Expression of the Per1 gene in the hamster: Brain atlas and circadian characteristics in the suprachiasmatic nucleus

Recent progress in study an the molecular component of mammalian clocks has claimed that mammals and Drosophila share the similar fundamental clock os cillating system. In the present study, we investigated expression of Per1, the first gene of the mammalian homolog of the Drosophila clock gene perio d, in the hamster brain, and we also examined its circadian expression patt ern in the mammalian clock center, the suprachiasmatic nucleus (SCN). In si tu hybridization using isotope-labeled cRNA probes revealed a wide and regi on-specific distribution of Per1 in the hamster brain and spinal cord. High levels of Per1 were found in the internal granular layer of the granular c ells of the olfactory bulb, anterior olfactory nuclei, tenia tecta, olfacto ry tubercle, piriform cortex,suprachiasmatic nucleus, and gyrus dentatus of hippocampus. Moderate levels of expression were detected in many brain reg ions including the granular layer of the cerebellum, anterior paraventricul ar thalamic nucleus, caudate-putamen, inferior colliculus, pontine nuclei, inferior olive, and nucleus of the solitary tract. We examined the circadia n profile of hamster Per1 mRNA in the SCN in constant darkness and found th at Per1 expression showed a peak at subjective day (circadian time [CT] 4) and formed a trough at subjective night (CT16-CT20). A brief exposure of li ght at CT16 could acutely induce large quantities of Per1 mRNA in the hamst er SCN, except for its dorsomedial subdivision. These findings suggest that the characteristics of Per1 gene expression in the mammalian circadian cen ter (showing a peak in the daytime and a trough in the nighttime and a rapi d inducibility by light) are common among mammalian species. Lastly, in ham ster brain, Per1 gene is also inducible in extra-SCN brain nuclei, since li ght at night also elicited Per1 mRNA in neurons of the hypothalamic paraven tricular nucleus. (C) 2001 Wiley-Liss, Inc.