Teiichi Etoh

LONG-TERM CULTURED NEURONS FROM RAT SUPRACHIASMATIC NUCLEUS RETAIN THE CAPACITY FOR CIRCADIAN OSCILLATION OF VASOPRESSIN RELEASE

We have developed a dissociated suprachiasmatic nucleus (SCN) cell culture system in order to begin a cellular analysis of the mammalian circadian oscillator. Monolayer-cultured neurons prepared from the SCN regions of 1-day-old rats were maintained in serum-free culture medium for 3-4 weeks and then perfused. In 12 out of 40 wells, a circadian oscillation of vasopressin release persisted for at least 4-5 cycles until the end of the perfusion period with no damping of the amplitude. This finding suggests that cultured SCN neurons retain the capacity for circadian oscillation for a long time, and should provide a useful model for the analysis of a mammalian circadian system at the cellular level.

Rapid reentrainment of the circadian clock itself, but not the measurable activity rhythms, to a new light-dark cycle in the rat

Experiments were performed to determine if the circadian clock reentrains more quickly to an 8-hour phase shift in light-dark (LD) cycles than does the overt rhythm of activity. To investigate the reentrainment of the clock itself to an 8-hour advance or delay in the LD cycle, the rats were released into constant darkness only two or three days after a shift in LD cycle, and the amount of the phase shift of the clock itself was estimated from where free-running rhythm started by backward extrapolation. If the circadian clock could rapidly reset itself to the new LD cycle, it was predicted that the free-running rhythm of activity would start from near the dark period of the new LD cycle rather than the preceding one. When rats were released into constant darkness three days after the LD cycle was advanced by 8 hours, the activity of the free-running rhythm started near time of dark period of the new LD cycle in all rats (n = 16). When rats (n = 24) were released into constant darkness two days after the LD cycle was advanced by 8 hours, 12 rats started the activity near time of dark period of the new LD cycle, while 9 rats started the activity near time of dark period of the preceding LD cycle. The remaining 3 rats showed the activity of the free-running rhythm near intermediate phase (transient phase). On the other hand, when the rats were not released into constant darkness after LD cycle was advanced by 8 hours, it took 6.4 days for activity rhythm to reentrain to the advanced LD cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin release from pineal cells of diurnal and nocturnal birds

Melatonin release from the pineal cells of chicks, pigeons and crows (diurnal birds) in vitro was compared with that from owls (a nocturnal bird). The pineal cells of diurnal birds secreted large amounts of melatonin during the dark period, whereas owl pineal cells released virtually no melatonin over 24 h and did not respond to exogenous stimulant agents. Histological examination revealed that the owl pineal gland is very small and has a poor vascular network. These results suggest that the pineal gland of owls may have degenerated and is not involved in the circadian clock mechanism in this species.