Concentrations of dopamine and norepinephrine in discrete hypothalamic nuclei during the rat estrous cycle.

The norepinephrine (NE) and dopamine (DA) concentrations of the medial preoptic nucleus (MPN), suprachiasmatic nucleus (SCN), arcuate nucleus (AN), ventromedial nucleus (VMN) and median eminence (ME) were measured during the estrous cycle. Nuclei were microdissected and assayed using the catechol-0-methyl transferase enzymatic method. A significant increase in NE was observed between the morning and afternoon of proestrus (P) in the SCN. In contrast, no significant changes in DA were detected in any area on P. No change in NE or DA was found between the morning and afternoon of diestrus 1 (D1). These findings are consistent with NE-containing neurons being involved in the surge of LH on the afternoon of proestrus.