Systemic delivery of human GlyR IgG antibody induces GlyR internalization into motor neurons of brainstem and spinal cord with motor dysfunction in mice.

AIMS: Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a life-threatening condition often associated with highly raised serum antibodies to glycine receptors (GlyRs); these bind to the surface of large neurons and interneurons in rodent brain and spinal cord sections and, in vitro, inhibit function and reduce surface expression of the GlyRs. The effects in vivo have not been reported. METHODS: Purified plasma IgG from a GlyR antibody-positive patient with PERM, and a healthy control (HC), was injected daily into the peritoneal cavity of mice for 12 days; lipopolysaccharide (LPS) to open the blood-brain barrier, was injected on days 3 and 8. Based on preliminary data, behavioural tests were only performed 48 h post-LPS on days 5-7 and 10-12. RESULTS: The GlyR IgG injected mice showed impaired ability on the rotarod from days 5 to 10 but this normalized by day 12. There were no other behavioural differences but, at termination (d13), the GlyR IgG-injected mice had IgG deposits on the neurons that express GlyRs in the brainstem and spinal cord. The IgG was not only on the surface but also inside these large GlyR expressing neurons, which continued to express surface GlyR. CONCLUSIONS: Despite the partial clinical phenotype, not uncommon in passive transfer studies, the results suggest that the antibodies had accessed the GlyRs in relevant brain regions, led to antibody-mediated internalization and increased GlyR synthesis, compatible with the temporary loss of function.

Glycine Receptor Autoantibodies Impair Receptor Function and Induce Motor Dysfunction.

OBJECTIVE: Impairment of glycinergic neurotransmission leads to complex movement and behavioral disorders. Patients harboring glycine receptor autoantibodies suffer from stiff-person syndrome or its severe variant progressive encephalomyelitis with rigidity and myoclonus. Enhanced receptor internalization was proposed as the common molecular mechanism upon autoantibody binding. Although functional impairment of glycine receptors following autoantibody binding has recently been investigated, it is still incompletely understood. METHODS: A cell-based assay was used for positive sample evaluation. Glycine receptor function was assessed by electrophysiological recordings and radioligand binding assays. The in vivo passive transfer of patient autoantibodies was done using the zebrafish animal model. RESULTS: Glycine receptor function as assessed by glycine dose-response curves showed significantly decreased glycine potency in the presence of patient sera. Upon binding of autoantibodies from 2 patients, a decreased fraction of desensitized receptors was observed, whereas closing of the ion channel remained fast. The glycine receptor N-terminal residues 29 A to 62 G were mapped as a common epitope of glycine receptor autoantibodies. An in vivo transfer into the zebrafish animal model generated a phenotype with disturbed escape behavior accompanied by a reduced number of glycine receptor clusters in the spinal cord of affected animals. INTERPRETATION: Autoantibodies against the extracellular domain mediate alterations of glycine receptor physiology. Moreover, our in vivo data demonstrate that the autoantibodies are a direct cause of the disease, because the transfer of human glycine receptor autoantibodies to zebrafish larvae generated impaired escape behavior in the animal model compatible with abnormal startle response in stiff-person syndrome or progressive encephalitis with rigidity and myoclonus patients. ANN NEUROL 2020;88:544-561.

Antiglycine receptor antibody related disease: a case series and literature review.

BACKGROUND AND PURPOSE: Antibodies to glycine receptors (GlyR-Abs) were first defined in progressive encephalopathy with rigidity and myoclonus (PERM) but were subsequently identified in other clinical presentations. Our aim was to assess the clinical associations of all patients identified with GlyR-Abs in Queensland, Australia, between April 2014 and May 2017 and to compare these to cases reported in the literature. METHODS: A literature review identified the clinical features of all published GlyR-Ab-positive cases through online databases. A case series was undertaken via collection of clinical information from all patients diagnosed or known to immunology, pathology or neurological services in Queensland during the study period of 3 years. RESULTS: In all, 187 GlyR-Ab-positive cases were identified in the literature. The majority (47.6%) had PERM, 22.4% had epilepsy, but the remaining 30% included mixed phenotypes consisting of cerebellar ataxia, movement disorders, demyelination and encephalitis/cognitive dysfunction. By contrast, in our series of 14 cases, eight had clinical presentations consistent with seizures and epilepsy and only three cases had classical features of PERM. There was one case each of global fatiguable weakness with sustained clonus, laryngeal dystonia and movement disorder with hemiballismus and tics. The rate of response to immune therapy was similar in all groups. CONCLUSION: Antibodies to glycine receptors are linked to a spectrum of neurological disease. The results of the literature review and our case series suggest a greater relationship between GlyR-Abs and epilepsy than previously reported.

