Sleep variations in C57BL and BALBc mice from 3 weeks to 14 weeks of age.

The evolution of sleep patterns during the diurnal period was studied in C57BL and BALBc mice from 3 to 14 weeks of age. Quantitative analysis of the hypnograms reveals that the main sleep changes occur between weeks 3 and 4 in the two strains. This period is characterized by a decrease of the percentage of paradoxical sleep in BALBc strain, due to a simultaneous drop in the mean number and duration of the episodes. During this time C57BL strain exhibits an increase in the percentage of slow wave sleep, resulting from a rise in the mean number of episodes. At the same time the percentage of awake state decreases in C57BL mice. In the adults these changes result in differences between the strains in sleep pattern that are characterized by a higher percentage of paradoxical and slow wave sleep in C57BL than in BALBc mice. As regards the results obtained, the maturation of sleep mechanisms and particularly of the paradoxical sleep seems to be different in C57BL and in BALBc mice.