Regional pacemakers composed of multiple oscillator neurons in the rat suprachiasmatic nucleus

  • Nakamura W
  • Honma S
  • Shirakawa T
 et al. 
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Regional specificities of the dorsal and ventral regions of the suprachiasmatic nucleus {(SCN)} were examined to elucidate the structure of multioscillator circadian organization. The circadian rhythms of arginine vasopressin {(AVP)} and vasoactive intestinal polypeptide {(VIP)} release, and of electrical activity of individual neurons were measured in an organotypic, static slice culture of the {SCN} obtained from neonatal rats. Five days after the start of culture, robust circadian rhythms were detected in {AVP} release with a peak located consistently at the middle of the original light phase, while the 24 h profiles of {VIP} release were either arrhythmic or rhythmic. In the latter case, a phase delay of 5-7 h was observed in the circadian peak from the {AVP} rhythm. Multi-channel, extracellular recording revealed that 51 (76.1%) out of 67 firing neurons, examined in the {SCN,} showed circadian rhythms in their firing rate. The percentage of rhythmic neurons was significantly larger in the dorsal (86.8%) than in the ventral (62.1%) region of the {SCN,} where the {AVP} and {VIP} containing neurons predominate, respectively. Twenty-seven percent of the firing rhythms were almost antiphasic from the majority of rhythms. There was no regional specificity in the distribution of the antiphasic rhythm. These findings, that the dorsal and ventral regions of the {SCN} both contain circadian pacemakers with different properties that regulate the {AVP} and {VIP} release separately, is probably due to differences in the number and, hence, the coupling strength of oscillating neurons.

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