Redefining progressive encephalomyelitis with rigidity and myoclonus after the discovery of antibodies to glycine receptors.

PURPOSE OF REVIEW: This review highlights the recent discovery of antibodies to glycine receptor (GlyR-Ab) and discusses the relationship between these antibodies and neurological disorders. RECENT FINDINGS: Since the initial description in 2008 of antibodies to glycine receptors (GlyR-Abs) in a patient with progressive encephalomyelitis with rigidity and myoclonus (PERM), these antibodies have been found in PERM and in some patients with a variety of stiff person spectrum (SPS) or related disorders. Patients with GlyR-Abs often improve with aggressive immunotherapy, and antibody titres correlate with disease severity. Around 25% of patients have another autoimmune condition and 10-20% have an underlying malignancy. GlyR-Abs bind to extracellular determinants, are mainly Immunoglobulin G1 subclass and induce GlyR internalization in Human embryonic kidney 293 cells, suggesting pathogenicity. The spectrum of neurological disease associated with GlyR-Abs has not been fully characterized, and lower titres may not be syndrome specific, but GlyR-Abs, like antibodies to other neuronal cell-surface antigens, define immunotherapy-responsive disease and are likely to be pathogenic. This distinguishes them from the glutamic acid decarboxylase antibodies that can also be found at high titres in patients with classical stiff person syndrome which is more often chronic and relatively resistant to immunological treatments. SUMMARY: Irrespective of the clinical features, GlyR-Abs are helpful in the diagnosis of patients who very often have a subacute, progressive and life-threatening disorder which shows a favourable response to immunotherapy.

Neuronal central nervous system syndromes probably mediated by autoantibodies.

In the last few years, a rapidly growing number of autoantibodies targeting neuronal cell-surface antigens have been identified in patients presenting with neurological symptoms. Targeted antigens include ionotropic receptors such as N-methyl-d-aspartate receptor or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, metabotropic receptors such as mGluR1 and mGluR5, and other synaptic proteins, some of them belonging to the voltage-gated potassium channel complex. Importantly, the cell-surface location of these antigens makes them vulnerable to direct antibody-mediated modulation. Some of these autoantibodies, generally targeting ionotropic channels or their partner proteins, define clinical syndromes resembling models of pharmacological or genetic disruption of the corresponding antigen, suggesting a direct pathogenic role of the associated autoantibodies. Moreover, the associated neurological symptoms are usually immunotherapy-responsive, further arguing for a pathogenic effect of the antibodies. Some studies have shown that some patients' antibodies may have structural and functional in vitro effects on the targeted antigens. Definite proof of the pathogenicity of these autoantibodies has been obtained for just a few through passive transfer experiments in animal models. In this review we present existing and converging evidence suggesting a pathogenic role of some autoantibodies directed against neuronal cell-surface antigens observed in patients with central nervous system disorders. We describe the main clinical symptoms characterizing the patients and discuss conflicting arguments regarding the pathogenicity of these antibodies.

Paediatric brainstem encephalitis associated with glial and neuronal autoantibodies.

