CIRCADIAN PERIODICITY AND STRESS RESPONSIVENESS OF THE PITUITARY–ADRENAL SYSTEM OF RATS AFTER CENTRAL ADMINISTRATION OF 6-HYDROXYDOPAMINE

Abstract

SUMMARY Injection of 250 μg 6-hydroxydopamine (6-OHDA) into the lateral ventricle of adult male and female rats resulted 1 week later in: (1) a lowered brain content of noradrenaline to 20% and dopamine to 40–50% that of control levels but no change in brain serotonin content; (2) a slight reduction in male and no change in female body weight; (3) no change in adrenal weight; (4) minor or no changes in diurnal pituitary–adrenal periodicity or in the responsiveness of this system to ether stress, laparotomy or exposure to a strange environment and handling. Dexamethasone blockade of the diurnal rise in adrenocortical activity was also unchanged. Intracerebral administration of 200 μg 6-OHDA to newborn male and female rats in three sequential doses of 40, 60 and 100 μg, resulted at 12 weeks of age in (1) a lowered brain content of noradrenaline and dopamine to 10% that of control levels but no change in brain serotonin; (2) a 30% decrease in body weight; (3) no change in adrenal weight; (4) minor or no changes in pituitary–adrenal periodicity nor in the responsiveness to ether stress and exposure to a strange environment and handling. When minor changes after 6-OHDA treatment of adult or neonatal rats were found, they always pointed to a stimulatory function of brain catecholamines in pituitary–adrenal activity. It is concluded however that a severe and chronic depletion of brain catecholaminergic systems has no important consequences for the normal functioning of the pituitary–adrenal system.