EVIDENCE FOR AN ENDOGENOUS CLOCK IN THE RETINA OF RAINBOW-TROUT - II - CIRCADIAN RHYTHMICITY OF SEROTONIN METABOLISM

THE purpose of the present study was to investigate patterns of circad ian rhythmicity in the retina of a salmonid fish, the rainbow trout (O ncorhynchus mykiss). Our data present the first demonstration of intra retinal variations of serotonergic substances under light/dark-conditi ons (LD) and during continuous darkness (DD). All substances examined (serotonin, N-acetyl serotonin, 5-hydroxytryptophol, 5-hydroxyindole a cetic acid) were rhythmic in LD. Serotonin, N-acetyl-serotonin, and 5- hydroxyindole acetic acid showed a preservation of specific features o f rhythmicity in DD indicating the involvement of an endogenous pacema ker in the regulation of serotonin metabolism in the rainbow trout eye . (C) 1998 Rapid Science Ltd.