Gamma-aminobutyric Acid Type B Receptor Research Articles

Transcriptome Sequencing Analysis of Sex-Related Genes in the Gonads of Mytilus unguiculatus

In the cultivation of Mytilus unguiculatus, the broodstock are shade-dried to stimulate sperm and egg production. To identify the functional genes affecting gonad development in M. unguiculatus, the transcriptome of gonads in mussels stimulated by shade-drying and those not stimulated were compared. Differential gene expression analysis revealed that there were 22 differentially expressed genes (DEGs) in the testis and 70 DEGs in the ovary among the experimental groups. KEGG enrichment analysis identified a total of 11 pathways that might be related to environmental stimuli affecting gonadal development. Nicotinic acetylcholine receptors (AChRs), the cholecystokinin A receptor (CCKAR), hypocretin (orexin) receptor 2 (HCRTR2), and gamma-aminobutyric acid type B receptor (GABBR) were highly expressed in the neuroactive ligand-receptor interaction pathway, indicating that these genes might be involved in the transduction of environmental information that stimulates gonadal development. Meanwhile, nuclear receptor co-repressor 2 (NCoR2) was highly expressed in the notch signaling pathway, indicating that NCoR2 might be involved in the regulation of gonad development. To validate the transcriptome data, we selected five DEGs in the KEGG signaling pathway, including AChRs, CCKAR, HCRTR2, GABAB, and NCoR2, for real-time quantitative PCR (RT-qPCR), which produced results consistent with the RNA-Seq data. The transcriptome analysis and gene pathway identification in this study have enhanced our comprehension of the reproductive mechanisms in M. unguiculatus.

Dysfunction of inhibitory interneurons contributes to synaptic plasticity via GABABR-pNR2B signaling in a chronic migraine rat model.

According to our previous study, the loss of inhibitory interneuron function contributes to central sensitization in chronic migraine (CM). Synaptic plasticity is a vital basis for the occurrence of central sensitization. However, whether the decline in interneuron-mediated inhibition promotes central sensitization by regulating synaptic plasticity in CM remains unclear. Therefore, this study aims to explore the role of interneuron-mediated inhibition in the development of synaptic plasticity in CM. A CM model was established in rats by repeated dural infusion of inflammatory soup (IS) for 7 days, and the function of inhibitory interneurons was then evaluated. After intraventricular injection of baclofen [a gamma-aminobutyric acid type B receptor (GABABR) agonist] or H89 [a protein kinase A (PKA) inhibitor), behavioral tests were performed. The changes in synaptic plasticity were investigated by determining the levels of the synapse-associated proteins postsynaptic density protein 95 (PSD95), synaptophysin (Syp) and synaptophysin-1(Syt-1)]; evaluating the synaptic ultrastructure by transmission electron microscopy (TEM); and determining the density of synaptic spines via Golgi-Cox staining. Central sensitization was evaluated by measuring calcitonin gene-related peptide (CGRP), brain-derived neurotrophic factor (BDNF), c-Fos and substance P (SP) levels. Finally, the PKA/Fyn kinase (Fyn)/tyrosine-phosphorylated NR2B (pNR2B) pathway and downstream calcium-calmodulin-dependent kinase II (CaMKII)/c-AMP-responsive element binding protein (pCREB) signaling were assessed. We observed dysfunction of inhibitory interneurons, and found that activation of GABABR ameliorated CM-induced hyperalgesia, repressed the CM-evoked elevation of synapse-associated protein levels and enhancement of synaptic transmission, alleviated the CM-triggered increases in the levels of central sensitization-related proteins, and inhibited CaMKII/pCREB signaling via the PKA/Fyn/pNR2B pathway. The inhibition of PKA suppressed the CM-induced activation of Fyn/pNR2B signaling. These data reveal that the dysfunction of inhibitory interneurons contributes to central sensitization by regulating synaptic plasticity through the GABABR/PKA/Fyn/pNR2B pathway in the periaqueductal gray (PAG) of CM rats. Blockade of GABABR-pNR2B signaling might have a positive influence on the effects of CM therapy by modulating synaptic plasticity in central sensitization.

