Maternal memory in adult, nulliparous rats: Effects of testing interval on the retention of maternal behavior

The retention of maternal behavior (i.e., maternal memory) was measured in adult, nulliparous rats induced to respond maternally by continuous exposure to foster pups. Specifically, the effects of the interval duration between the initial induction and the reinduction of maternal behavior were determined. Intact virgin rats were first exposed to foster young to induce maternal behavior. During the initial induction phase, females were required to be fully maternal on 2 consecutive test days. Animals were then assigned to one of three interval groups (10, 20, or 40 days). After being isolated from rat pups for these designated periods, females in each group were tested again for their latencies to induce maternal behavior. Whereas the initial median latencies to display full maternal behavior ranged from 4.5 to 5 days for each group, upon retesting, median latencies for each group declined to 1 to 4 days. The greatest reduction in latency was present in the 10-day group (80%), and the smallest reduction was detected in the 40-day group (20%). A significant negative linear correlation was found between test interval and percentage reduction in behavioral latency. Based upon this relationship and under these test conditions, "maternal memory" in the adult, nulliparous rat would be expected to be nondetectable after about an interval of 50 days between tests. The pattern of maternal memory acquisition and loss appears similar to that reported in parous animals. The present study highlights similarities and possible differences underlying the establishment of the retention of maternal behavior (i.e., maternal memory).