GABABR1 in DRN mediated GABA to regulate 5-HT expression in multiple brain regions in male rats with high and low aggressive behavior.

The identity of the mechanism that controls aggressive behavior in rodents is unclear. Serotonin (5-HT) and GABA are associated with aggressive behavior in rodents. However, the regulatory relationship between these chemicals in the different brain regions of rats has not been fully defined. This study aimed to clarify the role of GABABR1 in DRN-mediated GABA to regulate 5-HT expression in multiple brain regions in male rats with high and low aggressive behavior. Rat models of highly and less aggressive behavior were established through social isolation plus resident intruder. On this basis, GABA content in the DRN and 5-HT contents in the PFC, hypothalamus, hippocampus and DRN were detected using ELISA. Co-expression of 5-HT and GB1 in the DRN was detected by immunofluorescence and immunoelectron microscopy at the tissue and subcellular levels, respectively. GB1-specific agonist baclofen and GB1-specific inhibitor CGP35348 were injected into the DRN by stereotaxic injection. Changes in 5-HT levels in the PFC, hypothalamus and hippocampus were detected afterward. After modeling, rats with highly aggressive behavior exhibited higher aggressive behavior scores, shorter latencies of aggression, and higher total distances in the open field test than rats with less aggressive behavior. The contents of 5-HT in the PFC, hypothalamus and hippocampus of rats with high and low aggressive behavior (no difference between the two groups) were significantly decreased, but the change in GABA content in the DRN was the opposite. GB1 granules could be found on synaptic membranes containing 5-HT granules, which indicated that 5-HT neurons in the DRN co-expressed with GB1, which also occurred in double immunofluorescence results. At the same time, we found that the expression of GB1 in the DRN of rats with high and low aggressive behavior was significantly increased, and the expression of GB1 in the DRN of rats with low aggressive behavior was significantly higher than that in rats with high aggressive behavior. Nevertheless, the expression of 5-HT in DRN was opposite in these two groups. After microinjection of baclofen into the DRN, the 5-HT contents in the PFC, hypothalamus and hippocampus of rats in each group decreased significantly. In contrast, the 5-HT contents in the PFC, hypothalamus and hippocampus of rats in each group increased significantly after injection with CGP35348. The significant increase in GABA in the DRN combined with the significant increase in GB1 in the DRN further mediated the synaptic inhibition effect, which reduced the 5-HT level of 5-HT neurons in the DRN, resulting in a significant decrease in 5-HT levels in the PFC, hypothalamus and hippocampus. Therefore, GB1-mediated GABA regulation of 5-HT levels in the PFC, hypothalamus and hippocampus is one of the mechanisms of highly and less aggressive behavior originating in the DRN. The increased GB1 level in the DRN of LA-behavior rats exhibited a greater degree of change than in the HA-group rats, which indicated that differently decreased 5-HT levels in the DRN may be the internal mechanisms of high and low aggression behaviors.

Effects of activating GABAB1 receptor on proliferation, migration, invasion and epithelial-mesenchymal transition of ovarian cancer cells.

OBJECTIVE: This study aimed to explore the effects of activating GABAB1 receptor by baclofen on proliferation, migration, invasion and epithelial-mesenchymal transition (EMT) of ovarian cancer cells. RESULTS: One hundred µmol/L, 200 µmol/L and 300 µmol/L were selected as low, medium and high baclofen concentrations respectively. Cells were divided into four groups: Control, 100 µmol/L, 200 µmol/L and 300 µmol/L. Compared with the control group, the viability, colony formation, migration and invasion of SKOV3 cells were inhibited, and the apoptosis of SKOV3 cells were enhanced significantly at 200 µmol/L and 300 µmol/L baclofen. Moreover, they changed significantly with the increase of baclofen concentration. Compared with the control group, the expression of E-cadherin and GABAB1 increased and the N-cadherin expression decreased significantly in 200 µmol/L and 300 µmol/L groups. Higher concentration of baclofen induced higher expression of E-cadherin and lower expression of N-cadherin. CONCLUSION: Baclofen inhibited the proliferation, cloning, migration, invasion and EMT of ovarian cancer cells by activating GABAB1 receptor. These results might contribute a lot to clarify the role and possible mechanism of GABAB1 receptor in ovarian cancer.

