The effects of hippocampal and fimbria-fornix lesions on prepulse inhibition

The present experiments tested the effects of conventional (dorsal aspirati on and electrolytic) and excitotoxic (N-methyl-D-aspartate [NMDA]) hippocam pal lesions and fimbria-fornix (FF) transection on prepulse inhibition (PPI ) of startle response and on open-field activity. Activity was increased by FF transection and by conventional but not excitotoxic hippocampal lesions ; complete NMDA lesion increased amphetamine-induced activity. Whereas dors al hippocampal aspiration lesion disrupted PPI, the phenomenon was not affe cted by dorsal hippocampal electrolytic lesion, partial or complete excitot oxic (NMDA) hippocampal lesions, or complete FF transection, which interrup ted the cholinergic input to the hippocampus as well as the hippocampal-sub icular input to the nucleus accumbens. Systemic apomorphine disrupted PPI i n both FF-transected rats and their controls. It is suggested that the hipp ocampus is essential for PPI disruption rather than for PPI expression.