Responses of the hypophyseal-adrenal system to stress and immune stimuli in gray rats selected for behavior.

The characteristics of the responses of the hypothalamo-hypophyseal-adrenal system to restriction stress and administration of lipopolysaccharide and interleukin-2 were studied in gray rats selected for the maintenance and absence of aggressive behavior in relation to humans. These experiments demonstrated decreased levels of corticosterone and ACTH in the plasma of tame rats in restriction stress and after administration of lipopolysaccharide as compared with non-tame rats. After administration of interleukin-2, the corticosterone level was identical in both groups of animals, though it reached the basal level in tame rats more quickly than in rats selected for maintaining aggressive behavior. Thus, selection of gray rats for tame behavior induces not only decreases in the responses of the hypophyseal-adrenal system to restriction stress, but also changes its response to immune stimuli and also, perhaps, its interaction with the immune system.