The effect of intrathecal injection of irisin on pain threshold and expression rate of GABAB receptors in peripheral neuropathic pain model.

BACKGROUND: and aim: Irisin is a new myokine that is secreted by myocytes during exercise, and plays a role in creating the beneficial effects of exercise on metabolism. Considering the benefits of exercise in reducing pain, this study was carried out to determine the probable effect of irisin on neuropathic pain in the chronic constriction injury (CCI) model in male rats. METHODS: To induce neuropathic pain CCI model was used. Animals were divided into groups of control, CCI, sham, CCI + vehicle, and CCI + irisin. Animals that had undergone CCI were divided into 6 groups and each received a different intrathecal dose of irisin (30, 10, 3, 1, 0.3, and 0.1 µg/kg) via intrathecal administration. To evaluate the chronic effect of irisin, its effective dose was injected for 14 days in another group of animals. At the end of the experiment, animals were ranscardially perfused and their spinal cord tissue was prepared for immunohistochemical and hematoxylin-eosin staining. RESULTS: The results showed that in acute intrathecal injection of irisin, 1 µg/kg dose has the highest analgesic effect compared to other doses. Nevertheless, in chronic administration of irisin with 1 µg/kg dose, no analgesic effect was detected. In addition, irisin administration could not increase the expression level of GABAB1 and B2 or prevent the decline in the number of neurons. CONCLUSION: The findings of the present study showed that acute administration of Irisin increases the pain threshold, but the chronic injection of resin does not have an effect on pain reduction and the expression of GABA receptors and it seems that this peptide is not a proper replacement for exercise in patients with neuropathic pain, who cannot exercise.

Circuit specificity in the inhibitory architecture of the VTA regulates cocaine-induced behavior.

Afferent inputs to the ventral tegmental area (VTA) control reward-related behaviors through regulation of dopamine neuron activity. The nucleus accumbens (NAc) provides one of the most prominent projections to the VTA; however, recent studies have provided conflicting evidence regarding the function of these inhibitory inputs. Using optogenetics, cell-specific ablation, whole cell patch-clamp and immuno-electron microscopy, we found that NAc inputs synapsed directly onto dopamine neurons, preferentially activating GABAB receptors. GABAergic inputs from the NAc and local VTA GABA neurons were differentially modulated and activated separate receptor populations in dopamine neurons. Genetic deletion of GABAB receptors from dopamine neurons in adult mice did not affect general or morphine-induced locomotor activity, but markedly increased cocaine-induced locomotion. Collectively, our findings demonstrate notable selectivity in the inhibitory architecture of the VTA and suggest that long-range GABAergic inputs to dopamine neurons fundamentally regulate behavioral responses to cocaine.

Sleep-promoting effects of a GABA/5-HTP mixture: Behavioral changes and neuromodulation in an invertebrate model.

AIMS: This study was to investigate the sleep promoting effects of combined γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP), by examining neuronal processes governing mRNA level alterations, as well as assessing neuromodulator concentrations, in a fruit fly model. MAIN METHODS: Behavioral assays were applied to investigate subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep of two amino acids and GABA/5-HTP mixture with caffeine treated flies. Also, real-time PCR and HPLC analysis were applied to analyze the signaling pathway. KEY FINDINGS: Subjective nighttime activity and sleep patterns of individual flies significantly decreased with 1% GABA treatment in conjunction with 0.1% 5-HTP treatment (p<0.001). Furthermore, GABA/5-HTP mixture resulted in significant differences between groups related to sleep patterns (40%, p<0.017) and significantly induced subjective nighttime sleep in the awake model (p<0.003). These results related to transcript levels of the GABAB receptor (GABAB-R1) and serotonin receptor (5-HT1A), compared to the control group. In addition, GABA/5-HTP mixture significantly increased GABA levels 1h and 12h following treatment (2.1 fold and 1.2 fold higher than the control, respectively) and also increased 5-HTP levels (0 h: 1.01 µg/protein, 12h: 3.45 µg/protein). SIGNIFICANCE: In this regard, we successfully demonstrated that using a GABA/5-HTP mixture modulates subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep to a greater extent than single administration of each amino acid, and that this modulation occurs via GABAergic and serotonergic signaling.

