[Diurnal rhythm of rectal temperature in mice during various lighting conditions]

The study of circadian rhythm of rectal temperature (t degrees) during 4.5 months in mice under conditions of continuous lighting (LL) and natural alteration of day and night (LD), considering astronomic time of sunrise and sunset, revealed the following regularities: In winter and in summer t degrees maximum in LD was marked at the beginning of the dark period of time (twilight period), t degrees minimum was observed at the end of the dark period. In winter, when the dark period lasts 14-15 hours, t degrees falls from maximum to minimum during all the dark period (12-14 hours), and in summer, when the period of darkness lasts 6 hours, t degrees falls only during 2 hours. In spring t degrees minimum shifts to the middle of the light period. Under conditions of LL, circadian rhythm of t degrees "splits" periodically into bimodal with periods of 10-14 hours. Long keeping (during 4.5 months) under conditions of LL results in levelling of t degrees circadian rhythm. The character of t degrees circadian rhythm in laboratory animals (mice) is not inverted to that in human beings.