Glycine receptors in the striatum, globus pallidus, and substantia nigra of the human brain: An immunohistochemical study

Glycine Receptor β-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 GlyRβ 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 GlyRβ making it not unlikely that GlyRβ-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 GlyRβ. Studies in microarray format, cell-based assays, and primary spinal cord neurons and spinal cord tissue immunohistochemistry were performed to determine specific GlyRβ 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 GlyRβ 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 GlyRβ aAb. Quantitative protein cluster analysis demonstrated aAb binding to synaptic GlyRβ colocalized with the scaffold protein gephyrin independent of the presence of GlyRα1. At the functional level, binding of GlyRβ aAb from both patients to its target impair glycine efficacy.

DISCUSSION

Our study establishes GlyRβ as novel target of aAb in patients with SPS/PERM. In contrast to exclusively GlyRα1-positive sera, which alter glycine potency, aAbs against GlyRβ impair receptor efficacy for the neurotransmitter glycine. Imaging and functional analyses showed that GlyRβ aAbs antagonize inhibitory neurotransmission by affecting receptor function rather than localization.

A case of unusual presentation with anti-glycine receptor (GlyR) and myelin oligodentrocyte glycoprotein (MOG) antibody

Movement disorders can be a prominent feature in autoimmune encephalitis. Here we present a rare case of a 73-year-old woman, who presented with a complex phenotype with encephalopathy, parkinsonism, cervical dystonia, left-sided hemidystonia and hemifacial spasm of subacute onset and was found to have breast cancer and positive anti-Glycine Receptor (GlyR) and Myelin Oligodentrocyte Glycoprotein (MOG) antibodies.

Long-Term Depression of Striatal DA Release Induced by mGluRs via Sustained Hyperactivity of Local Cholinergic Interneurons

The cellular mechanisms regulating dopamine (DA) release in the striatum have attracted much interest in recent years. By in vitro amperometric recordings in mouse striatal slices, we show that a brief (5 min) exposure to the metabotropic glutamate receptor agonist DHPG (50 μM) induces a profound depression of synaptic DA release, lasting over 1 h from DHPG washout. This long-term depression is sensitive to glycine, which preferentially inhibits local cholinergic interneurons, as well as to drugs acting on nicotinic acetylcholine receptors and to the pharmacological depletion of released acetylcholine. The same DHPG treatment induces a parallel long-lasting enhancement in the tonic firing of presumed striatal cholinergic interneurons, measured with multi-electrode array recordings. When DHPG is bilaterally infused in vivo in the mouse striatum, treated mice display an anxiety-like behavior. Our results demonstrate that metabotropic glutamate receptors stimulation gives rise to a prolonged depression of the striatal dopaminergic transmission, through a sustained enhancement of released acetylcholine, due to the parallel long-lasting potentiation of striatal cholinergic interneurons firing. This plastic interplay between dopamine, acetylcholine, and glutamate in the dorsal striatum may be involved in anxiety-like behavior typical of several neuropsychiatric disorders.

Involuntary movement in stiff-person syndrome with amphiphysin antibodies: A case report

RATIONALE

Stiff-person syndrome (SPS) is a rare neurological immune disorder characterized by progressive axial and proximal limb muscle rigidity, stiffness, and painful muscle spasms. Amphiphysin antibodies are positive in approximately 5% of SPS patients. To date, there have been no relevant reports on involuntary movement in cases of SPS with amphiphysin antibodies.

PATIENT CONCERNS

We describe the case of a 69-year-old man with a 2-year history of progressive stiffness in the neck, bilateral shoulders, and chest muscles, and a more-than-a-year history of dyspnea accompanied by mandibular involuntary movement. The patient was a vegetarian and had good health in the past. The family's medical history was unremarkable.

DIAGNOSES

He was diagnosed with SPS based on the progressive muscle stiffness, the amphiphysin antibody seropositivity, the continuous motor activity on electromyography, and the effective treatment with benzodiazepines.

INTERVENTIONS

The patient was orally administered clonazepam and baclofen, and corticosteroid IV followed by prednisone orally.

OUTCOMES

In the hospital, after treatment with methylprednisolone, clonazepam, and baclofen, the patient's rigidity, stiffness, and dyspnea significantly improved. The involuntary movement of the mandible persisted throughout the treatment process. Currently, under oral treatment with baclofen and clonazepam, the patient's symptoms of muscle stiffness and dyspnea exist, and follow-up is continued.

LESSONS

We report a rare and novel case of involuntary movement in SPS with amphiphysin antibodies. The present report explores the relationship between SPS and involuntary movement and expands the spectrum of clinical manifestations of SPS.

