Gamma-aminobutyric Acid Reuptake Inhibitor Research Articles

Central GABAA Receptors Provoke Inflammatory and Cardiovascular Consequences of Endotoxemia in Conscious Rats

Gamma‐aminobutyric acid (GABA), the principal brain inhibitory neurotransmitter, plays a key role in inflammatory and neurodegenerative disease. In this study, we tested the hypothesis that central GABAergic neurotransmission mediates the detrimental inflammatory, hemodynamic, and cardiac autonomic actions of endotoxemia. The effects of drugs that block GABA receptors or interfere with GABA uptake or degradation on blood pressure (BP), heart rate (HR), and HR variability (HRV) responses elicited by i.v. lipopolysaccharide (LPS) were assessed in conscious rats. The BP lowering effect of LPS (10 mg/kg) was blunted after intracisternal (i.c.) administration of bicuculline (GABAA receptor antagonist, 3 μg/rat) or saclofen (selective GABAB receptor antagonist, 50 μg/rat). By contrast, the concomitant LPS‐evoked tachycardia and decreases in time‐ and frequency domain indices of HRV, measures of cardiac autonomic control, were abolished upon treatment with bicuculline but not saclofen. The increases in serum tumor necrosis factor‐α and interleukin‐6 caused by LPS disappeared in rats treated concurrently with bicuculline or saclofen, whereas the LPS‐evoked increases in serum nitric oxide metabolites was reversed by bicuculline only. We also report that none of the effects of endotoxemia was altered in rats treated with i.c. tiagabine (GABA reuptake inhibitor, 100 μg/rat) or vigabatrin (GABA transaminase inhibitor, 200 μg//rat). These data suggest a major role for central GABAA receptors in the inflammatory and cardiovascular effects of endotoxemia.Support or Funding InformationSupported by the Science and Technology Development Fund, Egypt (STDF Grant No. 14895).

Novel gamma-aminobutyric acid reuptake inhibitor improves spatial learning and memory in Morris water maze and radial arm water maze tests

Novel gamma-aminobutyric acid reuptake inhibitor improves spatial learning and memory in Morris water maze and radial arm water maze tests

Diverse effects of GABA-mimetic drugs on cocaine-evoked self-administration and discriminative stimulus effects in rats

Recent data indicate that gamma-aminobutyric acid (GABA) is a modulator of behavioral responses to cocaine. The efficacy of gabapentin (a cyclic GABA analogue), tiagabine (a GABA reuptake inhibitor), or vigabatrin (an inhibitor of GABA transaminase and reuptake) to alter cocaine-seeking behavior and discriminative effects was examined in rats. Rats were trained to press a lever for cocaine (0.5 mg/kg per infusion) paired with a cue (light + tone) using a fixed ratio (FR) 5 schedule of reinforcement. After extinction, the cocaine-seeking behavior was reinstated by cocaine priming (10 mg/kg). Another group of rats was trained to discriminate cocaine (10 mg/kg) from saline in a two-lever FR 20 task. Vigabatrin (150-250 mg/kg) decreased cocaine-maintained responding, whereas tiagabine (10 mg/kg) significantly reduced responses on the "active" lever. Vigabatrin (150-250 mg/kg) significantly decreased responding to the cocaine-priming dose and a nonsignificant attenuation of cocaine-induced reinstatement was seen after tiagabine (5-10 mg/kg). Gabapentin (10-30 mg/kg) failed to alter maintenance of cocaine self-administration or drug-induced reinstatement. Pretreatment with either gabapentin, tiagabine, or vigabatrin resulted in neither reinstatement of cocaine seeking nor alterations in cocaine discrimination. Our study demonstrates that vigabatrin (only at the 150 mg/kg dose) exerted inhibitory actions on cocaine-maintained responding and attenuated the reinstatement of extinguishing responding more effectively than gabapentin or tiagabine and with less evidence of motor impairment than the latter drugs. Present findings do not support a role for gabapentin or tiagabine for the possible treatment of cocaine relapse, whereas albeit limited effects of vigabatrin may be seen.

