Selective Gamma-aminobutyric Acid Research Articles

Capacitation of mouse sperm is modulated by gamma-aminobutyric acid (GABA) concentration.

In mammals, ejaculated sperm acquire their fertilizing ability during migration through the female reproductive tract, which secretes several factors that contribute to sperm capacitation. Gamma-aminobutyric acid (GABA) is a well-known neurotransmitter in the central nervous system, but additionally enhances the sperm acrosome reaction in the rat and cow. However, the detailed effects of GABA concentration on sperm function remain unclear. In this study, we detected the presence of the GABA type A receptor (GABA A) in mouse epididymal sperm by western blot analysis and in the sperm acrosome by immunocytochemistry. We also investigated the effects of GABA on sperm fertilizing ability. We found that GABA facilitated the tyrosine phosphorylation of sperm proteins, which is an index of sperm capacitation. GABA also promoted the acrosome reaction, which was suppressed by a selective GABA A receptor antagonist. We then found that the effective GABA concentration for the acrosome reaction corresponds to sperm concentration, but we did not detect any marked effect of GABA on sperm motility using a computer-assisted sperm analysis system. Using immunohistochemistry, we also detected GABA expression in the epithelia of the mouse uterus and oviduct. Furthermore, we found that the mRNA levels of glutamate decarboxylase (Gad), which generates GABA from L-glutamate, were higher in the oviduct than in the uterus, and that Gad mRNA levels were higher at estrus than at the diestrus stage. These results indicate that the GABA concentration can act as a modulator of the acrosome reaction and sperm capacitation in the female reproductive tract.

Monoaminergic and aminoacidergic receptors are involved in the antidepressant-like effect of ginsenoside Rb1 in mouse hippocampus (CA3) and prefrontal cortex

Ginsenoside Rb1 (Rb1), as the major bioactive ingredient of Panax ginseng C.A. Meyer, elicited a novel antidepressant-like effect in the forced swim test (FST) in chronic unpredictable mild stress (CUMS) rats in our previous study. To further explore the molecular mechanism of Rb1 on the neurotransmitters such as 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), norepinephrine (NE), dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), glutamate (Glu) and gamma-aminobutyric acid (GABA) in this antidepressant-like effect, the neurochemical changes in the monoaminergic and aminoacidergic receptors were investigated in the present pharmacological study by using reuptake inhibitors, receptors agonists and antagonists. The results showed that a sub-effective dose of Rb1 (5 mg/kg, p.o.) co-administered with fluoxetine (1 mg/kg, i.p., a selective serotonin reuptake inhibitor), reboxetine (2.5 mg/kg, i.p., a noradrenalin reuptake inhibitor), bupropion (10 mg/kg, i.p., a dopaminergic reuptake inhibitor), Mk-801 (0.05 mg/kg, i.p., an N-methyl-d-aspartic acid (NMDA) receptor antagonist) or baclofen (0.1 mg/kg, i.p., a selective GABA agonist) significantly decreased the immobility time in the FST. In addition, pretreating mice with NAN190 (0.5 mg/kg, i.p., a 5-HT1A receptor antagonist), ketanserin (5 mg/kg, i.p., a 5-HT2A/2C receptor antagonist), ondansetron (1 mg/kg, i.p., a 5-HT3A receptor antagonist), prazosin (1 mg/kg, i.p., an α1-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α2-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, i.p., a selective D1 receptor antagonist), haloperidol (0.2 mg/kg, i.p., a non-selective D2 receptor antagonist), NMDA (75 mg/kg, i.p., an agonist at the glutamate site) or bicuculline (4 mg/kg, i.p., a competitive GABA antagonist) reversed the antidepressant-like effect of Rb1 (10 mg/kg, p.o.) in the FST. The results obtained for the neurotransmitters in the mouse hippocampus (CA3) and prefrontal cortex showed that Rb1 up-regulated the levels of 5-HT, 5-HIAA, NE, DA, and GABA and decreased the level of Glu. However, there were no significant differences in HVA or DOPAC. Furthermore, there were no significant alterations in the total path of spontaneous locomotor activity in all treatments. These results suggest that both monoaminergic (serotonergic, noradrenergic and dopaminergic) and aminoacidergic (glutamatergic and GABAergic) receptors may be involved in the antidepressant-like effect of Rb1.