BHF177 Suppresses Diabetic Neuropathic Pain by Blocking PKC/CaMKII/ERK1/2/CREB Signaling Pathway through Activating GABAB Receptor

The gamma-aminobutyric acid type B (GABAB) receptor may participate in the development of diabetic neuropathic pain (DNP). BHF177 serves as a positive allosteric modulator of the GABAB receptor. In the current study, we sought to study the role of the BHF177-GABAB receptor in DNP and its underlying mechanism. Streptozotocin was adopted to induce a rat model of DNP, followed by determination of the paw withdrawal threshold (PWT), paw withdrawal latency (PWL), and glucose level. The effect of BHF177 on DNP by regulating the GABAB receptor in vivo was determined by the injection of BHF177 and/or CGP46381 (a GABAB receptor antagonist) into rat models of DNP. Hippocampal neuronal cells were isolated and cultured, and the neurons and DNP model rats were treated with activators of PKC (PMA), CaMKII (CaCl2), or ERK1/2 (EGF) to study the role of GABAB receptors in DNP via regulation of the NR2B-PKC-CaMKII-ERK-CREB pathway. BHF177 suppressed DNP symptoms by activating the GABAB receptors, as evidenced by increased PWT and PWL of DNP rats and the increased number of neurons expressing the GABAB receptor, but this effect was reversed by CGP46381 treatment. BHF177 treatment markedly repressed PKC, CaMKII, p-ERK1/2, and p-CREB expressions in the rat DNP model, but these suppressive effects were abrogated by treatments with PMA, CaCl2, or EGF treatment, respectively. To sum up, BHF177 suppresses DNP symptoms by blocking the PKC/CaMKII/ERK1/2/CREB signaling pathway to activate the GABAB receptors.

Increased Voluntary Alcohol Consumption in Mice Lacking GABAB(1) Is Associated With Functional Changes in Hippocampal GABAA Receptors.

Gamma-aminobutyric acid type B receptor (GABABR) has been extensively involved in alcohol use disorders; however, the mechanisms by which this receptor modulates alcohol drinking behavior remain murky. In this study, we investigate alcohol consumption and preference in mice lacking functional GABABR using the 2-bottle choice paradigm. We found that GABAB(1), knockout (KO), and heterozygous (HZ) mice drank higher amounts of an alcoholic solution, preferred alcohol to water, and reached higher blood alcohol concentrations (BACs) compared to wild-type (WT) littermates. The GABABR agonist GHB significantly reduced alcohol consumption in the GABAB(1) HZ and WT but not in the KO mice. Next, because of a functional crosstalk between GABABR and δ-containing GABAA receptor (δ-GABAAR), we profiled δ subunit mRNA expression levels in brain regions in which the crosstalk was characterized. We found a loss of the alcohol-sensitive GABAAR δ subunit in the hippocampus of the GABAB(1) KO alcohol-naïve mice that was associated with increased ɣ2 subunit abundance. Electrophysiological recordings revealed that these molecular changes were associated with increased phasic inhibition, suggesting a potential gain of synaptic GABAAR responsiveness to alcohol that has been previously described in an animal model of excessive alcohol drinking. Interestingly, voluntary alcohol consumption did not revert the dramatic loss of hippocampal δ-GABAAR occurring in the GABAB(1) KO mice but rather exacerbated this condition. Finally, we profiled hippocampal neuroactive steroids levels following acute alcohols administration in the GABAB(1) KO and WT mice because of previous involvement of GABABR in the regulation of cerebral levels of these compounds. We found that systemic administration of alcohol (1.5 g/kg) did not produce alcohol-induced neurosteroid response in the GABAB(1) KO mice but elicited an expected increase in the hippocampal level of progesterone and 3α,5α-THP in the WT controls. In conclusion, we show that genetic ablation of the GABAB(1) subunit results in increased alcohol consumption and preference that were associated with functional changes in hippocampal GABAAR, suggesting a potential mechanism by which preference for alcohol consumption is maintained in the GABAB(1) KO mice. In addition, we documented that GABAB(1) deficiency results in lack of alcohol-induced neurosteroids, and we discussed the potential implications of this finding in the context of alcohol drinking and dependence.