AIM: Central nervous system (CNS) autoantibodies have been reported in a range of neuroimmune diseases, but there has not been a systematic evaluation of autoantibodies in paediatric patients with brainstem encephalitis. METHOD: Serum samples from 57 children (40 male, 17 female, median age 12y, range 0.6-18y) with a diagnosis of brainstem encephalitis were tested retrospectively for antibodies to GQ1b, aquaporin-4 (AQP4), myelin oligodendrocyte glycoprotein (MOG), N-methyl-D-aspartate receptor, LGI1, CASPR2, glycine receptor (GlyR), DPPX, and the voltage gated potassium channel (VGKC)-complex. RESULTS: Disease localized to the brainstem was seen in 19 patients: Bickerstaff's brainstem encephalitis (n=14) and clinically isolated syndrome (n=5). Polyfocal presentation was seen in 38 children, with predominantly white matter disease in 18 patients and grey matter in 20 patients. CNS surface antibodies were found in 22/57 patients (two patients with double positivity): GQIb (n=6), NMDAR (n=7), GlyR (n=5), MOG (n=5), and one AQP4. Three patients were positive for VGKC-complex antibodies. All patients were negative for antibodies to DPPX and the VGKC-complex antigens LGI1, CASPR2, and contactin-2. Although there were some partial differences in the presentations, the clinical features and outcomes did not relate clearly to the presence or absence of specific antibodies. INTERPRETATION: As determined retrospectively, 39% of patients had cell surface antibodies. The results did not suggest any relationship with treatment or outcomes obtained but it is possible that specific antibody detection could be a helpful guide to more intensive immunotherapies in some cases.

Glycine receptor antibodies in PERM and related syndromes: characteristics, clinical features and outcomes.

The clinical associations of glycine receptor antibodies have not yet been described fully. We identified prospectively 52 antibody-positive patients and collated their clinical features, investigations and immunotherapy responses. Serum glycine receptor antibody endpoint titres ranged from 1:20 to 1:60 000. In 11 paired samples, serum levels were higher than (n = 10) or equal to (n = 1) cerebrospinal fluid levels; there was intrathecal synthesis of glycine receptor antibodies in each of the six pairs available for detailed study. Four patients also had high glutamic acid decarboxylase antibodies (>1000 U/ml), and one had high voltage-gated potassium channel-complex antibody (2442 pM). Seven patients with very low titres (<1:50) and unknown or alternative diagnoses were excluded from further study. Three of the remaining 45 patients had newly-identified thymomas and one had a lymphoma. Thirty-three patients were classified as progressive encephalomyelitis with rigidity and myoclonus, and two as stiff person syndrome; five had a limbic encephalitis or epileptic encephalopathy, two had brainstem features mainly, two had demyelinating optic neuropathies and one had an unclear diagnosis. Four patients (9%) died during the acute disease, but most showed marked improvement with immunotherapies. At most recent follow-up, (2-7 years, median 3 years, since first antibody detection), the median modified Rankin scale scores (excluding the four deaths) decreased from 5 at maximal severity to 1 (P < 0.0001), but relapses have occurred in five patients and a proportion are on reducing steroids or other maintenance immunotherapies as well as symptomatic treatments. The glycine receptor antibodies activated complement on glycine receptor-transfected human embryonic kidney cells at room temperature, and caused internalization and lysosomal degradation of the glycine receptors at 37°C. Immunoglobulin G antibodies bound to rodent spinal cord and brainstem co-localizing with monoclonal antibodies to glycine receptor-α1. Ten glycine receptor antibody positive samples were also identified in a retrospective cohort of 56 patients with stiff person syndrome and related syndromes. Glycine receptor antibodies are strongly associated with spinal and brainstem disorders, and the majority of patients have progressive encephalomyelitis with rigidity and myoclonus. The antibodies demonstrate in vitro evidence of pathogenicity and the patients respond well to immunotherapies, contrasting with earlier studies of this syndrome, which indicated a poor prognosis. The presence of glycine receptor antibodies should help to identify a disease that responds to immunotherapies, but these treatments may need to be sustained, relapses can occur and maintenance immunosuppression may be required.

Glycine receptor antibody mediated Progressive Encephalomyelitis with Rigidity and Myoclonus (PERM): a rare but treatable neurological syndrome.

A 40-year-old man presented with respiratory compromise and was intubated. After tracheostomy, he was found to have ophthalmoplegia, severe limb rigidity, stimulus-sensitive myoclonus and autonomic dysfunction. For 1 week before admission, there had been a prodromal illness with low mood, hallucinations and limb myoclonus. Serum glycine receptor antibodies were strongly positive: we diagnosed progressive encephalomyelitis with rigidity and myoclonus. Despite a relapse, he has done well following immunotherapies. The clinical syndrome of encephalomyelitis with rigidity, described in 1976, often has a severe progressive course. A minority of patients have glutamic acid decarboxylase antibodies. The association with glycine receptor antibody was first reported in 2008, and we briefly review subsequent case reports to illustrate the range of clinical features. The antibody is likely to be disease mediating, although this remains unproven. The spectrum of diagnosable and treatable antibody mediated neurological syndromes is expanding. It is vital to recognise these conditions early to reduce morbidity and mortality.

