One-trial tolerance to the effects of chlordiazepoxide in the elevated plus-maze is not due to acquisition of a phobic avoidance of open arms during initial exposure.
A single exposure to the elevated plus-maze (EPM) test of anxiety reduces or abolishes the anxiolytic-like efficacy of benzodiazepines. This phenomenon called one-trial tolerance has been suggested to represent the acquisition of a phobic-like response to the open arms during trial 1. The present study was designed to examine the effects of chlordiazepoxide (5 mg/kg, ip) on the behaviour of rats in a conventional EPM apparatus after previous exposure to a four-open-arm EPM, a four-enclosed arm EPM or a conventional EPM, as well as in naive rats. Chlordiazepoxide had clear-cut anxiolytic-like effects (increased percentage of time spent on the open arms) in a traditional EPM in naive rats and in animals previously exposed to a four-open-arm EPM. However, it was ineffective in rats previously exposed to a traditional or a four-closed-arm EPM. Thus, the phenomenon of one-trial tolerance does not depend upon initial open-arm experience.
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Departamento de Farmacologia, Escola Paulista de Medicina, Universidade Federal de São Paulo, Rua Botucatu 862, Edifício José Leal Prado, CEP 04023-062, SP, São Paulo, Brazil. rosanari@terra.com.br
Ribeiro
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D000704:Analysis of Variance; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D001007:Anxiety / Q000188:drug therapy*; D001522:Behavior, Animal / Q000187:drug effects; D002707:Chlordiazepoxide / Q000494:pharmacology*; D004361:Drug Tolerance; D008297:Male; D018782:Maze Learning; D010698:Phobic Disorders; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar
D014151:Anti-Anxiety Agents; D002707:Chlordiazepoxide