Daily rhythms in tryptophan and serotonin content in mouse brain: the apparent independence of these parameters from daily changes in food intake and from plasma tryptophan content.

Abstract

AJAX mice were given food for only 4 hours daily between 1000 and 1400 during the light phase of a 12:12 LD lighting regime (lights on 0900–2100). Control mice were given food ad libitum. These mice normally consume nearly 80 per cent of their food during the dark phase (2100-0900). The daily peak in plasma tryptophan content was correlated with the time of greater food consumption in both control and experimental animals. The daily rhythms in tryptophan and serotonin content in the brains of the experimental mice did not differ appreciably from similar rhythms in control mice. Some decrease in brain serotonin content was observed in the experimental mice but at only certain hours of the day. These results suggest that the daily rhythms in tryptophan and serotonin content in the mouse brain may be relatively independent of daily variations in food intake or plasma tryptophan content. A close correlation between the phasing of the daily rhythms in brain tryptophan and serotonin in both the experimental and control animals suggests an important interrelationship between these 2 parameters.