GABAB receptor upregulates fragile X mental retardation protein expression in neurons.

Fragile X mental retardation protein (FMRP) is an RNA-binding protein important for the control of translation and synaptic function. The mutation or silencing of FMRP causes Fragile X syndrome (FXS), which leads to intellectual disability and social impairment. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter of the mammalian central nervous system, and its metabotropic GABAB receptor has been implicated in various mental disorders. The GABAB receptor agonist baclofen has been shown to improve FXS symptoms in a mouse model and in human patients, but the signaling events linking the GABAB receptor and FMRP are unknown. In this study, we found that GABAB receptor activation upregulated cAMP response element binding protein-dependent Fmrp expression in cultured mouse cerebellar granule neurons via two distinct mechanisms: the transactivation of insulin-like growth factor-1 receptor and activation of protein kinase C. In addition, a positive allosteric modulator of the GABAB receptor, CGP7930, stimulated Fmrp expression in neurons. These results suggest a role for GABAB receptor in Fmrp regulation and a potential interest of GABAB receptor signaling in FXS improvement.

Thymoquinone and vitamin C attenuates pentylenetetrazole-induced seizures via activation of GABAB1 receptor in adult rats cortex and hippocampus.

Epilepsy is a common neurological disorder that leads to neuronal excitability and provoke various forms of cellular reorganization in the brain. In this study, we investigate the anti-convulsant and neuroprotective effects of thymoquinone (TQ) and vitamin C against pentylenetetrazole (PTZ)-induced generalized seizures. Epileptic seizures were induced in adult rats using systemic intraperitoneal injections of PTZ (50 mg/kg) for 7 days. Animals pretreated with either TQ or vitamin C or in combination attenuated PTZ-induced seizures and mortality in rats as well neurodegeneration in the cells. Compared to PTZ, TQ and vitamin C significantly prolonged the onset of seizures (p > 0.05) as well decrease the high-grade seizures. Analysis of electroencephalogram (EEG) recordings revealed that TQ or vitamin C supplementation significantly reduced polyspike and epileptiform discharges. Epileptic seizures caused a decline in expression of gamma-aminobutyric acid B1 receptor (GABAB1R) (p > 0.05), unchanged expression of protein kinase A (PKA), decreased calcium/calmodulin-dependent protein kinase II (CaMKII) (p > 0.05) and inhibit the phosphorylation of cAMP response element-binding protein (CREB) (p > 0.05) in cortex and hippocampus, respectively, compared with control. Changes in expression of GABAB1R, CaMKII and CREB by PTZ were reversed by TQ and vitamin C supplementation. Moreover, PTZ significantly increased Bax, decreased Bcl-2 expression and finally the activation of caspase-3. TQ and vitamin C pretreatment reversed all these deleterious effects induced by PTZ. TQ and vitamin C showed anticonvulsant effects via activation of GABAB1R/CaMKII/CREB pathway and suggest a potential therapeutic role in epilepsy.

Aggressive course in encephalitis with opsoclonus, ataxia, chorea, and seizures: the first pediatric case of γ-aminobutyric acid type B receptor autoimmunity.

