Roman high- and low-avoidance rats: Present status of the swiss sublines,RHA/Verh and RLA/Verh,and effects of amphetamine on shuttle-box performance

Following a recent change in location and shuttle-box testing conditions, RHA/Verh and RLA/Verh rats were found to have maintained their characteristic patterns of avoidance (RHA/Verh) vs nonavoidance (RLA/Verh) behavior, regardless of the time of day tested. A second experiment demonstrated dose-related differences in the effects of amphetamine in both lines. In a third experiment it was seen that, whereas 2 mg/kg amphetamine was capable of increasing two-way avoidance acquisition in naive RLA/Verh rats to the levels of nondrugged RHA/Verh rats, this improvement was accompanied by substantial increases in spontaneous activity (intertrial responses). That learning was not genuinely enhanced by amphetamine was further indicated by the observation that the avoidance improvement disappeared when the drug was abruptly, or gradually, discontinued. The return toward control levels of avoidance and freezing responses was accompanied by a similar normalization of activity levels.