Endogenous opioid facilitation of maternal memory in rats

In rats, contact with pups at parturition establishes a form of maternal me mory that enables female rats to respond rapidly to pups in the future. Tre atment of pregnant female rats with the long-lasting mu opioid receptor ant agonist, beta-funaltrexamine (beta-FNA), prior to parturition interfered wi th the establishment of maternal memory. Similar treatment 3 hr postpartum resulted in disrupted retention of maternal memory that appeared nonspecifi c, with both drug- and vehicle-treated rats displaying a deficit. However, infusion of the opioid antagonist 24 hr postpartum had no effect on the ret ention of maternal memory tested 7 days later. These findings indicate that the establishment of maternal memory is mediated by endogenous opioid acti vity around the time of parturition.