[Effects of chlordiazepoxide on passive avoidance learning in Wistar-Imamichi and F344/Du strain rats]

The present study was designed to investigate the effects of chlordiazepoxide (CDP; 5 and 10 mg/kg, ip) on one-trial step-through passive avoidance learning in Wistar-Imamichi (W-I) and F344/Du (F) strain rats. Step-through latency and the time spent in safety-box were significantly longer in W-I than F rats. The number of animals that attained the 300-s criterion was also larger in W-I than F rats. Therefore, it was concluded that W-I rats showed superior performance in the passive avoidance task as compared to F rats. Taken together, these and the previous results (Iwasaki et al, 1984) that F rats acquired the active avoidance learning more easily than W-I rats, the differences of performance in the two strains would reflect differences of strain-specific response patterns in aversive situations, but not of learning ability. Further, CDP produced a dose-dependent state-dependency in W-I but not in F rats. These strain differences in the effect of CDP were considered to derive from differences in sensitivity to the drug, rather than in the baseline performance level, because comparable strain differences in drug effect were reported in active avoidance learning.