Stress induces rapid changes in serotonergic activity: restraint and exertion.

Rapid activation of central serotonergic systems occurs in response to the social stress of aggression in dominant lizards. The most rapid expression of serotonergic activity occurs in nucleus accumbens, hippocampus and brainstem. To compare previously measured responses induced by social stressors with those provoked by physical stress, serotonergic activity was examined following restraint stress (handling) and forced physical exertion. After handling, some male Anolis carolinensis were placed on a race track and either run until there was no movement following 1 min of prodding, or half that time. Controls were killed without treatment. Lizards stressed by handling showed rapid (25 s) increases in serotonergic activity (5-HIAA/5-HT) in striatum, dorsal cortex, locus ceruleus, and nucleus accumbens. Other changes in serotonergic systems caused by stress occurred in raphe and hippocampus. Serotonergic changes induced by handling stress were reversed by exercise (to 50% maximal exertion time) in subiculum, striatum and nucleus accumbens. The serotonergic profile of lizards run until they would no longer respond to prodding (maximal exertion time) was significantly different from that for more acute exertion in hippocampus, subiculum, striatum, medial amygdala, locus ceruleus, area postrema, and raphe. Physical stress (handling) mimicked social stress by producing rapid serotonergic changes in hippocampus, subiculum, nucleus accumbens and locus ceruleus. In contrast, the medial amygdala, which has previously been demonstrated to respond serotonergically to social stress only after a temporal delay, did not show a rapid response to restraint stress.