Clock controls circadian period in isolated suprachiasmatic nucleus neurons

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker in mamm als, and one molecular regulator of circadian rhythms is the Clock gene. He re we studied the discharge patterns of SCN neurons isolated from Clock mut ant mice. Long-term, multielectrode recordings showed that heterozygous Clo ck mutant neurons have,lengthened periods and that homozygous Clock neurons are arrhythmic, paralleling the effects on locomotor activity in the anima l. In addition, cells in dispersals expressed a wider range of periods and phase relationships than cells in explants. These results suggest that the Clock gene is required for circadian rhythmicity in individual SCN cells an d that a mechanism within the SCN synchronizes neurons and restricts the ra nge of expressed circadian periods.