Opposite effects of diazepam and beta-CCE on immobility and straw-climbing behavior of rats in a modified forced-swim test.

The present study was undertaken to examine how two ligands of the benzodiazepine receptor, which possess anxiolytic or anxiogenic actions, affect both the duration of immobility and the incidence of straw-climbing behavior in rats in a modified forced-swim test. Rats were injected IP with either vehicle, diazepam (0.5, 1, 5 mg/kg), or beta-carboline-3-carboxylic acid ethyl ester (beta-CCE; 0.5, 1, 2, 5 mg/kg), or a combination of diazepam at 1 mg/kg and beta-CCE at 2 mg/kg. In addition, Ro 15-1788 (1 mg/kg), a specific benzodiazepine antagonist, was injected IP 20 min after diazepam injection and immediately after beta-CCE injection, respectively. In the first 5-min period of the forced-swim test, diazepam at 5 mg/kg prolonged the duration of immobility, whereas beta-CCE at 1, 2 and 5 mg/kg reduced its duration. Immediately after the first 5-min test period, 4 straws were suspended above the surface of the water, and the number of straw-climbing attempts and the duration of immobility were measured for a subsequent 5-min test period. Straw-suspension elicited straw-climbing behavior in forced swimming rats, resulting in a shortening of the duration of immobility in this period. All doses of diazepam inhibited straw-climbing attempts and prolonged the duration of immobility in a dose-dependent manner. beta-CCE at 1 or 2 mg/kg enhanced straw-climbing attempts, but did not significantly affect the duration of immobility. Furthermore, the combined administration of diazepam and beta-CCE antagonized the respective drug effects on the duration of immobility and the number of straw-climbing attempts.(ABSTRACT TRUNCATED AT 250 WORDS)