Effect of independent deafferentation of each border of the medial basal hypothalamus on catecholamine content of the median eminence and on serum LH and prolactin levels in ovariectomized rats

Abstract

The purpose of this work was to correlate the norepinephrine (NE) and dopamine (DA) content in the region of the median eminence (ME) with serum levels of LH and prolactin in ovariectomized rats after independent deafferentation of each one of the borders of the medial basal hypothalamus (MBH). Surgical transections of the MBH or sham operations, followed by ovariectomy, were performed in adult female Holtzman rats. The following types of transections were performed: bilateral, dorsal or rostral and caudal. One week later, the animals were decapitated, trunk blood was collected for LH and prolactin quantification by RIA and the region of the ME was dissected out for catecholamine assay. Both NE and DA were measured in each individual sample by a highly sensitive enzymatic-isotopic method. Bilateral transections of the MBH induced a significant decrease in NE in the region of the ME, without altering DA levels in the same area or LH and prolactin values. Cuts of the rostral and caudal or dorsal borders of the MBH did not modify any of the parameters evaluated. These results indicate that: (a) Most noradrenergic fibers innervating the ME enter the MBH through the lateral borders. However, some residual NE activity in the ME can be detected, suggesting other sources of noradrenergic innervation of the ME. (b) Normal levels of NE in the ME are not required for the LH post-castration rise to take place.