Differences in the behaviour of Sprague-Dawley and Lewis rats during repeated passive avoidance procedure: Effect of amphetamine

The present paper investigated the differences in passive avoidance learnin g between Sprague-Dawley and Lewis rats. After initial habituation (experim ental Part 1), measured as latencies to enter the dark, preferable compartm ent, the effect of treatment with amphetamine (8 mg kg(-1) b.w.), the reten tion performance compared with controls (saline) was tested in both rat str ains in Parts 2-4. The intervals between Parts 2-4 were 24 or 49 days. Each experimental part consisted of testing lasting 6 days. On the 7th day the rats received drug treatment 1 h before the application of foot shock. The differences between rat strains were already detectable at the beginning of the study. During the repeated exposures of rats in Part 1, only Lewis rat s, in contrast to Sprague-Dawley rats, exhibited the habituation. The repea ted testing of rats in Parts 2-4, due to previous experience with an aversi ve stimulus, was considered as the retention test. In Parts 2-3 we observed only minor differences in the responses of both rat strains tested. Also n o significant differences were observed between rat strains after amphetami ne treatment that induced an amnesia-like effect in all retention trials. H owever, data shown in Part 4 revealed the largest differences between both strains. Control Lewis rats exhibited significantly higher retention respon ses than Sprague-Dawley rats. In the latter strain we observed no differenc es in avoidance latencies between controls and amphetamine treated rats. In Lewis rats the difference in avoidance performance between controls and am phetamine treated animals was highly significant due to their enhanced rete ntion performance. In conclusion, the results presented in this study exten d the known behavioural differences in tested rat strains to the passive av oidance procedure that, in addition, was performed for a total period of 4 months. Due to a known deficiency of hypothalamo-pituitary-adrenal axis act ivity in Lewis rats it can be hypothesized that the behavioural dissociatio n of this strain from Sprague-Dawley rats could be related to the different activity of this regulatory axis in the rat strains tested. (C) 2001 Acade mic Press.