In situ Estradiol and Progestin (R5020) Localization in the Vascularly Separated and Isolated Hypothalamus of the Rhesus Monkey

Abstract

A neurosurgical procedure has been developed for vascular isolation of the hypothalamus-thalamus region of the rhesus monkey brain. Utilizing this preparation, the left and right halves of the hypothalamus were perfused simultaneously, but separately, with a dextran-blood solution. Radiolabeled steroids were directly perfused in the dextran-blood into either the left or right half of the hypothalamus. Studies with radiolabeled gonadal steroids indicate that the majority of the carotid circulation is confined to the hypothalamus-thalamus area in this brain preparation and the cross-circulation of labelled steroids between the left and right sides of the hypothalamus is less than 10%. The usefulness of the preparation is illustrated by an autoradiographic study of the in situ hypothalamic distribution of (³H)estradiol in ovariectomized rhesus monkeys and of the synthetic progestin (³H)R5020 in estrogen-primed, ovariectomized rhesus monkeys. The direct perfusion of the (³H) steroids into the hypothalamus greatly increases the sensitivity of such a study compared to systemic administration of the (³H) steroids. The perfusion of one-half of the hypothalamus with (³H) steroid and the other half with (³H)steroid plus radioinert steroids permits in 1 animal, acting as its own control, the examination of a saturable distribution of a gonadal steroid in the rhesus monkey hypothalamus.