Abstract
In mammals,the circadian peacemaker is located in the suprachiasmatic nucleus(SCN).Many of the SCN neurons exhibit spontaneous firing rhythms with periods specific to each neuron,suggesting that neuronal interaction is critical for the SCN to function as a master peacemaker.Hundreds of gene transcriptions are circadianly regulated,yet,a little is known about the intracellular transduction of the circadian signal.The purpose of our study is to identify the molecules which transmit the circadian signal to the membrane potential.Tetrodotoxin(TTX) inhibits synaptic communication,but a line of evidence supports it does not affect the intracellular circadian oscillation.To exclude the effect of the circadian rhythm of the membrane potential on the intracellular signal transduction,we applied TTX to pull out Na+ channel independent genes.We cultured the SCN slice of 300μm thick from the adult mouse using culture membranes.We separately monitored Per1-luciferase expression rhythms in the SCN to determine the timing of TTX administration.The SCN slices were sampled for 24h in 4 h intervals.Using serial frozen sections,we systematically analyzed circadian expression rhythms of clock and clock controlled genes by in situ hybridization.Our results indicated a number of genes showed a robust circadian expression rhythm under the TTX treatment,and some gene expressions were severely dumped by the treatment while others were not.These findings suggest that the rhythmic input is necessary for the former,while the latter involves in the core oscillation and/or rhythmic signal transduction. [J Physiol Sci. 2006;56 Suppl:S208]
