A comparison of acute stress paradigms: Hormonal responses and hypothalamic serotonin

The effects of stress on plasma renin activity (PRA), plasma prolactin and corticosterone levels, and hypothalamic 5-HT and 5-HIAA concentrations were investigated using a 3 and 12 min conditioned fear (CER) paradigm; 20 min immobilization; 20 min exposure to shallow or deep cold water; 2, 12 and 22 min of intermittent footshock with or without 20 min recovery; and, a 3 min CER with 0, 10, 30 and 60 min recovery. PRA was increased by all the stressors, except shallow cold water, reaching a maximun after 12 min and returning to control values within 10-20 min post-stress. Prolactin levels also were increased by all the stressors, except shallow and deep cold water. Prolactin levels were maximal after 12 min and returned to baseline within 20-60 min post-stress, depending on the stressor. Corticosterone levels were elevated by all the stressors, but not as rapidly as PRA or prolactin, reaching a maximum after about 20 min and returning to baseline concentrations within 30-60 min post-stress. None of the stressors produced significant changes in hypothalamic 5-HT and 5-HIAA concentrations.