The chronomutagenic effect of deuterium oxide on the period and entrainment of a biological rhythm.

The effect of deuterium oxide on the locomotor activity rhythm of the house mouse, Mus musculus, was measured in various environmental conditions.1. In the initial experiments, in which mice were kept in constant low (0.2 foot candle) illumination, D2O concentrations of 5% through 30% (in 5% increments) were administered via the drinking water. Increased concentrations lengthened the period, proportionally, with 30% D2O causing a mean period lengthening of 7.4%.2. Increasing the intensity of illumination in constant conditions can lengthen the period of the mouse locomotor activity rhythm. It was felt that deuterium might be changing the way in which the mice interpreted the light intensity, thus changing the period. Both blind mice, and mice kept in constant darkness were tested at various dosages. The results did not differ significantly from those obtained for mice in constant low illumination, thus showing D2O does not act to alter the period by changing the way in which the mice interpret light inten...