Acute inflammation reveals GABAA receptor-mediated nociception in mouse dorsal root ganglion neurons via PGE2 receptor 4 signaling.

Gamma‐aminobutyric acid (GABA) depolarizes dorsal root ganglia (DRG) primary afferent neurons through activation of Cl− permeable GABAA receptors but the physiologic role of GABAA receptors in the peripheral terminals of DRG neurons remains unclear. In this study, we investigated the role of peripheral GABAA receptors in nociception using a mouse model of acute inflammation. In vivo, peripheral administration of the selective GABAA receptor agonist muscimol evoked spontaneous licking behavior, as well as spinal wide dynamic range (WDR) neuron firing, after pre‐conditioning with formalin but had no effect in saline‐treated mice. GABAA receptor‐mediated pain behavior after acute formalin treatment was abolished by the GABAA receptor blocker picrotoxin and cyclooxygenase inhibitor indomethacin. In addition, treatment with prostaglandin E2 (PGE 2) was sufficient to reveal muscimol‐induced licking behavior. In vitro, GABA induced sub‐threshold depolarization in DRG neurons through GABAA receptor activation. Both formalin and PGE 2 potentiated GABA‐induced Ca2+ transients and membrane depolarization in capsaicin‐sensitive nociceptive DRG neurons; these effects were blocked by the prostaglandin E2 receptor 4 (EP4) antagonist AH23848 (10 μmol/L). Furthermore, potentiation of GABA responses by PGE 2 was prevented by the selective Nav1.8 antagonist A887826 (100 nmol/L). Although the function of the Na+‐K+‐2Cl‐ co‐transporter NKCC1 was required to maintain the Cl‐ ion gradient in isolated DRG neurons, NKCC1 was not required for GABAA receptor‐mediated nociceptive behavior after acute inflammation. Taken together, these results demonstrate that GABAA receptors may contribute to the excitation of peripheral sensory neurons in inflammation through a combined effect involving PGE 2‐EP4 signaling and Na+ channel sensitization.

Amnestic Somnambulism and Nocturnal Eating Disorder Associated with Zolpidem Use as a Contributing Factor in Accidental Death

Zolpidem is a selective gamma-aminobutyric acid (GABA) receptor modulator used commonly in the treatment of insomnia. It is effective at initiating sleep and has primary effects similar to benzodiazepines. Zolpidem has gained some notoriety for its association with rare but unusual side effects of compulsive nocturnal activity with anterograde amnesia. Review of the literature documents zolpidem-associated nocturnal activities, which include walking, eating, and more complex activities such as house cleaning or driving. During these events, the sleeper may be able to converse and initially appear normal to an observer, but has limited, if any, recollection of the event. Other literature reviewing zolpidem-related deaths, hospital admissions, falls, and somnambulism found a high rate of concurrent alcohol and/or other drug use than when using Zolpidem alone. We present a case of a 67-year-old woman with a history of somnambulism and amnestic eating during the night after using Zolpidem who was found deceased on the pavement below her opened second story bedroom window. Autopsy revealed nonocclusive food substances in her airways, and head and neck trauma, consistent with a fall from the second story window. Toxicological analysis of peripheral blood revealed Zolpidem (69 ng/mL), pseudoephedrine (150 ng/mL), citalopram/escitalopram (400 ng/mL), and caffeine. Blood and vitreous ethanol concentrations were 194 mg/dL and 160 mg/dL, respectively. Given the decedent's nocturnal activity history associated with Zolpidem, Zolpidem use combined with ethanol was considered contributory to her death.

Functional gastroduodenal disorders

Functional gastroduodenal disorders are chronic, heterogeneous conditions experienced by adults worldwide. The Rome III consensus recognizes four syndromes: functional dyspepsia, belching disorders, nausea and vomiting disorders and ruminating syndrome. Considerable advances have occurred in the field of functional gastroduodenal disorders. This review provides an overview of the definitions, epidemiology, clinical features, investigations and treatments of some of these disorders. Functional dyspepsia is divided into post-prandial distress syndrome (PDS) and epigastric pain syndrome (EPS). The prevalence of functional dyspepsia is about 11–20% in the western world. Dysfunctional gastrointestinal motility and hypersensitivity are involved in the generation of symptoms in some patients. Several classes of drugs are used to treat patients with functional dyspepsia, and the increasing understanding of pathophysiology will greatly affect future treatment regimens. Belching disorders may have either a behavioural or a physiological background, and therefore behavioural and speech therapies show promise, but definitive studies are required. The effect of fundoplication and drugs, such as a selective gamma-aminobutyric acid agonist baclofen, on belching await confirmatory studies on their usefulness. Mechanisms of functional nausea and vomiting are poorly understood, and their treatment currently focuses on pharmacological and non-pharmacological therapies, including antidepressants and psychological approaches.

