MR/Har and MNRA/Har Maudsley rat strains: Differences in acoustic startle habituation

Female Maudsley Reactive (MR/Har) and Nonreactive (MNRA/Har) rats were tested for initial acoustic startle reactivity and within-session startle habituation. Subjects were exposed in each of five weekly sessions to 12 acoustic startle noise bursts at a 20-s interstimulus interval, a procedure in which genetically heterogeneous Sprague Dawley rats have been shown to exhibit robust within-session habituation. Although initial startle reactivity was comparable in the two strains, significant differences in withinssession habituation were observed. Specifically, MR/Har rats were observed to exhibit substantial within-session habituation to these acoustic stimuli, while rats of the MNRA/Har strain exhibited little, if any, habituation to these repeated acoustic stimuli. The basis for this dramatic difference in within-session startle habituation in these Maudsley rats is at present unexplained and under investigation.This work was supported in part by the WSU Biomedical Research Award Program, the American Heart Association of Michigan Grant-in-Aid Program, the Pharmaceutical Manufacturers Association Research Starter Grant and MH 42501-01 to R.L.C., and the National Science Foundation to G.M.H.