IMPORTANCE: Autoantibodies to the γ-aminobutyric acid type B (GABAB) receptor have recently been identified as a cause of autoimmune encephalitis. Most patients with GABAB encephalitis have presented with limbic encephalitis. About half of the cases reported have been paraneoplastic in origin, with the majority of tumors representing small cell lung cancer. OBSERVATIONS: We describe a 3-year-old boy who presented with a mixed movement disorder (opsoclonus, ataxia, and chorea) as well as seizures refractory to treatment. His seizures required continuous pentobarbital sodium infusion to be controlled. Despite treatment with intravenous corticosteroids and immunoglobulins, the patient ultimately died of overwhelming sepsis. CONCLUSIONS AND RELEVANCE: To our knowledge, this report represents the first pediatric case of GABAB-associated encephalitis. Our patient presented with encephalopathy, refractory seizures, and a mixed movement disorder rather than limbic encephalitis. γ-Aminobutyric acid type B receptor autoimmunity deserves consideration in pediatric patients presenting with encephalitis. Immune-mediated encephalitis with autoantibodies directed against synaptic proteins has become an important component of the differential diagnosis of patients with encephalitis. Current estimates suggest that a substantial proportion of patients once suspected to have viral encephalitis in fact have an autoimmune etiology for their symptoms.1 Additional autoantigen targets continue to be identified, and the phenotypic spectrum associated with autoimmune encephalitis continues to expand. We describe a 3-year-old patient who presented with acute-onset confusion, opsoclonus, chorea, and intractable seizures. Neuroimaging disclosed involvement of the brainstem, basal ganglia, and hippocampi. γ-Aminobutyric acid type B (GABAB) receptor autoantibodies were identified in the serum and cerebrospinal fluid (CSF). Despite immunomodulating therapy, the patient died of overwhelming sepsis. To our knowledge, this is the first description of a pediatric patient with GABAB receptor autoantibodies. The presence of opsoclonus, ataxia, and chorea expands the clinical phenotype and indicates that GABAB receptor autoimmunity should be considered in cases of pediatric encephalitis

AMPA and GABA(A/B) receptor subunit expression in the cuneate nucleus of adult squirrel monkeys during peripheral nerve regeneration.

The primate somatosensory neuroaxis provides an excellent model system with which to investigate adult neural plasticity. Here, we report immunohistochemical staining data for AMPA and GABAA/B receptor subunits in the cuneate nucleus of adult squirrel monkeys 1 and 5 months after median nerve compression. This method of nerve injury allowed the investigation of the way in which patterns of receptor correlates change during peripheral nerve regeneration. These results are compared to cortical data collected within the same animals. As observed in the cortex, the pattern of subunit staining in the brainstem 1 month after nerve compression suggests that the sensory deprived nucleus enters a state of reorganization. That is, the expression of GluR2/3 AMPA receptor subunits is significantly increased, while GABA α1 and GABABR1b receptor subunits are significantly decreased. Five months after nerve injury, the pattern of subunit expression is again very similar to that observed in the infragranular layers of cortex. At this later time we observe a significant increase in GluR2/3 and GABABR1a, with no change in GABAAα1, and a significant decrease in GABABR1b. Together these results suggest that during reorganization and recovery from injury the brainstem and cortex are governed by homogeneous mechanisms of plasticity.

Expression of a GABA(B) - receptor in olfactory sensory neurons of sensilla trichodea on the male antenna of the moth Heliothis virescens.

In the olfactory pathway of Drosophila, a GABAB receptor mediated presynaptic gain control mechanism at the first synapse between olfactory sensory neurons (OSNs) and projection neurons has been suggested to play a critical role in setting the sensitivity and detection range of the sensory system. To approach the question if such a mechanism may be realized in the pheromone recognition system of male moths in this study attempts were made to explore if moth's pheromone-responsive cells express a GABAB- receptor. Employing a combination of genome analysis, RT-PCR experiments and screening of an antennal cDNA library we have identified a cDNA which encodes the GABAB-R1 receptor of Heliothis virescens. Moreover, based on the HvirGABAB-R1 sequence we could predict a GABAB-R1 protein from genome sequences of the silkmoth Bombyx mori. To assess whether HvirGABAB-R1 is expressed in OSNs of male antenna we performed whole-mount in situ hybridization (WM-ISH) experiments. Several HvirGABAB-R1 positive cells were visualized under long sensilla trichodea, known to contain pheromone-responsive OSNs. In parallel it was shown that cells under long trichoid hairs were labelled with pheromone receptor specific probes. In addition, the HvirGABAB-R1 specific probe also labelled several cells under shorter olfactory sensilla, but never stained cells under mechanosensory/gustatory sensilla chaetica. Together, the results indicate that a GABAB receptor is expressed in pheromone-responsive OSNs of H. virescens and suggest a presynaptic gain control mechanism in the axon terminals of these cells.

