In addition, the nocifensive response was higher at 45 days than at 20 days. During diabetes, the expression of the glycine receptor was altered in the spinal cord, which strongly suggests its involvement in diabetic neuropathy.

Research progress on ecology and sustainable development of Guilin Lijiang River Basin, China, based on bibliometric analysis.

Guilin is a typical representative of karst landform in South China. Because of its unique geographical landform and hydrological environment, Lijiang River Basin has received a certain degree of attention in field of ecology and sustainable development. Explore and visualize the hotspots and frontiers of Guilin Lijiang River Basin Ecology and Sustainable Development (GLRBESD) by using bibliometrics, CiteSpace, and VOSviewer. Results showed that number of published papers was in a fluctuating upward trend from 1992 to 2022 and from 2011 to 2022, respectively. Work of scholars in this field has been continuously strengthened and deepened, and overall scientific research results show an increasing trend. Research objects and topics are mainly aimed at the water resources, climate, and environment of GLRB Landscape ecology and SDG index construction. Research of GLRBESD-published documents has the characteristics of multi-disciplinary and interdisciplinary integration. High-frequency keywords in research field focus on ecotourism, ecological restoration, and sustainable development, mainly based on the research of ecotourism development. Impact of environmental factor changes and human activities on land use change in different periods is an important research topic. Core research field of GLRBESD on macro-scale can be divided into ESV and function, ecological compensation and ecotourism, ecological environment and ecological restoration, ecological network and ecological risk assessment, and sustainable development. This research provides systematic scientific research basis for enhancing sustainable development ability and ecosystem functions and services of World Natural Heritage Site.

[Strychnine, in The Mysterious Affair at Styles: Blocking Glycinergic Synaptic Transmission].

Strychnine is a poison that often appears in classical mysteries and has been used for medicine and various purposes. Clearly, its point of action is glycine receptors, and it inhibits glycinergic synaptic transmission. Because of its powerful stimulant effect on the nervous system, if taken orally, characteristic symptoms that are intense and agonizing, such as tonic convulsions, opisthotonus or posterior arch tension, and convulsive laughter, appear. These symptoms are linked to the pathological basis of tetanus, and the drug is an important topic ranging from neuroscience to medical care.

Modelling and Molecular Dynamics Predict the Structure and Interactions of the Glycine Receptor Intracellular Domain.

Glycine receptors (GlyRs) are glycine-gated inhibitory pentameric ligand-gated ion channels composed of α or α + ß subunits. A number of structures of these proteins have been reported, but to date, these have only revealed details of the extracellular and transmembrane domains, with the intracellular domain (ICD) remaining uncharacterised due to its high flexibility. The ICD is a region that can modulate function in addition to being critical for receptor localisation and clustering via proteins such as gephyrin. Here, we use modelling and molecular dynamics (MD) to reveal details of the ICDs of both homomeric and heteromeric GlyR. At their N and C ends, both the α and ß subunit ICDs have short helices, which are major sites of stabilising interactions; there is a large flexible loop between them capable of forming transient secondary structures. The α subunit can affect the ß subunit ICD structure, which is more flexible in a 4α2:1ß than in a 4α1:1ß GlyR. We also explore the effects of gephyrin binding by creating GlyR models bound to the gephyrin E domain; MD simulations suggest these are more stable than the unbound forms, and again there are α subunit-dependent differences, despite the fact the gephyrin binds to the ß subunit. The bound models also suggest that gephyrin causes compaction of the ICD. Overall, the data expand our knowledge of this important receptor protein and in particular clarify features of the underexplored ICD.

Regulation of ethanol-mediated dopamine elevation by glycine receptors located on cholinergic interneurons in the nucleus accumbens.

Alcohol use disorder is one of the major psychiatric disorders worldwide, and there are many factors and effects contributing to the disorder, for example, the experience of ethanol reward. The rewarding and reinforcing properties of ethanol have been linked to activation of the mesolimbic dopamine system, an effect that appears to involve glycine receptors (GlyRs) in the nucleus accumbens. On which neuronal subtypes these receptors are located is, however, not known. The aim of this study was to explore the role of GlyRs on cholinergic interneurons (CIN) in sustaining extracellular dopamine levels and in ethanol-induced dopamine release. To this end, CIN were ablated by anti-choline acetyltransferase-saporin administered locally in the nucleus accumbens of male Wistar rats. Changes in dopamine levels induced by ablation, ethanol and/or a GlyR antagonist were monitored using in vivo microdialysis. The GlyRs antagonist strychnine depressed extracellular dopamine in a similar manner independent on local ablation, suggesting that GlyRs on CIN are not important for sustaining the extracellular dopamine tone. However, a low concentration of strychnine hampered ethanol-induced dopamine release in sham-treated animals, whilst no reduction was seen in ablated animals, suggesting that GlyRs located on CIN are involved in ethanol-induced dopamine release. Further, in ablated rats, ethanol-induced increases of the extracellular levels of the GlyR agonists glycine and taurine were attenuated. In conclusion, this study suggests that CIN are not important for GlyR-mediated regulation of basal dopamine output, but that CIN ablation blunts the ethanol-induced dopamine release, putatively by reducing the release of GlyR agonists.

Dual Role of Dysfunctional Asc-1 Transporter in Distinct Human Pathologies, Human Startle Disease, and Developmental Delay.