Anxiolytic-like Effects of the Positive GABAB Receptor Modulator GS39783 Correlate with Mice's Individual Basal Anxiety and Stress Reactivity.

Positive gamma-aminobutyric acid type B (GABAB) receptor modulators such as GS39783 have showed anxiolytic-like effects in several studies while such effects were absent in other studies. These conflicting findings led us hypothesize that the anxiolytic-like effects of such compounds depend on the individual basal anxiety and/or the anxiogenic properties of the used tests. The present study addresses this hypothesis by testing GS39783 effects on mice’s anxiety-like behavior in a light–dark box. We found that GS39783 had no effects on a whole-group level. However, after grouping the mice for their basal anxiety, GS39783 reduced anxiety-like behavior in the subgroup with highest basal anxiety. Moreover, GS39783 effects correlated with individual basal anxiety. Next, the anxiogenic properties of the light–dark box test were increased by prior stress exposure. Again, GS39783 was not effective on a whole-group level. However, GS39783 had an anxiolytic-like effect in the most stress-responsive subgroup. Moreover, GS39783 effects correlated with individual stress responsiveness. Finally, we show that GS39783 brain levels were within a behaviorally relevant range. Overall, our study demonstrates that GS39783 effects depend on individual basal anxiety and stress responsiveness. This suggests that anxiety tests should generally be designed to capture individual basal anxiety and/or stress responsiveness as well as individual compound effects.

GABAB receptor signaling in the caudate putamen is involved in binge-like consumption during a high fat diet in mice

Previous studies suggest that signaling by the gamma-aminobutyric acid (GABA) type B receptor (GABABR) is involved in the regulation of binge eating, a disorder which might contribute to the development of obesity. Here, we show that intermittent access to a high fat diet (HFD) induced binge-like eating behavior with activation of dopamine receptor d1 (drd1)-expressing neurons in the caudate putamen (CPu) and nucleus accumbens (NAc) in wild-type (WT) mice. The activation of drd1-expressing neurons during binge-like eating was substantially increased in the CPu, but not in the NAc, in corticostriatal neuron-specific GABABR-deficient knockout (KO) mice compared to WT mice. Treatment with the GABABR agonist, baclofen, suppressed binge-like eating behavior in WT mice, but not in KO mice, as reported previously. Baclofen also suppressed the activation of drd1-expressing neurons in the CPu, but not in the NAc, during binge-like eating in WT mice. Thus, our data suggest that GABABR signaling in CPu neurons expressing drd1 suppresses binge-like consumption during a HFD in mice.

GABAB receptor inhibits tumor progression and epithelial-mesenchymal transition via the regulation of Hippo/YAP1 pathway in colorectal cancer.

Gamma-Aminobutyric Acid Type B Receptor (GABABR) plays essential roles in tumor progression. However, the function of GABABR in colorectal cancer (CRC) needs further clarification. As the main part of GABABR, GABABR1 expression was identified significantly lower in tumor tissues than those in non-tumor normal tissues and that CRC patients with high GABABR1 expression lived longer. Further studies indicated that knockdown of GABABR1 elevated CRC cell proliferation, migration, and invasion. Furthermore, knockdown of GABABR1 activated the expression of the epithelial-mesenchymal transition (EMT)-related proteins N-cadherin and Vimentin, whereas decrease the protein level of E-cadherin. In addition, activation of Hippo/YAP1 signaling contributes to the GABABR1 down-regulation promoted proliferation, migration, invasion and EMT in CRC cells. At last, we verified the contribution of Hippo/YAP1 signaling in the GABABR1 down-regulation impaired biological phenotype of colon cancer cells in vivo. In summary, these data indicate that GABABR1 impairs the migration and invasion of CRC cells by inhibiting EMT and the Hippo/YAP1 pathway, suggesting that GABABR1 could be a potential therapeutic target for CRC.

