Rat strain differences in open-field behavior and the locomotor stimulating and rewarding effects of amphetamine.

Fischer 344 (F344) and Lewis (LEW) rats show considerable neuroanatomical and neurophysiological differences within the mesolimbic dopamine system. The aim of our experiments was to study the functional correlates of such differences by examining open-field behavior and the sensitivity towards the psychostimulant and rewarding effects of amphetamine in male and female, F344 and LEW rats. In addition, the consequences of short versus extended habituation to open-field testing on amphetamine locomotion in these two rat strains was assessed. LEW but not F344 rats irrespective of gender showed between-session habituation of open-field activity. Amphetamine-induced locomotion was higher in F344 compared to LEW rats and in females compared to male rats. In addition, extended habituation increased the locomotor effects of amphetamine. The rewarding effects of amphetamine as measured by the conditioned place preference test were more pronounced in F344 than in LEW rats. Our results suggest that the two rat strains differed in their behavioral response to mild stress and to amphetamine and that these differences may depend upon differences within the mesolimbic dopamine system.