Diazepam increases gamma-aminobutyric acid in human cerebrospinal fluid

Impacts of chronic exposure to sublethal diazepam on behavioral traits of female and male zebrafish (Danio rerio)

Residues of the psychoactive drug diazepam (DZP) may pose potential risks to fish in aquatic environments, especially by disrupting their behavioral traits. In this study, female and male zebrafish were subjected to chronic exposure (21 days) to sublethal doses (120 and 12 µg/L) of DZP, aimed to compare the characteristics of their behavioral responses to DZP exposure, and to investigate the possible links between those behavioral responses and variations in their brain γ-aminobutyric acid (GABA) and acetylcholinesterase (AChE) levels. Chronic exposure to DZP significantly decreased the swimming velocity and locomotor activity of both genders, indicating a typical sedative effect. Compared with males, whose locomotor activity was only significantly decreased by exposure to DZP for 21 days, females became hypoactive on day 14 (i.e., more sensitive), and they developed tolerance to the hypoactive effect induced by 120 μg/L DZP by day 21. Exposure to DZP significantly disturbed the behavioral traits related to social interactions in females but not in males. Those results indicate that DZP exhibits sex-dependent effects on the behaviors of fish. Moreover, exposure to DZP for 21 days significantly disturbed almost all of the tested behavioral traits associated with courtship when both genders were put together. Sex-dependent responses in brain GABA and AChE levels due to DZP exposure were also identified. Significant relationships between the brain GABA/AChE levels and some behavioral parameters related to locomotor activity were detected in females, but not in males.

Short-term and persistent impacts of sublethal exposure to diazepam on behavioral traits and brain GABA levels in juvenile zebrafish (Danio rerio)

Environmental pollution by the psychoactive drug diazepam (DZP) has been suggested to disrupt various behavioral traits of fishes. Exposure to DZP in natural waters may be of episodic duration, but there are few reports on the persistence of abnormal behaviors of fishes caused by such acute exposure. In the current study, we exposed juvenile zebrafish (Danio rerio) to sublethal doses of DZP (1200, 120, and 12 μg/L) for four days and evaluated their behavioral traits and brain γ-aminobutyric acid (GABA) levels at days 0 (i.e., immediately after the 4-day exposure), 7, and 21 of the recovery period. Exposure to DZP induced short-term impairment of swimming ability and two-fish interactions of zebrafish. In contrast, DZP induced persistent and/or delayed effects on locomotor activity of zebrafish, i.e., hypoactivity at 1200 μg/L and hyperactivity at 120 and 12 μg/L, that could be still observed on days 7 and/or 21 during the recovery period. DZP exposure also exhibited concentration-specific effects on brain GABA levels in zebrafish, i.e., decreased at 1200 μg/L and increased at 120 and 12 μg/L. Correlation analysis suggested that the changes in brain GABA levels may contribute to the persistence of abnormalities in the locomotor activity of zebrafish. Our findings suggest that zebrafish need a long time to recover from acute exposure to DZP, thus highlighting that the persistence of behavioral abnormalities induced by such psychoactive drugs should be considered in order to better assess their risks in natural ecosystems.

Clobazam monotherapy for focal or generalized seizures

BACKGROUND

This is an updated version of the original Cochrane Review published in Issue 10, 2014. There is a need to expand monotherapy options available to a clinician for the treatment of new focal or generalized seizures. A Cochrane systematic review for clobazam monotherapy is expected to define its place in the treatment of new-onset or untreated seizures and highlight gaps in evidence.

OBJECTIVES

To evaluate the efficacy, effectiveness, tolerability and safety of clobazam as monotherapy in people with new-onset focal or generalized seizures.

SEARCH METHODS

For the latest update we searched the following databases on 19 March 2018: the Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group Specialized Register and the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid, 1946- ), BIOSIS Previews (1969- ), ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform (ICTRP). There were no language restrictions.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials comparing clobazam monotherapy versus placebo or other anti-seizure medication in people with two or more unprovoked seizures or single acute symptomatic seizure requiring short-term continuous anti-seizure medication, were eligible for inclusion.

DATA COLLECTION AND ANALYSIS

Primary outcome measure was time on allocated treatment (retention time), reflecting both efficacy and tolerability. Secondary outcomes included short- and long-term effectiveness measures, tolerability, quality of life, and tolerance measures. Two authors independently extracted the data.

