Evidence for an endogenous clock in the retina of rainbow trout: II. Circadian rhythmicity of serotonin metabolism

Neuroreport. 1998 May 11;9(7):1475-9. doi: 10.1097/00001756-199805110-00042.


The purpose of the present study was to investigate patterns of circadian rhythmicity in the retina of a salmonid fish, the rainbow trout (Oncorhynchus mykiss). Our data present the first demonstration of intraretinal variations of serotonergic substances under light/dark-conditions (LD) and during continuous darkness (DD). All substances examined (serotonin, N-acetyl serotonin, 5-hydroxytryptophol, 5-hydroxyindole acetic acid) were rhythmic in LD. Serotonin, N-acetyl-serotonin, and 5-hydroxyindole acetic acid showed a preservation of specific features of rhythmicity in DD indicating the involvement of an endogenous pacemaker in the regulation of serotonin metabolism in the rainbow trout eye.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Circadian Rhythm*
  • Darkness
  • Hydroxyindoleacetic Acid / metabolism
  • Hydroxytryptophol / metabolism
  • Light
  • Oncorhynchus mykiss / physiology*
  • Photoperiod
  • Retina / metabolism*
  • Serotonin / analogs & derivatives
  • Serotonin / metabolism*


  • Hydroxytryptophol
  • Serotonin
  • Hydroxyindoleacetic Acid
  • N-acetylserotonin