Gamma-aminobutyric Acid Receptor Type Research Articles

Anxiolytic potential of resveratrol and rufinamide combination by modulating GABA-ergic transmission: insights from experiments, molecular docking and dynamics simulations.

Resveratrol is a polyphenolic phytocompound known to possess anxiolytic-like effects but its impact on central gammaaminobutyric acid (GABA) modulation has never been explored. The purpose of this study was to analyze the anxiolytic-like effects of resveratrol alone and in combination with rufinamide, an antiepileptic drug which has never been studied for its anxiolytic potential. The BALB/c mice were tested in a battery of behavior testing after administration of resveratrol (50 mg/kg) and rufinamide (50 mg/kg) alone and in combination. Moreover, molecular docking studies were also carried out to understand the interaction of resveratrol and rufinamide with GABA aminotransferase, GABA receptor and GABA-A transporter type 1. Resveratrol alone exerted notable anxiolytic-like effects and improved outcomes in few experiments but rufinamide alone did not yield any beneficial outcomes. However, the animal co-administered with resveratrol and rufinamide behaved exceptionally well (p<0.05) and preferred open, illuminated and exposed areas of open field, light/dark and elevated plus maze. Further, these animals showed reduced anxiety towards anxiogenic stimuli i.e. holes and marbles in hole board and marble bury tests, respectively. Resveratrol and rufinamide showed moderate to strong binding affinities with GABA proteins, indicating the potential to treat anxiety-like neurological disorders. Moreover, resveratrol and rufinamide were analyzed using molecular docking to determine their interaction with GABA receptors, transporters, and transaminase. The results suggest that their anxiolytic-like effects may be due to inhibiting GABA reuptake transporter 1 protein, leading to increased synaptic levels of GABA neurotransmitter, as seen in stable molecular dynamics results with the 7SK2 GABA transporter protein.

Heukharang lettuce (Lactuca sativa L.) leaf extract displays sleep-promoting effects through GABAA receptor

Ethnopharmacological relevanceAlthough lettuce is traditionally known to have hypnotic and sedative effects, to date, only a few studies have documented its sleep-promoting effects and elucidated the related mechanisms. Aim of the studyWe aimed to investigate the sleep-promoting activity of Heukharang lettuce leaf extract (HLE) with increased lactucin content, known as a sleep-promoting substance in lettuce, in animal models. Materials and methodsTo evaluate the effect of HLE on sleep behavior, analysis of electroencephalogram (EEG), gene expression of brain receptors, and activation mechanisms using antagonists were investigated in rodent models. ResultsHigh-performance liquid chromatography analysis showed that HLE contained lactucin (0.78 mg/g of extract) and quercetin-3-glucuronide (1.3 mg/g of extract). In the pentobarbital-induced sleep model, the group administered 150 mg/kg of HLE showed a 47.3% increase in sleep duration time as compared to the normal group (NOR). The EEG analysis showed that the HLE significantly increased non-rapid eye movement (NREM), where delta waves were improved by 59.5% when compared to the NOR, resulting in increased sleep time. In the caffeine-induced arousal model, HLE significantly decreased the awake time increased by caffeine administration (35.5%) and showed a similar level to NOR. In addition, HLE increased the gene and protein expression of gamma-aminobutyric acid receptor type A (GABAA), GABA type B, and 5-hydroxytryptamine (serotonin) receptor 1A. In particular, in comparison to the NOR, the group administered 150 mg/kg HLE showed an increase in expression levels of GABAA and protein by 2.3 and 2.5 times, respectively. When the expression levels were checked using GABAA receptor antagonists, HLE showed similar levels to NOR, as the sleep duration was reduced by flumazenil (45.1%), a benzodiazepine antagonist. ConclusionsHLE increased NREM sleep and significantly improved sleep behavior due to its action on the GABAA receptors. The collective findings suggest that HLE can be used as a novel sleep-enhancing agent in the pharmaceutical and food industries.

