Asymmetrical Determination of Circadian Period by Synaptic Interactions in a Multi-Oscillatory System in the Suprachiasmatic Nucleus
S. Honma1*; W.- Nakamura1,2; T.- Shirakawa2; K. Honma1
Society for Neuroscience, 77.5 (2002)
1. Dept Physiol, Hokkaido Univ Sch Med, Sapporo, Japan
2. Dept Oral Functional Science, Hokkaido Univ Sch Den, Sapporo, Japan
The suprachiasmatic nucleus (SCN) of the hypothalamus, the site of master clock in mammals, is composed of multiple neurons displaying circadian rhythms in firing and gene expressions. It is still unclear how individual cellular oscillators synchronize to each other and express a coherent periodicity in the SCN. Previously, we reported that individual SCN neurons were synaptically coupled to show up synchronized circadian firing rhythms in dispersed cell culture on a multi-electrode dish (MED). In the present experiment, we examined the role of neuronal interactions in the rhythm synchronization by blocking them with tetrodotoxin (TTX). The coronal SCN slices of newborn Wistar rats were plated on an MED and cultured with serum free medium. Continuous recording of spontaneous discharges were started from 1-2 weeks after plating from 8 electrodes simultaneously. Following the baseline recording (>5 days), slices were treated with 200nM TTX for two days and spontaneous discharges were monitored for 1-4 weeks. Before TTX treatment, firing rhythms in the same slice were synchronized. Spontaneous firing was completely abolished during TTX administration. In 13 slices out of 15, the circadian periods of rhythmic neurons were changed after the TTX treatment. The findings suggest that Na+ -channel dependent neuronal couplings are critical for determination of the period of coherent circadian rhythm in the SCN.
Supported by: Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan
