IMMUNOCYTOCHEMICAL LOCALIZATION OF POMC-DERIVED PEPTIDES (ADRENOCORTICOTROPIC HORMONE, ALPHA-MELANOCYTE-STIMULATING HORMONE AND BETA-ENDORPHIN) IN THE PITUITARY, BRAIN AND OLFACTORY EPITHELIUM OF THE FROG, RANA-ESCULENTA, DURING DEVELOPMENT

Developmental stages of Rana esculenta, starting with the posterior li mb-bud stage (stage 26) up to a few days after metamorphosis, were exa mined immunohistochemically to localize cells and fibers producing som e POMC-derived peptides, namely, alpha-MSH, ACTH and beta-END. Anti AC TH and anti alpha-MSH revealed a positive reaction in the pars interme dia during all stages of development included in this study, whereas n o immunoreactivity in this pituitary zone was ever evidenced with anti beta-END. In the pars distalis strongly positive cells were seen with anti ACTH and anti beta-END, while anti alpha-MSH yielded weakly posi tive cells. Interestingly, these peptides were colocalized in the same cells. Immunoreactivity for alpha-MSH was no longer present in the pa rs distalis during metamorphic climax and postmetamorphosis. In the br ain of premetamorphic tadpoles, belonging to stages 26 to 30, a few ne urons in the posterior telencephalon showed a positive reaction only w ith anti alpha-MSH,but from stage 31 (prometamorphosis) onwards, ACTH and beta-endorphin-like peptide producing cells, together with alpha-M SH-immunoreactive cells, were seen in this region and in the anterior preoptic area and infundibulum. This situation persisted in the subseq uent stages of development. Anti alpha-MSH also revealed weakly positi ve cells in the olfactory epithelium in premetamorphic tadpoles; stron g immunoreactivity with anti alpha-MSH was seen in olfactory epitheliu m cells in animals during prometamorphosis, metamorphic climax and pos tmetamorphosis. The possible significance of these findings is briefly discussed.