Anxiety and Startle Phenotypes in Glrb Spastic and Glra1 Spasmodic Mouse Mutants

A GWAS study recently demonstrated single nucleotide polymorphisms (SNPs) in the human GLRB gene of individuals with a prevalence for agoraphobia. GLRB encodes the glycine receptor (GlyRs) β subunit. The identified SNPs are localized within the gene flanking regions (3' and 5' UTRs) and intronic regions. It was suggested that these nucleotide polymorphisms modify GlyRs expression and phenotypic behavior in humans contributing to an anxiety phenotype as a mild form of hyperekplexia. Hyperekplexia is a human neuromotor disorder with massive startle phenotypes due to mutations in genes encoding GlyRs subunits. GLRA1 mutations have been more commonly observed than GLRB mutations. If an anxiety phenotype contributes to the hyperekplexia disease pattern has not been investigated yet. Here, we compared two mouse models harboring either a mutation in the murine Glra1 or Glrb gene with regard to anxiety and startle phenotypes. Homozygous spasmodic animals carrying a Glra1 point mutation (alanine 52 to serine) displayed abnormally enhanced startle responses. Moreover, spasmodic mice exhibited significant changes in fear-related behaviors (freezing, rearing and time spent on back) analyzed during the startle paradigm, even in a neutral context. Spastic mice exhibit reduced expression levels of the full-length GlyRs β subunit due to aberrant splicing of the Glrb gene. Heterozygous animals appear normal without an obvious behavioral phenotype and thus might reflect the human situation analyzed in the GWAS study on agoraphobia and startle. In contrast to spasmodic mice, heterozygous spastic animals revealed no startle phenotype in a neutral as well as a conditioning context. Other mechanisms such as a modulatory function of the GlyRs β subunit within glycinergic circuits in neuronal networks important for fear and fear-related behavior may exist. Possibly, in human additional changes in fear and fear-related circuits either due to gene-gene interactions e.g., with GLRA1 genes or epigenetic factors are necessary to create the agoraphobia and in particular the startle phenotype.

Taurine Suppression of Central Amygdala GABAergic Inhibitory Signaling via Glycine Receptors Is Disrupted in Alcohol Dependence

BACKGROUND

Alcohol use disorder (AUD) increases brain stress systems while suppressing reward system functioning. One expression of stress system recruitment is elevated GABAergic activity in the central amygdala (CeA), which is involved in the excessive drinking seen with AUD. The sulfonic amino acid taurine, a glycine receptor partial agonist, modulates GABAergic activity in the rewarding effects of alcohol. Despite taurine abundance in the amygdala, its role in the dysregulation of GABAergic activity associated with AUD has not been studied. Thus, here, we evaluated the effects of taurine on locally stimulated GABAergic neurotransmission in the CeA of naïve- and alcohol-dependent rats.

METHODS

We recorded intracellularly from CeA neurons of naïve- and alcohol-dependent rats, quantifying locally evoked GABA_A receptor-mediated inhibitory postsynaptic potentials (eIPSP). We examined the effects of taurine and alcohol on CeA eIPSP to characterize potential alcohol dependence-induced changes in the effects of taurine.

RESULTS

We found that taurine decreased amplitudes of eIPSP in CeA neurons of naïve rats, without affecting the acute alcohol-induced facilitation of GABAergic responses. In CeA neurons from dependent rats, taurine no longer had an effect on eIPSP, but now blocked the ethanol (EtOH)-induced increase in eIPSP amplitude normally seen. Additionally, preapplication of the glycine receptor-specific antagonist strychnine blocked the EtOH-induced increase in eIPSP amplitude in neurons from naïve rats.

CONCLUSIONS

These data suggest taurine may act to oppose the effects of acute alcohol via the glycine receptor in the CeA of naïve rats, and this modulatory system is altered in the CeA of dependent rats.

Novel clinical features of glycine receptor antibody syndrome: A series of 17 cases

Objective

To describe novel clinical features of GlyRα1-IgG-positive patients.

Methods

Patients with a positive serum GlyRα1-IgG were identified during a 2-year period from July 2016 to December 2018 at 2 academic centers and followed prospectively. All patients in this series were evaluated in the Neuroimmunology and Autoimmune Neurology clinics at the University of Utah or the University of Colorado.

Results

Thirteen of 17 patients had phenotypes more typically associated with glutamic acid decarboxylase (GAD65) antibody syndromes, consisting of stiff-person syndrome (SPS) with parkinsonism or cerebellar signs. One patient with parkinsonism had a presentation similar to rapidly progressive multiple system atrophy with severe dysautonomia. Ten of 17 patients had various visual symptoms including visual snow, spider web-like images forming shapes and 3-dimensional images, palinopsia, photophobia, visual hallucinations, synesthesia, and intermittent diplopia. Three of 17 patients presented with primarily autoimmune epilepsy accompanied by psychiatric symptoms.