MAIN RESULTS

We identified three trials fulfilling the review criteria, which included 206 participants. None of the identified studies reported the preselected primary outcome measure. A meta-analysis was not possible. Lack of detail regarding allocation concealment and a high risk of performance and detection bias in two studies prompted us to downgrade the quality of evidence (by using the GRADE approach) for some of our results due to risk of bias.Regarding retention at 12 months, we detected no evidence of a statistically significant difference between clobazam and carbamazepine (risk ratio (RR) 0.83, 95% confidence interval (CI) 0.61 to 1.12; low-quality evidence). There was low-quality evidence that clobazam led to better retention compared with phenytoin (RR 1.43, 95% CI 1.08 to 1.90). We could not determine whether participants receiving clobazam were found to be less likely to discontinue it due to adverse effects as compared to phenytoin (RR 0.10, 95% CI 0.01 to 1.65, low-quality evidence).

AUTHORS' CONCLUSIONS

We found no advantage for clobazam over carbamazepine for retention at 12 months in drug-naive children and a slight advantage of clobazam over phenytoin for retention at six months in adolescents and adults with neurocysticercosis in a single clinical trial each. At present, the available evidence is insufficient to inform clinical practice.

CSF GABA is reduced in first-episode psychosis and associates to symptom severity

Schizophrenia is characterized by a multiplicity of symptoms arising from almost all domains of mental function. γ-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the brain and is increasingly recognized to have a significant role in the pathophysiology of the disorder. In the present study, cerebrospinal fluid (CSF) concentrations of GABA were analyzed in 41 first-episode psychosis (FEP) patients and 21 age- and sex-matched healthy volunteers by high-performance liquid chromatography. We found lower CSF GABA concentration in FEP patients compared with that in the healthy volunteers, a condition that was unrelated to antipsychotic and/or anxiolytic medication. Moreover, lower CSF GABA levels were associated with total and general score of Positive and Negative Syndrome Scale, illness severity and probably with a poor performance in a test of attention. This study offers clinical in vivo evidence for a potential role of GABA in early-stage schizophrenia.

Clobazam monotherapy for partial-onset or generalized-onset seizures

BACKGROUND

There is a need to expand monotherapy options available to a clinician for the treatment of new partial-onset or generalized-onset seizures. A Cochrane systematic review for clobazam monotherapy is expected to define its place in the treatment of new-onset or untreated seizures and highlight gaps in evidence.

OBJECTIVES

To evaluate the efficacy, effectiveness, tolerability and safety of clobazam as monotherapy in people with new-onset partial or generalized seizures.

SEARCH METHODS

We searched the following databases: Cochrane Epilepsy Group Specialized Register (5 March 2013), Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, January 2013, Issue 1), MEDLINE (Ovid, 1946 to July 1, 2014), Database of Abstracts of Reviews of Effectiveness (DARE, January 2013, Issue 1), BIOSIS Previews (all years, searched on 5 March 2013). There were no language restrictions.

SELECTION CRITERIA

Randomized or quasi-randomised controlled trials comparing clobazam monotherapy versus placebo or other anti-seizure medication in people with two or more unprovoked seizures or single acute symptomatic seizure requiring short-term continuous anti-seizure medication, were eligible for inclusion.

DATA COLLECTION AND ANALYSIS

Primary outcome measure was time on allocated treatment (retention time), reflecting both efficacy and tolerability. Secondary outcomes included short- and long-term effectiveness measures, tolerability, quality of life, and tolerance measures. Two authors independently extracted the data.

MAIN RESULTS

We identified two trials fulfilling the review criteria, which included 163 participants. None of the identified studies reported the preselected primary outcome measure. A meta-analysis was not possible. Lack of detail regarding concealment of allocation and a high risk of performance and detection bias in one study prompted us to downgrade the quality of evidence for some of our results due to risk of bias.Regarding retention at 12 months, we detected no evidence of a statistically significant difference between clobazam and carbamazepine (risk ratio (RR) 0.83, 95% confidence interval (CI) 0.61 to 1.12); low quality evidence. There was low quality evidence that clobazam led to better retention compared with phenytoin (RR 1.43, 95% CI 1.08 to 1.90). We could not determine whether participants receiving clobazam were found to be less likely to discontinue it due to adverse effects as compared to phenytoin (RR 0.10, 95% CI 0.01 to 1.65, low quality evidence).

AUTHORS' CONCLUSIONS

We found no advantage for clobazam over carbamazepine for retention at 12 months in drug-naïve children and a slight advantage of clobazam over phenytoin for retention at six months in adolescents and adults with neurocysticercosis in a single clinical trial each. At present, the available evidence is insufficient to inform clinical practice.

