THE EFFECT OF NEUROINTERMEDIATE LOBE DENERVATION ON HYPOTHALAMIC NEUROENDOCRINE DOPAMINERGIC-NEURONS

The contribution of tuberohypophyseal and periventricular-hypophyseal dopaminergic neurons to the regulation of the secretion of prolactin ( PRL) has yet to be clarified. In this study, we used pituitary stalk c ompression to disrupt hypothalamic neural input to the neurointermedia te lobe (NIL). Neurointermediate lobe denervation (NIL-D) selectively disrupts the axons of tuberohypophyseal and periventricular-hypophysea l dopaminergic neurons, while leaving tuberoinfundibular dopaminergic neurons and the vascular supply of the pituitary gland intact. NIL-D w as performed in ovariectomized (OVX) rats. The concentration of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence (ME) an d various regions of the pituitary gland of OVX and OVX + NIL-D rats w ere measured by HPLC-EC, The concentration of PRL, alpha-melanocyte st imulating hormone (alpha-MSH), and luteinizing hormone (LH) in serum w ere determined by radioimmunoassay. Successful NIL-D was confirmed by increased water intake. One week after NIL-D, serum PRL and alpha-MSH were elevated, but there was no change in the concentration of LH in s erum. The concentration of DA was increased in the median eminence (ME ), decreased in the outer zone of the anterior lobe (AL-OZ), as well a s the intermediate (IL) and neural lobes (NL), and remained unchanged in the inner zone of the anterior lobe (AL-IZ). The concentration of D OPAC was increased in the ME and NL, decreased in the IL, and remained unchanged in both the AL-IZ and AL-OZ, These data confirm that pituit ary stalk compression denervates the NIL, Moreover, decreases in the c oncentration of DA in the IL and AL-OZ, coupled with elevation of seru m PRL and alpha-MSH indicate that DA from the NIL contributes to the i ncreased inhibition of the secretion of PRL and alpha-MSH in OVX rats. (C) 1998 Elsevier Science B.V. All rights reserved.