Conclusions

Clinicians should consider testing for GlyR antibodies in GAD65 antibody-negative or low-positive GAD65 antibody patients with SPS-like presentations, especially in the setting of atypical features such as visual disturbances, parkinsonism, or epilepsy.

Differential Fatty Acid-Binding Protein Expression in Persistent Radial Glia in the Human and Sheep Subventricular Zone

Fatty acid-binding proteins (FABPs) are a family of transport proteins that facilitate intracellular transport of fatty acids. Despite abundant expression in the brain, the role that FABPs play in the process of cell proliferation and migration in the subventricular zone (SVZ) remains unclear. Our results provide a detailed characterisation of FABP3, 5, and 7 expression in adult and fetal human and sheep SVZ. High FABP5 expression was specifically observed in the adult human SVZ and co-labelled with polysialylated neural cell adhesion molecule (PSA-NCAM), glial fibrillary acidic protein (GFAP), GFAPδ, and proliferating cell nuclear antigen (PCNA), indicating a role for FABP5 throughout the full maturation process of astrocytes and neuroblasts. Some FABP5+ cells had a radial glial-like appearance and co-labelled with the radial glia markers vimentin (40E-C) and GFAP. In the fetal human brain, FABP5 was expressed by radial glia cells throughout the ventricular zone. In contrast, radial glia-like cells in sheep highly expressed FABP3. Taken together, these differences highlight the species-specific expression profile of FABPs in the SVZ. In this study, we demonstrate the distribution of FABP in the adult human SVZ and fetal ventricular zone and reveal its expression on persistent radial glia that may be involved in adult neurogenesis.

Tonically Active α2 Subunit-Containing Glycine Receptors Regulate the Excitability of Striatal Medium Spiny Neurons

Medium spiny neurons (MSNs) of the dorsal striatum represent the first relay of cortico–striato–thalamic loop, responsible for the initiation of voluntary movements and motor learning. GABAergic transmission exerts the main inhibitory control of MSNs. However, MSNs also express chloride-permeable glycine receptors (GlyRs) although their subunit composition and functional significance in the striatum is unknown. Here, we studied the function of GlyRs in MSNs of young adult mice. We show that MSNs express functional GlyRs, with α2 being the main agonist binding subunit. These receptors are extrasynaptic and depolarizing at resting state. The pharmacological inhibition of GlyRs, as well as inactivation of the GlyR α2 subunit gene hyperpolarize the membrane potential of MSNs and increase their action potential firing offset. Mice lacking GlyR α2 showed impaired motor memory consolidation without any changes in the initial motor performance. Taken together, these results demonstrate that tonically active GlyRs regulate the firing properties of MSNs and may thus affect the function of basal ganglia.

Single Channel Analysis of Isoflurane and Ethanol Enhancement of Taurine-Activated Glycine Receptors

The amino acid taurine is an endogenous ligand acting on glycine receptors (GlyRs), which is released by astrocytes in many brain regions, such as the nucleus accumbens and prefrontal cortex. Taurine is a partial agonist with an efficacy significantly lower than that of glycine. Allosteric modulators such as ethanol and isoflurane produce leftward shifts of glycine concentration-response curves but have no effects at saturating glycine concentrations. In contrast, in whole-cell electrophysiology studies these modulators increase the effects of saturating taurine concentrations. A number of possible mechanisms may explain these enhancing effects, including modulator effects on conductance, channel open times, or channel closed times. We used outside-out patch-clamp single channel electrophysiology to investigate the mechanism of action of 200 mM ethanol and 0.55 mM isoflurane in enhancing the effects of a saturating concentration of taurine. Neither modulator enhanced taurine-mediated conductance. Isoflurane increased the probability of channel opening. Isoflurane also increased the lifetimes of the two shortest open dwell times while both agents decreased the likelihood of occurrence of the longest-lived intracluster channel-closing events. The mechanism of enhancement of GlyR functioning by these modulators is dependent on the efficacy of the agonist activating the receptor and the concentration of agonist tested.

Ziziphus spinosa seeds for insomnia: A review of chemistry and psychopharmacology

BACKGROUND

In Chinese medicine, Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chou is widely used for the treatment of insomnia.

PURPOSE/SECTIONS

This paper summarises the chemistry, psychopharmacology, and compares the pharmaceutical effects of the seeds of Ziziphus jujuba plant, Ziziphus spinosa (ZS) seeds, with benzodiazepines. Whole extracts and constituent compounds have been evaluated in preclinical and clinical studies.

