The objective of this proposal is to study the aromatization of androgens to estrogens and other closely related steroid interconversions in primary surface cultures of fetal rat hypothalamic cells. Such cultures, in which neuronal growth and morphology is enhanced by treatment with cytosine arabinoside, have proved to be a reliable and quantitative system in which to follow estrogen biosynthesis. Such cultures also provide the means by which the regulation of steroid biosynthesis can be easily examined. Preliminary experiments have provided the impetus for the proposed undertaking. First, the addition of norepinephrine or dopamine to the cultures for at least two days causes a marked decline in aromatization. Second, the effect of catecholamines is mimicked by a 2-hydroxyestrone, a catechol estrogen, but not by estrone itself. This proposal is aimed, therefore, at answering the following questions: (1) What is the nature of the catecholamine-induced decrease in aromatization in hypothalamic cultures? (2) What is the effect of steroid hormones on aromatization? (3) What is the effect of catecholamines and steroids on other potentially important steroidogenic enzymes found in the hypothalamus, the 5alpha-reductase and 2-hydroxylase? (4) What cell type(s) in the hypothalamus contain the aromatase, 5alpha-reductase, and 2-hydroxylase? Concurrent with our study of steroidogenic enzymes, the effect of addition of the various catecholamines and steroids on the concentration of immunoreactive neurotensin, substance P, and GnRh will be monitored.