Regional mRNA expression of GABAergic receptor subunits in brains of C57BL/6J and 129P3/J mice: strain and heroin effects.

C57BL/6J and 129 substrains of mice are known to differ in their basal levels of anxiety and behavioral response to drugs of abuse. We have previously shown strain differences in heroin-induced conditioned place preference (CPP) between C57BL/6J (C57) and 129P3/J (129) mice, and in the regional expression of several receptor and peptide mRNAs. In this study, we examined the contribution of the GABAergic system in the cortex, nucleus accumbens (NAc), caudate putamen (CPu) and the region containing the substantia nigra and ventral tegmental area (SN/VTA) to heroin reward by measuring mRNA levels of 7 of the most commonly expressed GABA-A receptor subunits, and both GABA-B receptor subunits, in these same mice following saline (control) or heroin administration in a CPP design. Using real-time PCR, we studied the effects of strain and heroin administration on GABA-A α1, α2, α3, ß2, and γ2 subunits, which typically constitute synaptic GABA-A receptors, GABA-A α4 and δ subunits, which typically constitute extrasynaptic GABA-A receptors, and GABA-B R1 and R2 subunits. In saline-treated animals, we found an experiment-wise significant strain difference in GABA-Aα2 mRNA expression in the SN/VTA. Point-wise significant strain differences were also observed in GABA-Aα2, GABA-Aα3, and GABA-Aα4 mRNA expression in the NAc, as well as GABA-BR2 mRNA expression in the NAc and CPu, and GABA-BR1 mRNA expression in the cortex. For all differences, 129 mice had higher mRNA expression compared to C57 animals, with the exception of GABA-BR1 mRNA in the cortex where we observed lower levels in 129 mice. Therefore, it may be possible that known behavioral differences between these two strains are, in part, due to differences in their GABAergic systems. While we did not find heroin dose-related changes in mRNA expression levels in C57 mice, we did observe dose-related differences in 129 mice. These results may relate to our earlier behavioral finding that 129 mice are hyporesponsive to the rewarding effects of heroin.

GABAB receptor gene transfer into the nucleus tractus solitarii induces chronic blood pressure elevation in normotensive rats.

BACKGROUND: Increasing evidence indicates that GABAergic neurons in the nucleus of the solitary tract (NTS) play a significant role in the arterial baroreceptor reflex and control of cardiovascular homeostasis. However, the role of these neurons in the development of hypertension is not yet fully clear. METHODS AND RESULTS: In the present study, we first confirmed that GABAB receptor (GBR) expression is enhanced in the NTS of SHR as compared with WKY rats using real-time RT-PCR and western blots. To study the functional consequence of upregulated GBR expression, GBR was overexpressed in the NTS by bilateral microinjection of the AAV2-GBR1 viral vector into the NTS of WKY rats. Immunofluorescence staining and western blots demonstrated that microinjection of AAV2-GBR1 into the NTS of WKY rats resulted in a significant increase in GBR1 expression in the NTS neurons. Overexpression of GBR in the NTS induced a chronic elevation in blood pressure and heart rate in the normotensive WKY rats. In an acute study, the pressor response to baclofen microinjected into the NTS was enhanced in SHR as compared with WKY rats. CONCLUSIONS: GBR1 expression is enhanced in the NTS of SHR vs. WKY rats and overexpression of this gene in the NTS results in chronic elevation of blood pressure and heart rate in normotensive rats.