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.

Clinical features in antiglycine receptor antibody-related disease: a case report and update literature review.

Background and objectives: Antiglycine receptor (anti-GlyR) antibody mediates multiple immune-related diseases. This study aimed to summarize the clinical features to enhance our understanding of anti-GlyR antibody-related disease. Methods: By collecting clinical information from admitted patients positive for glycine receptor (GlyR) antibody, the clinical characteristics of a new patient positive for GlyR antibody were reported in this study. To obtain additional information regarding anti-GlyR antibody-linked illness, clinical data and findings on both newly reported instances in this study and previously published cases were merged and analyzed. Results: A new case of anti-GlyR antibody-related progressive encephalomyelitis with rigidity and myoclonus (PERM) was identified in this study. A 20-year-old man with only positive cerebrospinal fluid anti-GlyR antibody had a good prognosis with first-line immunotherapy. The literature review indicated that the common clinical manifestations of anti-GlyR antibody-related disease included PERM or stiff-person syndrome (SPS) (n = 179, 50.1%), epileptic seizure (n = 94, 26.3%), and other neurological disorders (n = 84, 24.5%). Other neurological issues included demyelination, inflammation, cerebellar ataxia and movement disorders, encephalitis, acute psychosis, cognitive impairment or dementia, celiac disease, Parkinson's disease, neuropathic pain and allodynia, steroid-responsive deafness, hemiballism/tics, laryngeal dystonia, and generalized weakness included respiratory muscles. The group of PERM/SPS exhibited a better response to immunotherapy than others. Conclusions: The findings suggest the presence of multiple clinical phenotypes in anti-GlyR antibody-related disease. Common clinical phenotypes include PERM, SPS, epileptic seizure, and paraneoplastic disease. Patients with RERM/SPS respond well to immunotherapy.

Prevalence of neurologic autoantibodies in cohorts of patients with new and established epilepsy.

PURPOSE: Autoantibodies to specific neurologic proteins are associated with subacute onset encephalopathies, which often present with seizures that are poorly controlled by conventional antiepileptic drugs (AEDs). Previous cross-sectional studies have found specific neurologic antibodies in a small proportion of people with established epilepsy, but these investigations have seldom included patients with recent diagnosis. METHODS: We screened two large epilepsy cohorts to investigate the prevalence of multiple autoantibodies in adult patients with either established or newly diagnosed, untreated epilepsy. KEY FINDINGS: Eleven percent of patients had antibodies to one or more antigen: voltage-gated potassium channel (VGKC) complex proteins (5%), glycine receptors (3%), and glutamic acid decarboxylase (GAD) and N-methyl-D-aspartate (NMDA) receptors (1.7% each). There was no difference in the prevalence of antibodies, individually or collectively, between patients with established and newly diagnosed epilepsy or with generalized or focal epilepsy. There was, however, a significantly higher prevalence of positive antibody titers in patients with focal epilepsy of unknown cause than in those with structural/metabolic focal epilepsy (14.8% vs. 6.3%; p < 0.02). Newly diagnosed antibody-positive patients were less likely to achieve adequate seizure control with initial treatment than antibody-negative patients, but this difference failed to reach statistical significance. SIGNIFICANCE: The presence of autoantibodies is equally common in newly diagnosed and established epilepsy, it is therefore unlikely to be an epiphenomenon of long-standing refractory seizures.

Antiglycine-receptor encephalomyelitis with rigidity.

