Brain tryptophan in isolated aggressive mice.

Circadian variations in whole brain tryptophan level and food intake were investigated in both normally grouped and isolated male Albino-Swiss mice, maintained on a 12:12 light-dark regimen (lights on 08.00--20.00). A significant diurnal rhythm in brain tryptophan level was evidenced only by grouped animals, in contrast to the relatively sustained and significantly lower tryptophan level found to exist in isolated mice. Significant, daily rhythms in food intake, for both isolated and grouped mice were found to exist, that were highly correlated in phase. Isolated mice, however, consistently demonstrated an increased food consumption throughout the 24-hour period. These results suggest that a possible alteration in tryptophan metabolism exists in isolated mice, as tryptophan, an essential amino acid, is obtained by mammals only through their diet.