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Immunocytochemical localisation of hydroxyindole‐O‐methyltransferase in pineal photoreceptor cells of several fish species
Author(s) -
Falcón Jack,
Bégay Valérie,
Goujon Jean Michel,
Voisin Pierre,
Guerlotté Jérome,
Collin JeanPierre
Publication year - 1994
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903410410
Subject(s) - biology , melatonin , pineal gland , pinealocyte , trout , killifish , pike , zoology , microbiology and biotechnology , fish <actinopterygii> , endocrinology , fishery
Melatonin is an internal “Zeitgeber,” involved in the timing and control of a number of rhythmic functions and behaviours. Its synthesising cells remain to be identified in the fish pineal. The last step in the melatonin biosynthetic pathway is catalysed by the enzyme hydroxyindole‐O‐methyltransferase. An affinity‐purified antibody, directed against chicken pineal hydroxyindole‐O‐methyltransferase, was used in the present study to identify the melatonin synthesising cells in four fish species: a primitive chondrostean (sturgeon), a saltwater teleost (dorado), and two freshwater teleosts (pike, trout). Western blot immunolabeling of pike and trout pineal proteins revealed a single band at 38 KDa, which corresponds to the known molecular weight of the enzyme in bovine, rat, and chicken pineal. Regardless of the species, a specific immunocytochemical labeling, visualised by means of the peroxidaseantiperoxidase method, was exclusively associated with the photoreceptor cells. These results provide evidence that photoreceptors of the fish pineal are responsible for the biosynthesis of 5‐methoxyindoles, including melatonin. In the pike, reactions were less intense in the distal portion of the pineal vesicle than in the other regions of the organ. It is questioned whether this might be related to the existence of a germinative zone, generating new photoreceptor cells in this distal portion. Hydroxyindole‐O‐methyltransferase has been previously demonstrated in mammalian pinealocytes, and modified photoreceptors of the avian pineal. It is now demonstrated in pineal photoreceptors of a primitive fish and of more evolved saltwater and freshwater fish. The results strengthen the view that these cells are related through phylogeny and that their well conserved melatoninergic function appears early in the course of evolution.