Deficiency in the function of inhibitory interneurons contributes to glutamate-associated central sensitization through GABABR2-SynCAM1 signaling in chronic migraine rats.

The occurrence of pain has always been closely related to a break in the balance between excitatory and inhibitory systems, and the internal relationship between these two systems has not been studied in the pathogenesis of chronic migraine (CM). In this study, we explored how inhibitory interneurons specifically modulate the glutamate-induced hyperexcitability in the periaqueductal gray (PAG) of CM rats. The CM model was established by repeated dural infusion of inflammatory soup (IS) in rats. Then, Baclofen, a gamma-aminobutyric acid type B receptor (GABABR) agonist; CGP35348, a GABABR antagonist; H89, a protein kinase A (PKA) inhibitor; and 8-Bromo-cAMP, a PKA agonist, were applied by intraventricular injection to investigate the detailed CM mechanism. Our results showed that GABABR2 mRNA and protein levels were significantly downregulated (P<.01) in the PAG of CM rats. Similarly, gamma-aminobutyric acid (GABA) and its synthetase glutamate decarboxylase 65/67 (GAD65/67) seriously decreased (P<.01), implying a deficit in the function of inhibitory interneurons in the PAG of CM rats. Afterward, the application of Baclofen and H89 alleviated the IS-evoked hyperalgesia and extenuated vesicular glutamate transporter 2 (VGLUT2), glutamate, calcitonin gene-related peptide (CGRP), and c-Fos expression by regulating the GABABR2/PKA/SynCAM1 pathway in the PAG of CM rats, while the application of CGP35348 and 8-Bromo-cAMP exactly exerted the opposite effect. Importantly, CGP35348 induced an elevation of CGRP, and VGLUT2 expression was relieved by H89. These data suggest that the loss in the function of inhibitory interneurons contributes to glutamate-associated central sensitization through the GABABR2/PKA/SynCAM1 pathway in the PAG of CM rats.

Non-genetic factors that influence methamphetamine intake in a genetic model of differential methamphetamine consumption.

Genetic and non-genetic factors influence substance use disorders. Our previous work in genetic mouse models focused on genetic factors that influence methamphetamine (MA) intake. The current research examined several non-genetic factors for their potential influence on this trait. We examined the impact on MA intake of several non-genetic factors, including MA access schedule, prior forced MA exposure, concomitant ethanol (EtOH) access, and gamma-aminobutyric acid type B (GABAB) receptor activation. Selectively bred MA high drinking(MAHDR) and low drinking (MALDR) mice participated in this research. MAHDR, but not MALDR, mice increased MA intake when given intermittent access, compared with continuous access, with a water choice under both schedules. MA intake was not altered by previous exposure to forced MA consumption. Male MAHDR mice given simultaneous access to MA, EtOH, and an EtOH+MA mixture exhibited a strong preference for MA over EtOH and EtOH+MA; MA intake was not affected by EtOH in female MAHDR mice. When independent MAHDR groups were given access to MA, EtOH, or EtOH+MA vs. water in each case, MA intake was reduced in the water vs. EtOH+MA group, compared with the water vs. MA group. The GABAB receptor agonist R(+)-baclofen (BAC) not only reduced MA intake but also reduced water intake and locomotor activity in MAHDR mice. There was a residual effect of BAC, such that MA intake was increased after termination of BAC treatment. These findings demonstrate that voluntary MA intakein MAHDR mice is influenced by non-genetic factors related to MA access schedule and co-morbid EtOH exposure.