Distribution of metabotropic receptors of serotonin, dopamine, GABA, glutamate, and short neuropeptide F in the central complex of Drosophila.

The central complex is a prominent set of midline neuropils in the insect brain, known to be a higher locomotor control center that integrates visual inputs and modulates motor outputs. It is composed of four major neuropil structures, the ellipsoid body (EB), fan-shaped body (FB), noduli (NO), and protocerebral bridge (PB). In Drosophila different types of central complex neurons have been shown to express multiple neuropeptides and neurotransmitters; however, the distribution of corresponding receptors is not known. Here, we have mapped metabotropic, G-protein-coupled receptors (GPCRs) of several neurotransmitters to neurons of the central complex. By combining immunocytochemistry with GAL4 driven green fluorescent protein, we examined the distribution patterns of six different GPCRs: two serotonin receptor subtypes (5-HT(1B) and 5-HT(7)), a dopamine receptor (DopR), the metabotropic GABA(B) receptor (GABA(B)R), the metabotropic glutamate receptor (DmGluR(A)) and a short neuropeptide F receptor (sNPFR1). Five of the six GPCRs were mapped to different neurons in the EB (sNPFR1 was not seen). Different layers of the FB express DopR, GABA(B)R, DmGluR(A,) and sNPFR1, whereas only GABA(B)R and DmGluR(A) were localized to the PB. Finally, strong expression of DopR and DmGluR(A) was detected in the NO. In most cases the distribution patterns of the GPCRs matched the expression of markers for their respective ligands. In some nonmatching regions it is likely that other types of dopamine and serotonin receptors or ionotropic GABA and glutamate receptors are expressed. Our data suggest that chemical signaling and signal modulation are diverse and highly complex in the different compartments and circuits of the Drosophila central complex. The information provided here, on receptor distribution, will be very useful for future analysis of functional circuits in the central complex, based on targeted interference with receptor expression.

Expression of functional γ-aminobutyric acid type A receptors in Schwann-like adult stem cells.

γ-Aminobutyric acid (GABA) receptors are present in peripheral and central glia and modulate important physiological parameters of glial cells. Schwann cells (SC), the peripheral nervous system glial cells, play essential roles in nerve regeneration, but they are unsuitable for bioengineering of nerve repair. Increasing interest has been focused on adult stem cells derived from bone marrow (BM-MSC) or adipose tissue (ASC), which can be differentiated into SC-like phenotype and used as SC replacements. SC-like adult stem cells express GABA-B receptors that can modulate their proliferation. The aim of this study was to investigate GABA-A receptors functional expression in differentiated stem cells. BM-MSC and ASC were found to express GABA-A α2 and ß3, but not ß1 mRNA transcripts. Protein expression levels of GABA-A α2 and ß3 receptors were upregulated following SC-like differentiation as shown by Western blot studies. GABA-A receptor stimulation with muscimol increased the proliferation rate of SC, differentiated BM-MSC and differentiated ASC. In conclusion, GABA-A α2 and ß3 receptor subunits are present in BM-MSC and ASC and upregulated following glial differentiation. GABA-A subunits in differentiated stem cells and SC assemble in functional receptors modulating cell proliferation. Functional GABA-A and GABA-B receptors represent a possible pharmacological target to modulate SC-like stem cells physiology.

Localization of mGluR5, GABAB, GABAA, and cannabinoid receptors on the vago-vagal reflex pathway responsible for transient lower esophageal sphincter relaxation in humans: an immunohistochemical study.