Open-Label Tiagabine Monotherapy for Major Depressive Disorder With Anxiety

Gamma-aminobutyric acid (GABA) plays a key role in the pathophysiology and treatment of depression and anxiety. Tiagabine, a selective GABA reuptake inhibitor (SGRI) that enhances normal GABA tone, was evaluated for its efficacy and safety in the treatment of depression comorbid with significant anxiety. In this 8-week, single-center, open-label study, adults with DSM-IV-diagnosed major depressive disorder and significant anxiety (i.e., "anxious depression") received tiagabine monotherapy, initiated at 4 mg/day and titrated for optimum response as tolerated to a maximum dose of 20 mg/day. Symptoms, function, and adverse events were assessed at regular intervals. Patients were entered from April 2002 to February 2003. Nineteen patients entered the study and 15 met criteria for intent-to-treat analyses. Of those, 6 (40%) discontinued treatment and 9 (60%) completed the 8-week protocol. Tiagabine significantly improved depression, as shown by a reduction in mean +/- SD Hamilton Rating Scale for Depression scores from baseline (31.9 +/- 6.1) to endpoint (17.0 +/- 12.4; p = .002). Categorical response rate was 47% (N = 7). Tiagabine also significantly improved anxiety (Hamilton Rating Scale for Anxiety baseline score of 22.7 +/- 4.9 vs. endpoint score of 12.5 +/- 8.8; p = .002). The mean +/- SD final daily dose was 12.8 +/- 5.8 mg. The most commonly reported adverse events were dizziness, headache, and gastrointestinal upset/nausea. These results suggest the potential of the SGRI tiagabine in the treatment of depression with anxiety. Large, placebo-controlled trials are needed.

Tiagabine for posttraumatic stress disorder: effects of open-label and double-blind discontinuation treatment

Preliminary results suggest a potential benefit of agents that enhance gamma-aminobutyric acid (GABA) neurotransmission in treating posttraumatic stress disorder (PTSD). It is the aim of this study to evaluate the effect of a selective GABA reuptake inhibitor (SGRI), tiagabine, in patients with PTSD. Twenty-nine adult outpatients with PTSD were treated with open-label tiagabine for 12 weeks. Those who responded to treatment (i.e., demonstrated at least minimal clinical improvement) were randomly assigned to double-blind treatment with either tiagabine or matching placebo. Efficacy assessments included measures of PTSD, anxiety, depression, sleep quality, resilience, and disability. Safety evaluation included changes in vital signs and weight and treatment-emergent adverse events. In subjects completing open-label treatment (n=19), significant improvement was observed on all outcome measures (P<0.05) and the treatment was well tolerated. Eighteen subjects responded and were randomized into the double-blind phase. Following randomization, benefits of treatment were generally upheld, but there was no greater incidence of relapse in the placebo group. However, continued treatment with tiagabine was associated with a greater trend toward likelihood of remission than if one was switched to placebo (P<0.08). These findings suggest a possible role for the SGRI tiagabine in the treatment of PTSD. As the role of GABAergic drugs in PTSD is poorly defined, larger, randomized, double-blind, placebo-controlled trials are needed.

The Selective GABA Reuptake Inhibitor Tiagabine for the Treatment of Generalized Anxiety Disorder