A novel GABAB receptor positive allosteric modulator, ASP8062, exerts analgesic effects in a rat model of fibromyalgia

The gamma-aminobutyric acid type B (GABAB) receptor agonist, the sodium salt of gamma-hydroxybutyrate (GHB), significantly improved pain, sleep disturbance and fatigue in fibromyalgia (FM) patients. However, the use of GABAB receptor agonists is limited by their undesirable side-effects. To clarify whether GABAB receptor positive allosteric modulator (PAM) approach would achieve analgesia with less side-effects than GABAB receptor agonist in FM, we investigated the potential of a novel GABAB receptor PAM, ASP8062, for FM treatment. We examined the in vitro profiles of ASP8062, the effects of a GABAB receptor PAM and an agonist on pain in a rat model of FM, and the sleep/wake cycle, EEG during sleep stages and motor coordination in rats. ASP8062 showed PAM activity on human and rat GABAB receptors. Oral administration of ASP8062 significantly reversed the decrease in muscle pressure threshold in reserpine-induced myalgia rats. The analgesic effects of ASP8062 were significantly blocked by a GABAB receptor antagonist. ASP8062 had a significant effect on motor coordination at a 1000-fold higher dose than the analgesic dose in rats. ASP8062 significantly decreased total REM sleep time and frequency of sleep interruptions, and increased the power in delta waves frequency during non-REM sleep in rats. ASP8062, a novel GABAB receptor PAM, has therapeutic potential to exert analgesic effects with less side-effects compared to GABAB receptor agonists in patients with FM.

GABAB Receptor Signaling in the Mesolimbic System Suppresses Binge-like Consumption of a High-Fat Diet.

SummaryBinge eating could contribute to the development of obesity, and previous studies suggest that gamma-aminobutyric acid (GABA) type B receptor (GABABR) signaling is involved in the regulation of binge eating. Here, we show that time-restricted access to a high-fat diet (HFD) induces binge-like eating behavior in wild-type mice. HFD consumption during restricted time was significantly increased in corticostriatal neuron-specific GABABR-deficient mice compared with wild-type mice. Furthermore, the GABABR agonist baclofen suppressed HFD intake during restricted time in wild-type mice but not in corticostriatal or dopaminergic neuron-specific GABABR-deficient mice. In contrast, there were no significant differences in food consumption among genotypes under ad libitum access to HFD. Thus, our data show that the mesolimbic system regulates food consumption under time-restricted but not ad libitum access to HFD and have identified a mechanism by which GABABR signaling suppresses binge-like eating of HFD.

Spinal GABA-B receptor modulates neutrophil recruitment to the knee joint in zymosan-induced arthritis.

Recent studies have demonstrated that the central nervous system controls inflammatory responses by activating complex efferent neuroimmune pathways. The present study was designed to evaluate the role that central gamma-aminobutyric acid type B (GABA-B) receptor plays in neutrophil migration in a murine model of zymosan-induced arthritis by using different pharmacological tools. We observed that intrathecal administration of baclofen, a selective GABA-B agonist, exacerbated the inflammatory response in the knee after zymosan administration characterized by an increase in the neutrophil recruitment and knee joint edema, whereas saclofen, a GABA-B antagonist, exerted the opposite effect. Intrathecal pretreatment of the animals with SB203580 (an inhibitor of p38 mitogen-activated protein kinase) blocked the pro-inflammatory effect of baclofen. On the other hand, systemic administration of guanethidine, a sympatholytic drug that inhibits catecholamine release, and nadolol, a beta-adrenergic receptor antagonist, reversed the effect of saclofen. Moreover, saclofen suppressed the release of the pro-inflammatory cytokines into the knee joint (ELISA) and pain-related behaviors (open field test). Since the anti-inflammatory effect of saclofen depends on the sympathetic nervous system integrity, we observed that isoproterenol, a beta-adrenergic receptor agonist, mimics the central GABA-B blockade decreasing knee joint neutrophil recruitment. Together, these results demonstrate that the pharmacological manipulation of spinal GABAergic transmission aids control of neutrophil migration to the inflamed joint by modulating the activation of the knee joint-innervating sympathetic terminal fibers through a mechanism dependent on peripheral beta-adrenergic receptors and central components, such as p38 MAPK.

