INHIBITORY EFFECTS OF NALTREXONE ON THE INDUCTION OF PARENTAL BEHAVIOR IN JUVENILE RATS

Juvenile rats are rapidly responsive to pups soon after weaning, displ aying maternal-like behaviors such as licking, retrieving, grouping, a nd crouching over pups. As juveniles reach 30 days of age, they become less responsive to pups and show increased latencies to display the s ame parental behaviors. In light of previous data implicating opiates in the display of ongoing maternal behavior, we administered naltrexon e, a long-acting opiate antagonist, beginning 5 and 9 days prior to an d continuing throughout the period of behavioral testing, which starte d at 26 or 30 days of age. Male and female juveniles treated with 10 m g/kg of naltrexone SC for 9 days (days 21 to 29 of age) prior to and d uring behavioral testing (days 30 to 37) showed longer latencies to re trieve, group, and crouch over pups than did the vehicle-injected cont rols. These results suggest that opioids may have a stimulatory role i n parental behavior during this prepubertal period.