SEX-DIFFERENCES AND ESTROUS-CYCLE CHANGES IN HIPPOCAMPUS-DEPENDENT FEAR CONDITIONING

Male and naturally cycling female rats were tested in a fear condition ing paradigm that encompassed both hippocampus-dependent and -independ ent components. The females were bath conditioned and tested for reten tion at the same stage of the estrous cycle, during either estrus or p roestrus. Male rats followed a regime similar to that for the female r ats, Approximately 2 weeks after conditioning, the animals were examin ed for retention of the spatial context and of an explicitly paired co nditioning tone, All animals showed a similar degree of conditioning t o the tone. However, female proestrous rats showed Less spatial-contex tual conditioning than did male or estrous female rats. These results suggest that the changes found during the proestrous part of the cycle are related to hippocampal information processing and not to general changes in learning ability, to shock sensitivity, or to state-depende nt learning. The results are discussed and related to previous finding s regarding estrous cycle changes in behavior, anatomy, and physiology .