To evaluate the efficacy and tolerability of tiagabine, a selective gamma-aminobutyric acid (GABA) reuptake inhibitor, in adults with generalized anxiety disorder (GAD). This 8-week, randomized, double-blind, multicenter, placebo-controlled study enrolled patients with GAD (DSM-IV). Tiagabine was initiated at 4 mg/day and then flexibly dosed twice a day to a maximum dose of 16 mg/day. Study drug was tapered after week 8 in decrements of 2 mg every other day. Efficacy assessments included the Hamilton Rating Scale for Anxiety (HAM-A) and Sheehan Disability Scale. Adverse events, sexual functioning, and change in depressive symptoms were monitored. Data were collected from May 2003 to January 2004. A total of 266 patients (tiagabine, N = 134; placebo, N = 132) were included in safety analyses; 260 patients (tiagabine N = 130; placebo N = 130) were included in efficacy analyses. Tiagabine reduced symptoms of GAD according to the observed case and mixed models repeated-measures (MMRM) analyses but not the primary last-observation-carried-forward (LOCF) analysis. At final visit, the reduction from baseline in mean HAM-A total score was 11.8 for tiagabine, compared with 10.2 for placebo (LOCF analysis, p = .27). In a post hoc MMRM analysis, a significant difference in the mean reduction in HAM-A total score over the efficacy evaluation period was found, favoring tiagabine over placebo (p < .01). Tiagabine had an early onset of effect, as shown by significant reduction from baseline in mean HAM-A total score compared with placebo at week 1 (observed cases, p < .05). Tiagabine was generally well tolerated and not associated with changes in sexual functioning or depressive status. Symptoms of a discontinuation syndrome during taper were not observed. The primary LOCF analysis was negative; however, results from the observed case and MMRM analyses suggest that tiagabine may be a useful treatment option for adult patients diagnosed with GAD. These findings warrant further evaluation in randomized clinical studies.

Effects of GABAergic modulators on food and cocaine self-administration in baboons

Drugs that indirectly alter dopaminergic systems may alter the reinforcing effects of cocaine. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) has extensive neural connections in mesolimbic regions that appear to modulate dopamine. The current study evaluated the effects of GABA B receptor agonists baclofen and CGP44532, the benzodiazepine agonist alprazolam, and the GABA reuptake inhibitor tiagabine on lever responding maintained by low dose cocaine injections (0.032 mg/kg) or by food pellet (1 g) delivery in baboons. The benzodiazepine antagonist flumazenil was tested as a negative control. Cocaine or food was available under a fixed ratio (FR 10) schedule of reinforcement during daily 2-h sessions. During baseline conditions, cocaine and pellets maintained similar numbers of reinforcers per session. Baclofen, CGP44532 and tiagabine dose-dependently reduced the number of cocaine injections, where as the benzodiazepine antagonist flumazenil did not. Baclofen, CGP44532 and tiagabine also produced dose-related decreases in food-maintained behavior. In contrast, the benzodiazepine agonist alprazolam, which positively modulates GABA A receptors via the benzodiazepine site, produced decreases in cocaine self-injection, but not food-maintained behavior. Thus, the effects of alprazolam were specific for cocaine-maintained behavior, where as the effects of baclofen and CGP44532 were not.

An Open-label Study of Tiagabine as Augmentation Therapy for Anxiety

At least 50% of patients with anxiety disorders experience only partial response to pharmacotherapy and require augmentation therapy. Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the CNS, and agents that modulate GABA neurotransmission have shown promise in the treatment of anxiety disorders and are often used as augmentation agents. This study evaluated tiagabine, a selective GABA reuptake inhibitor (SGRI), as augmentation therapy. This 8-week, open-label study enrolled patients who remained symptomatic despite adequate drug trials for treatment of anxiety symptoms. Tiagabine augmentation therapy was initiated at 4 mg/d (taken in 2 doses; one in the morning with breakfast and one in the evening with a snack) for 2 days and increased to 8 mg/d for 10 days. Dose was then adjusted according to efficacy/tolerability in increments of 2 mg every 3 days up to a maximum of 20 mg/d. Effect was assessed using the Hamilton Rating Scale for Anxiety (HAM-A), Beck Anxiety Inventory (BAI), Clinical Global Impression (CGI) scale, Pittsburgh Sleep Quality Index (PSQI), and 36-item Short-Form Health Survey (SF-36). Of the 18 patients enrolled, 17 were included in the efficacy analysis; one withdrew due to an adverse event prior to post-baseline assessment. Mean final dose of tiagabine was 13 mg/d. Tiagabine as augmentation therapy further reduced anxiety symptoms, as shown by significant decreases in mean HAM-A total and BAI scores at Week 8 (P<0.001). Thirteen patients (76%) responded (> or =50% reduction in HAM-A total score), and 10 patients (59%) achieved remission (HAM-A total score < or =7) at Week 8. Tiagabine improved sleep quality, with a significant reduction seen in PSQI global score at Week 8 (P=.001). Augmentation therapy with tiagabine was generally well tolerated. These preliminary findings suggest that the SGRI tiagabine may be an effective and generally well tolerated augmentation therapy in patients with anxiety who remain symptomatic despite adequate drug trials for treatment of anxiety symptoms.