Cerebrospinal fluid GABA concentration: relationship with impulsivity and history of suicidal behavior, but not aggression, in human subjects

The objective of this study was to assess the relationship between cerebrospinal fluid concentrations of the neurotransmitter gamma-aminobutyric acid (GABA) and measures of impulsivity and related behaviors (aggression and suicidality) in healthy volunteer and personality disordered subjects. CSF GABA levels, and measures of impulsivity, aggression, and history of suicidal behavior were obtained by morning lumbar puncture in 57 healthy volunteer subjects and in subjects with personality disorder. CSF GABA levels were not found to correlate with measures of aggression but were found to correlate directly with measures of impulsivity; e.g., a composite measure of impulsivity in all subjects (r=0.35, df=46, P=0.015) and in personality disordered subjects examined separately (r=0.39, df=30, P=0.029). In the personality disorder group, CSF GABA levels were higher among subjects with a history of suicidal behavior compared with those without this history. These data suggest that central GABAergic function correlates directly with impulsiveness and history of suicidal behavior, but not aggressiveness, in personality disordered subjects. This may be consistent with observations that high doses of benzodiazepines can lead to "behavioral disinhibition" in human subjects. Further work assessing this and other aspects of the central GABA system in personality disordered subjects are warranted.

Effects of acute tiagabine administration on aggressive responses of adult male parolees

Experimental and clinical studies have supported a relationship between gamma-aminobutyric acid (GABA) and aggressive behavior in non-humans and humans. Tiagabine is a GABA uptake inhibitor that has been shown to produce acute behavioral effects in animals. In addition, tiagabine has been shown to decrease aggression in agitated patients when administered chronically. The present study was designed to investigate the effects of acute administration of tiagabine on aggressive responding on a laboratory task in adult humans. Ten adult males participated in experimental sessions on the Point Subtraction Aggression Paradigm (PSAP), which provided subjects with aggressive, escape, and monetary-reinforced response options. All subjects received four acute oral doses of Tiagabine (4, 8, 12 and 16 mg) separated by placebo sessions. Tiagabine decreased aggression at doses that either did not affect, or affected to a lesser extent, monetary-reinforced responding. The results are consistent with some prior research using the PSAP showing a possible unique role for GABA in the regulation of human aggression. A possible behavioral mechanism for the rate-decreasing effects on aggressive responding produced in the present study is that tiagabine may modify aggressive responding by suppressing reactions to aversive stimuli.

Effects of drugs acting on the GABA-benzodiazepine receptor complex on flurothyl-induced seizures in Mongolian gerbils

In the present study, the mechanism behind flurothyl-induced seizures was examined using drugs acting on the GABA-benzodiazepine receptor complex in Mongolian gerbils. In addition, amino acid concentrations in the brain were also investigated. In behavioral experiments, the incidence of tonic extensor was 83.3% in both the control and picrotoxin (0.5 mg/kg)-treated groups, 0% in the valproate (200 mg/kg)-treated group, and 50% in the picrotoxin plus valproate-treated group. However, picrotoxin did not antagonize the effect of valproate on clonic seizure latency at all. Flumazenil, a benzodiazepine receptor antagonist, was found to have an inhibitory effect on the anticonvulsant action of diazepam (0.5 mg/kg). The incidence of tonic extensor was 83.3% in flumazenil (10 mg/kg)-treated group, 0% in the diazepam (0.5 mg/kg)-treated group, and 83% in the flumazenil plus diazepam-treated group as well as the control group. Flumazenil also completely reversed the effect of diazepam on clonic seizure latency. In biochemical experiments, the concentration of the inhibitory amino acid, GABA, was significantly increased in the hippocampus (P<0.05) and cerebellum (P<0.01) in diazepam-treated animals. The increase of GABA in the hippocampus and cerebellum was antagonized by the administration of flumazenil. These results suggested that the anticonvulsant action of diazepam may be linked to increase in hippocampus and cerebellum GABA concentrations. The findings suggest that the mechanism of flurothyl-induced seizures, in part, is related to the highly sensitive benzodiazepine site of the GABA-benzodiazepine receptor complex.

Multiple synaptic and membrane sites of anesthetic action in the CA1 region of rat hippocampal slices

BACKGROUND

Anesthesia is produced by a depression of central nervous system function, however, the sites and mechanisms of action underlying this depression remain poorly defined. The present study compared and contrasted effects produced by five general anesthetics on synaptic circuitry in the CA1 region of hippocampal slices.

