Temperature-dependent effects of maternal separation on growth, activity, and amphetamine sensitivity in the rat

This study was conducted to examine the effects of an early stressor, maternal separation, on development, arousal, and sensitivity to amphetamine in the rat. Rat pups were maternally separated at nest temperature (WARM), room temperature (COLD), or nest temperature with agitation (AGIT) for 6 hr each day from 2 to 15 days of age. A control group (CONT) remained with the mother in the nest during this time. COLD subjects were developmentally delayed and had lower body and brain weights than the other three groups into adulthood. WARM and AGIT subjects (both maternally separated at nest temperature) had significant growth delays compared to CONT, but grew more quickly than COLD subjects. COLD subjects were less active than the other maternally separated groups, and WARM and AGIT groups were more active. Activity did not differ at 28 or 75 days of age. However, adult WARM subjects were less sensitive and COLD subjects were more sensitive to amphetamine as measured by locomotor activity than CONT and AGIT subjects, who did not differ from each other. The relationship between early stress, changes in dopaminergic systems, and altered drug responsiveness are discussed in terms of the implications for the etiology of drug abuse.