ELECTROLYTIC LESIONS OF THE FIMBRIA FORNIX, DORSAL HIPPOCAMPUS, OR ENTORHINAL CORTEX PRODUCE ANTEROGRADE DEFICITS IN CONTEXTUAL FEAR CONDITIONING IN RATS/

Recent data indicate that dorsal hippocampal (DH) lesions disrupt Pavl ovian fear conditioning to contextual cues in rats. In the present stu dy, we examined the effects of electrolytic lesions of the fimbria/for nix (FX) or entorhinal cortex (EC), the primary afferent projection sy stems to the DH, on contextual fear conditioning in rats. Conditioning consisted of the delivery of unsignaled footshocks in a novel observa tion chamber, and freezing served as the measure of conditional fear. Electrolytic lesions of the FX, DH, or EC made 1 week before training produced anterograde impairments in both immediate postshock freezing on the conditioning day and freezing during the context extinction tes t 24 h following training. The deficits in conditional freezing produc ed by FX, DH, and EC lesions were not statistically different, althoug h the deficits in rats with FX or EC lesions tended to be more severe than those in rats with DH lesions. In addition to producing deficits in conditional freezing, FX, DH, or EC lesions produced a pronounced l ocomotor hyperactivity. Within the lesion and sham groups, however, lo comotor activity was not significantly correlated with conditional fre ezing. These results indicate that contextual fear deficits in rats wi th hippocampal formation damage are equivalent following either FX, DH , or EC lesions. The relationship of freezing deficits and locomotor h yperactivity in rats with hippocampal formation lesions is discussed. (C) 1997 Academic Press.