Prolonged Alprazolam Treatment Alters Components of Glutamatergic Neurotransmission in the Hippocampus of Male Wistar Rats—The Neuroadaptive Changes following Long-Term Benzodiazepine (Mis)Use

Alprazolam (ALP), a benzodiazepine (BDZ) used to treat anxiety, panic, and sleep disorders, is one of the most prescribed psychotropic drugs worldwide. The side effects associated with long-term (mis)use of ALP have become a major challenge in pharmacotherapy, emphasizing the unmet need to further investigate their underlying molecular mechanisms. Prolonged BDZ exposure may induce adaptive changes in the function of several receptors, including the primary target, gammaaminobutyric acid receptor type A (GABAAR), but also other neurotransmitter receptors such as glutamatergic. The present study investigated the potential effects of prolonged ALP treatment on components of glutamatergic neurotransmission, with special emphasis on N-Methyl-D-aspartate receptor (NMDAR) in the hippocampus of adult male Wistar rats. The study revealed behavioral changes consistent with potential onset of tolerance and involvement of the glutamatergic system in its development. Specifically, an increase in NMDAR subunits (NR1, NR2A, NR2B), a decrease in vesicular glutamate transporter 1 (vGlut1), and differential modulation of excitatory amino acid transporters 1 and 2 (EAAT1/2, in vivo and in vitro) were observed, alongside a decrease in α1-containing GABAAR following the treatment. By describing the development of compensatory actions in the glutamatergic system, the present study provides valuable information on neuroadaptive mechanisms following prolonged ALP intake.

Leucine-Rich Repeats and Transmembrane Domain 2 Controls Protein Sorting in the Striatal Projection System and Its Deficiency Causes Disturbances in Motor Responses and Monoamine Dynamics.

The striatum is involved in action selection, and its disturbance can cause movement disorders. Here, we show that leucine-rich repeats and transmembrane domain 2 (Lrtm2) controls protein sorting in striatal projection systems, and its deficiency causes disturbances in monoamine dynamics and behavior. The Lrtm2 protein was broadly detected in the brain, but it was enhanced in the olfactory bulb and dorsal striatum. Immunostaining revealed a strong signal in striatal projection output, including GABAergic presynaptic boutons of the SNr. In subcellular fractionation, Lrtm2 was abundantly recovered in the synaptic plasma membrane fraction, synaptic vesicle fraction, and microsome fraction. Lrtm2 KO mice exhibited altered motor responses in both voluntary explorations and forced exercise. Dopamine metabolite content was decreased in the dorsal striatum and hypothalamus, and serotonin turnover increased in the dorsal striatum. The prefrontal cortex showed age-dependent changes in dopamine metabolites. The distribution of glutamate decarboxylase 67 (GAD67) protein and gamma-aminobutyric acid receptor type B receptor 1 (GABABR1) protein was altered in the dorsal striatum. In cultured neurons, wild-type Lrtm2 protein enhanced axon trafficking of GAD67-GFP and GABABR1-GFP whereas such activity was defective in sorting signal-abolished Lrtm2 mutant proteins. The topical expression of hemagglutinin-epitope-tag (HA)-Lrtm2 and a protein sorting signal abolished HA-Lrtm2 mutant differentially affected GABABR1 protein distribution in the dorsal striatum. These results suggest that Lrtm2 is an essential component of striatal projection neurons, contributing to a better understanding of striatal pathophysiology.

GABA-A and GABA-B Receptors in Filial Imprinting Linked With Opening and Closing of the Sensitive Period in Domestic Chicks (Gallus gallus domesticus).