Differential effects of aging on EEG after baclofen administration

Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses, such as in analgesics and drug addiction treatment. In addition, evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging. This study investigated whether baclofen administration (5 mg kg(-1)) induces differential effects on cortical electrical activity with age. Electroencephalograms (EEGs) were recorded from young (3-4 months) and aged (15-17 months) rats, and both the absolute and relative powers in five frequency bands (delta: 2-4 Hz; theta: 4-8 Hz; alpha: 8-12 Hz; beta: 12-20 Hz; gamma: 20-100 Hz) were analyzed. Before administration of baclofen, we found that the EEG relative power in the beta band was higher in the aged than that in the young rats. After administration of baclofen, there was a slower increase in the relative power in the delta band in the aged than that in the young rats. Moreover, there was no significant difference between the two age groups in absolute power in any frequency band. These findings indicate that baclofen treatment appears to differentially modify cortical EEG activity as a function of age. Our data further elucidate the relationship between GABA(B) receptor-mediated neurotransmission and aging.

Hypothalamic oxytocin attenuates CRF expression via GABA A receptors in rats

Centrally released oxytocin (OXT) has anxiolytic and anti-stress effects . Delayed gastric emptying (GE) induced by acute restraint stress (ARS) for 90 min is completely restored following 5 consecutive days of chronic homotypic restraint stress (CHS), via up-regulating hypothalamic OXT expression in rats. However, the mechanism behind the restoration of delayed GE following CHS remains unclear. Gamma-aminobutyric acid (GABA)-projecting neurons in the paraventricular nucleus (PVN) have been shown to inhibit corticotropin releasing factor (CRF) synthesis via GABA A receptors. We hypothesized that GABA A receptors are involved in mediating the inhibitory effect of OXT on CRF expression in the PVN, which in turn restores delayed GE following CHS. OXT (0.5 μg) and selective GABA A receptor antagonist, bicuculline methiodide (BMI) (100 ng), were administered intracerebroventricularly (icv). Solid GE was measured under non-stressed (NS), ARS and CHS conditions. Expression of CRF mRNA in the PVN was evaluated by real time RT-PCR. Neither OXT nor BMI changed GE and CRF mRNA expression under NS conditions. Delayed GE and increased CRF mRNA expression induced by ARS were restored by icv-injection of OXT. The effects of OXT on delayed GE and increased CRF mRNA expression in ARS were abolished by icv-injection of BMI. Following CHS, delayed GE was completely restored in saline (icv)-injected rats, whereas daily injection of BMI (icv) attenuated the restoration of delayed GE. Daily injection of BMI (icv) significantly increased CRF mRNA expression following CHS. It is suggested that central OXT inhibits ARS-induced CRF mRNA expression via GABA A receptors in the PVN. GABAergic system is also involved in OXT-mediated adaptation response of delayed GE under CHS conditions.

The effects of zolpidem treatment and withdrawal on the in vitro expression of recombinant α1β2γ2s GABAA receptors expressed in HEK 293 cells

