[State of the hypothalamic centers in short-term cooling in rats].

It has been shown morphometrically that a short-term cold exposure of rats (4 degrees C for 2 h) gives rise to an activation of the thyroid gland, paraventricular and ventromedial nuclei of the hypothalamus and to the enhanced neurohormonal release into the posterior pituitary vessels and into some areas of the median eminence. No significant changes were recorded in the supraoptic nucleus. The activity of the arcuate nucleus is likely to be reduced, being manifested in the diminution of nucleolar size. It might be thus assumed that function of the paraventricular and ventromedial nuclei correlates well with that of the thyroid gland. The arcuate and supraoptic nuclei apparently exert no activating effect on the thyroid gland.