CONCLUSIONS

ZS secondary metabolites modulate GABAergic activity and the serotonergic system. The actual therapeutic agents require further confirmation/identification so that new insomnia phytomedicines can be discovered.

Dopaminergic Regulation of Striatal Interneurons in Reward and Addiction: Focus on Alcohol

Corticobasal ganglia networks coursing through the striatum are key structures for reward-guided behaviors. The ventral striatum (nucleus accumbens (nAc)) and its reciprocal connection with the ventral tegmental area (VTA) represent a primary component of the reward system, but reward-guided learning also involves the dorsal striatum and dopaminergic inputs from the substantia nigra. The majority of neurons in the striatum (>90%) are GABAergic medium spiny neurons (MSNs), but both the input to and the output from these neurons are dynamically controlled by striatal interneurons. Dopamine is a key neurotransmitter in reward and reward-guided learning, and the physiological activity of GABAergic and cholinergic interneurons is regulated by dopaminergic transmission in a complex manner. Here we review the role of striatal interneurons in modulating striatal output during drug reward, with special emphasis on alcohol.

Distribution of the creatine transporter throughout the human brain reveals a spectrum of creatine transporter immunoreactivity

Creatine is a molecule that supports energy metabolism in cells. It is carried across the plasma membrane by the creatine transporter. There has been recent interest in creatine for its neuroprotective effects in neurodegenerative diseases and its potential as a therapeutic agent. This study represents the first systematic investigation of the distribution of the creatine transporter in the human brain. We have used immunohistochemical techniques to map out its location and the intensity of staining. The transporter was found to be strongly expressed, especially in the large projection neurons of the brain and spinal cord. These include the pyramidal neurons in the cerebral cortex, Purkinje cells in the cerebellar cortex, and motor neurons of the somatic motor and visceromotor cranial nerve nuclei and the ventral horn of the spinal cord. Many other neurons in the brain also had some degree of creatine transporter immunoreactivity. By contrast, the medium spiny neurons of the striatum and the catecholaminergic neurons of the substantia nigra and locus coeruleus, which are implicated in neurodegenerative diseases, showed a very low to almost absent level of immunoreactivity for the transporter. We propose that the distribution may reflect the energy consumption by different cell types and that the extent of creatine transporter expression is proportional to the cell's energy requirements. Furthermore, the distribution indicates that supplemented creatine would be widely taken up by brain cells, although possibly less by those cells that degenerate in Huntington's and Parkinson's diseases.

Differential Changes in Postsynaptic Density Proteins in Postmortem Huntington's Disease and Parkinson's Disease Human Brains

NMDA and AMPA-type glutamate receptors and their bound membrane-associated guanylate kinases (MAGUKs) are critical for synapse development and plasticity. We hypothesised that these proteins may play a role in the changes in synapse function that occur in Huntington's disease (HD) and Parkinson's disease (PD). We performed immunohistochemical analysis of human postmortem brain tissue to examine changes in the expression of SAP97, PSD-95, GluA2 and GluN1 in human control, and HD- and PD-affected hippocampus and striatum. Significant increases in SAP97 and PSD-95 were observed in the HD and PD hippocampus, and PSD95 was downregulated in HD striatum. We observed a significant increase in GluN1 in the HD hippocampus and a decrease in GluA2 in HD and PD striatum. Parallel immunohistochemistry experiments in the YAC128 mouse model of HD showed no change in the expression levels of these synaptic proteins. Our human data show that major but different changes occur in glutamatergic proteins in HD versus PD human brains. Moreover, the changes in human HD brains differ from those occurring in the YAC128 HD mouse model, suggesting that unique changes occur at a subcellular level in the HD human hippocampus.

Physiological concentrations of zinc reduce taurine-activated GlyR responses to drugs of abuse

Taurine is an endogenous ligand acting on glycine receptors in many brain regions, including the hippocampus, prefrontal cortex, and nucleus accumbens (nAcc). These areas also contain low concentrations of zinc, which is known to potentiate glycine receptor responses. Despite an increasing awareness of the role of the glycine receptor in the rewarding properties of drugs of abuse, the possible interactions of these compounds with zinc has not been thoroughly addressed. Two-electrode voltage-clamp electrophysiological experiments were performed on α1, α2 α1β and α2β glycine receptors expressed in Xenopus laevis oocytes. The effects of zinc alone, and zinc in combination with other positive modulators on the glycine receptor, were investigated when activated by the full agonist glycine versus the partial agonist taurine. Low concentrations of zinc enhanced responses of maximally-effective concentrations of taurine but not glycine. Likewise, chelation of zinc from buffers decreased responses of taurine- but not glycine-mediated currents. Potentiating concentrations of zinc decreased ethanol, isoflurane, and toluene enhancement of maximal taurine currents with no effects on maximal glycine currents. Our findings suggest that the concurrence of high concentrations of taurine and low concentrations of zinc attenuate the effects of additional modulators on the glycine receptor, and that these conditions are more representative of in vivo functioning than effects seen when these modulators are applied in isolation.

