| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2003: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2001: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
In mammals, circadian rhythms are driven by a pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The pacemaker is composed of an ensemble of multiple, single-cell oscillators in the SCN. The isolated rat suprachiasmatic cells cultured in vitro express circadian oscillation of vasopressin (AVP) release for weeks. The amplitude of the rhythm was higher in the cultures plated at high density. The large amplitude of the rhythm indicates the individual rhythms in the dissociated AVP-releasing cells are synchronized to each other. Synchronization was observed between groups of the cells. When two groups of the cells with different phase were co-cultured, the phase of one group was synchronized to another one. The cell-to-cell contact was not necessarily required for this synchronization.
Since GABA has been postulated as a coupling agent for the SCN cells, we examined the effect of GABA on the rhythm of AVP release. When GABA was added to the culture medium, AVP releas
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e from the cells was markedly reduced. The GABA-induced inhibition occurred at all phases of the circadian cycle. While GABA disturbed. the circadian oscillation of AVP release) it was gradually restored. After the recovery of the rhythm, slight phase-shift was observed. Magnitude and direction of the shift depended on timing of the application, maximum phase delay at the beginning of subjective day, and the maximum phase advance at the beginning of subjective night. Bicuculline, a GABA-A antagonist, increased AVP release, but did not inhibit the synchronization among the AVP cells even under long-term application.
The SCN slice culture showed circadian oscillation of AVP release with a period length (±S.E..M) of 23.84±0.03 h. This period is very similar to the one we previously reported in dispersed SCN cultures and is also close to that of behavioral rhythms. When the ventral part was removed by surgical cut across the slice in the horizontal plane, however, the period became shorter (23.22 h± 0.08 h). On the other hand, the removal of the dorsal part did not affect period length. These results suggest that the oscillators in ventral and dorsal cells contribute differently to period length and that the dorsal oscillators are regulated by ventral one to form a single integrated oscillator. Less
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