Zolpidem, a widely used hypnotic drug which acts through benzodiazepine binding sites, is a positive allosteric modulator of gamma-aminobutyric acid (GABA) action with preferential affinity for GABA(A) receptors containing alpha1 subunit. The pharmacological profile of zolpidem is different from that of classical benzodiazepines. The aim of this study was to find out whether zolpidem treatment triggers adaptive changes in the recombinant alpha1 subunit-containing GABA(A) receptors other than those observed following treatment with classical benzodiazepine-diazepam. Radioligand binding studies showed that 2-day exposure of human embryonic kidney (HEK) 293 cells stably expressing recombinant alpha1beta2gamma2s GABA(A) receptors to zolpidem (10 muM) up-regulated the maximum number (B (max)) of [(3)H]flunitrazepam, [(3)H]muscimol, and [(3)H]t-butylbicycloorthobenzoate ([(3)H]TBOB) binding sites without changing their affinity (K (d)), suggesting an increase in total GABA(A) receptor number. Semi-quantitative RT-PCR analysis demonstrated increased levels of alpha1 subunit mRNA, while Western blot demonstrated up-regulated gamma2 subunit proteins, suggesting that zolpidem induced de novo synthesis of receptors proteins, at both the transcriptional and translational levels. GABA-induced potentiation of [(3)H]flunitrazepam binding to membranes obtained from zolpidem-treated cells was markedly reduced, indicating allosteric uncoupling between GABA and benzodiazepine binding sites. The number of benzodiazepine and convulsant binding sites as well as the functional coupling between GABA and benzodiazepine binding sites normalized in 24 h following discontinuation of zolpidem treatment. The results of our in vitro studies suggest that a 2-day exposure of recombinant alpha1 subunit-containing GABA(A) receptors stably transfected in HEK 293 cells to zolpidem induces adaptive changes in this selective GABA(A) receptor subtype, which are not substantially different from those obtained after prolonged exposure of cells to high concentrations of diazepam.

Circular Swimming by the Medaka, Oryzias latipes, Induced by Microinjection of GABA-ergic Agonists and Antagonists into the Posterior Thalamus

The thalamic mechanism involved in locomotor control, particularly in steering control, was studied in a teleost, Oryzias latipes. Ipsilateral circular swimming was induced by injection of bicuculline, a selective gamma-aminobutyric acid (GABA)-A antagonist, into the unilateral posterior thalamus. δ-Amino-valeric acid, phaclofen and 2-hydroxysaclofen (weak GABA-B antagonists) had weak, but similar effects. In contrast to antagonists, injection of GABA, muscimol (GABA-A agonist), baclofen (GABA-B agonist), nipecotic acid (blocker of Na + -coupled GABA uptake carrier), and γ-hydroxybutyric acid (possible GABA-A and -B agonist) into the unilateral posterior thalamus induced contralateral circular swimming

A convergent approach to (R)-Tiagabine by a regio- and stereocontrolled hydroiodination of alkynes

The occurrence of unsaturated systems in natural products combined with the mildness and the wide range of applicability of CeCl(3) promoted methodologies suggest several potential future synthetic applications within the field of total synthesis of biologically active molecules. On this concept, the use of CeCl(3).7H(2)O-NaI system as an efficient heterogeneous promoter has been highlighted in the iodofunctionalization of carbon-carbon triple bonds. The study has shown that this method would be particularly interesting for the stereoselective formation of trisubstituted (Z)- or (E)-iodoalkenes by simply changing the nature of the solvent. The methodology has been successfully applied to the synthesis of (R)-1-[4,4-bis-(3-methyl-2-thienyl)-3-butenyl]-3-piperidinecarboxylic acid , named (R)-Tiagabine, which is a potent and selective gamma-aminobutyric acid (GABA) uptake inhibitor with proven anticonvulsant efficacy in humans.

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Long-term anxiolytic and antidepressant-like behavioural effects of tiagabine, a selective GABA transporter-1 (GAT-1) inhibitor, coincide with a decrease in HPA system activity in C57BL/6 mice

Gamma-aminobutyric acid (GABA) system plays a pivotal role in the pathophysiology of anxiety and mood disorders. This study was aimed to assess the anxiolytic and antidepressant-like properties of tiagabine, an inhibitor of the GABA transporter-1 (GAT-1), after acute and chronic administration in C57BL/6JOlaHsD mice with paroxetine as a positive control. In first experiments, the acute administration of tiagabine (7.5 mg/kg, orally [PO]) and paroxetine (10 mg/kg PO) induced anxiolytic effects in the elevated plus maze test and the modified hole board test and an antidepressant-like effect in the forced swim test. Chronic application of tiagabine (7.5 mg/kg PO) and paroxetine (10 mg/kg PO) for 22 days revealed an anxiolytic and antidepressant-like efficacy of tiagabine only. In a further experiment, we analysed the impact of chronic tiagabine versus paroxetine treatment on the hypothalamic-pituitary-adrenocortical (HPA) system regulation. GAT-1 blockade induced a setpoint-shift of the stress hormone system toward lower levels as indicated by decreased plasma corticosterone concentrations and attenuated gene expression levels of corticotropin-releasing factor in the paraventricular nucleus of the hypothalamus and of hippocampal steroid receptors. This data indicate that both acute and long-term anxiolytic and antidepressant-like properties of brain GAT-1 inhibition coincide with a reduction in HPA system activity in mice.

