Antiphase oscillation of the left and right suprachiasmatic nuclei

An unusual property of the circadian timekeeping systems of animals is rhyt hm "splitting," in which a single daily period of physical activity (usuall y measured as wheel running) dissociates into two stably coupled components about 12 hours apart; this behavior has been ascribed to a clock composed of two circadian oscillators cycling in antiphase. We analyzed gene express ion in the hypothalamic circadian clock, the suprachiasmatic nucleus (SCN), of behaviorally "split" hamsters housed in constant Light. The results sho w that the two oscillators underlying the split condition correspond to the Left and right sides of the bilaterally paired SCN.