Effects of colistin on amino acid neurotransmitters and blood-brain barrier in the mouse brain

Neurotoxicity is one of the major potential side effects of colistin therapy. However, the mechanistic aspects of colistin-induced neurotoxicity remain largely unknown. The objective of this study was to examine the effects of colistin on the blood-brain barrier (BBB) and amino acid neurotransmitters in the cerebral cortex of mouse. Mice were divided into four groups (n=5) and were administrated intravenously with 15mg/kg/day of colistin sulfate for 1, 3 and 7days successively while the control group was administrated intravenously with saline solution. The permeability and ultrastructure of the BBB were detected using the Evans blue (EB) dye and transmission electron microscopy (TEM), and the expression of Claudin-5 were determined by real-time PCR examination and western blotting. The brain uptake of colistin was measured by high-performance liquid chromatography (HPLC). The effects of colistin on amino acid neurotransmitters and their receptors were also examined by HPLC and real-time PCR. The results of EB extravasation, TEM and expression of Claudin-5 showed that colistin treatment did not affect the BBB integrity. In addition, multiple doses of colistin could induce accumulation of this compound in the brain parenchyma although there was poor brain uptake of colistin. Moreover, colistin exposure significantly increased the contents of glutamate (Glu) and gamma aminobutyric acid (GABA), and enhanced the mRNA expression levels of gamma aminobutyric acid type A receptor (GABAAR), gamma aminobutyric acid type B receptor (GABABR), N-methyl-d-aspartate 1 receptor (NR1), N-methyl-d-aspartate 2A receptor (NR2A) and N-methyl-d-aspartate 2B receptor (NR2B) in the cerebral cortex. Our data demonstrate that colistin is able to accumulate in the mouse brain and elevate the levels of amino acid neurotransmitters. These findings may be associated with colistin-induced neurotoxicity.

The GABAB receptor agonist, baclofen, contributes to three distinct varieties of amnesia in the human brain – A detailed case report

We describe a patient in whom long-term, therapeutic infusion of the selective gamma-amino-butyric acid type B (GABAB) receptor agonist, baclofen, into the cerebrospinal fluid (CSF) gave rise to three distinct varieties of memory impairment: i) repeated, short periods of severe global amnesia, ii) accelerated long-term forgetting (ALF), evident over intervals of days and iii) a loss of established autobiographical memories. This pattern of impairment has been reported in patients with temporal lobe epilepsy (TLE), in particular the subtype of Transient Epileptic Amnesia (TEA). The amnesic episodes and accelerated forgetting remitted on withdrawal of baclofen, while the autobiographical amnesia (AbA) persisted. This exceptional case highlights the occurrence of ‘non-standard’ forms of human amnesia, reflecting the biological complexity of memory processes. It suggests a role for GABAB signalling in the modulation of human memory over multiple time-scales and hints at its involvement in ‘epileptic amnesia’.

Altered Gamma-Aminobutyric Acid Type B Receptor Subunit 1 Splicing In Alcoholics

Chronic alcohol exposure can change splice variant expression. The gamma-aminobutyric acid type B (GABAB) receptor undergoes splicing and is an alcoholism treatment target, but there is little information about splicing changes in this receptor in alcoholics. We studied GABAB receptor subunit 1 (GABAB1) splicing in alcoholic postmortem brains. To maximize GABAB1 splice junction identification, we combined gene specific libraries with RNA-seq. Splice junctions and mapped reads were also found from intronic and intergenic regions. We compared GABAB1 splice junctions in prefrontal cortices from 14 alcoholic and 15 control subjects and introduced new strategies, reads per kilobase of splice junction model per million mapped reads and reads per kilobase of gene model per million mapped reads, for quantitating splice junction and gene expression. Novel splice junction detection indicated that the GABAB1 gene is at least two times longer than the previously reported gene length. GABAB1 exon and intron expression data showed low expression at the 5' end exons and exon grouping. This indicated that there are short splicing variants in addition to GABAB receptor subunit GABAB1a, the longest known major transcript. We found that chronic alcohol altered exon/intron expression and splice junction levels. Decreased expression of the gamma-aminobutyric acid binding site, a transmembrane domain and a microRNA binding site may decrease normal GABAB1 transcript population and thereby decrease normal signal transduction in alcoholics. We discovered novel, complex splicing of GABAB1 in human brain and showed that chronic alcohol produces additional splicing complexity.