Filial imprinting of domestic chicks has a well-defined sensitive (critical) period lasting in the laboratory from hatching to day 3. It is a typical model to investigate the molecular mechanisms underlying memory formation in early learning. We recently found that thyroid hormone 3,5,3′-triiodothyronine (T3) is a determinant of the sensitive period. Rapid increases in cerebral T3 levels are induced by imprinting training, rendering chicks imprintable. Furthermore, the administration of exogenous T3 makes chicks imprintable on days 4 or 6 even after the sensitive period has ended. However, how T3 affects neural transmission to enable imprinting remains mostly unknown. In this study, we demonstrate opposing roles for gamma-aminobutyric acid (GABA)-A and GABA-B receptors in imprinting downstream of T3. Quantitative reverse transcription polymerase chain reaction and immunoblotting showed that the GABA-A receptor expression increases gradually from days 1 to 5, whereas the GABA-B receptor expression gradually decreases. We examined whether neurons in the intermediate medial mesopallium (IMM), the brain region responsible for imprinting, express both types of GABA receptors. Immunostaining showed that morphologically identified putative projection neurons express both GABA-A and GABA-B receptors, suggesting that those GABA receptors interact with each other in these cells to modulate the IMM outputs. The roles of GABA-A and GABA-B receptors were investigated using various agonists and antagonists. Our results show that GABA-B receptor antagonists suppressed imprinting on day 1, while its agonists made day 4 chicks imprintable without administration of exogenous T3. By contrast, GABA-A receptor agonists suppressed imprinting on day 1, while its antagonists induced imprintability on day 4 without exogenous T3. Furthermore, both GABA-A receptor agonists and GABA-B receptor antagonists suppressed T3-induced imprintability on day 4 after the sensitive period has ended. Our data from these pharmacological experiments indicate that GABA-B receptors facilitate imprinting downstream of T3 by initiating the sensitive period, while the GABA-A receptor contributes to the termination of the sensitive period. In conclusion, we propose that opposing roles of GABA-A and GABA-B receptors in the brain during development determine the induction and termination of the sensitive period.

A systematic review of Gamma-aminobutyric Acid Receptor Type B autoimmunity.

To review the available research to describe the clinical characteristics and neoplastic associations of patients with gamma-aminobutyric acid receptor type B (GABAB-R) autoantibodies. Literature was reviewed on PubMed, Mendeley literature search, and the American Academy of Neurology database for articles published from June 2008 to October of 2018 using a variety of key words. These key words include: "gamma-aminobutyric acid seizures," "gamma-aminobutyric acid limbic encephalitis", "GABA(B) receptor antibodies," "autoimmune encephalitis," "autoimmune epilepsy," "GABA(B) encephalitis, " and "GABA paraneoplastic." With the results, the papers were reviewed in a systematic manner. A total of 10 studies were reviewed. A summary of the demographic, clinical, and serological findings of the cases detailed in the literature are provided. An additional illustrative case is described. In total, 94 patients were reviewed. GABAB-R autoimmune disease is characterized by refractory seizures or status epilepticus and frequent association with small cell lung cancer. Additionally, a substantial minority of patients have non-inflammatory CSF.

Induction of functional erythropoietin and erythropoietin receptor gene expression by gamma-aminobutyric acid and piperine in kidney epithelial cells

AimsThe aim of this study was to evaluate gamma-aminobutyric acid (GABA)- and piperine-induced erythropoietin (EPO) and EPO-receptor expression. Materials and methodsThe effect of GABA and piperine on cell viability was examined using kidney epithelial cells. Expression levels of EPO and EPO-R mRNA and protein were evaluated in response to GABA and piperine treatments. GABA- and piperine-mediated activation of the mitogen-activated protein kinase (MAPK) signaling pathway was investigated. Additionally, EPO function was evaluated using conditioned media containing EPO. The GABA receptor type involved in this process was identified. Key findingsMessenger RNA and protein expression levels of EPO and EPO-R significantly increased in response to treatment with GABA, piperine, or the combination of both, compared with control. GABA plus piperine synergistically enhanced EPO and EPO-R expression through p38 and c-Jun N-terminal kinase (JNK) MAPK signaling pathways, but not through the extracellular signal-regulated kinase (ERK) MAPK pathway. SB203580 and SP600125 (p38 and JNK pathway inhibitors, respectively) attenuated GABA plus piperine-induced EPO and EPO-R expression. Treatment of macrophages with EPO-containing conditioned media induced mRNA expression of interleukin (IL)-10 and nuclear factor (NF)-κB due to the interaction between EPO and EPO-R. Interestingly, GABA-induced EPO and EPO-R expression was mediated through GABAA, not GABAB, receptor activation. SignificanceThese findings demonstrate that GABA plus piperine-mediated p38 and JNK MAPK activation increases EPO and EPO-R expression, resulting in up-regulation of IL-10 and NF-κB.