RESULTS

At clinically relevant and equi-effective concentrations, presynaptic and postsynaptic anesthetic actions were evident at glutamate-mediated excitatory synapses and at GABA-mediated inhibitory synapses. In addition, depressant effects on membrane excitability were observed for CA1 neuron discharge in response to direct current depolarization. Combined actions at several of these sites contributed to CA1 circuit depression, but the relative degree of effect at each site was different for each anesthetic studied. For example, most of propofol's depressant effect (> 70 %) was reversed with a GABA antagonist, but only a minor portion of isoflurane's depression was reversed (< 20 %). Differences were also apparent on glutamate synapses-pentobarbital depressed transmission by > 50 %, but thiopental by only < 25 %.

CONCLUSIONS

These results, in as much as they may be relevant to anesthesia, indicate that general anesthetics act at several discrete sites, supporting a multi-site, agent specific theory for anesthetic actions. No single effect site (e.g. GABA synapses) or mechanism of action (e.g. depressed membrane excitability) could account for all of the effects produced for any anesthetic studied.

GABAergic dysfunction in mood disorders

The authors review the available literature on the preclinical and clinical studies involving GABAergic neurotransmission in mood disorders. Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter present almost exclusively in the central nervous system (CNS), distributed across almost all brain regions, and expressed in interneurons modulating local circuits. The role of GABAergic dysfunction in mood disorders was first proposed 20 years ago. Preclinical studies have suggested that GABA levels may be decreased in animal models of depression, and clinical studies reported low plasma and CSF GABA levels in mood disorder patients. Also, antidepressants, mood stabilizers, electroconvulsive therapy, and GABA agonists have been shown to reverse the depression-like behavior in animal models and to be effective in unipolar and bipolar patients by increasing brain GABAergic activity. The hypothesis of reduced GABAergic activity in mood disorders may complement the monoaminergic and serotonergic theories, proposing that the balance between multiple neurotransmitter systems may be altered in these disorders. However, low GABAergic cortical function may probably be a feature of a subset of mood disorder patients, representing a genetic susceptibility. In this paper, we discuss the status of GABAergic hypothesis of mood disorders and suggest possible directions for future preclinical and clinical research in this area.

Positive and negative modulation of the GABA(A) receptor and outcome after traumatic brain injury in rats

Glutamate-mediated excitotoxicity has been shown to contribute to cellular dysfunction following traumatic brain injury (TBI). Increasing inhibitory function through stimulation of gamma-aminobutyric acid (GABA(A)) receptors may attenuate excitotoxic effects and improve outcome. The present experiment examined the effects of diazepam, a positive modulator at the GABA(A) receptor, on survival and cognitive performance in traumatically brain-injured animals. In experiment 1, 15 min prior to central fluid percussion brain injury, rats (n=8 per group) were injected (i.p.) with saline or diazepam (5 mg/kg or 10 mg/kg). Additional rats (n=8) were surgically prepared but not injured (sham-injury). Rats pre-treated with the 5 mg/kg dose of diazepam had significantly lower mortality (0%) than injured, saline-treated rats (53%). Also, diazepam-treated (5 mg/kg) rats had significantly shorter latencies to reach the goal platform in the Morris water maze test performed 11-15 days post-injury. In experiment 2, at 15 min post-injury, rats were given either saline (n=5) or 5 mg/kg diazepam (n=6). Rats treated with diazepam did not differ in mortality from injured rats treated with vehicle. However, rats treated with diazepam at 15 min post-injury had significantly shorter latencies to reach the goal platform in the Morris water maze than injured, vehicle-treated rats. In experiment 3, the post-injury administration of bicuculline (1.5 mg/kg, n=8), a GABA(A) antagonist, increased Morris water maze goal latencies compared to injured animals treated with saline (n=8). These results suggest that enhancing inhibitory function during the acute post-injury period produces beneficial effects on both survival and outcome following experimental TBI.

The pharmacologic basis of antiepileptic drug action

The development of medications used in the treatment of epilepsy has accelerated over the past decade, and has benefited from a parallel growth in our knowledge of the basic mechanisms underlying neuronal excitability and synchronization. This understanding of the pharmacologic basis of antiepileptic drug (AED) action has, in large part, arisen from recent advances in cellular and molecular biology, coupled with avenues of drug discovery that have departed somewhat from the largely empiric approaches of the past. Physicians now have available to them an ever-growing armentarium of AEDs, necessitating a firmer appreciation of their mechanisms of action if more rational approaches toward both clinical application and research are to be adopted. An important example in this regard is the concept of rational polypharmacy for patients with epilepsy who are refractory to monotherapy. This review summarizes our current understanding of the molecular targets of clinically significant AEDs, comparing and contrasting their differing mechanisms of action.

