Adrenalcortical influence on rat brain tryptophan hydroxylase activity

Tryptophan hydroxylase activity in the midbrain of the rat increases as a consequence of electric foot shock, ether anesthesia, and cold exposure, all of which elevate plasma corticosterone levels. Bilateral adrenalectomy prevents this stress-induced increase in enzyme activity. Tryptophan hydroxylase activity and plasma corticosterone are both elevated at 6 p.m. compared to 8 a.m. Administration of corticosterone increases tryptophan hydroxylase activity in normal rats. Parachlorophenylalanine inhibits the stress-induced tryptophan hydroxylase activity. Tryptophan was found not to be directly involved in the stimulation of tryptophan hydroxylase activity but may be involved in the depression of tryptophan hydroxylase activity. Evidence is provided for suspecting that the serotonin neuronal system and the pituitary-adrenal endocrine system may participate in a reciprocal control loop.