The Effect of Endocrinological Manipulations on Tyrosine Hydroxylase and Dopamine-β-Hydroxylase Activities in Individual Hypothalamic Nuclei of the Adult Male Rat11

Abstract

Using a recently developed microdissection method, individual hypothalamic nuclei were removed from the brains of adult male rats, and the tyrosine hydroxylase (TH) and dopamine-β- hydroxylase (DBH) activities in each nucleus were determined 9 days after adrenalectomy, thyroidectomy or gonadectomy. Following gonadectomy there was a significant rise in the TH activity in only the median eminence (ME). This increased TH activity was partially reversed by treatment of gonadectomized animals with testosterone. Thyroidectomy induced a significant increase in the TH activity in the ME, the dorsomedial (NDM), the periventricular (NPE) and the arcuate (NARC) nuclei. Twelve hr after administration of thyroxine, the TH activity in the ME of thyroidectomized rats was significantly reduced to levels below those of controls, whereas the TH activities of the other nuclei were returned to control values. Adrenalectomy produced a significant fall in TH activity in the ME, whereas dexamethasone significantly increased the TH activity of the ME of adrenalectomized animals. DBH activity was not altered by any of these endocrine manipulations, nor by treatment with reserpine for 7 days. It is concludedthat hypothalamic catecholaminergic nerve terminals participate in the feedback regulation of the thyroid, adrenals and gonads, and that these terminals are located in the ME. (Endocrinology95: 799, 1974)