GRADED EFFECT OF SOCIAL STIMULATION UPON d-AMPHETAMINE TOXICITY, AGGRESSIVENESS AND HEART AND ADRENAL WEIGHT

¹ Laboratory of Population Ecology, Department of Biology, College of William and Mary, Williamsburg, Virginia

Susceptibility to the toxic effects of the indirectly acting sympathomimetic amine, d-amphetamine, was found to be: greater for individually caged mice than for mice grouped for the same 1-wk or 5- to 8-wk period; inversely related to the number of mice living together in a graded series including isolated animals and groups of 2, 5 and 10; and reduced by the stimulus of living in maximally compatible social situations. Both spontaneous aggressiveness within groups and aggressiveness towards strange mice encountered in a strange cage quantitatively declined with increasing group size of prior housing, paralleling the reduction in central nervousexcitability as indicated by d-amphetamine. In those experiments in which they were obtained, the weights of the ventricles of the heart and of the paired adrenals were smallest in isolated animals and increased with increasing group size, paralleling the reductions in aggressiveness and in sensitivity to d-amphetamine. These parallel incremental changes produced by grouping may bear common relation to a stimulus-dependent enhancement of the basal level of peripheral and central catecholamine release.