| Research Abstract |
Present experiment was undertaken to clarify the coupling mechanisms of oscillatory neurons in the suprachiasmatic nucleus (SCN) which enables the pacemaker to drive a single stable circadian rhythm in the various physiological functions.
1. Clock gene expression rhythms : Expression of clock genes, Clock and BMAL1, was examined by in situ hybridization. Clock and BMAL1 are strongly expressed in the SCN with a circadian fashion and the rhythms were 180 degree out of phase. To a 30 min light pulse given at various circadian times, BMAL1 expression was increased at all phases examined, while that of Clock, phase-dependently. The two genes may separately play one of the two roles in the light entrainment, parametric and non-parametric.
2. AVP and VIP rhythms in the SCN slice : SCN slices cultured on a culture-insert membrane showed robust rhythms in AVP which phased to maternal AVP rhythm and desynchronized rhythms in VIP, but both rhythms damped out during the culture. The results suggest that AVP and VIP are driven by separate oscillators which are desynchronized during the culture.
3. Coupling of neuronal oscillation and peptide rhythm generation : Single SCN neurons were cultured on a multi-electrode dish, and the circadian firing rhythms and peptide rhythms were compared. Significant circadian peptide rhythms were detected only in cultured dishes with synchronized neuronal rhythms, suggesting the peptide rhythm reflects the coupling of cellular oscillations.
4. Synaptic coupling of individual SCN neuronal oscillator : The role of functional synapses in the coupling of cellular oscillations was studied by examining cross-correlation of spikes of a pair of SCN neurons which showed synchronized circadian firing rhythms and that with desynchronized rhythms. The result showed that an excitatory synaptic interaction with a short synaptic delay synchronizes the circadian firing rhythm oscillating neurons in the SCN.
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