Gamma-aminobutyric acid receptor type B agonist baclofen inhibits acid-induced excitation of secondary peristalsis but not heartburn sensation.

Acute esophageal acid infusion promotes distension-induced secondary peristalsis. The gamma-aminobutyric acid receptor type B (GABA-B) receptors activation inhibits secondary peristalsis. This study aimed to test the hypothesis whether acid excitation of secondary peristalsis can be influenced by baclofen. Secondary peristalsis was performed with intra-esophageal slow and rapid air injections in 13 healthy subjects. Direct esophageal infusion of 0.1N HCl following pretreatment with placebo or baclofen was randomly performed at least 1week apart. Symptom intensity, distension thresholds, and peristaltic parameters were determined and compared between each study protocol. The intensity of heartburn symptom in response to esophageal acid infusion was significantly greater with baclofen than the placebo (P=0.002). The threshold volume of secondary peristalsis during slow air injections in response to acid infusion was significantly greater with baclofen than the placebo (P=0.001). Baclofen significantly increased the threshold volume of secondary peristalsis during rapid air injections in response to acid infusion (P=0.001). The frequency of secondary peristalsis in response to acid infusion was significantly decreased by baclofen as compared with the placebo (P=0.001). Baclofen significantly decreased peristaltic amplitudes in response to acid infusion during rapid air injections (P=0.007). Gamma-aminobutyric acid receptor type B agonist baclofen inhibits acid excitation of secondary peristalsis in human esophagus, which is probably mediated by both muscular and mucosal mechanoreceptors. This work supports the evidence of potential involvement of GABA-B receptors in negative modulation of acid excitation of esophageal perception as well as secondary peristalsis.

Methods for the Discovery of Novel Compounds Modulating a Gamma-Aminobutyric Acid Receptor Type A Neurotransmission

This manuscript presents a step-by-step protocol for screening compounds at gamma-aminobutyric acid type A (GABAA) receptors and its use towards the identification of novel molecules active in preclinical assays from an in vitro recombinant receptor to their pharmacological effects at native receptors in rodent brain slices. For compounds binding at the benzodiazepine site of the receptor, the first step is to set up a primary screen that consists of developing radioligand binding assays on cell membranes expressing the major GABAA subtypes. Then, taking advantage of the heterologous expression of rodent and human GABAA receptors in Xenopus oocytes or HEK 293 cells, it is possible to explore, in electrophysiological assays, the physiological properties of the different receptor subtypes and the pharmacological properties of the identified compounds. The Xenopus oocyte system will be presented here, starting with the isolation of the oocytes and their microinjection with different mRNAs, up to the pharmacological characterization using two-electrode voltage clamps. Finally, recordings conducted in rodent brain slices will be described that are used as a secondary physiological test to assess the activity of molecules at their native receptors in a well-defined neuronal circuit. Extracellular recordings using population responses of multiple neurons are demonstrated together with the drug application.

Methods for the Discovery of Novel Compounds Modulating a Gamma-Aminobutyric Acid Receptor Type A Neurotransmission.