Dissociated expression of mitochondrial and cytosolic creatine kinases in the human brain: a new perspective on the role of creatine in brain energy metabolism

The phosphocreatine/creatine kinase (PCr/CK) system in the brain is defined by the expression of two CK isozymes: the cytosolic brain-type CK (BCK) and the ubiquitous mitochondrial CK (uMtCK). The system plays an important role in supporting cellular energy metabolism by buffering adenosine triphosphate (ATP) consumption and improving the flux of high-energy phosphoryls around the cell. This system is well defined in muscle tissue, but there have been few detailed studies of this system in the brain, especially in humans. Creatine is known to be important for neurologic function, and its loss from the brain during development can lead to mental retardation. This study provides the first detailed immunohistochemical study of the expression pattern of BCK and uMtCK in the human brain. A strikingly dissociated pattern of expression was found: uMtCK was found to be ubiquitously and exclusively expressed in neuronal populations, whereas BCK was dominantly expressed in astrocytes, with a low and selective expression in neurons. This pattern indicates that the two CK isozymes are not widely coexpressed in the human brain, but rather are selectively expressed depending on the cell type. These results suggest that the brain cells may use only certain properties of the PCr/CK system depending on their energetic requirements.

GABA(A) receptor characterization and subunit localization in the human sub-ventricular zone

It is now well established that the human brain continuously produces new stem cells until well into old age. One of these stem-cell rich areas in the human brain is the sub-ventricular zone (SVZ). The human SVZ is organized in four distinctive layers containing type A, B and C cells. To date, no studies have investigated the distribution of inhibitory neurotransmitters such as γ-aminobutyric acid (GABA) and their respective receptors on the different cell types in the human SVZ. GABA(A) receptors (GABA(A)R) are ubiquitously expressed, inhibitory heteropentameric chloride ion channels comprised of a variety of subunits that are targeted by many prescribed drugs. In this study we present detailed immunohistochemical data on the regional and cellular localization of α₁, α₂, α3, β₂,₃ and γ₂ subunits of GABA(A)R in the human SVZ. The results from our double and triple labeling studies demonstrate that the cell types and subunit composition throughout the SVZ is heterogeneous; the thickness of the SVZ and GABA(A)R α₂ and γ₂ expression is increased especially in the vicinity of large SVZ blood vessels. GABA(A)R γ₂ is the most specific to the SVZ and present on various cells that express, either glial fibrillary acidic protein (GFAPδ) or polysialic acid-neural cell adhesion molecule (PSA-NCAM) separately, or together in a respective ratio of 7:6:2. Proliferating (type C) cells in the SVZ express GAD65/67, GFAPδ and GABA(A)R β₂,₃ receptor subunits. Within the SVZ the majority of cells have an unexpected nuclear GABA(A)R β₂,₃ expression that is inversely proportional to that of PCNA (proliferating cell nuclear antigen marker), which is a very different pattern of expression compared with underlying caudate nucleus cells. Taken together our results provide a detailed description of the chemo-architecture of the adult human SVZ demonstrating the importance of GABA and GABA(A) receptors on the various cell types in the SVZ.

GLRB is the third major gene of effect in hyperekplexia

Glycinergic neurotransmission is a major inhibitory influence in the CNS and its disruption triggers a paediatric and adult startle disorder, hyperekplexia. The postsynaptic α(1)-subunit (GLRA1) of the inhibitory glycine receptor (GlyR) and the cognate presynaptic glycine transporter (SLC6A5/GlyT2) are well-established genes of effect in hyperekplexia. Nevertheless, 52% of cases (117 from 232) remain gene negative and unexplained. Ligand-gated heteropentameric GlyRs form chloride ion channels that contain the α(1) and β-subunits (GLRB) in a 2α(1):3β configuration and they form the predominant population of GlyRs in the postnatal and adult human brain, brainstem and spinal cord. We screened GLRB through 117 GLRA1- and SLC6A5-negative hyperekplexia patients using a multiplex-polymerase chain reaction and Sanger sequencing approach. The screening identified recessive and dominant GLRB variants in 12 unrelated hyperekplexia probands. This primarily yielded homozygous null mutations, with nonsense (n = 3), small indel (n = 1), a large 95 kb deletion (n = 1), frameshifts (n = 1) and one recurrent splicing variant found in four cases. A further three cases were found with two homozygous and one dominant GLRB missense mutations. We provide strong evidence for the pathogenicity of GLRB mutations using splicing assays, deletion mapping, cell-surface biotinylation, expression studies and molecular modelling. This study describes the definitive assignment of GLRB as the third major gene for hyperekplexia and impacts on the genetic stratification and biological causation of this neonatal/paediatric disorder. Driven principally by consanguineous homozygosity of GLRB mutations, the study reveals long-term additive phenotypic outcomes for affected cases such as severe apnoea attacks, learning difficulties and developmental delay.

