Early handling and maternal behavior: Effect on d-amphetamine responsiveness in rats

This study determined whether early handling and maternal behavior could influence the behavioral changes associated with chronic amphetamine administration. In Experiment 1, seven litters received early handling (rat pups were removed from the nest for 3 min daily during the first week following parturition) and 7 litters were undisturbed. At 105 days of age, male animals from non-handled litters showed a decline in rearings induced by 2.0 mg/kg d-amphetamine across 12 test days in a Y-maze but handled animals showed no such pattern. Handling had no effect on entries. In Experiment 2, four litters were handled and returned to a mother-present nest (H), 4 litters were handled and returned to a mother-absent nest 1 hr prior to reunion with the rat mother (HMS), 4 litters were separated from mothers for 1 hr (MS), and 4 litters were undisturbed (C). At 55 days of age, a handling (Groups H and HMS) effect on open-field activity was observed. At 75 days of age, male animals were injected with 0.0, 2.5 or 10.0 mg/kg d-amphetamine and tested in a Y-maze. At 2.5 mg/kg handled animals, whether maternally separated or not (H and HMS) showed no decline in drug-induced rearings; maternally separated animals whether handled or not (MS and HMS) showed fewer entries and increased body weight. However, only animals at 2.5 mg/kg from handled, mother-present litters (H) showed a retarded increase in stereotypy across 8 test days. These results indicated that behavioral manipulations early in life may influence responsiveness to d-amphetamine in adulthood, either directly or through associated changes in maternal behavior.