Effects Of Tiagabine, A γ-Aminobutyric Acid Re-Uptake Inhibitor, on Normal Rat Bladder Function

Previous reports have demonstrated the inhibitory effect of exogenous gamma-aminobutyric acid (GABA) on micturition. In the current study we tested whether tiagabine (Sanofi Synthelab., Newcastle-upon Tyne, United Kingdom), a GABA re-uptake inhibitor increasing endogenous GABA concentrations, would affect micturition in awake rats or influence rat detrusor contraction in vitro. Nonanesthetized female Sprague-Dawley rats underwent cystometric investigation in a metabolic cage. Micturition was stimulated by infusing saline intravesically. Micturition parameters were recorded and compared before and after drug administration. In vitro the effects of tiagabine on electrical and carbachol induced contractions in bladder strips were investigated. Furthermore, it was studied whether tiagabine interfered with electrically induced release of acetylcholine. Intravenous administration of 5 and 20 mg. kg.-1 tiagabine in 7 and 9 rats decreased micturition pressure a mean plus or minus standard error of mean of 21% +/- 11% and 42% +/- 9%, and decreased voided volume a mean of 31% +/- 9% and 33% +/- 9%, respectively. At 20 mg. kg.-1 tiagabine intravenously increased post-void residual volume a mean of 300% +/- 120% and decreased bladder capacity a mean of 14% +/- 3%. Tiagabine (100 microg.) intrathecally in 7 rats reduced micturition pressure a mean of 34% +/- 10% and increased bladder capacity a mean of 30% +/- 9% and post-void residual volume a mean of 250% +/- 75%. However, voided volume was not changed. In vitro studies demonstrated that tiagabine attenuated bladder contractions induced by electrical field stimulation to a mean of 69% +/- 6% of controls at 100 microM. but did not affect contractions induced by carbachol. Release studies revealed that tiagabine inhibited electrical induced acetylcholine release to a mean of 82% +/- 5% of controls at 100 microM. The current results show that tiagabine has an inhibitory action on rat micturition. The site of action may be central and peripheral.

Gamma-Aminobutyric acidA receptor pharmacology in rat cerebral cortical synaptoneurosomes.

Equilibrium binding interactions at the gamma-aminobutyric acid (GABA) and benzodiazepine recognition sites on the GABAA receptor-Cl- ionophore complex were studied using a vesicular synaptoneurosome (microsacs) preparation of rat brain in a physiological HEPES buffer similar to that applied successfully in recent GABAergic 36Cl- flux measurements. NO 328, a GABA reuptake inhibitor, was included in the binding assays to prevent the uptake of [3H]muscimol. Under these conditions, the equilibrium dissociation constant (KD) values for [3H]muscimol and [3H]diazepam bindings are 1.9 microM and 40 nM, respectively. Binding affinities for these and other GABA and benzodiazepine agonists and antagonists correlate well with the known physiological doses required to elicit functional activity. This new in vitro binding protocol coupled with 36Cl- flux studies should prove to be of value in reassessing the pharmacology of the GABAA receptor complex in a more physiological environment.