Glycine receptor mutants of the mouse: what are possible routes of inhibitory compensation?

Defects in glycinergic inhibition result in a complex neuromotor disorder in humans known as hyperekplexia (OMIM 149400) with similar phenotypes in rodents characterized by an exaggerated startle reflex and hypertonia. Analogous to genetic defects in humans single point mutations, microdeletions, or insertions in the Glra1 gene but also in the Glrb gene underlie the pathology in mice. The mutations either localized in the α (spasmodic, oscillator, cincinnati, Nmf11) or the β (spastic) subunit of the glycine receptor (GlyR) are much less tolerated in mice than in humans, leaving the question for the existence of different regulatory elements of the pathomechanisms in humans and rodents. In addition to the spontaneous mutations, new insights into understanding of the regulatory pathways in hyperekplexia or glycine encephalopathy arose from the constantly increasing number of knock-out as well as knock-in mutants of GlyRs. Over the last five years, various efforts using in vivo whole cell recordings provided a detailed analysis of the kinetic parameters underlying glycinergic dysfunction. Presynaptic compensation as well as postsynaptic compensatory mechanisms in these mice by other GlyR subunits or GABA_A receptors, and the role of extra-synaptic GlyRs is still a matter of debate. A recent study on the mouse mutant oscillator displayed a novel aspect for compensation of functionality by complementation of receptor domains that fold independently. This review focuses on defects in glycinergic neurotransmission in mice discussed with the background of human hyperekplexia en route to strategies of compensation.

Novel mutation of GLRA1 in Omani families with hyperekplexia and mild mental retardation

Hyperekplexia is characterized by neonatal hypertonia and exaggerated startle reflex in response to loud noise or tactile stimuli. Mutations in patients with hyperekplexia were evident in several genes encoding proteins involved in glycinergic neurotransmission, i.e., glycine receptor α and β subunits, collybistin, gephyrin, and glycine transporter 2. We clinically and genetically characterized two large, unrelated consanguineous families with hyperekplexia. Affected members of the two families manifested hyperekplexia with mild mental retardation. Patients exhibited a novel homozygote c.593G>C missense mutation in GLRA1, resulting in amino acid substitution p.W170S in the corresponding mature glycine receptor α1 subunit. This mutation was absent in 400 randomly selected chromosomes in the same population. In conclusion, a novel p.W170S mutation in the extracellular ligand binding domain of glycine receptor α1 subunit was detected in patients with hyperekplexia and mild mental retardation.

Subregion-Specific Modulation of Excitatory Input and Dopaminergic Output in the Striatum by Tonically Activated Glycine and GABA(A) Receptors

The flow of cortical information through the basal ganglia is a complex spatiotemporal pattern of increased and decreased firing. The striatum is the biggest input nucleus to the basal ganglia and the aim of this study was to assess the role of inhibitory GABA_A and glycine receptors in regulating synaptic activity in the dorsolateral striatum (DLS) and ventral striatum (nucleus accumbens, nAc). Local field potential recordings from coronal brain slices of juvenile and adult Wistar rats showed that GABA_A receptors and strychnine-sensitive glycine receptors are tonically activated and inhibit excitatory input to the DLS and to the nAc. Strychnine-induced disinhibition of glutamatergic transmission was insensitive to the muscarinic receptor inhibitor scopolamine (10 μM), inhibited by the nicotinic acetylcholine receptor antagonist mecamylamine (10 μM) and blocked by GABA_A receptor inhibitors, suggesting that tonically activated glycine receptors depress excitatory input to the striatum through modulation of cholinergic and GABAergic neurotransmission. As an end-product example of striatal GABAergic output in vivo we measured dopamine release in the DLS and nAc by microdialysis in the awake and freely moving rat. Reversed dialysis of bicuculline (50 μM in perfusate) only increased extrasynaptic dopamine levels in the nAc, while strychnine administered locally (200 μM in perfusate) decreased dopamine output by 60% in both the DLS and nAc. Our data suggest that GABA_A and glycine receptors are tonically activated and modulate striatal transmission in a partially subregion-specific manner.