Effect of diazepam on plasma gamma-aminobutyric acid in sons of alcoholic fathers

A subgroup of abstinent alcoholics, display low levels of plasma gamma-aminobutyric acid (GABA). Two previous studies of plasma GABA in sons of alcoholic fathers (SOAs) have yielded conflicting results. The aim of the current study was to measure plasma GABA both at baseline and after challenge with diazepam, a GABAA receptor agonist, in a group of SOAs already shown to display decreased eye movement, memory, and sedative effects of diazepam. Twenty-seven SOAs and 23 male control subjects received four logarithmically increasing doses of diazepam or placebo in randomized order on 2 days at least 1 week apart. Plasma GABA was measured at baseline and after the last dose. There were no significant differences between SOAs and controls in baseline plasma GABA levels. In the whole sample, there were significant correlations between baseline plasma GABA and both high novelty-seeking and low-harm avoidance scores on the Tridimensional Personality Questionnaire. Both SOAs and controls displayed decreases in plasma GABA over time on both testing days, but there was no effect of diazepam on plasma GABA and no significant difference between groups in plasma GABA response to diazepam. These results suggest that neither low plasma GABA at baseline nor altered plasma GABA response to diazepam is associated with increased genetic risk for alcoholism.

Levels of gamma-aminobutyric acid in cerebrospinal fluid and plasma during alcohol withdrawal

Aminobutyric acid (GABA) is implicated in the biochemical pathophysiology of alcohol intoxication, dependence and withdrawal. We therefore measured GABA in both cerebrospinal fluid (CSF) and plasma from 14 male alcohol-dependent patients during acute alcohol withdrawal (day 1) and again after 21 days of inpatient treatment (day 21). Plasma GABA levels on admission correlated with indices of liver function. When corrected for differences in liver function, plasma levels of GABA levels on day 1 were significantly higher than on day 21. CSF GABA concentrations were also significantly higher during withdrawal compared with concentrations after 3 weeks of abstinence. The change in plasma GABA levels correlated significantly with the change in CSF GABA levels, although there was no correlation between plasma and CSF levels at either time. These findings demonstrate that changes in CSF GABA may be reflected in plasma GABA, and they highlight the potential importance of the GABA system in alcohol dependence and withdrawal.

Treatment of aggressive children with clonidine: results of an open pilot study

Seventeen aggressive children (14 boys and 3 girls) aged 5 to 15 years, who were characterized by cruel behavior to others and destruction of property, entered an open pilot study using clonidine to evaluate its efficacy and safety and drug-induced changes in plasma gamma aminobutyric acid (GABA). Aggression decreased in 15 children with minimal side effects. In five cases, GABA increased from 105.4 +/- 15.2 ng/mL at baseline to 125.2 +/- 10.8 ng/mL at follow-up (p < 0.01). A sixth patient was noncompliant. These findings suggest that GABA may be correlated with childhood aggressiveness and may be a useful marker of drug compliance. Pharmacotherapy with clonidine should be further assessed for the control of aggression.

Milacemide effects on the temporal inter-relationship of amino acids and monoamine metabolites in rat cerebrospinal fluid

The temporal inter-relationship of various amino acids and monoamine metabolites in rat cerebrospinal fluid was examined after acute administration of milacemide (100, 200 or 400 mg/kg i.p.), a glycine prodrug. Glycine concentrations rose linearly and dose dependently (20-190%) but were only significantly elevated at the higher milacemide dose (200 and 400 mg/kg). In animals given 400 mg/kg, glycine values were still significantly elevated 8 h later. A concomitant increase (20-25%) in serine and taurine and a decrease in alanine cerebrospinal fluid values were observed at the highest milacemide dose. Other amino acids were unaffected. While cerebrospinal fluid 5-hydroxyindoleacetic acid concentrations were unaffected, the dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, exhibited a linear dose-dependent reduction. However, only homovanillic acid values were significantly decreased after 400 mg/kg milacemide. Cerebrospinal fluid analysis may be useful as a first screen in ascertaining putative neurochemical changes associated with drug administration.