BACKGROUND: Glycine receptor antibodies (GlyR-ab) were reported in a patient with progressive encephalomyelitis with rigidity and myoclonus (PERM). METHODS: Three additional patients were clinically described. GlyR-ab was detected with a cell-based assay of HEK293 cells transfected with the α1 subunit of the GyR. RESULTS: A 33-year-old woman presented with diplopia, dysphagia and gait ataxia that improved in 5 weeks. Then, she developed a typical stiff-person syndrome (SPS) that resolved with corticosteroids, but relapsed 17 months later with a stiff limb syndrome. After treatment with intravenous immunoglobulins (IVIG), she has been asymptomatic for 8 years. A 60-year-old man developed, dysphagia, diplopia, left facial palsy and right trigeminal hypoaesthesia in a few days, followed by muscular rigidity, corticospinal signs, myoclonic jerks and severe dysautonomia. He developed seizures and suffered a cardiac arrest that left him in a persistent vegetative state. A 48-year-old man presented with leg rigidity and frequent spells of trismus, muscle spasms followed by opisthotonus and diaphoresis. The symptoms were antedated by pruritus of the left scapulae, right arm and T11-T12 dermatome. At the same time he became progressively more aggressive with emotional irritability. He also developed dysgeusia (metallic taste) and severe concurrent behavioural changes and diurnal hypersomnia. Only the rigidity and the spasms improved after therapy. CONCLUSIONS: The clinical picture associated with GlyR-ab is wider than the classical view of PERM. GlyR-ab should be examined in patients with core symptoms of muscle rigidity and spasms atypical for SPS.

Progressive encephalomyelitis with rigidity: A Taiwanese case and review of literature.

INTRODUCTION: Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a rare disorder. However, the outcome is still variable with different serological and tumor associations, and the elements to good response with less relapse is yet to be elucidated. METHOD: We present a case and obtain a literature review of patients with PERM and make comparisons based on different serological groups. We also analyze patients with idiopathic PERM that had detailed medical records. RESULTS: 81 patients were collected and analyzed. The largest group were glycine receptor-antibody (GlyR-Ab)-positive (70%), and the seropositive-GlyR-Ab-negative group had better response to immunotherapy. Malignancy can occur up to 2 years from the presentation of PERM. Among the 18 cases with detailed records, the patients who had good outcome initiate immunotherapy within 2 months from presentation. 9 of the 12 patients who experienced no relapse had non-steroid immunotherapy. The maximal interval time of relapse was 24 months. CONCLUSION: We recommend tumor surveillance up to 2 years in patients with PERM and early administration of immunotherapies and maintain with non-steroid immunotherapy with or without oral corticosteroid for a minimum of 2 years to reduce the risk of relapse in GlyR-Ab-positive patients.

Routine diagnostics for neural antibodies, clinical correlates, treatment and functional outcome.

OBJECTIVE: To determine frequencies, interlaboratory reproducibility, clinical ratings, and prognostic implications of neural antibodies in a routine laboratory setting in patients with suspected neuropsychiatric autoimmune conditions. METHODS: Earliest available samples from 10,919 patients were tested for a broad panel of neural antibodies. Sera that reacted with leucine-rich glioma-inactivated protein 1 (LGI1), contactin-associated protein-2 (CASPR2), or the voltage-gated potassium channel (VGKC) complex were retested for LGI1 and CASPR2 antibodies by another laboratory. Physicians in charge of patients with positive antibody results retrospectively reported on clinical, treatment, and outcome parameters. RESULTS: Positive results were obtained for 576 patients (5.3%). Median disease duration was 6 months (interquartile range 0.6-46 months). In most patients, antibodies were detected both in CSF and serum. However, in 16 (28%) patients with N-methyl-D-aspartate receptor (NMDAR) antibodies, this diagnosis could be made only in cerebrospinal fluid (CSF). The two laboratories agreed largely on LGI1 and CASPR2 antibody diagnoses (κ = 0.95). The clinicians (413 responses, 71.7%) rated two-thirds of the antibody-positive patients as autoimmune. Antibodies against the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), NMDAR (CSF or high serum titer), γ-aminobutyric acid-B receptor (GABABR), and LGI1 had ≥ 90% positive ratings, whereas antibodies against the glycine receptor, VGKC complex, or otherwise unspecified neuropil had ≤ 40% positive ratings. Of the patients with surface antibodies, 64% improved after ≥ 3 months, mostly with ≥ 1 immunotherapy intervention. CONCLUSIONS: This novel approach starting from routine diagnostics in a dedicated laboratory provides reliable and useful results with therapeutic implications. Counseling should consider clinical presentation, demographic features, and antibody titers of the individual patient.

Stiff person spectrum disorders: An illustrative case series of their phenotypic and antibody diversity.