Differential localization of gamma-aminobutyric acid type A and glycine receptor subunits and gephyrin in the human pons, medulla oblongata and uppermost cervical segment of the spinal cord: an immunohistochemical study

Gephyrin is a multifunctional protein responsible for the clustering of glycine receptors (GlyR) and gamma-aminobutyric acid type A receptors (GABA(A)R). GlyR and GABA(A)R are heteropentameric chloride ion channels that facilitate fast-response, inhibitory neurotransmission in the mammalian brain and spinal cord. We investigated the immunohistochemical distribution of gephyrin and the major GABA(A)R and GlyR subunits in the human light microscopically in the rostral and caudal one-thirds of the pons, in the middle and caudal one-thirds of the medulla oblongata, and in the first cervical segment of the spinal cord. The results demonstrate a widespread pattern of immunoreactivity for GlyR and GABA(A)R subunits throughout these regions, including the spinal trigeminal nucleus, abducens nucleus, facial nucleus, pontine reticular formation, dorsal motor nucleus of the vagus nerve, hypoglossal nucleus, lateral cuneate nucleus, and nucleus of the solitary tract. The GABA(A)R alpha(1) and GlyR alpha(1) and beta subunits show high levels of immunoreactivity in these nuclei. The GABA(A)R subunits alpha(2), alpha(3), beta(2,3), and gamma(2) present weaker levels of immunoreactivity. Exceptions are intense levels of GABA(A)R alpha(2) subunit immunoreactivity in the inferior olivary complex and high levels of GABA(A)R alpha(3) subunit immunoreactivity in the locus coeruleus and raphe nuclei. Gephyrin immunoreactivity is highest in the first segment of the cervical spinal cord and hypoglossal nucleus. Our results suggest that a variety of different inhibitory receptor subtypes is responsible for inhibitory functions in the human brainstem and cervical spinal cord and that gephyrin functions as a clustering molecule for major subtypes of these inhibitory neurotransmitter receptors.

Localization of glycine receptors in the human forebrain, brainstem, and cervical spinal cord: an immunohistochemical review

Inhibitory neurotransmitter receptors for glycine (GlyR) are heteropentameric chloride ion channels that are comprised of four functional subunits, alpha1–3 and beta and that facilitate fast-response, inhibitory neurotransmission in the mammalian brain and spinal cord. We have investigated the distribution of GlyRs in the human forebrain, brainstem, and cervical spinal cord using immunohistochemistry at light and confocal laser scanning microscopy levels. This review will summarize the present knowledge on the GlyR distribution in the human brain using our established immunohistochemical techniques. The results of our immunohistochemical labeling studies demonstrated GlyR immunoreactivity (IR) throughout the human basal ganglia, substantia nigra, various pontine regions, rostral medulla oblongata and the cervical spinal cord present an intense and abundant punctate IR along the membranes of the neuronal soma and dendrites. This work is part of a systematic study of inhibitory neurotransmitter receptor distribution in the human CNS, and provides a basis for additional detailed physiological and pharmacological studies on the inter-relationship of GlyR, GABA_AR and gephyrin in the human brain. This basic mapping exercise, we believe, will provide important baselines for the testing of future pharmacotherapies and drug regimes that modulate neuroinhibitory systems. These findings provide new information for understanding the complexity of glycinergic functions in the human brain, which will translate into the contribution of inhibitory mechanisms in paroxysmal disorders and neurodegenerative diseases such as Epilepsy, Huntington's and Parkinson's Disease and Motor Neuron Disease.

The borderland of epilepsy: clinical and molecular features of phenomena that mimic epileptic seizures

Paroxysmal losses of consciousness and other episodic neurological symptoms have many causes. Distinguishing epileptic from non-epileptic disorders is fundamental to diagnosis, but even this basic dichotomy is often challenging and is certainly not new. In 1907, the British neurologist William Richard Gowers published his book The Border-land of Epilepsy in which he discussed paroxysmal conditions "in the border-land of epilepsy-near it, but not of it" and their clinical differentiation from epilepsy itself. Now, a century later, we revisit the epilepsy borderland, focusing on syncope, migraine, vertigo, parasomnias, and some rarer paroxysmal disorders. For each condition, we review the clinical distinction from epileptic seizures. We then integrate current understanding of the molecular pathophysiology of these disorders into this clinical framework. This analysis shows that, although the clinical manifestations of paroxysmal disorders are highly heterogeneous, striking similarities in molecular pathophysiology are seen among many epileptic and non-epileptic paroxysmal phenomena.

