IMMUNOCYTOCHEMICAL EVIDENCE FOR THE PRESENCE OF MET-ENKEPHALIN AND LEU-ENKEPHALIN IN DISTINCT NEURONS IN THE BRAIN OF THE ELASMOBRANCH FISHSCYLIORHINUS-CANICULA

Immunohistochemical methods have been used to investigate the distribu tion of various opioid peptides derived from mammalian proenkephalin i n the central nervous system of Scyliorhinus canicula. The results ind icate that both Leu- and Met-enkephalin-immunoreactive peptides are pr esent in the dogfish brain. In contrast, enkephalin forms similar to M et-enkephalin-Arg-Phe or Met-enkephalin-Arg-Gly-Leu, and mammalian alp ha-neo-endorphin, dynorphin A (1-8), dynorphin A (1-13), and dynorphin A (1-17) were not detected. Met- and Leu-enkephalin immunoreactivitie s were found in distinct neurons of the telencephalon and hypothalamus . In particular, cell bodies reacting only with the Metenkephalin anti serum were localized in the preoptic nucleus and in the suprachiasmati c region of the hypothalamus. Conversely, cell bodies reacting only wi th the Leu-enkephalin antiserum were localized in the pallium and the nucleus lobi lateralis hypothalami. Several areas of the telencephalon and diencephalon exhibited both Met- and Leu-enkephalin-like immunore activity, but the two immunoreactive peptides were clearly contained i n distinct perikarya. The overall distribution of Met-enkephalin-immun oreactive elements in the dogfish brain exhibited similarities to the distribution of proenkephalin-derived peptides previously reported for the brain of tetrapods. The fact that Met- and Leu-enkephalin-like pe ptides were detected in distinct neurons, together with the absence of dynorphin-related peptides, suggests the existence of a novel Leu-enk ephalin-containing precursor in the dogfish brain. (C) 1994 Wiley-Liss , Inc.