Impact of social conflict between mice on testosterone binding in the central nervous system

Adult male mice previously isolated for 14 days, were maintained in pairs as residents and intruders. They were categorized as dominant or subordinate on the basis of initiation of attacks and of wounding. After 10 days, the amount of free cytoplasmic testosterone receptors was determined in a part of the basal forebrain consisting of septum, diencephalon, corpus striatum, and amygdala. In addition, the plasma testosterone level and the activity of the adrenal tyrosine hydroxylase were measured. The adrenal tyrosine hydroxylase activity was increased in the dominant and the subordinate mice compared to isolated controls. Subordinates had higher tyrosine hydroxylase activities than dominants. The specific testosterone in brain cytosol of dominants were freed like those of 6-day castrates despite the fact that the plasma testosterone concentration of dominants (717 ng/100 ml) was not significantly decreased compared to controls (1,003 ng/100 ml). In subordinates, the plasma testosterone content fell to 265 ng/100 ml while castrated mice showed 20-43 ng/100 ml. The amount of free testosterone specific binding sites in the brain cytosol of subordinates corresponded to that of 10-day castrates. Thus, the amount of circulating total testosterone does not seem to be the only factor determining the binding of available testosterone in brain cytosol.