CYCLIC VARIATIONS OF CATECHOLAMINE CONTENT IN HYPOTHALAMIC NERVE CELLS DURING THE ESTROUS CYCLE OF THE RAT, WITH A CONCOMITANT STUDY OF THE SUBSTANTIA NIGRA

¹ Department of Pharmacology, University of Zürich, Zürich, Switzerland

The intensity of the catecholamine fluorescence was measured in nerve cells of the tuberal region and of the substantia nigra by means of an adaptation for microfluorimetry of the fluorescence method of Falck and Hillarp. At 2 P.M. on each day of the 4-day estrous cycle, the frequency distribution of fluorescence intensities (relative to a norepinephrine standard) was established by measuring the fluorescence of individual cells in sections from the brains of five rats. It was found that the mean relative fluorescence intensity and the symmetry of the frequency distribution change significantly in the tuberal region from one day to the other, with a general shift toward increased fluorescence intensities from diestrous day 1 to estrous day. The substantia nigra shows a different rhythm with only a slight change in the mean relative fluorescence intensity and no change in the symmetry of the frequency distribution. These findings are interpreted as reflecting activity changes of the neurons and are discussed with regard to a possible role of tubero-infundibular catecholamine-containing neurons in the control of anterior pituitary function.