DISTRIBUTION OF PROOPIOMELANOCORTIN AND ITS PEPTIDE END-PRODUCTS IN THE BRAIN AND HYPOPHYSIS OF THE AQUATIC TOAD, XENOPUS-LAEVIS

Using in situ hybridization with a pro-opio-melanocortin (POMC)-mRNA p robe and immunocytochemistry with antisera to POMC and to various POMC -derived peptides, it is shown that melanotrope cells in the pars inte rmedia of the hypophysis of the South African aquatic toad Xenopus lae vis contain POMC, alpha-melanophore-stimulating hormone (alpha-MSH), g amma-MSH, acetylated and non-acetylated endorphins and adrenocorticotr opic hormone (ACTH). With the exception of gamma-MSH, these peptides a re also found in the corticotrope cells in the rostral pars distalis. In the Xenopus brain, neuronal cell bodies in the ventral hypothalamic nucleus express POMC, alpha-MSH, gamma-MSH, non-acetylated endorphins and ACTH, neurones in the anterior preoptic area reveal POMC, alpha-M SH, gamma-MSH and non-acetylated endorphin, neurones in the suprachias matic nucleus contain alpha-MSH, non-acetylated endorphin and ACTH and neurones in the posterior tubercle show alpha-MSH, non-acetylated end orphin and ACTH immunoreactivities. In the locus coeruleus POMC and AC TH coexist, whereas alpha-MSH and non-acetylated endorphin occur toget her in the nucleus accumbens, the striatum and the nucleus of the para ventricular organ. Finally, alpha-MSH alone is present in the olfactor y bulb, the medial septum, the medial and lateral parts of the amygdal a, the ventromedial and posterior thalamic nuclei, the optic tectum an d the anteroventral tegmental nucleus, and non-acetylated endorphin al one appears in the epiphysis. It is suggested that neurones that form POMC-derived peptides may play a direct or indirect role in the contro l of POMC-producing hypophyseal cells and/or in the physiological proc esses these endocrine cells regulate. This idea is supported by the fa ct that the suprachiasmatic nucleus and the locus coeruleus, both invo lved in melanotrope cell control, show POMC and POMC-peptide expressio n. A possible involvement in melanotrope and/or corticotrope control o f the anterior preoptic and ventral hypothalamic nuclei, which both ex press POMC and various POMC-derived peptides, deserves future attentio n.