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The development of emotional behavior is dependent on the early experiences of the infant and the quality of maternal care. In these experiments, the effects of social isolation during the preweaning period on both pup behavior and maternal responsivity were examined. In the first study, the number of ultrasonic vocalizations (USVs) emitted after brief maternal separation was measured in neonatal rats with differing histories of social isolation. The social isolation procedure consisted of 5 days of daily separation from the dam and littermates for either 3 or 6 hr. At both ages tested, socially isolated pups vocalized significantly less than control pups. In the second study, the effects of prior isolation either daily for 5 previous days (Chronic Isolation) or for 4 hr prior to testing (Acute Isolation) were examined in a T-maze choice test. Pup vocalizations in the presence of the dam and dams' maternal behavior were assessed. When the dam was confined to the start box or during the maternal free access period, both Chronic and Acute Isolates vocalized less than pups that had never left the home nest. Dams spent more time with and licked and groomed more frequently and for a longer time both Chronic and Acute Isolates compared to pups that had always been with dams in the home nest. These results suggest that early isolation experience can alter subsequent responses to separation stress in neonatal rats and that maternal behavior is sensitive to the prior experiences of offspring.

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.

Spatial (left or right) preferences were determined for rats given foot shock in a T-maze. The animals were killed, and left and right striata were assayed separately for dopamine and left and right teldiencephalic regions were assayed for norepinephrine. Dopamine content was significantly higher (by 12 percent) in the striata contralateral to rats' side preferences than in the ipsilateral striata; there was no such difference for teldiencephalic norepinephrine. The small asymmetry in striatal dopamine content is not due to any learning- or stress-related change induced by the testing procedure but is probably inherent in normal rats. Some spatial behavior appears to be the manifestation of a normal and specific difference in the activity of left and right nigrostriatal systems.

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