Effects of single and repeated administration of vigabatrin on the performance of rats in a 5-choice serial reaction time task

Neurobehavioral effects of vigabatrin and its ability to induce DNA damage in brain cells after acute treatment in rats

RATIONALE

Vigabatrin (VGB) is a drug indicated mostly for the treatment of spasms in childhood and West's syndrome patients. This drug inhibits irreversibly the enzyme GABA-transaminase (GABA-T), increasing GABA concentrations and enhancing GABAergic neurotransmission in the brain, which is known to induce behavioral changes.

OBJECTIVES

The aims of this study were to evaluate the effects of VGB in the short-term memory (STM), long-term memory (LTM), motivation, locomotion, and exploratory behavior tests and to detect deleterious or protective effects on DNA in target tissues of the drug.

METHODS

Male Wistar rats were treated with a single dose of VGB (100, 250, or 500 mg/kg) or saline solution before the inhibitory avoidance and open-field tasks. DNA damage was evaluated using the alkaline comet assay in peripheral blood, cerebral cortex, and hippocampus after behavioral testing.

RESULTS

There was no significant difference in the inhibitory avoidance task between the treated groups and the saline group. In all tested doses, VGB reduced the number of rearings in the open-field task. Besides, VGB 500 mg/kg affected locomotion, though it was not able to induce any DNA damage.

CONCLUSIONS

VGB did not affect STM and LTM, but the drug impaired the exploration and locomotion likely associated with its sedative effect. In addition, no DNA damage in cortex and hippocampus was detected after behavioral testing, when brain GABA levels are already increased.

The influence of NMDA and GABA(A) receptors and glutamic acid decarboxylase (GAD) activity on attention

RATIONALE

Attention dysfunction is the hallmark of cognitive deficits associated with major psychiatric illnesses including schizophrenia. Cognitive deficits of schizophrenia have been attributed to reduced function of the N-methyl-D-aspartate (NMDA) receptor or reduced expression of the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid decarboxylase-67, which presumably leads to attenuated neurotransmission at GABA(A) receptors.

OBJECTIVE

The present study used a rodent model to compare the inhibition of NMDA and GABA(A) receptors, and GAD activity on attention. We tested the impact of inhibiting these proteins brain wide or in the anterior cingulate cortex (ACC), a prefrontal cortex region critical for attentional processing.

METHODS

Rats were trained on the three choice serial reaction time task (3-CSRT), an attention test. The impact of systemic or intra-ACC injection of drugs on performance was measured in well-trained rats.

RESULTS

Reducing GABA(A) receptor function within the ACC with the direct antagonist SR95531 (1 or 3 ng/side) or brain wide using systemic injection of the benzodiazepine inverse agonist FG7142 (5 mg/kg) impaired accuracy and increased omissions. Systemic or intra-ACC inhibition of NMDA receptors using MK-801 (at 3 mg/kg or 3 μg, respectively) also impaired performance. Inhibition of GAD with 3-mercaptopropionic acid, even at high doses, had no effect on 3-CSRT accuracy or omissions when administered systemically or within the ACC.

CONCLUSIONS

These data demonstrate that, while tonic stimulation of NMDA and GABA(A) receptors within the ACC are critical for attentional performance, reduction in GAD activity may have little functional significance and is not indicative of reduced GABA neurotransmission.

Gamma-vinyl GABA, an irreversible inhibitor of GABA transaminase, alters the acquisition and expression of cocaine-induced sensitization in male rats

