Hippocampal long-term potentiation (LTP) is believed to be the mechanism underlying certain types of memory,which is exquisitely sensitive to stress.In the present study,we introduced a naïve female rat to a stressed male rat that just experienced contextual fear conditioning,for 24 hours in home cage where they showed sexual behaviors.Remarkably,these male rats exhibited much lower contextual fear than those without female rats,and their impaired LTP of the field excitatory postsynaptic potentials in hippocampal CA1 was restored.In marked contrast,when we introduced a naïve male rat to a stressed male rat that was trained in contextual fear conditioning,the male rats still showed high levels of contextual fear and the impaired LTP.In addition,the effects of female both on behavior and electrophysiology were prevented by the dopamine D1/D5 receptor antagonist SCH 23390.These novel findings suggest that heterosexual contact decreases contextual fear and prevents the impairment of hippocampal LTP,thereby providing potential explanation why heterosexual contacts modulate mood and promote work efficacy in humans.