The present study was designed to determine whether the medial preoptic area (MPOA) and the amygdala (AMYG) are involved in the expression of ``maternal'' behavior in juvenile rats as they are in the adult. Juveniles show many behaviors that are similar to the maternal behaviors shown by the postpartum female rat. Whether these behaviors are social in function, as opposed to parental, and hence mediated by different mechanisms from those regulating adult maternal behavior is not known. To test the roles of the MPOA and AMYG in mediating these behaviors, 21‐day‐old female juvenile rats received MPOA, AMYG, or SHAM (MPOA/AMYG) lesions and were tested at 22 days of age for maternal and other responses to pups. Major findings demonstrate that MPOA lesions disrupt components of maternal behavior, including retrieving and nest building, while AMYG lesions facilitate these behaviors. These findings indicate striking similarities between the juvenile and rat brain for parental responding. © 2000 John Wiley & Sons, Inc. Dev Psychobiol 37: 253–265, 2000

We examined the effects of odor exposure in the nest on the offspring's subsequent adult responsivity to pups scented with the same odor or a different odor. It was hypothesized that animals receiving exposure to the odor in the nest would be more maternally responsive to pups scented with the (same) exposed odor than to unscented (water-scented) pups. In the first part of the study (Part A), Sprague-Dawley female rat pups (days 1-18 of age) either received exposure to an artificial lemon odor or to the natural (water) odor in the nest. In the second part of the study (Part B), rat pups were exposed daily to lemon or neutral odorants in an incubator at a distance from the mother and the nest. On day 21, animals received odor preference tests for lemon versus neutral pine bedding. On day 60, animals were mated and their pups were removed at 15-min intervals at the time of parturition. Animals were then tested for maternal behavior to foster pups on day 1 or 7 after parturition. Foster pups were scented either with the lemon odor or with water (unscented). Early exposure to lemon in the nest context enhanced animals' attraction to the lemon odor in juvenile tests. In adult maternal tests, exposure to odor on the mother and in the nest had two effects. It increased the latency for animals to express maternal behavior; however, once mothers expressed maternal behavior, they spent more time licking and crouching over pups scented with the same odorant to which they had been exposed earlier on their own mothers. Simple exposure to the lemon odorant out of context of the nest had no effect on adult maternal latencies or behavior.

The present study was designed to determine whether the medial preoptic area (MPOA) and the amygdala (AMYG) are involved in the expression of "maternal" behavior in juvenile rats as they are in the adult. Juveniles show many behaviors that are similar to the maternal behaviors shown by the postpartum female rat. Whether these behaviors are social in function, as opposed to parental, and hence mediated by different mechanisms from those regulating adult maternal behavior is not known. To test the roles of the MPOA and AMYG in mediating these behaviors, 21-day-old female juvenile rats received MPOA, AMYG, or SHAM (MPOA/AMYG) lesions and were tested at 22 days of age for maternal and other responses to pups. Major findings demonstrate that MPOA lesions disrupt components of maternal behavior, including retrieving and nest building, while AMYG lesions facilitate these behaviors. These findings indicate striking similarities between the juvenile and rat brain for parental responding.