SEX-DIFFERENCES IN HIPPOCAMPAL LONG-TERM POTENTIATION (LTP) AND PAVLOVIAN FEAR CONDITIONING IN RATS - POSITIVE CORRELATION BETWEEN LTP AND CONTEXTUAL LEARNING

Three experiments investigated sex differences in hippocampal long-ter m potentiation (LTP) and Pavlovian fear conditioning in rats. Experime nt 1 revealed a robust sex difference in the magnitude of LTP induced at perforant path synapses in the dentate gyrus of pentobarbital-anest hetized rats. This sex difference in LTP was evident in rats of 35 and 60 days of age and was not the result of pre-LTP sex differences in p erforant path synaptic transmission; 20-day-old rats did not show LTP. An analysis of field potentials evoked during LTP induction revealed a sex difference in the magnitude of N-methyl-D-aspartate (NMDA) recep tor activation that was highly correlated with the magnitude of LTP. E xperiment 2 showed that males condition more fear, measured as freezin g, to the contextual conditional stimuli (CSs) of a conditioning chamb er compared to their female counterparts. This sex difference in condi tional freezing was apparent with both low and high unconditional stim ulus (US, footshock) intensities. Experiment 3 revealed that the enhan ced fear conditioning in males was specific to contextual CSs, and con sisted of a more rapid rate of conditioning. Together, these experimen ts reveal a positive correlation between the magnitude of hippocampal LTP and a form of learning that depends on the hippocampus. Furthermor e, they suggest a neural basis for sex differences in hippocampus-depe ndent learning tasks.