Time course of discriminative stimulus effects of bretazenil and chlordiazepoxide in rats

Comparison of the behavioral effects of bretazenil and flumazenil in triazolam-dependent and non-dependent baboons

Behavioral effects of the benzodiazepine receptor partial agonist bretazenil were compared with those of the benzodiazepine receptor antagonist flumazenil under conditions in which three baboons received continuous intragastric (i.g.) infusion of vehicle and then continuous i.g. infusion of triazolam (1.0 mg/kg/day). In each condition, acute doses of flumazenil (0.01-3.2 mg/kg) and bretazenil (0.01-10.0 mg/kg) were administered every 2 weeks (beginning after 30 days of treatment in the triazolam-dependent condition). Food pellets were available during daily 20-h sessions. Following test injections, 60-min behavioral observations were conducted followed by a fine motor assessment. During chronic vehicle administration, neither drug produced changes in observed behaviors. Bretazenil increased pellets earned and time to complete the fine-motor task (10.0 mg/kg dose). During chronic triazolam dosing, both bretazenil and flumazenil precipitated benzodiazepine withdrawal syndromes, characterized by vomiting, tremors/jerks, and a decrease in pellets earned. Thus, bretazenil can function as an antagonist under conditions of benzodiazepine physical dependence.

Prenatal protein malnutrition enhances stimulus control by CDP, but not a CDP/THIP combination in rats

In the present study, the effects of prenatal protein malnutrition on stimulus control exerted by the benzodiazepine (BZ), chlordiazepoxide (CDP) and the GABA-A receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) were characterized. The adult, male offspring of female Sprague-Dawley rats fed either low (6% casein) or adequate (25% casein) protein diets 5 weeks prior to mating and throughout pregnancy served as subjects. Subjects were first trained to discriminate CDP (8.0 mg/kg ip) from saline using drug discrimination procedures. Once a criterion level of performance was achieved, generalization tests were performed to lower doses of CDP (4.0, 2.0, 1.0, 0.5 and 0.25 mg/kg) and then to several doses of THIP (10.0, 7.5, 5.6 and 3.2 mg/kg). Lastly, the ability of a single dose of THIP (3.0 mg/kg) to enhance discriminative control by several low doses of CDP (4.0, 2.0, 1.0 and 0.5 mg/kg) was assessed. Although both diet groups acquired the original CDP/saline discrimination at the same rate, malnourished rats exhibited significantly more generalization to low doses of CDP than their well-nourished counterparts. Neither diet group exhibited significant generalization to THIP nor a difference in THIP's ability to enhance the CDP cue. These results suggest that a subject's sensitivity to the stimulus properties of drugs can be selectively modified by prenatal malnutrition.

Effects of benzodiazepine receptor ligands and ethanol in rats trained to discriminate pregnanolone

Although GABA(A) receptor positive modulators share many behavioral effects, subtle differences have been detected among their discriminative stimulus effects. The purpose of the present study was to determine the extent of shared discriminative stimulus effects of pregnanolone with various benzodiazepine receptor ligands and with ethanol. Naive male Sprague-Dawley rats were trained to discriminate the endogenous neuroactive steroid pregnanolone (5.6 or 8.0 mg/kg) from vehicle. The benzodiazepine receptor agonists, triazolam and lorazepam, the benzodiazepine receptor partial agonist, bretazenil, the benzodiazepine1 (BZ1) receptor subtype selective agonists, zolpidem and zaleplon and ethanol were tested. Triazolam, lorazepam and bretazenil substituted for pregnanolone. Lorazepam, but not triazolam or bretazenil, decreased response rates at the highest dose tested. Zaleplon completely substituted for pregnanolone with no effect on response rates. Zolpidem substituted for pregnanolone only at a dose that severely disrupted response rates. Ethanol partially substituted for pregnanolone and decreased response rates. The results are consistent with GABA(A) receptor mediation of the discriminative stimulus effects of pregnanolone. The effects on response rates suggest subtle differentiation among the GABA(A) receptor-mediated cues.