This manuscript presents a step-by-step protocol for screening compounds at gamma-aminobutyric acid type A (GABAA) receptors and its use towards the identification of novel molecules active in preclinical assays from an in vitro recombinant receptor to their pharmacological effects at native receptors in rodent brain slices. For compounds binding at the benzodiazepine site of the receptor, the first step is to set up a primary screen that consists of developing radioligand binding assays on cell membranes expressing the major GABAA subtypes. Then, taking advantage of the heterologous expression of rodent and human GABAA receptors in Xenopus oocytes or HEK 293 cells, it is possible to explore, in electrophysiological assays, the physiological properties of the different receptor subtypes and the pharmacological properties of the identified compounds. The Xenopus oocyte system will be presented here, starting with the isolation of the oocytes and their microinjection with different mRNAs, up to the pharmacological characterization using two-electrode voltage clamps. Finally, recordings conducted in rodent brain slices will be described that are used as a secondary physiological test to assess the activity of molecules at their native receptors in a well-defined neuronal circuit. Extracellular recordings using population responses of multiple neurons are demonstrated together with the drug application.

Tranexamic acid impairs hippocampal synaptic transmission mediated by gamma aminobutyric acid receptor type A

High-dose application of tranexamic acid (TXA), a widely used antifibrinolytic drug, can cause seizures in patients undergoing surgery. Mechanistically, seizures are considered to arise from an imbalance between inhibitory and excitatory synaptic transmission, whose main transmitters are gamma-aminobutyric acid (GABA) and glutamate. In the present study, we investigated the effects of TXA on neuronal excitability and synaptic transmission in the hippocampus, a structure that plays a pivotal role in human epilepsy.In acute slices of the murine hippocampus, fast depolarization-mediated imaging signals (FDSs) and postsynaptic currents (PSCs) were recorded using voltage-sensitive dye imaging and whole-cell patch clamp technique, respectively. FDSs and PSCs were evoked upon stimulation of the dentate gyrus and Schaffer collateral/associational commissural pathway, respectively. GABAA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and N-methyl-d-aspartate (NMDA) receptor-mediated postsynaptic currents were isolated pharmacologically.Application of TXA enhanced FDS propagation in the hippocampus. Neither the resting membrane potential of the investigated neurones nor synaptic transmission mediated by AMPA or NMDA receptors was changed by the application of 1mM TXA. In contrast, TXA dose-dependently reduced GABAA receptor-mediated synaptic transmission.TXA induced the inhibition of GABAA receptor-mediated synaptic transmission in the hippocampus with a potency similar to that of its antagonistic properties against GABAA receptors in the basolateral amygdala (Kratzer et al., 2014). Since impairment of GABAergic transmission is a major cause of epileptic seizures, the observed effect might contribute to the proconvulsive properties of TXA.

Effects of Traumatic Stress Induced in the Juvenile Period on the Expression of Gamma-Aminobutyric Acid Receptor Type A Subunits in Adult Rat Brain.

Studies have found that early traumatic experience significantly increases the risk of posttraumatic stress disorder (PTSD). Gamma-aminobutyric acid (GABA) deficits were proposed to be implicated in development of PTSD, but the alterations of GABA receptor A (GABAAR) subunits induced by early traumatic stress have not been fully elucidated. Furthermore, previous studies suggested that exercise could be more effective than medications in reducing severity of anxiety and depression but the mechanism is unclear. This study used inescapable foot-shock to induce PTSD in juvenile rats and examined their emotional changes using open-field test and elevated plus maze, memory changes using Morris water maze, and the expression of GABAAR subunits (γ2, α2, and α5) in subregions of the brain in the adulthood using western blotting and immunohistochemistry. We aimed to observe the role of GABAAR subunits changes induced by juvenile trauma in the pathogenesis of subsequent PTSD in adulthood. In addition, we investigated the protective effects of exercise for 6 weeks and benzodiazepine (clonazepam) for 2 weeks. This study found that juvenile traumatic stress induced chronic anxiety and spatial memory loss and reduced expression of GABAAR subunits in the adult rat brains. Furthermore, exercise led to significant improvement as compared to short-term BZ treatment.

