Repeated morphine administration during pregnancy attenuates maternal behavior

The present study tested the hypothesis that repeated administration of mor phine on days 11-18 of pregnancy alters maternal behavior. Saline- and morp hine-treated mothers were observed with their pups in two experiments. Rats were always tested twice a day during the light and dark phases of the rev erse light/dark cycle. In Experiment 1, 12 types of activities and three ty pes of nursing positions of mothers were recorded ten times during each 50- minute session for the 23-day lactation period. A decrease in nursing and a ctive maternal behavior, and an increase in self-care, rearing and sniffing was found in morphine-created mothers. Additionally, both saline- and morp hine-treated mothers exhibited significantly more maternal behavior during the light, and non-maternal activities during the dark sessions of each day . Moreover, both saline- and morphine-treated mothers displayed significant ly less maternal behavior and more non-maternal activities as postpartum ti me progressed. In Experiment 2, a different group of mothers was tested for pup retrieval from postnatal days 1 through 12. Morphine-treated mothers w ere slower than saline-treated mothers in retrieving all pups into the nest . However, there were no differences in latency to carry the first pup and return him/her to the nest. No unusual maternal behaviors were observed dur ing the retrieval tests. Thus, the present study suggests that morphine adm inistration during the second half of pregnancy attenuates some components of maternal behavior and increases non-maternal activities of mothers. (C) 2001 Elsevier Science Ltd. All rights reserved.