We examined the effect of (+/-)-gamma-vinyl GABA (GVG, Vigabatrin), an irreversible inhibitor of the enzyme GABA transaminase, on the acquisition and expression of cocaine-induced sensitization in albino male Sprague-Dawley rats. Animals received a single injection of 1 ml/kg i.p. of 0.9% saline or 15 mg/kg i.p. of (-)-cocaine and locomotor activity was assessed using automated locomotor cages and stereotyped behaviors were scored using a 4-point rating scale (Day 1). Subsequently, animals were given 15 mg/kg i.p. of cocaine every 48 h in their home cage for 1 week (Days 3, 5, and 7) and then given no treatment for 1 week. A challenge injection of 15 mg/kg i.p. of cocaine, but not vehicle, produced a significant increase in locomotor activity and stereotyped behaviors on Day 15 compared to animals that received cocaine on Day 1. Administration of 75 mg/kg i.p. of GVG 2.5 h before the cocaine injections did not significantly alter the acquisition of cocaine-induced locomotor sensitization. However, 150 mg/kg i.p. of GVG significantly attenuated the acquisition of cocaine-induced locomotor sensitization. Administration of 150 mg/kg i.p. of GVG 2.5 h before the cocaine challenge injection on Day 15 significantly attenuated the expression of cocaine-induced locomotor sensitization. Acquisition and expression of cocaine-induced sensitization of stereotypy was also significantly attenuated by 150 mg/kg i.p. of GVG. Since sensitization may be one of the factors involved in relapse to drug use, the present results, in combination with previous findings that GVG blocks the rewarding and incentive motivating effects of cocaine, suggest that GVG might prove useful in the treatment of cocaine addiction.

GABAergic drugs inhibit amphetamine-induced distractibility in the rat

Drugs facilitating GABAergic neurotransmission have been reported to block some behavioral actions of dopaminergic stimulation but not others. The present experiments were performed with the purpose to extend the range of behaviors in which the interaction between GABA and dopamine have been studied. The ability of the GABAB agonist baclofen and the GABA transaminase inhibitor sodium valproate to block the enhanced distractibility produced by amphetamine was evaluated in a procedure especially designed for analyzing drugs' effects on distractibility. Briefly, rats were trained to traverse a straight runway with a sucrose solution as reinforcement. Once the response had been acquired, an additional runway ending in an empty box was connected. The time spent investigating this additional runway is the measure of distractibility. Male rats treated with amphetamine, 1 mg/kg, displayed an increase of the time spent in the additional runway. Baclofen, 2.5 and 5 mg/kg, and sodium valproate, 100 and 200 mg/kg, had no effect on distraction behavior when administered alone. However, when these drugs were administered together with amphetamine, 1 mg/kg, they completely inhibited the effects of the stimulant on distractibility. These data show that distractibility is similar to discrimination learning with regard to the capacity of GABAergic drugs to block the effects of dopaminergic stimulation. It is different from locomotor activity, however, where GABAergic drugs are ineffective in this respect.

Possible confounding influence of strain, age and gender on cognitive performance in rats

There are substantial differences in the performance of various rat strains in tasks of learning, memory and attention. Strain, age and sex differences are not consistent over procedures: poor performance in one paradigm does not predict poor performance in a different paradigm. Some strain differences are not readily apparent until a direct comparison is made between one or more strains. Moreover, large differences in nominally the same strain but obtained from different suppliers have been observed in behavioural, pharmacological and physiological parameters and can have important consequences for interpretation of drug effects. Longevity, and the effects of ageing can differ dramatically from one strain to another; drug effects can alter radically with increasing age and show strain (and individual) differences in their action. Sex can further complicate interpretation of results. Thus, non-cognitive factors may exert a major effect on results in cognitive testing, and strain-dependent effects may account for many conflicting results in the literature concerning mnemonic performance. Strain differences in particular must be identified and used to help identify fundamental effects on memory, rather than continue to be ignored and allowed to obscure interpretation of drug effects on cognitive processes.

Effects of single and repeated administration of vigabatrin on the performance of non-epileptic rats in a delayed non-matching to position task

The present experiments were performed to investigate the effects of single and repeated administration of vigabatrin (gamma-vinyl-GABA), a novel antiepileptic drug, on a working memory task (delayed non-matching to position task) in non-epileptic rats. At doses of 100, 300 and 500 mg/kg single administrations of vigabatrin and 50, 100 and 200 mg/kg repeated administrations, vigabatrin did not affect the choice accuracy in the delayed non-matching to position task employing delays of 0, 1, 2, 4, 8 and 16 s, whereas repeated administration with 300 mg/kg and a single dose of 1000 mg/kg decreased the behavioral activity as compared to saline treatment. Previous studies have shown that at doses of 50-200 mg/kg (daily administration) and 200-1000 mg/kg (single administration) vigabatrin has anticonvulsant activity. The present results suggest that vigabatrin does not markedly impair working memory in the low range of antiepileptic/anticonvulsive doses.