Treatment paradigms for cataplexy in narcolepsy: past, present, and future.

Cataplexy is defined as episodes of sudden loss of voluntary muscle tone triggered by emotions generally lasting <2 minutes. Cataplexy is most commonly associated with and considered pathognomonic for narcolepsy, a sleep disorder affecting ~0.05% of the general population. Knowledge of the pathophysiology of cataplexy has advanced through study of canine, murine, and human models. It is now generally considered that loss of signaling by hypothalamic hypocretin/orexin-producing neurons plays a key role in the development of cataplexy. Although the cause of hypocretin/orexin neuron loss in narcolepsy with cataplexy is unknown, an autoimmune etiology is widely hypothesized. Despite these advances, a literature review shows that treatment of cataplexy remains limited. Multiple classes of antidepressants have been commonly used off-label for cataplexy in narcolepsy and are suggested for this use in expert consensus guidelines based on traditional practice, case reports, and small trials. However, systematic research evidence supporting antidepressants for cataplexy is lacking. The single pharmacotherapy indicated for cataplexy and the guideline-recommended first-line treatment in Europe and the US is sodium oxybate, the sodium salt of gamma-hydroxybutyrate. Clinical trial evidence of its efficacy and safety in cataplexy is robust, and it is hypothesized that its therapeutic effects may occur through gamma-aminobutyric acid receptor type B-mediated effects at noradrenergic, dopaminergic, and thalamocortical neurons. Additional possible mechanisms for cataplexy therapy suggested by preliminary research include antagonism of the histamine H3 autoreceptor with pitolisant and intravenous immunoglobulin therapy for amelioration of the presumed autoimmune-mediated hypocretin/orexin cell loss. Further research and development of therapeutic approaches to cataplexy are needed.

The Effect of Intrathecal Administration of Muscimol on Modulation of Neuropathic Pain Symptoms Resulting from Spinal Cord Injury; an Experimental Study.

Neuropathic pain can be very difficult to treat and it is one of the important medical challenging about pain treatments. Muscimol as a new agonist of gamma-Aminobutyric acid receptor type A (GABAA) have been introduced for pain management. Thus, the present study was performed to evaluate the pain alleviating effect of intrathecal injection of different doses of muscimol as GABAA receptor agonist in spinal cord injury (SCI) model of neuropathic pain. In the present experimental study, male Wistar rats were treated by muscimol 0.01, 0.1 or 1 µg/10ul, intrathecally (i.t.) three weeks after induction of spinal cord injury using compression injury model. Neuropathic pain symptoms were assessed at before treatment, 15 minutes, one hour and three hours after muscimol administration. The time of peak effect and optimum dosage was assessed by repeated measures analysis of variance and analysis of covariance, respectively. Muscimol with the dose of 0.01 µg in 15 minutes caused to improve the thermal hyperalgesia (df: 24, 5; F= 6.6; p<0.001), mechanical hyperalgesia (df: 24, 5; F= 7.8; p<0.001), cold allodynia (df: 24, 5; F= 6.96; p<0.001), and mechanical allodynia (df: 24, 5; F= 15.7; p<0.001). The effect of doses of 0.1 µg and 1 µg were also significant. In addition, the efficacy of different doses of muscimol did not have difference on thermal hyperalgesia (df: 24, 5; F= 1.52; p= 0.24), mechanical hyperalgesia (df: 24, 5; F= 0.3; p= -0.75), cold allodynia (df: 24, 5; F= 0.8; p= -0.56), and mechanical allodynia (df: 24, 5; F= 1.75; p= 0.86). The finding of the present study revealed that using muscimol with doses of 0.01µg, 0.1µg, and 1 µg reduces the symptoms of neuropathic pain. In addition, the effect of GABAA agonist is short term and its effectiveness gradually decreases by time.

