Breeder differences within Wistar strain rats in acquisition of discrete shuttle avoidance response and in sensitivity to chlorpromazine.

Characteristics of acquisition processes of discrete shuttle avoidance response were investigated in 3 lines of Wistar strain rats: HLA:Wistar, JLA:Wistar, Std:Wistar and in F344/Du Crj rats. Std:Wistar and F344/Du Crj rats rapidly acquired the avoidance response, showing an avoidance rate of higher than 90% until the middle stage of the 1st training session in which 120 trials were carried out, and they also maintained a high level of avoidance response in the latter sessions. HLA:Wistar and JLA:Wistar rats, however, exhibited a poorer acquisition of the avoidance response than Std:Wistar and F344/Du Crj rats. These two lines of Wistar rats finally achieved average avoidance rates of around 80% after 5 sessions of training and showed a long-lasting warm-up period in each session. Std:Wistar and F344/Du Crj rats had more resistance than the other two lines to extinction of the acquired avoidance response. Chlorpromazine (2-8 mg/kg, i.p.) suppressed the avoidance response in a dose-dependent manner. The sensitivities to chlorpromazine were higher in the order of JLA:Wistar greater than HLA:Wistar greater than Std:Wistar not equal to F344/Du Crj rats. These results suggest that there are major breeder differences even in the same strain of rats in their behavioral and physiological characteristics. The present results also suggest that Std:Wistar rats show extremely close characteristics with those of F344/Du Crj rats.