Correlations between circadian changes in serum amino acids or brain tryptophan and the contents of serotonin and 5-hydroxyindoleacetic acid in regions of the rat brain

Abstract

Circadian changes in tryptophan, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were investigated in the cerebral cortex and the brain stem of male Sprague-Dawley rats previously exposed to a 14:10 light-dark (LD) lighting regimen. Control rats were provided food and water ad libitum while experimental rats were given food daily only between 10.00 and 14.00 h. Statistically significant circadian changes in 5-HIAA were observed in the cerebral cortex of the control and the experimental animals and in the brain stem of the experimental animals. Circadian changes in tryptophan were observed in the cortex and brain stem of control animals, but the magnitude of the daily changes in tryptophan in experimental animals was comparatively reduced so that a statistically significant change was observed only in the brain stem. Highly statistically significant correlations were demonstrated between brain tryptophan and 5-HIAA suggesting a possible interrelationship between these parameters. Circadian changes in 5-HT were observed in the cerebral cortex of the experimental and in the brain stem of control animals. The inconsistency of the 5-HT rhythms may be a reflection of the daily disturbance of the animals. Significant circadian changes in free and also total plasma tryptophan were observed in both the control and experimental animals. Levels of 5-hydroxyindoleacetic acid or tryptophan in the brain were not consistently correlated with free plasma tryptophan or free plasma tryptophan/tyrosine in either control or experimental rats.