Differential effects of cohort removal stress on the acoustic startle response of the Roman/Verh rat strains

Male and female rats of the inbred Roman/Verh strains, which have been psyc hogenetically selected and bred for good (RHA-I/Verh) and extremely poor (R LA-I/Verh) two-way avoidance acquisition, were evaluated in an acoustic sta rtle response test. One half of the rats of each strain and sex were previo usly subjected to 30 min of isolation by removal of their cage partners ("c ohort removal"). During the testing session each animal received 40 acousti c stimuli at interstimulus intervals of 30 seconds. The hyperemotional RLA- I/Verh rats (especially the males) showed stronger acoustic startle respons es than did their RHA-I/Verh counterparts. Startle amplitudes of the RLA-I/ Verh males were further enhanced by the stress of 30 min isolation, whereas cohort removal did not significantly affect startle response amplitudes in RHA-I/Verh rats of either sex or in females of the RLA-I/Verh strain.