Carassius RFamide, a novel FMRFa-related peptide, is produced within the retina and involved in retinal information processing in cyprinid fish

Carassius RFamide (C-RFa) is a novel peptide, isolated originally from the brain of the Japanese crucian carp and sharing homologies with mammalian pr olactin-releasing peptide (PrF;P). It has been demonstrated previously that C-RFa mRNA is abundant in the proximal half (fundus) of the Japanese cruci an carp eye. In the present work, we localized C-RFa by immunohistochemistr y mainly to perikarya, in the proximal half of the inner nuclear layer (ama crine cell layer). This distribution is different from that of FMRFamide, w hich is confined to axon terminals of terminal nerve efferent fibers in the inner plexiform layer. Electrophysiological recording revealed that C-RFa depolarized some amacrine cells and hyperpolarized L-type horizontal cells in the carp. These results suggest that C-RFa is produced within the cyprin id retina and functions as a transmitter or neuromodulator in retinal image processing. (C) 2000 Published by Elsevier Science Ireland Ltd.