Abstract
Metabolic activity in a suprachiasmatic nucleus (SCN), a center of biological rhythm, is higher during the daytime than at the night. The rhythmic oscillation in the SCN is feedback controlled by the CLOCK/BMAL1 heterodimer binding to the E-box in target genes (e.g., Per2, Arg-vasopressin). Similar transcriptional regulation by NPAS2/BMAL1 heterodimer formation is operating in the forebrain, which is depending on the redox state (i.e., NAD/NADH). To clarify the metabolic function of SCN in relation to the redox state, we measured biochemicals in mitochondria and cytosol in the SCN homogenate. The integrity of JC-1 fluorescent dye, which is the index of mitochondrial electric potential gradients was higher at the light-dark transition time. Mitochondrial cyctochrome C oxidase activity, measured by the changes in absorption at 550nm, was higher during the light period than during the dark period. The proteins, extracts from mitochondrial fraction in SCN, obtained from the rats kept under the light dark cycle, were analyzed by two-dimension electrophoresis. The electrophoretic pattern revealed that an enolase, catalyzing the interconversion of 2-phosphoglycorate and 2-phosphoenol-pyruvate content in mitochondria was higher during the subjective daytime than that in the night. However, the enolase mRNA content in cytosol fraction of SCN, measured using RT-PCR, showed higher levels during the dark period than during the light. The results suggest the glycolysis with energy producing pathway might concern to preserve the higher metabolic activity during the day than at night. [Jpn J Physiol 54 Suppl:S208 (2004)]
