Reproductive experience and activation of maternal memory.

The maternal and neurobiological responses of biological mothers and pup-induced maternal virgin rats were compared 55 and 80 days after an initial 2-day maternal experience. When tested for home cage responsiveness after prolonged isolation from young, the biological, primiparous rats displayed shorter maternal latencies. Primiparous females tested in the presence of pups on the elevated plus-maze displayed increased exploration of the open arms and increased c-Fos expression in the cortical nucleus of the amygdala. Pup exposure and parity also enhanced activation of the nucleus accumbens shell and medial nucleus of the amygdala, respectively. Therefore, although both nulliparous and primiparous rats retain a maternal memory for a prolonged time, the memory and neurochemical response appear stronger in primiparous mothers.