Circadian rhythm in metabolic activity of suprachiasmatic, supraoptic and raphe nuclei.

Previous studies using 2-deoxyglucose (2-DG) autoradiography have demonstrated that the suprachiasmatic nucleus (SCN) of the hypothalamus, a putative neural circadian pacemaker, displays circadian rhythmicity in its metabolic activity. In the present study, we show that distinct circadian variations in 2-DG uptake occur not only in the suprachiasmatic, but also in the supraoptic and median raphe nuclei of the rat brain. On the other hand, several other brain areas failed to display systematic circadian variations in 2-DG uptake. These results indicate that circadian metabolic rhythms are not unique to the SCN. Further studies are required to precisely define the extent of such phenomena.