The localization of inhibitory neurotransmitter receptors on dopaminergic neurons of the human substantia nigra

The substantia nigra pars compacta (SNc) is comprised mainly of dopaminergic pigmented neurons arranged in groups, with a small population of nonpigmented neurons scattered among these groups. These different types of neurons possess GABAA, GABAB, and glycine receptors. The SNc-pigmented dopaminergic neurons have postsynaptic GABAA receptors (GABAAR) with a subunit configuration containing alpha3 and gamma2 subunits, with a small population of pigmented neurons containing alpha1 beta2,3 gamma2 subunits. GABAB receptors comprised of R1 and R2 subunits and glycine receptors are also localized on pigmented neurons. In contrast, nonpigmented (mainly parvalbumin positive neurons) located in the SNc are morphologically and neurochemically similar to substantia nigra pars reticulata (SNr) neurons by showing immunoreactivity for parvalbumin and GABAARs containing immunoreactivity for alpha1, alpha3, beta2,3, and gamma2 subunits as well as GABAB R1 and R2 subunits and glycine receptors. Thus, these two neuronal types of the SNc, either pigmented dopaminergic neurons or nonpigmented parvalbumin positive neurons, have similar GABAB and glycine receptor combinations, but differ mainly in the subunit composition of the GABAARs located on their membranes. The different types of GABAARs suggest that GABAergic inputs to these neuronal types operate through GABAARs with different pharmacological and physiological profiles, whereas GABABR and glycine receptors of these cell types are likely to have similar properties.

Cyclopeptide alkaloid fraction from Zizyphi Spinosi Semen enhances pentobarbital-induced sleeping behaviors

This study aimed to investigate effects of cyclopeptide alkaloid fraction of ZSS (CAFZ) on pentobarbital-induced sleeping behaviors and to determine whether these effects were mediated by gamma-aminobutyric acid (GABA) receptors Cl(-) channel activation, using a Western blot technique and Cl(-) sensitive fluorescence probe. GABA receptors subunits expression and Cl(-) influx were investigated in cultured cerebellar granule cells. CAFZ shortened sleeping onset and prolonged sleeping time induced by pentobarbital (42 mg/kg). It also significantly increased the falling asleep rate and duration of sleeping time at a sub-hypnotic dosage of pentobarbital (28 mg/kg). In addition, CAFZ in combination with GABA A receptors agonist, muscimol, synergistically prolonged pentobarbital-induced sleeping time. Both of CAFZ and pentobarbital treatment decreased GABA A receptors alpha-subunit expression, but did not change beta- and gamma-subunit expression. However, we found CAFZ and pentobarbital increased Cl(-) influx, CAFZ showed similar effects with muscimol in potentiating Cl(-) influx inducing effects of low-dose pentobarbital. In conclusion, it is suggested that the enhancement of Cl(-) influx by CAFZ may play an important role in the potentiation of pentobarbital-induced sleeping behaviors.

Sanjoinine A Isolated from Zizyphi Spinosi Semen Augments Pentobarbital-Induced Sleeping Behaviors through the Modification of GABA-ergic Systems

Zizyphi Spinosi Semen (ZSS) has been widely used for the treatment of insomnia in oriental countries. This experiment was performed to investigate whether sanjoinine A, one of major alkaloid compounds of ZSS, has hypnotic effects and/or enhances pentobarbital-induced sleeping behaviors through the gamma-aminobutyric acid (GABA)-ergic systems. Sanjoinine A itself did not induce sleeping at the higher dose used in this experiment. However, sanjoinine A prolonged sleeping time and reduced the sleeping latency induced by pentobarbital in a dose-dependent manner similar to muscimol, a GABA(A) receptor agonist. Sanjoinine A also increased sleeping rate and sleeping time when administered combined with pentobarbital at a sub-hypnotic dosage and showed synergistic effects with muscimol in potentiating sleeping onset and enhancing sleeping time induced by pentobarbital. In addition, both sanjoinine A and pentobarbital increased chloride influx in primary cultured cerebellar granule cells. Sanjoinine A also showed similar effects with muscimol in potentiating chloride influx inducing effects of low dose pentobarbital. Sanjoinine A decreased GABA(A) receptor alpha-subunit expression and increased gamma-subunit expression, and had no effects on the abundance of beta-subunits in primary cultured cerebellar granule cells, showing different subunit expression from pentobarbital. In addition, we found that sanjoinine A also enhanced expression of glutamic acid decarboxylase (GAD), but pentobarbital did not. In conclusion, sanjoinine A itself does not induce sleeping, but it augments pentobarbital-induced sleeping behaviors through the modification of GABA-ergic systems.