Development of the circadian rhythm of neuronal activity in suprachiasmatic nucleus of rat hypothalamic slices.

Development of the circadian rhythm of neuronal activity in the suprachiasmatic nucleus (SCN) was studied in rat hypothalamic slices. The firing rate of SCN neurons of 7- and 11-day-old rat pups was low during all of the day, whereas that of 14- and 21-day-old pups was high during daytime and low during nighttime. The present results suggest that the circadian rhythm of SCN neuronal activity is established between 11 and 14 days of age, corresponding closely to the time of onset of the other various hormonal and behavioral circadian rhythms.