Human startle disease is associated with mutations in distinct genes encoding glycine receptors, transporters or interacting proteins at glycinergic synapses in spinal cord and brainstem. However, a significant number of diagnosed patients does not carry a mutation in the common genes GLRA1, GLRB, and SLC6A5 Recently, studies on solute carrier 7 subfamily 10 (SLC7A10; Asc-1, alanine-serine-cysteine transporter) knock-out (KO) mice displaying a startle disease-like phenotype hypothesized that this transporter might represent a novel candidate for human startle disease. Here, we screened 51 patients from our patient cohort negative for the common genes and found three exonic (one missense, two synonymous), seven intronic, and single nucleotide changes in the 5' and 3' untranslated regions (UTRs) in Asc-1. The identified missense mutation Asc-1G307R from a patient with startle disease and developmental delay was investigated in functional studies. At the molecular level, the mutation Asc-1G307R did not interfere with cell-surface expression, but disrupted glycine uptake. Substitution of glycine at position 307 to other amino acids, e.g., to alanine or tryptophan did not affect trafficking or glycine transport. By contrast, G307K disrupted glycine transport similar to the G307R mutation found in the patient. Structurally, the disrupted function in variants carrying positively charged residues can be explained by local structural rearrangements because of the large positively charged side chain. Thus, our data suggest that SLC7A10 may represent a rare but novel gene associated with human startle disease and developmental delay.

Asymmetric gating of a human hetero-pentameric glycine receptor.

Hetero-pentameric Cys-loop receptors constitute a major type of neurotransmitter receptors that enable signal transmission and processing in the nervous system. Despite intense investigations into their working mechanism and pharmaceutical potentials, how neurotransmitters activate these receptors remains unclear due to the lack of high-resolution structural information in the activated open state. Here we report near-atomic resolution structures resolved in digitonin consistent with all principle functional states of the human α1ß GlyR, which is a major Cys-loop receptor that mediates inhibitory neurotransmission in the central nervous system of adults. Glycine binding induces cooperative and symmetric structural rearrangements in the neurotransmitter-binding extracellular domain but asymmetrical pore dilation in the transmembrane domain. Symmetric response in the extracellular domain is consistent with electrophysiological data showing cooperative glycine activation and contribution from both α1 and ß subunits. A set of functionally essential but differentially charged amino acid residues in the transmembrane domain of the α1 and ß subunits explains asymmetric activation. These findings provide a foundation for understanding how the gating of the Cys-loop receptor family members diverges to accommodate specific physiological environments.

A phospho-deficient α3 glycine receptor mutation alters synaptic glycine and GABA release in mouse spinal dorsal horn neurons.

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.

Immunotherapy-Responsive Neuropathic Pain and Allodynia in a Patient With Glycine Receptor Autoantibodies: A Case Report.

OBJECTIVES: Neuropathic pain is common and distressing. Improved mechanistic understanding and pharmacotherapies are urgently needed. Molecularly specific pain syndromes may provide insights with translational relevance. Glycine receptors are known to play a key role in inhibitory neurotransmission in the spinal dorsal horn and have therefore been considered as targets for analgesic development. While autoantibodies directed against glycine receptors may rarely arise spontaneously in humans, a detailed phenotype of neuropathic pain and allodynia in association with these autoantibodies has not been described. METHODS: We describe the case of a previously well adult presenting with severe neuropathic pain and allodynia as part of an autoimmune brainstem and spinal syndrome with glycine receptor autoantibodies. RESULTS: Our patient experienced a severe illness, including marked neuropathic pain and allodynia, hypoventilation, tetraparesis, and ophthalmoplegia. A diagnosis of progressive encephalomyelitis with rigidity and myoclonus was made. Neuropathic pain was characterized with validated instruments and responded promptly to cause-directed immunotherapy. DISCUSSION: A detailed longitudinal phenotyping, using validated pain measurement instruments, of severe neuropathic pain and allodynia associated with likely pathogenic glycine receptor autoantibodies is reported. This case may have relevance for translational development of analgesics targeting glycinergic neurotransmission.

Corticosteroids as Selective and Effective Modulators of Glycine Receptors.

The mechanism of the negative impact of corticosteroids on the induction and progress of mental illness remains unclear. In this work, we studied the effects of corticosteroids on the activity of neuronal glycine receptors (GlyR) and GABA-A receptors (GABAAR) by measuring the chloride current induced by the application of GABA (2 or 5 µM) to isolated cerebellar Purkinje cells (IGABA) and by the application of glycine (100 µM) to pyramidal neurons of the rat hippocampus (IGly). It was found that corticosterone, 5α-dihydrodeoxycorticosterone, allotetrahydrocorticosterone, cortisol, and 17α,21-dihydroxypregnenolone were able to accelerate the desensitization of the IGly at physiological concentrations (IC50 values varying from 0.39 to 0.72 µM). Next, cortisone, 11-deoxycortisol, 11-deoxycorticosterone, 5ß-dihydrodeoxycorticosterone, and tetrahydrocorticosterone accelerated the desensitization of IGly with IC50 values varying from 10.3 to 15.2 µM. Allotetrahydrocorticosterone and tetrahydrocorticosterone potentiated the IGABA albeit with high EC50 values (18-23 µM). The rest of the steroids had no effect on IGABA in the range of concentrations of 1-100 µM. Finally, our study has suggested a structural relationship of the 3ß-hydroxyl group/3-oxo group with the selective modulatory activity on GlyRs in contrast to the 3α-hydroxyl group that is pivotal for GABAARs. In summary, our results suggest that increased GlyR desensitization by corticosteroids may contribute to brain dysfunction under chronic stress and identify corticosteroids for further development as selective modulators of GlyRs.