Gamma-aminobutyric acid B receptor mediated inhibition of gonadotropin-releasing hormone neurons is suppressed by kisspeptin-G protein-coupled receptor 54 signaling.

Gamma-aminobutyric acid (GABA) is one of the most important neurotransmitters that regulate the excitability of GnRH neurons. Numerous studies have shown that GABA activates Cl(-) currents in GnRH neurons, and these effects are antagonized by GABA(A) receptor antagonists. The GABA(B) receptor is a heterodimer composed of GABA(B) R1 and R2, and although both subunits have been localized in GnRH neurons, nothing is known about the cellular signaling of this G alpha(i,o)-coupled receptor in GnRH neurons. Using whole-cell recordings from mouse enhanced green fluorescent protein-GnRH neurons, we found that the GABA(B) receptor agonist baclofen hyperpolarized GnRH neurons through activation of an inwardly rectifying K(+) current in a concentration-dependent manner. The effects of baclofen were antagonized by the selective GABA(B) receptor antagonist CGP 52432 with a K(i) (inhibitory constant) of 85 nm. Furthermore, in the presence of the GABA(A) receptor antagonist picrotoxin, GABA hyperpolarized GnRH neurons in a similar manner. Treatment with 17beta-estradiol as compared with oil vehicle did not significantly alter either the EC(50) for the baclofen-induced response (0.8 +/- 0.1 vs. 1.0 +/- 0.1 microM, respectively) or the maximal outward current (10.8 +/- 1.7 pA vs. 11.4 +/- 0.6 pA, respectively) in GnRH neurons. However, the outward current (and membrane hyperpolarization) was abrogated by submaximal concentrations of the G protein-coupled receptor 54 (GPR54) agonist kisspeptin-10 in both groups, indicating that G alpha(q)-coupled (GPR54) can desensitize the GABA(B) receptor-mediated response. Therefore, the activation of GABA(B) receptors in GnRH neurons may provide increased inhibitory tone during estrogen-negative feedback states that is attenuated by kisspeptin during positive feedback.

Tiagabine: efficacy and safety in partial seizures – current status

Tiagabine hydrochloride (TGB) is a selective gamma-aminobutyric acid (GABA) reuptake inhibitor. TGB is effective as an add-on medication in adults and children 12 years and older in the treatment of partial seizures. Results of nonrandomized add-on trials with TGB show treatment success with seizure reduction of at least 50% in 33% to 46% of patients. In newly diagnosed patients with partial epilepsy, TGB monotherapy was as effective as carbamazepine. Comedication with TGB elevates the risk of nonconvulsive status (7.8% vs 2.7% without TGB). The most common side effects include dizziness/lightheadedness, asthenia/lack of energy and somnolence. TGB has no negative effects on cognition; it does not increase the risk of fractures or rash. TGB may interfere with color perception. TGB presents an intermediate risk for depression in patients with epilepsy (approximately 4%). Regarding the risk of overdose, 96-680 mg TGB (mean 224 mg) caused seizures or coma. TGB is an antiepileptic drug exhibiting a specific anticonvulsive mechanism of action, the efficacy of which is relatively low when used in comedication. Critical side effects, such as the induction of nonconvulsive status epilepticus, further limit its use.