BACKGROUND: Transient lower esophageal sphincter relaxations (TLESRs) are the predominant mechanisms underlying gastro-esophageal reflux. TLESRs are mediated by a vago-vagal reflex, which can be blocked by interaction with metabotropic Glutamate Receptor 5 (mGluR5), γ-aminobutyric acid type B (GABA(B)), γ-aminobutyric acid type A (GABA(A)), and cannabinoid (CB) receptors. However, the distribution of these receptors in the neural pathway underlying the triggering of TLESRs has not been evaluated in humans. METHODS: Using immunohistochemistry, we investigated the distribution of mGluR5, GABA(A), GABA(B), CB1, and CB2 receptors in the human nodose ganglion, the brain stem, and the myenteric plexus of the esophagus. KEY RESULTS: MGluR5, GABA(B), CB1, and CB2 receptors are abundantly expressed in neurons of the myenteric plexus of the LES, nodose ganglion cell bodies and nerve fibers, the dorsal motor nucleus, and nucleus of the solitary tract in the brain stem. GABA(A) receptors are expressed in the same regions except in the nodose ganglion and myenteric plexus of the LES. CONCLUSIONS & INFERENCES: Human mGluR5, GABA(A,B), and CB(1,2) receptors are abundantly expressed along the vago-vagal neural pathway and involved in the triggering of TLESRs. These findings are not only in line with the central side effects observed during treatment with reflux inhibitors such as GABA(B) receptor agonists and mGluR5 antagonists, but also suggest that peripherally acting compounds may be effective.

Cholinergic and GABAergic receptor functional deficit in the hippocampus of insulin-induced hypoglycemic and streptozotocin-induced diabetic rats.

Neurotransmitter receptor functional regulation plays an important role in controlling the excitability and responsiveness of hippocampal neurons. Deregulation of its function is associated with seizure generation, motor deficits, and memory impairment. In the present study we investigated the changes in hippocampal cholinergic and GABA receptor binding and gene expression in insulin-induced hypoglycemic and streptozotocin-induced diabetic rats. Expression of cholinergic enzymes; acetylcholine esterase (AChE) and choline acetyltransferase (ChAT) upregulated and downregulated, respectively, in diabetic group, which was further exacerbated by hypoglycemia. Total muscarinic receptor, muscarinic M1, and GABA maximal binding (B(max)) significantly decreased in hypoglycemic and diabetic rats. In hypoglycemic group, the B(max) showed further decline compared with diabetes. Muscarinic M3 receptor B(max) and gene expression upregulated in hypoglycemic and diabetic group. Alpha7 nicotinic acetylcholine receptor (α7 nAChR) expression significantly downregulated in hypoglycemic and diabetic rats. Gene expression of glutamate decarboxylase (GAD), GABAAα1, and GABAB in hypoglycemic and diabetic rats downregulated, with more significant decrease in hypoglycemic group. Present findings show altered cholinergic, muscarinic, nicotinic receptor expression and thereby function. Decreased GABA receptor expression is associated with decline in GABAergic neurotransmission. Thus cholinergic receptor dysfunction and decreased GABAergic neuroprotective inhibitory function in the hippocampus of hypoglycemic and diabetic rats account for the increased vulnerability of hippocampus predisposing to neuronal damage, which is suggested to contribute to cognitive impairment and memory deficit reported in hypoglycemia and diabetes. Also, recurrent hypoglycemia in diabetes exacerbates the hippocampal dysfunction induced by diabetes, which has clinical significance in diabetes therapy.

p38/MAPK inhibitor modulates the expression of dorsal horn GABA(B) receptors in the spinal nerve ligation model of neuropathic pain.

BACKGROUND: Neuropathic pain is one of the most challenging clinical problems due to a lack of understanding the mechanisms. Recent studies have suggested that activated microglia in spinal cord may play a vital role in nerve injury-induced neuropathic pain, but the exact mechanisms have not been fully determined. METHODS: First, we investigated the changes of dorsal horn GABA(B) receptor 1 (R1) expression in spinal nerve ligation rats. Second, we explored whether activated microglia contributed to such neuron changes by intrathecal administration of the p38 inhibitor, SB203580. RESULTS: In this study, we found a dynamic change of GABA(B)R1a protein expression after spinal nerve ligation, and the peripheral nerve injury-induced downregulation of GABA(B)R1a expression in the spinal dorsal horn could be prevented by intrathecal administration of a p38/MAPK inhibitor SB203580. CONCLUSIONS: Our results provide valuable information for a better understanding of neuropathic pain and may contribute to developing effective treatments in future studies.

