RESUMO
The hypothalamic suprachiasmatic nucleus (SCN) of the mammal is the circadian pacemaker responsible for generation of circadian rhythms. Several immediate-early genes are expressed in the SCN by light stimuli which induce phase shifts of animal activity rhythms. By using differential display-polymerase chain reaction, we investigated expression of several immediate-early genes in the light-stimulated SCN. In addition, we analyzed the light-induced expression changes of two known immediate-early genes, Arc and Rheb, in the SCN. We have screened and cloned 25 differentially expressed genes in the SCN, and identified a gene, a rat homologue of A6 kinase, which expression was regulated by light stimuli. One hour light stimuli during the subjective night dramatically induced the gene expression in the SCN, whereas light stimuli during the subjective light phase did not. This finding implies that a rat homolgue of A6 kinase may be involved in the photic entrainment of the circadian clock. On the other hand, Arc and Rheb mRNA expressions were not increased in the SCN by light stimuli.