Melatonin receptors in the pituitary of a teleost fish: mRNA expression, 2-[(125)I]iodomelatonin binding and cyclic AMP response.
Melatonin has for a long time been involved in the photoperiodic control of fish physiology (growth, reproduction) and behavior (locomotor activity); but its mechanisms of action are not understood. We show here that 2-[(125)I]iodomelatonin binds specifically to membrane preparations from Pike (Esox lucius, L.) pituitaries (K(D): 556 pM; B(max): 2.8 fmol/mg proteins). Radioautography indicated that the binding was restricted to a part of the pituitary only. Using polymerase chain reaction from pike genomic DNA, we subcloned two partial cDNAs encoding the P1.4 (Mel(1a)) and the P2.6 (Mel(1b)) melatonin receptor subtypes. The two corresponding transcripts were expressed in the pituitary as revealed by RT-PCR assay and Southern blot hybridization. In culture, melatonin inhibited in a time- and dose-dependent manner cyclic AMP levels in pituitaries cultured in the presence of forskolin, an adenylyl cyclase activator. This is the first evidence for the expression of melatonin receptors and binding sites, and for the modulation of a second messenger by melatonin in the pituitary of a nonmammalian species. We suggest that in fish, the melatonin-mediated photoperiodic control of neuroendocrine functions involves, at least, a direct effect on the pituitary.
Département des Neurosciences, Laboratoire de Neurobiologie Cellulaire, CNRS UMR 6558, Université de Poitiers, France.
P
P
Gaildrat
J
J
Falcón
D000818:Animals; D002478:Cells, Cultured; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism*; D018076:DNA, Complementary; D017859:Esocidae / Q000235:genetics*; D005260:Female; D015870:Gene Expression / Q000502:physiology; D007457:Iodine Radioisotopes; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics; D010902:Pituitary Gland / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
C094611:2-iodomelatonin receptor; D018076:DNA, Complementary; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C044556:2-iodomelatonin; D000242:Cyclic AMP; D008550:Melatonin