Norepinephrine and Dopamine Turnover Rates in the Medial Preoptic Area and the Mediobasal Hypothalamus of the Rat Brain after Various Endocrinological Manipulations*

Abstract

Norepinephrine (NE) and dopamine (DA) turnover rates were measured in the medial preoptic area (MPO) and in the anterior and posterior mediobasal hypothalamus (AMBH and PMBH) in groups of rats subjected to various endocrinological manipulations. NE turnover in the MPO was high in proestrous, ovariectomized, ovariectomized estrogenprimed, and ovariectomized, estrogen-primed, progesteronetreated rats when the experiments were carried out during afternoon hours. Diestrous rats had low NE turnover rates in the MPO. The NE turnover rate was also low when measured in ovariectomized, estrogen-primed animals decapitated in the morning. These turnover rates parallel low serum LH levels. NE turnover in the AMBH and PMBH was low in diestrous and ovariectomized animals during afternoon hours and was also low in ovariectomized estrogen-primed rats during morning hours. High NE turnover rates in these structures were measured in proestrous, ovariectomized, estrogen-primed and estrogenprimed, progesterone-treated rats killed in the afternoon. These turnover rates parallel high serum PRL levels. No relationship could be established between DA turnover rates in the MPO, AMBH, or PMBH and serum hormone levels. It is suggested that NE stimulates LHRH release by acting in the MPO. Because of the parallelism between NE turnover in the MBH and serum PRL levels as well as the lack of inverse parallelism between NE turnover and DA turnover in this structure, it is suggested that NE acts in the MBH either to stimulate the release of a PRL-releasing factor or to inhibit the release of a PRL-inhibiting factor. (Endocrinology106: 1848, 1980)