Effects of Low-Frequency Hippocampal Stimulation on Gamma-Amino Butyric Acid Type B Receptor Expression in Pharmacoresistant Amygdaloid Kindling Epileptic Rats

To observe the effect of low-frequency hippocampal stimulation on gamma-amino butyric acid type B (GABA-B) receptor expression in hippocampus pharmacoresistant epileptic rats. Sixteen pharmacoresistant epileptic rats were selected by testing their seizure response to phenytoin and phenobarbital, and they were randomly divided into a pharmacoresistant control group (PRC group, eight rats) and a pharmacoresistant stimulation group (PRS group, eight rats). Another 16 pharmacosensitive epileptic rats were served as control, also divided randomly into a pharmacosensitive control group (PSC group) and a pharmacosensitive stimulation group (PSS group). A stimulation electrode was implanted into the rats' hippocampus in the four groups. Low-frequency hippocampal stimulation was administered twice per day for two weeks. Following these weeks of stimulation, GABA-B receptor-positive neurons were counted and the gray values of GABA-B receptor expression in the rats' hippocampal tissues were measured. The amygdale stimulus-induced epileptic seizures were decreased significantly in the PRS group compared with the PRC group. The parameters of the amygdale after discharge also were improved after hippocampal stimulation. Simultaneously, the GABA-B receptor-positive neurons increased and the GABA-B expression gray values decreased markedly in the PRS group compared with the PRC group. The same phenomenon also was observed between the PSS group and the PSC group. However, no significant difference was found in the GABA-B receptor-positive neurons and the gray values of GABA-B between the PRS group and the PSC group. The low-frequency hippocampal stimulation may inhibit the amygdale stimulus-induced epileptic seizures and the after discharges. The antiepileptic effects of the hippocampal stimulation may be achieved partly by increasing the expression of the GABA-B receptor.

A complex of synaptic adhesion molecule CADM1, a molecule related to autism spectrum disorder, with MUPP1 in the cerebellum

Mutations in the synaptic adhesion protein CADM1 (RA175/SynCAM1) are associated with autism spectrum disorder (ASD), a neurodevelopmental disorder of uncertain molecular origin. Cadm1-knock out (KO) mice exhibit smaller cerebella with decreased number of synapse of Purkinje cells and some ASD-like symptoms, including impaired ultrasonic vocalization. In this study, we examined the alteration of the Cadm1 synaptic complex in the mouse cerebellum at post-natal stages. The C-terminal peptide of Cadm1 associated with Mupp1 at PSD-95/Dlg/ZO-1 (PDZ)(1-5), a scaffold protein containing 13 PDZ domains, which interacted with gamma-aminobutyric acid type B receptor (GABBR)2 at PDZ13, but not with PSD-95. The GABBR2 was detected in a set of proteins interacting with Cadm1 C-terminal. Cadm1 colocalized with Mupp1 and GABBR2 on the dendrites of Purkinje cells in the molecular layers of the developing cerebellum and on the dendrites of hippocampal neurons cultured in vitro. These observations suggest that the Cadm1 synaptic receptor complex, including Mupp1-GABBR2, is located on the dendrites of Purkinje cells. The amount of GABBR2 protein, but not mRNA, was increased in the cerebella of Cadm1 KO mice, suggesting that lack of Cadm1 does not affect transcription of GABBR2, but may stabilize the Mupp1-GABBR2 complex; the Mupp1-GABBR2 interaction may be stabilized by conformational change in Mupp1 or association with other adhesion molecules and by anchorage to the post-synaptic membrane. Up-regulation of GABBR2 in the cerebellum in the absence of CADM1 may be associated with ASD pathogenesis.

