Serotonin regulation of corticoid secretion in infant rats

The plasma corticosterone response to various doses of serotonin and 5-hydroxytryptophan was studied in the 3-day-old rat. The maximum response to both drugs occurred 60 min after injection. Increased corticosterone concentration was observed at lower doses of serotonin than of 5-hydroxytryptophan. The effects of serotonin injection on Days 1-7 after birth on the plasma corticosterone response to 3 min of novelty stimulation at weaning was also studied. Serotonin treatment resulted in reduced adrenocortical reactivity which was reduced further when fluoxetine was given prior to the serotonin. Shocking rat pups on Days 1-7 also reduced adrenocortical reactivity and fluoxetine prior to shock further reduced adrenocortical reactivity when administered twice per day.