Electrical Stimulation of the Hypothalamus: Simultaneous Effects on the Pituitary-Adrenal and Thyroid Systems of the Rat

Abstract

Electrical stimulation of various sites in the medial ventral hypothalami of adult female rats was done through chronically implanted electrodes in order to determine simultaneous effects on the pituitaryadrenal and thyroid systems. A series of stimulations (10 min daily, 4–9 days) delivered to preoptic, suprachiasmatic and anterior hypothalamic areas induced cytological activation of pars distalis basophils, markedly reduced pituitary thyrotrophin (TSH) stores, increased plasma TSH concentrations 4- to 5-fold, and resulted in histological stimulation of the thyroid gland. Comparable excitation of the posterior median eminence and arcuate nuclear regions of the tuberal hypothalamus produced effects of similar magnitude. The mere presence of electrodes in the hypothalamus without electrical stimulation had no significant effect on TSH secretion and histology of the thyroid, but caused adrenal hypertrophy and elevation of plasma corticosteroid levels in sham-stimulated rats. Excitation of the rostral or caudal hypothalamic regions induced further adrenal enlargement without substantial change in other indices of adrenocortical activity. Electrical stimulation of the anterior hypothalamus failed to reverse the atrophic changes in the adrenals and thyroids of hypophysectomized rats. No significant correlation between plasma corticosteroid levels and intensity of TSH secretion was observed. Propylthiouracil administration reduced the adrenal response to anterior hypothalamic stimulation. The results support the view that the portions of the hypothalamus involved in the regulation of TSH and ACTH secretion are overlapping and diffuse rather than discrete. Evidence is also presented which indicates that the increased adrenocortical function after stimulation of the ventral hypothalamus is mediated, in part, via a direct action of thyroid hormone on pituitary ACTH secretion. (Endocrinology75: 417, 1964)