A POSSIBLE GLIAL ROLE IN THE MAMMALIAN CIRCADIAN CLOCK

The primary mammalian circadian clock is located within the suprachias matic nuclei (SCN), but the cellular organization of the clock is not yet known. We investigated the potential role of glial cells in che cl ock mechanism by determining whether disrupting glial activity affects the in vitro circadian rhythm of neuronal activity and the in vivo ci rcadian activity rhythm in rats. We used two agents (octanol and halot hane) that block gap junctions, and one (fluorocitrate) that inhibits glial metabolism. All three agents disrupted the circadian pattern of neuronal activity. Octanol flattened the rhythm at the highest concent ration (200 mu M) and induced a small phase delay at a lower concentra tion (66 mu M). Halothane and fluorocitrate induced ultradian rhythmic ity. Fluorocitrate injected into the SCN of an intact rat induced arrh ythmicity for about 1 week, after which the rhythm reappeared with a 1 .6 h delay. These results suggest that glia play an important role in the SCN circadian clock.