Serotonin receptor binding in a colony model of chronic social stress.

Male rats housed in mixed-sex groups quickly established dominance hierarchies in which subordinates appeared severely stressed. Subordinate rats had elevated basal corticosterone (CORT) levels relative to dominants and individually housed controls. Several subordinates had blunted CORT responses to a novel stressor, leading to the classification of subordinates as either stress-responsive or nonresponsive. Binding to 5-HT1A receptors was reduced in stress-responsive subordinates compared to controls throughout hippocampus and dentate gyrus. Decreased binding was observed in nonresponsive subordinates only in CA3 of hippocampus. In addition, 5-HT1A binding was decreased in CA1, CA3, and CA4 in dominants compared to controls. Binding to 5-HT2 receptors was increased in parietal cortex in both responsive and nonresponsive subordinates compared to controls. No changes were observed in binding to 5-HT1B receptors. These results are discussed in the context of regulation of the serotonergic system by stress and glucocorticoids and possible relevance to the pathophysiology of depression.