Clinical potential, safety, and tolerability of arbaclofen in the treatment of autism spectrum disorder.

Autism spectrum disorder (ASD) is a behaviorally defined disorder which has increased in prevalence over the last two decades. Despite decades of research, no effective treatment is currently available. Animal models, as well as other lines of evidence, point to abnormalities in the balance of cortical excitation to inhibition in individuals with ASD, with this imbalance resulting in an overall increase in cortical excitation. To reduce cortical excitatory glutamate pathways, arbaclofen, a selective agonist of the gamma aminobutyric acid receptor type B, has been developed. This article reviews the evidence for this treatment for ASD using a systematic review methodology. Overall, a systematic search of the literature revealed 148 relevant references with the majority of these being review papers or news items that mentioned the potential promise of arbaclofen. Five original studies were identified, four of which used STX209, a form of arbaclofen developed by Seaside Therapeutics, Inc., and one which used R-baclofen. In an animal model, treatment of Fragile X, a genetic disease with ASD features, demonstrated a reversal of behavioral, neurological, and neuropathological features associated with the disease. One double-blind, placebo-controlled study treated children and adults with Fragile X. Results from this study were promising, with signs of improvement in social function, especially in the most severely socially impaired. Two studies, one open-label and one double-blind, placebo-controlled, were conducted in children, adolescents, and young adults with ASD. These studies suggested some improvements in socialization, although the effects were limited and may have been driven by individuals with ASD that were higher-functioning. These studies and others that have used arbaclofen for the treatment of gastroesophageal reflux suggest that arbaclofen is safe and well-tolerated. Clearly, further clinical studies are needed in order to refine the symptoms and characteristics of children with ASD that are best treated with arbaclofen.

The Paradox of the Paroxysm

An epileptic brain is permanently in a diseased state, but seizures occur rarely and without warning. Here we examine this paradox, common to paroxysmal diseases. We review the problem in the context of the prototypic acquired epilepsies of the medial temporal lobe. We ask how an epileptic temporal lobe differs from a healthy one and examine biological mechanisms that may explain the transition to seizure. Attempts to predict seizure timing from analyses of brain electrical activity suggest that the neurological processes involved may be initiated significantly before a seizure. Furthermore, whereas seizures are said to occur without warning, some patients say they know when a seizure is imminent. Several factors, including sleep deprivation, oscillations in hormonal levels, or withdrawal from drugs, increase the probability of a seizure. We ask whether these seizure precipitants might act through common neuronal mechanisms. Several precipitating factors seem to involve relief from a neurosteroid modulation of gamma-amino butyric acid receptor type A (GABAA) receptors. We propose tests of this hypothesis.

THU0329 Autoantibodies to GABAB Receptors Detected in Patients with Systemic Lupus Erythematosus

BackgroundThe gamma-aminobutyric acid receptor type B (GABARB) is a G-protein-coupled receptor involved in signal transduction by GABA, an inhibitory neurotransmitter. GABARB comprises two subunits: GABARB1 and GABARB2. Interestingly, these subunits...

Modulation of Spinal GABAergic Analgesia by Inhibition of Chloride Extrusion Capacity in Mice

