Changes in brain norepinephrine content in mice following neonatal 6-hydroxydopamine

Treatment of mice with various doses of 6-hydroxydopamine (6-OHDA) between days 1 and 5 after birth produced decreases in body, forebrain and cerebellum weight at 6 and 18 days of age. Doses of 6-OHDA larger than 3 injections of 50 mg/kg did not augment the norepinephrine (NE) depletion in the cerebellum at 6 days of age. Different patterns of NE depletion and recovery were observed in the cerebellum, cerebral cortex and brainstem after injections of 50 mg/kg on day 1, days 1 and 3 or days 1, 3, and 5. In the cerebellum, but not in the cortex, NE content increased significantly between 8 and 24 hr post-injection. Sequential injections of 6-OHDA produced additional NE depletion 24 hr post-injection only in the cortex. At 18 days of age the extent of NE recovery in the cerebellum, but not in the brainstem or cortex, depended on the number of 6-OHDA injections. After 2 or 3 injections, NE concentrations in the cortex were significantly higher at 18 days (50-60% of the control) than at 24 hr post-injection (10-15% of control).