ONTOGENY OF BETA-ENDORPHIN IN THE MEDULLA OBLONGATA

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There is evidence that Sudden Infant Death Syndrome occurs as a result of a dysfunction of the respiratory centers in the central nervous system. There is also evidence that exogenous administration of opioid peptides can exert depressor action on the medullary respiratory centers. Since the medulla oblongata is the site of several distinct sets of neurons which synthesize the opioid precursors pro-opio-melanocortin, pro-enkephalin and pro- dynorphin, the possibility exists that these endogenous opioid peptide systems may modulate the medullary respiratory centers. Research in this area would be aided by studies on animal model systems. This proposal focuses on the pro-opiomelanocortin system in the medulla oblongata of the rat during ontogeny. The objectives of these projects are to determine whether there are developmental changes in the degree of proteolytic processing of pro-opio- melanocortin and the degree of N-acetylation of beta-endorphin during late fetal and neonatal development. The project will be approached in two phases. The first series of experiments will involve a steady state analysis of the forms of pro-opiomelanocortin-related end products in the medulla. Tissue collected at fetal day 16, day 18 and neonatal day 1, 7, 14, and 21 will be separately fractionated by gel filtration and analyzed by series of radioimmunoassays specific for beta-endorphin, alpha- MSH and ACTH(1-39). The degree of N-acetylation of beta- endorphin and alpha-MSH will be determined by ion exchange chromatography and reverse phase HPLC, respectively. The second series of experiments will attempt to study the pro- opiomelanocortin biosynthetic pathway in medullary fetal neurons in culture. Dispersed neurons will be pulsed with tritiated tyrosine and the newly synthesized peptides will be isolated by immunoaffinity chromatography and analyzed by SDS PAGE. These projects will provide insights into the developmental appearance of the pro-opiomelanocortin system in the medulla oblongata. This information will be useful for designing experiments to test the potential involvement of endogenous beta-endorphin in the depression of the medullary respiratory complex.