Tiagabine in Adult Patients With Generalized Anxiety Disorder

The objective of these studies was to evaluate the efficacy and tolerability of tiagabine, a selective gamma-aminobutyric acid reuptake inhibitor, in adult patients with generalized anxiety disorder (GAD). Patients with a diagnosis of GAD were enrolled in 1 of 3 randomized, placebo-controlled, 10-week studies. In each study, tiagabine was taken twice daily in divided doses--4, 8, or 12 mg/d in a fixed-dose study and 4-16 mg/d in two flexible-dose trials. The primary efficacy measure was the change from baseline in the 14-item Hamilton Rating Scale for Anxiety (HAM-A) total score at the final visit (last observation carried forward). Additional measures included change from baseline in the anxiety subscale of the Hospital Anxiety and Depression Scale, the Sheehan Disability Scale, and Clinical Global Impressions-Improvement scale. Tolerability was assessed via spontaneous reports as well as rating scales throughout the study period. In all 3 studies, there was no significant differentiation from placebo on the primary measure (change in HAM-A) for any tiagabine dose (P > 0.05). In the 2 flexible-dose studies, the tiagabine group showed improvements over time in the HAM-A that reached significance only in those patients who completed 10 weeks of treatment (study 2, P = 0.018; study 3, P = 0.036). The most common adverse events were dizziness, headache, nausea, fatigue, and somnolence. In conclusion, the results of these studies do not support the efficacy of tiagabine in adult patients with GAD.

Discriminative stimulus effects of tiagabine and related GABAergic drugs in rats

Tiagabine is an anticonvulsant drug which may also have sleep-enhancing properties. It acts by inhibiting reuptake at the gamma-aminobutyric acid (GABA) transporter (GAT-1). The aim of the study was to determine whether tiagabine acted as a discriminative stimulus and, if so, whether other GABAergic compounds would generalise to it. Rats were trained to discriminate tiagabine (30 mg/kg p.o.) from vehicle, and generalisation to drugs that modulate GABA was assessed. Gaboxadol (5-20 mg/kg p.o.), a selective extrasynaptic GABA A agonist, generalised to tiagabine, although the extent of the generalisation was inconclusive. Indiplon (1 mg/kg p.o.), a benzodiazepine-like hypnotic, also partially generalised to tiagabine, although zolpidem and S-zopiclone did not. Baclofen, a GABA B receptor agonist, and gabapentin, which increases synaptic GABA, did not generalise to tiagabine. (+)-Bicuculline (3 mg/kg i.p.), a GABA A receptor antagonist, blocked the tiagabine cue, but the less brain-penetrant salt form, bicuculline methochloride, had no effect. These data suggest that tiagabine generates a discriminative stimulus in rats, and provides a central GABA-mediated cue, but is distinct from the other GABAergic compounds tested.

Synaptic and cognitive abnormalities in mouse models of down syndrome: Exploring genotype‐phenotype relationships

Down syndrome (DS) is caused by trisomy of human chromosome 21. Because Ts65Dn and Ts1Cje mice are segmentally trisomic for a region of mouse chromosome 16, they genetically model DS and are used to study pathogenic mechanisms. Previously, we provided evidence for changes in both the structure and function of pre- and postsynaptic elements in the Ts65Dn mouse. Striking changes were evident in the size of the dendritic spines and in the ability to induce long-term potentiation (LTP) in the fascia dentata (FD). To explore the genetic basis for these changes, we examined Ts1Cje mice, which are trisomic for a completely overlapping but smaller segment of mouse chromosome 16. As in the Ts65Dn mouse, there was a regionally selective decrease in the density of dendritic spines ( approximately 12%), an increase in the size of spine heads ( approximately 26%), a decrease in the length of spine necks ( approximately 26%), and reorganization of inhibitory inputs with a relative decrease in inputs to dendrite shafts and spine heads and a significant increase to the necks of spines (6.4%). Thus, all of the Ts65Dn phenotypes were present, but they were significantly less severe. In contrast, and just as was the case for the Ts65Dn mouse, LTP could not be induced unless the selective gamma-aminobutyric acid (GABA)(A) receptor antagonist picrotoxin was applied. Therefore, there was conservation of important synaptic phenotypes in the Ts1Cje mice. The analysis of data from this and earlier studies points to genotype-phenotype linkages in DS whose complexity ranges from relatively simple to quite complex.

Tiagabine for social anxiety disorder

Tiagabine, a selective gamma-aminobutyric acid (GABA) reuptake inhibitor was evaluated for the treatment of patients with social anxiety disorder (SAD). Adults with SAD received open-label tiagabine 4-16 mg per day for 12 weeks. Intent-to-treat data are available for 54 patients with improvement demonstrated in Liebowitz Social Anxiety Scale, Clinician Global Impression-Severity (CGI-S) and -Improvement (CGI-I), Social Phobia Inventory, and Sheehan Disability Scale scores. In all, 40.7% (22/54) of the intent to treat sample and 63.0% (17/27) of the completer sample were considered CGI responders (CGI-I score of one or two). Tiagabine was generally well tolerated. Results of this pilot study suggest that tiagabine may be an option for the treatment of patients with SAD. Larger, controlled studies are required to fully elucidate the potential of tiagabine for the treatment of SAD.

