Rhythmic properties of the hamster suprachiasmatic nucleus in vivo

We recorded multiple unit neural activity [multiunit activity (MUA)] from i nside and outside of the suprachiasmatic nucleus (SCN) in freely moving mal e golden hamsters housed in running-wheel cages under both light/dark cycle s and constant darkness. The circadian period of MUA in the SCN matched the period of locomotor activity; it was -24 hr in wild-type and 20 hr in homo zygous iau mutant hamsters. The peak of MUA in the SCN always occurred in t he middle of the day or, in constant darkness, the subjective day. There we re circadian rhythms of MUA outside of the SCN in the ventrolateral thalami c nucleus, the caudate putamen, the accumbens nucleus, the medial septum, t he lateral septum, the ventromedial hypothalamic nucleus, the medial preopt ic region, and the stria medullaris. These rhythms were out-of-phase with t he electrical rhythm in the SCN but in-phase with the rhythm of locomotor a ctivity, peaking during the night or subjective night. In addition to circa dian rhythms, there were significant ultradian rhythms present; one, with a period of similar to 80 min, was in antiphase between the SCN and other br ain areas, and another, with a period of similar to 14 min, was in-phase be tween the SCN and other brain areas. The periods of these ultradian rhythms were not significantly different in wild-type and tau mutant hamsters. Of particular interest was the unique phase relationship between the MUA of th e bed nucleus of the stria terminalis (BNST) and the SCN; in these two area s both circadian and ultradian components were always in-phase. This sugges ts that the BNST is strongly coupled to the SCN and may be one of its major output pathways. In addition to circadian and ultradian rhythms of MUA, ne ural activity both within and outside the SCN was acutely affected by locom otor activity. Whenever a hamster ran on its wheel, MUA in the SCN and the BNST was suppressed, and MUA in other areas was enhanced.