[I-125] BOLTON-HUNTER NEUROPEPTIDE-Y-BINDING SITES ON FOLLICULO-STELLATE CELLS OF THE PARS-INTERMEDIA OF XENOPUS-LAEVIS - A COMBINED AUTORADIOGRAPHIC AND IMMUNOCYTOCHEMICAL STUDY

It has previously been established that neuropeptide-Y (NPY) is a potent inhibitor of alpha-MSH release from the pars intermedia of the amphibian Xenopus laevis. The location of binding sites for NPY in the pars intermedia of the pituitary has now been studied with light microscopic autoradiography, using a dispersed cell labeling method with the specific NPY receptor ligand [I-125]Bolton-Hunter NPY. The majority of radioactive labeling was associated with folliculo-stellate cells; the percentage of labeling as well as the mean number of grains were approximately 5 times higher for folliculo-stellate cells than for melanotropes. An excess of nonlabeled NPY drastically reduced radiolabeling of folliculo-stellate cells, but had no effect on the degree of labeling of melanotropes. These results show that folliculo-stellate cells of X. laevis possess specific binding sites for NPY and indicate that NPY exerts its inhibitory action on the release of alpha-MSH in an indirect fashion, by acting on the folliculo-stellate cells.