Inhibitory action of midbrain raphe stimulation on stress-induced elevation of plasma corticosterone level in rats.

Electric stimulation of rat midbrain raphe nuclei by means of chronically implanted bipolar electrodes was able to reduce the stress-induced increase in plasma corticosterone level by about 40-50%. A serotonin receptor blocker, methysergide, prevented the stimulation-induced inhibition of the stress response. The results support the possible existence of serotoninergic inhibition of hypothalamo-pituitary-adrenocortical activation in rats.