Spinal gamma-aminobutyric acid receptor type A (GABAA) receptor modulation with agonists and allosteric modulators evokes analgesia and antinociception. Changes in K+-Cl− cotransporter isoform 2 (KCC2) expression or function that occur after peripheral nerve injury can result in an impairment in the Cl− extrusion capacity of spinal dorsal horn neurons. This, in turn, alters Cl−-mediated hyperpolarization via GABAA receptor activation, contributing to allodynia or hypersensitivity associated with nerve injury or inflammation. A gap in knowledge exists concerning how this loss of spinal KCC2 activity differentially impacts the analgesic efficacy or potency of GABAA agonists and allosteric modulators. We utilized intrathecal drug administration in the tail flick assay to measure the analgesic effects of general GABAA agonists muscimol and Z-3-[(aminoiminomethyl)thio]prop-2-enoic acid (ZAPA), the ∂-subunit-preferring agonist 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP), and allosteric modulators of the benzodiazepine (midazolam) and neurosteroid (ganaxolone) class, alone or in the presence of K+-Cl− cotransporter isoform (KCC) blockade. Intrathecal muscimol, ZAPA, THIP midazolam, and ganaxolone all evoked significant analgesia in the tail flick test. Coadministration of either agonists or allosteric modulators with [(dihydroindenyl)oxy] alkanoic acid (DIOA) (a drug that blocks KCC2) had no effect on agonist or allosteric modulator potency. On the other hand, the analgesic efficacy of muscimol and ZAPA and the allosteric modulator ganaxolone were markedly reduced whereas THIP and midazolam were unaffected. Finally, in the spared nerve injury model, midazolam significantly reversed tactile hypersensitivity while ganaxolone had no effect. These results indicate that the KCC2-dependent Cl− extrusion capacity differentially regulates the analgesic efficacy of agonists and allosteric modulators at the GABAA receptor complex. PerspectiveOur work suggests that drug discovery efforts for the treatment of chronic pain disorders should target benzodiazepine or ∂-subunit-containing sites at the GABAA complex.

Control of esophageal distension-induced secondary peristalsis by the GABAB agonist baclofen in humans

Secondary peristalsis is important for the clearance of retained food bolus or refluxate from the esophagus. The effects of the gamma aminobutyric acid receptor type B (GABA(B) ) agonist on secondary peristalsis remain unclear in humans. We aimed to investigate the effect of a GABA(B) agonist baclofen on esophageal secondary peristalsis. After a baseline recording of esophageal motility, secondary peristalsis was generated by slow and rapid mid-esophageal injections of air in 15 healthy subjects. Two separate sessions with 40mg oral baclofen or placebo were randomly performed to test their effects on secondary peristalsis. Baclofen increased the threshold volume for triggering secondary peristalsis during slow air distension (P=0.003) and rapid air distension (P=0.002). Baclofen reduced the rate of secondary peristalsis by rapid air distension from 90% to 30% (P=0.0002). Baclofen increased basal lower esophageal sphincter pressure (P=0.03). Baclofen did not affect any of peristaltic parameters during primary or secondary peristalsis. This study provides an evidence for inhibitory modulation of esophageal secondary peristalsis by the GABA(B) agonist baclofen. Activation of secondary peristalsis is probably modulated by GABA(B) receptors; however, baclofen does not lead to any motility change in secondary peristalsis.

Persistent Reflux Symptoms in the Proton Pump Inhibitor Era: The Changing Face of Gastroesophageal Reflux Disease

Given the widespread use of potent acid suppressive therapies and primary caregivers’ increasing comfort with prescribing these medications at high doses, the patient population presenting to gastroenterologists for symptoms of gastroesophageal reflux disease (GERD) has changed. Whereas previous consultation often revolved around the control of erosive disease and other mucosal manifestations of GERD, and terminated with the prescription of proton pump inhibitor (PPI) therapy, gastroenterologists often now only enter the scene after failure of PPI therapy, for symptoms either resistant or only partially responsive to these medications. Because of the high proportion of subjects with esophagitis who are healed with PPI, 1,2 upper endoscopy of such individuals is low yield, 3 with only a small minority demonstrating erosive disease. The care of such patients is challenging. High-quality evidence supporting useful diagnostic testing or alternative effective therapies is largely lacking. However, the number of subjects with GERD symptoms incompletely or nonresponsive to PPI therapies is high, and their utilization of healthcare resources is substantial. The purpose of this mini-review is to examine the definition and epidemiology of esophageal GERD symptoms incompletely responsive to PPI therapy, the potential pathophysiologic mechanisms behind these symptoms, the differential diagnosis and evaluation of such patients, and current and developing therapeutic options.