The gamma-aminobutyric acid type B (GABAB) receptor agonist baclofen inhibits morphine sensitization by decreasing the dopamine level in rat nucleus accumbens

BackgroundRepeated morphine exposure can induce behavioral sensitization. There are evidences have shown that central gamma-aminobutyric acid (GABA) system is involved in morphine dependence. However, the effect of a GABAB receptor agonist baclofen on morphine-induced behavioral sensitization in rats is unclear.MethodsWe used morphine-induced behavioral sensitization model in rat to investigate the effects of baclofen on behavioral sensitization. Moreover, dopamine release in the shell of the nucleus accumbens was evaluated using microdialysis assay in vivo.ResultsThe present study demonstrated that morphine challenge (3 mg/kg, s.c.) obviously enhanced the locomotor activity following 4-day consecutive morphine administration and 3-day withdrawal period, which indicated the expression of morphine sensitization. In addition, chronic treatment with baclofen (2.5, 5 mg/kg) significantly inhibited the development of morphine sensitization. It was also found that morphine challenge 3 days after repeated morphine administration produced a significant increase of extracellular dopamine release in nucleus accumbens. Furthermore, chronic treatment with baclofen decreased the dopamine release induced by morphine challenge.ConclusionsOur results indicated that gamma-aminobutyric acid system plays an important role in the morphine sensitization in rat and suggested that behavioral sensitization is a promising model to study the mechanism underlying drug abuse.

Administration of baclofen, a γ‐aminobutyric acid type B agonist in the thalamic ventrobasal complex, attenuates allodynia in monoarthritic rats subjected to the ankle‐bend test

gamma-Aminobutyric acid type B (GABAB) receptors are involved in the modulation of neuronal activity in response to chronic noxious input. However, the effect of their activation in chronic inflammatory pain in relay thalamic nuclei such as the ventrobasal complex (VB) is not known. In this study, experimental groups of 2, 4, and 14 days monoarthritic (MA) rats were injected with saline (controls) or baclofen (0.875 microg), a specific GABAB receptor agonist, in the VB contralateral to the inflamed joint, and the ankle-bend test was performed. Ankle-bend scores in control animals were near the maximum and were rather constant throughout the entire experimental period, indicating severe nociception. The same was observed in 2 days MA rats injected with baclofen. In the 4 days MA group, the response to baclofen injection was inconsistent among different animals, whereas, in 14 days MA rats, baclofen caused clear antinociceptive effects. Additionally, a 0.5 microg dose of baclofen was tested in 14 days MA rats, but no effect was observed, whereas a 1.25 mug dose produced visible side effects. Baclofen injections that did not target the VB but reached neighboring nuclei were ineffective in reducing nociception. Data demonstrate that the activation of the GABAB receptors by baclofen in the VB of MA rats leads to a decrease of nociception. Moreover, the response depends on the time course of the disease, suggesting the occurrence of different excitatory states of thalamic VB neurons. In conclusion, GABAB receptors in the VB play an important role in chronic inflammatory pain processing.

Molecular Determinants Involved in the Allosteric Control of Agonist Affinity in the GABAB Receptor by the GABAB2 Subunit

The gamma-aminobutyric acid type B (GABAB) receptor is an allosteric complex made of two subunits, GABAB1 (GB1) and GABAB2 (GB2). Both subunits are composed of an extracellular Venus flytrap domain (VFT) and a heptahelical domain (HD). GB1 binds GABA, and GB2 plays a major role in G-protein activation as well as in the high agonist affinity state of GB1. How agonist affinity in GB1 is regulated in the receptor remains unknown. Here, we demonstrate that GB2 VFT is a major molecular determinant involved in this control. We show that isolated versions of GB1 and GB2 VFTs in the absence of the HD and C-terminal tail can form hetero-oligomers as shown by time-resolved fluorescence resonance energy transfer (based on HTRF technology). GB2 VFT and its association with GB1 VFT controlled agonist affinity in GB1 in two ways. First, GB2 VFT exerted a direct action on GB1 VFT, as it slightly increased agonist affinity in isolated GB1 VFT. Second and most importantly, GB2 VFT prevented inhibitory interaction between the two main domains (VFT and HD) of GB1. According to this model, we propose that GB1 HD prevents the possible natural closure of GB1 VFT. In contrast, GB2 VFT facilitates this closure. Finally, such inhibitory contacts between HD and VFT in GB1 could be similar to those important to maintain the inactive state of the receptor.