Social status and the adrenal medulla in the house mouse ( Mus musculus, L.)

Abstract

The relationships between social status (behavioral comparisons between aggressive dominants and submissive subordinates) and adrenomedullary catecholamine metabolism were studied in male “TO” strain mice. Isolated mice subjected to brief daily encounters with conspecifics over a period of several weeks were investigated. Twenty-four hours after the final encounter, mice were sacrificed and adrenal epinephrine and norephinephrine content and phenylethanolamine N-methyltransferase activity were measured. Estimates of pituitary—adrenocortical and pituitary—gonadal activity were also made. In a number of different experimental designs, a distinction was made between mice repeatedly experiencing victory in the paired encounters and those experiencing defeat. Control animals were denied social contact with a conspecific. Generally, mice experiencing defeat showed a marked increase in adrenal weight, phenylethanolamine N-methyltransferase activity, and epinephrine content but no change in norepinephrine content. By contrast, victors were characterized by an increase in norepinephrine content but much smaller enhancements of adrenal weight, phenylethanolamine N-methyltransferase activity, and epinephrine. A series of daily injections of adrenocorticotrophic hormone produced some adrenal changes similar to those seen in defeated mice, i.e., a marked elevation of adrenal weight and phenylethanolamine N-methyltransferase activity. A depletion in epinephrine content was recorded in mice sacrificed 12 hr after the final injection, indicating that adrenocorticotrophic hormone may play some role in stimulating adrenal epinephrine release. It is suggested that the differences in the pattern of adrenal responses to intermale agonistic behavior in victors compared with defeated individuals indicate stimulation predominantly via a neural pathway in dominants and via a hormonal pathway in subordinates.