Can a population of suprachiasmatic nucleus neurons with different period lengths produce a stable circadian rhythm?

The firing rate of a population of SCN neurons in vivo exhibits stable circadian oscillations, but the period length of individual neurons is not known and may be different or similar to the population rhythm. To address this question we used published data from Bos and Mirmiran [Brain Res., 511 (1990) 158-162] that reported different period lengths and amplitudes for individual neurons recorded in explant cultures of the SCN. We reconstructed the individual rhythms for several cycles, calculated the population rhythm, and then tested its stability. The period and amplitude of the rhythm of groups of neurons with different period lengths were unstable. Furthermore, the stability of the rhythm was reduced as the number of sampled neurons increased. These results suggest that the stable circadian rhythm reported for neuron populations in the intact SCN emerges from the identical period length of individual neurons. The possible intercellular interactions in the SCN that may underlie the stable circadian rhythm are discussed.