Downregulation of GABAB receptors in the spinal cord dorsal horn in diabetic neuropathy.

Diabetic neuropathic pain is a common clinical problem and remains difficult to treat with classic analgesics. Spinal dorsal horn neurons are important in mediating nociceptive signaling, and the hyperactivity of these neurons is critical in diabetic neuropathy. In this study, we determined the GABA(B) receptor expression level in dorsal horn neurons in streptozotocin (STZ)-induced diabetes in rats by using reverse-transcription polymerase chain reaction (RT-PCR) and western blot analyses. Mean blood glucose concentrations were significantly higher and the paw withdrawal threshold was significantly lower in STZ-treated rats than in saline-treated rats. Immunohistochemical staining showed that the GABA(B) receptor was extensively expressed in the spinal dorsal horn neurons. The GABA(B1) mRNA level decreased in a time-dependent manner in STZ-treated rats compared with saline-treated controls. Furthermore, the protein expression level revealed by western blot analysis was lower in STZ-treated rats than in saline-treated rats. These data suggest that GABA(B) receptors are downregulated in the spinal dorsal horn in this model of STZ-induced diabetic neuropathic pain. The reduction of GABA(B) expression may contribute to the hyperactivity of spinal dorsal horn neurons and diabetic neuropathic pain.

The GABAB receptor inhibits activation of hepatic stellate cells.

BACKGROUND/AIMS: Angiotensin II (Ang II) plays an important role in the activation of hepatic stellate cells (HSCs). In this study it was found that expression of the GABA(B) receptor was elevated in HSCs treated with Ang II. We attempted to elucidate the mechanism of the GABA(B) receptor in HSCs activation. METHODS: First, the target gene (GABA(B) receptor) was screened by gene chip in HSCs treated with Ang II. Second, the biological function of the GABA(B) receptor was analyzed by MTT, cell-cycle assay, real-time PCR, and western blot. The methods of MTT and cell-cycle assay were used to evaluate the effect of the GABA(B) receptor on proliferation and DNA synthesis of HSCs. Expression of ECM, TGF-beta1, and alpha-SMA was analyzed by real-time PCR and western blot. RESULTS: The GABA(B) receptor's specific agonist CGP35348 inhibited the activation of HSCs, which could be partially reversed by the GABA(B) receptor's antagonist. CONCLUSIONS: Our in-vitro results demonstrated that the GABA(B) receptor could inhibit HSCs activation.

Ischaemia differentially regulates GABA(B) receptor subunits in organotypic hippocampal slice cultures.

Reduced synaptic inhibition due to dysfunction of ionotropic GABA(A) receptors has been proposed as one factor in cerebral ischaemia-induced excitotoxic cell death. However, the participation of the inhibitory metabotropic GABA(B) receptors in these pathological processes has not been extensively investigated. We used oxygen-glucose deprivation (OGD) and NMDA-induced excitotoxicity as models to investigate whether ischaemia-like challenges alter the protein levels of GABA(B1) and GABA(B2) receptor subunits in rat organotypic hippocampal slice cultures. Twenty-four hours after the insult both OGD and NMDA produced a marked decrease in the total levels of GABA(B2) (approximately 75%), while there was no significant change in the levels of GABA(B1) after OGD, but an increase after NMDA treatment (approximately 100%). The GABA(B) receptor agonist baclofen (100 microM) was neuroprotective following OGD or NMDA treatment if added before or during the insult. GABA(B) receptors comprise heterodimers of GABA(B1) and GABA(B2) subunits and our results suggest that the separate subunits are independently regulated in response to extreme neuronal stress. However, because GABA(B2) is required for functional surface expression, down-regulation of this subunit removes an important inhibitory feedback mechanism under pathological conditions.