The EEG effects of THIP (Gaboxadol) on sleep and waking are mediated by the GABAAδ‐subunit‐containing receptors

THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol, Gaboxadol) is a selective gamma-aminobutyric acid (GABA)(A) agonist, acting in vitro with high potency and efficacy at the extrasynaptic GABA(A)delta-containing receptors. THIP was suggested to be a potential hypnotic to treat insomnia, and it is currently in clinical trial. Here we assessed whether the GABA(A)delta-containing receptors mediate in vivo the effect of THIP on sleep and the sleep electroencephalogram (EEG). We performed EEG recordings in a mouse model deficient in the GABA(A)delta-subunit gene (delta(-/-) mice) and in wild-type littermate controls. THIP (4 and 6 mg/kg intraperitoneally) induced an abnormal EEG pattern, resulting in dramatic changes in the waking and non-rapid eye movement (NREM) sleep EEG spectra in wild-type mice. Indeed, a massive increase in EEG power lasting 2-3 h occurred in both the frontal and parietal derivation, especially in frequencies below 6 Hz. All effects were more prominent in the frontal EEG. Furthermore, the highest dose of THIP lengthened REM sleep latency and suppressed REM sleep. In contrast, vigilance states and sleep latencies were not affected in delta(-/-) mice. Moreover, only minor changes were observed in the NREM sleep EEG spectrum after THIP injection in the delta-subunit-deficient mice. The present findings do not indicate a sleep-promoting effect of THIP in mice, which is in accordance with a previous report in this species. Moreover, our results in vivo demonstrate that THIP acts preferentially at GABA(A) receptors containing the delta-subunit.

Evidence that GABA rho subunits contribute to functional ionotropic GABA receptors in mouse cerebellar Purkinje cells.

Ionotropic gamma-amino butyric acid (GABA) receptors composed of heterogeneous molecular subunits are major mediators of inhibitory responses in the adult CNS. Here, we describe a novel ionotropic GABA receptor in mouse cerebellar Purkinje cells (PCs) using agents reported to have increased affinity for rho subunit-containing GABA(C) over other GABA receptors. Exogenous application of the GABA(C)-preferring agonist cis-4-aminocrotonic acid (CACA) evoked whole-cell currents in PCs, whilst equimolar concentrations of GABA evoked larger currents. CACA-evoked currents had a greater sensitivity to the selective GABA(C) antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) than GABA-evoked currents. Focal application of agonists produced a differential response profile; CACA-evoked currents displayed a much more pronounced attenuation with increasing distance from the PC soma, displayed a slower time-to-peak and exhibited less desensitization than GABA-evoked currents. However, CACA-evoked currents were also completely blocked by bicuculline, a selective agent for GABA(A) receptors. Thus, we describe a population of ionotropic GABA receptors with a mixed GABA(A)/GABA(C) pharmacology. TPMPA reduced inhibitory synaptic transmission at interneurone-Purkinje cell (IN-PC) synapses, causing clear reductions in miniature inhibitory postsynaptic current (mIPSC) amplitude and frequency. Combined application of NO-711 (a selective GABA transporter subtype 1 (GAT-1) antagonist) and SNAP-5114 (a GAT-(2)/3/4 antagonist) induced a tonic GABA conductance in PCs; however, TPMPA had no effect on this current. Immunohistochemical studies suggest that rho subunits are expressed predominantly in PC soma and proximal dendritic compartments with a lower level of expression in more distal dendrites; this selective immunoreactivity contrasted with a more uniform distribution of GABA(A) alpha1 subunits in PCs. Finally, co-immunoprecipitation studies suggest that rho subunits can form complexes with GABA(A) receptor alpha1 subunits in the cerebellar cortex. Overall, these data suggest that rho subunits contribute to functional ionotropic receptors that mediate a component of phasic inhibitory GABAergic transmission at IN-PC synapses in the cerebellum.