Decreases in serotonergic activity in the central nucleus of the amygdala reduce responses to stressors, suggesting an important role for serotonin in this region of the amygdala in stress reactivity. However, it is not known whether exposure to stressors actually increases serotonin release in the central nucleus of the amygdala. The current experiment tested the hypothesis that restraint stress increases extracellular serotonin within the central nucleus of the amygdala and adjacent medial amygdala using in vivo microdialysis in awake male rats during the dark phase of the light-dark cycle. Serotonin release in the central nucleus increased immediately in response to restraint stress. In contrast, there was no change in serotonin release within the adjacent medial amygdala during or following restraint. Since corticotropin-releasing factor is an important mediator of both responses to stressors and serotonergic activity, subsequent experiments tested the hypothesis that central nucleus serotonergic response to restraint stress is mediated by central corticotropin-releasing factor receptors. Administration of the corticotropin-releasing factor type 1 and 2 receptor antagonist d-Phe-CRF (icv, 10 microg/5 microl) prior to restraint stress suppressed restraint-induced serotonin release in the central nucleus. The results suggest that restraint stress rapidly and selectively increases serotonin release in the central nucleus of the amygdala by the activation of central corticotropin-releasing factor receptors. Furthermore, the results imply that corticotropin-releasing factor mediated serotonergic activity in central nucleus of the amygdala may be an important component of a stress response.