Melanotrophs of Xenopus laevis do respond directly to neuropeptide-Y as evidenced by reductions in secretion and cytosolic calcium pulsing in isolated cells.
Neuropeptide-Y (NPY) is present, along with dopamine and gamma-aminobutyric acid, in the neurons innervating the intermediate lobe of the pituitary gland of Xenopus laevis, and all three neurotransmitters have been shown to inhibit melanotroph secretion from isolated neurointermediate lobes. However, unlike dopamine and gamma-aminobutyric acid, NPY has been reported to be without inhibitory effect on secretion from dispersions of intermediate lobe cells. Moreover, binding studies have been taken as indicating that Xenopus melanotrophs lack NPY receptors, although such receptors appear to be present on folliculostellate cells. For these reasons, NPY has been considered to act indirectly on Xenopus melanotrophs; the putative intermediary is supposed to be the folliculo-stellate cell. However, the present experiments show that NPY does strongly inhibit melanotroph secretion from cells dispersed from Xenopus intermediate lobes. In addition, they demonstrate that NPY acts directly on individual Xenopus melanotrophs (immunohistochemically identified and under conditions that preclude any interaction between cells) to inhibit the intermittent rises in cytosolic free Ca (cytosolic Ca pulsing). From these observations, we conclude that NPY does act directly on melanotrophs of Xenopus.
Kongsamut
S
S
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
Shibuya
I
I
Uehara
M
M
Douglas
W W
WW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009478:Neuropeptide Y / Q000494:pharmacology*; D010902:Pituitary Gland / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D014982:Xenopus laevis; D000521:alpha-MSH / Q000032:analysis
D009478:Neuropeptide Y; D000521:alpha-MSH; D009074:Melanocyte-Stimulating Hormones; D002118:Calcium