Effect of acute and chronic benzodiazepines on plasma GABA in anxious patients and controls

The acute effects of diazepam on plasma GABA were determined in 18 patients with panic disorder, 13 patients with generalized anxiety disorder and 20 healthy controls. All subjects were benzodiazepine-naive. Four logarithmically increasing doses of diazepam/placebo were administered intravenously at 15-min intervals on 2 separate days. Plasma GABA was measured at baseline and 3 min after the highest dose of diazepam/placebo. There was an overall decrease in plasma GABA that was significantly greater following diazepam compared with placebo, but no group differences in response. In a separate group of 18 panic disorder patients receiving chronic benzodiazepine treatment with alprazolam, the same diazepam infusion procedure (no placebo day) produced decreases in plasma GABA similar to those seen in the untreated panic disorder patients. The clinical and physiologic implications of these findings are discussed.

Anticonvulsant profiles of the potent and orally active GABA uptake inhibitors SK&F 89976-A and SK&F 100330-A and four prototype antiepileptic drugs in mice and rats

The anticonvulsant profiles of two potent and orally active gamma-aminobutyric acid (GABA) uptake inhibitors, 1-(4,4-diphenyl-3-butenyl)-3-piperidine-carboxylic acid hydrochloride (SK&F 89976-A) and 1-(4,4-diphenyl-3-butenyl)-1,2,5,6-tetrahydro-3-pyridine-carboxylic acid hydrochloride (SK&F 100330-A), were determined with a battery of well-standardized tests in mice and rats and compared with the profiles of phenytoin (PHT), carbamazepine (CBZ), valproate (VPA) and clonazepam (CZP) when subjected to the same tests. ED50 values were calculated and compared with TD50 values for minimal motor impairment to provide protective indexes (PI = TD50/ED50). The anticonvulsant profiles of SK&F 89976-A and SK&F 100330-A were similar and suggest that these compounds raise the threshold for seizure initiation rather than inhibit seizure spread. Like intraperitoneal (i.p.) PHT, CBZ, VPA, and CZP, SK&F 89976-A and SK&F 100330-A inhibited seizures in corneally kindled rats. The profiles of SK&F 89976-A and SK&F 100330-A were most similar to that of CZP and virtually opposite to that of PHT. Intraperitoneal SK&F 100330-A provided complete protection against pentylenetetrazol-induced seizures [subcutaneous (s.c.) PTZ] in mice but was ineffective against seizures induced by maximal electroshock (MES) at doses slightly greater than its TD50. SK&F 100330-A provided complete protection against picrotoxin-induced seizures (s.c. Pic) and against both clonus and forelimb tonic extension induced by NMDA N-methyl-D-aspartate [intracerebral ventricular (i.c.v.)-NMDA] in mice; however, SK&F 100330-A was ineffective against seizures induced by bicuculline (s.c. Bic) and strychnine (s.c. Strych) at doses slightly greater than its TD50. SK&F 89976-A was similar but provided partial protection against NMDA-induced clonus.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute barbiturate administration, tolerance and dependence on brain GABA system: comparison to alcohol and benzodiazepines

Central nervous system depressants, e.g., barbiturates, alcohol and benzodiazepines, have a wide spectrum of activity in humans and animals. Evidence accumulated suggests that some of the pharmacological actions exerted by these agents may be mediated through GABA system by mimicking GABAergic transmission. This review attempts to summarize the evidence available as to how the GABA system plays a part in the barbiturate actions and the development of tolerance to and physical dependence on barbiturates. The comparisons of the effects of alcohol, barbiturates and benzodiazepines at different steps of GABA synapse are also presented. Furthermore, the results which have been reported in the literature are inconsistent. This may be due to differences in: (a) animal models used; (b) brain regions used; (c) protocols (dose, duration, form and route of administration, etc.) used in treating animals and/or (d) techniques (pharmacological, biochemical, physiological, etc.) used.

Clinical relevance of measuring GABA concentrations in cerebrospinal fluid

Determination of GABA concentrations in human cerebrospinal fluid can be used to assess GABAergic activity in the central nervous system. As CSF free GABA concentrations may vary with age, sex, CSF fraction, and collection and storage conditions, careful attention to these factors are necessary to allow interpretation of results. Longitudinal studies to investigate the influence of pharmacological agents on CSF GABA have proven especially useful to define clinical biochemical activity and have been utilized to attribute the anti-epileptic action of vigabatrin, a selective inhibitor of GABA-transaminase, to its effects on brain GABA metabolism.