Stiff person spectrum disorders (SPSD) are a broad group of immune-mediated disorders. Clinical presentations include classical stiff person syndrome (SPS), focal SPS, and progressive encephalomyelitis with rigidity and myoclonus (PERM). The most frequently associated antibodies are anti-GAD65, anti-GlyR, anti-amphiphysin, and anti-DPPX. Immunotherapy is the primary treatment modality. We present an illustrative case series of three patients: anti-GlyR antibody-mediated PERM presenting as rapidly progressive dementia; anti-amphiphysin antibody-mediated SPS; and SPS presentation with anti-Zic4 antibodies, spasmodic laryngeal stridor and fluctuating eyelid ptosis. Clinical characteristics, CSF findings, neurophysiological features, adequate immunological assays and a high suspicion index are essential for prompt diagnosis and management.

Semantic Variant of Primary Progressive Aphasia With Glycine Receptor α1 Autoantibodies.

This case report describes a 54-year-old woman with naming deficits, comprehension impairment, and memory loss. Initial physical and neurological examination results were unremarkable.

[A case of stiff-limb syndrome with anti-glycine receptor antibody].

A 48-year-old woman with a 3-month history of spontaneously resolving stiff leg symptom at the age of 43 years presented with progressive onset of leg rigidity, walking difficulty, and myoclonic jerks. On admission she had marked stiffness in her foot joints with symmetric sustained dorsiflexion of the ankles and toes, with spontaneous and reflex myoclonic jerks easily provoked by knee tendon tap. She appeared to have a spastic gait due to stiffness in her legs. Needle electromyogram (EMG) examination revealed continuous motor unit activity in the tibialis anterior muscle at rest even when voluntary contraction of the gastrocnemius muscle was instructed, but no myokimic discharge or acute denervation sign was seen. The laboratory tests were unremarkable, including glutamic acid decarboxylase antibody. Cerebrospinal fluid (CSF) examination was also normal, without oligoclonal bands or elevated IgG index. She was diagnosed with stiff-limb syndrome based on neurologic examination and needle EMG findings, and she was treated with intravenous high-dose methylprednisolone (500 mg/day, 3 days), resulting in marked improvement in her symptoms. Anti-glycine receptor antibodies were subsequently identified in her archived serum and CSF obtained before immunotherapy. She was then started on oral prednisolone (30 mg/day) and had been free of symptoms.

Thyrotropin-Releasing-Hormone-Synthesizing Neurons of the Hypothalamic Paraventricular Nucleus Are Inhibited by Glycinergic Inputs.

Background: Glycine is a classical neurotransmitter that has role in both inhibitory and excitatory synapses. To understand whether glycinergic inputs are involved in the regulation of the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons, the central controllers of the hypothalamic-pituitary-thyroid axis, the glycinergic innervation of the TRH neurons was studied in the hypothalamic paraventricular nucleus (PVN). Methods: Double-labeling immunocytochemistry and patch-clamp electrophysiology were used to determine the role of glycinergic neurons in the regulation of TRH neurons in the PVN. Anterograde and retrograde tracing methods were used to determine the sources of the glycinergic input of TRH neurons. Results: Glycine transporter-2 (GLYT2), a marker of glycinergic neurons, containing axons were found to establish symmetric type of synapses on TRH neurons in the PVN. Furthermore, glycine receptor immunoreactivity was observed in these TRH neurons. The raphe magnus (RMg) and the ventrolateral periaqueductal gray (VLPAG) were found to be the exclusive sources of the glycinergic innervation of the TRH neurons within the PVN. Patch-clamp electrophysiology using sections of TRH-IRES-tdTomato mice showed that glycine hyperpolarized the TRH neurons and completely blocked the firing of these neurons. Glycine also markedly hyperpolarized the TRH neurons in the presence of tetrodotoxin demonstrating the direct effect of glycine. In more than 60% of the TRH neurons, spontaneous inhibitory postsynaptic currents (sIPSCs) were observed, even after the pharmacological inhibition of glutamatergic and GABAergic neuronal transmission. The glycine antagonist, strychnine, almost completely abolished these sIPSCs, demonstrating the inhibitory nature of the glycinergic input of TRH neurons. Conclusions: These data demonstrate that TRH neurons in the PVN receive glycinergic inputs from the RMg and the VLPAG. The symmetric type of synaptic connection and the results of the electrophysiological experiments demonstrate the inhibitory nature of these inputs.