Effect of 6-hydroxydopamine on hypothalamic norepinephrine and dopamine content, ultrastructure of the median eminence, and plasma corticosterone

Abstract

The effects of 6-hydroxydopamine on the catecholamine content of the hypothalamus and other tissues, the morphology of the median eminence of the hypothalamus, and plasma corticosterone were studied after intraperitoneal injection of the drug. The effect of injecting 6-hydroxydopamine into the third ventricle of the brain in unanesthetized animals was also studied. One day after injection by either route, hypothalamic norepinephrine was reduced and plasma corticosterone was elevated, suggesting increased secretion of ACTH from the pituitary. There were degenerative changes in a small number of neurons ending in the external layer of the median eminence, while other neurons in the median eminence were unaffected. Fifteen days after injection, hypothalamic norepinephrine and plasma corticosterone had returned to normal in the animals given 6-hydroxydopamine intraperitoneally. In the rats injected intraventricularly, hypothalamic norepinephrine was still reduced but plasma corticosterone was normal. In both groups at 15 days, neuronal debris had accumulated in phagocytic cells, but most neurons appeared normal. The data provide evidence that norepinephrine-containing neurons end in the external layer of the median eminence. They are also consistent with the hypothesis that a central adrenergic system inhibits ACTH secretion. Fifteen days after injection, an as yet unknown mechanism compensates for the decrease in norepinephrine content and ACTH secretion returns to normal.