Morphological approach to mechanisms of light input and synchronization to the circadian oscillator

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We investigated the mechanisms of light input and synchronization in the suprachiasmatic nucleus (SCN). Using rPer2 promoter::Luciferase rat, we have found that the SCN is divided into two regions in relevance to period length. One of which showed medial region of the SCN containing oscillators with a period shorter than 24 hours (SPR) and lateral region with a period longer than 24 hours (LPR). And we have found that synchrony between SPR and LPR is possibly attained by cAMP signaling. Then, We observed Per1 and cFos induction in the SCN by light when the environmental LD cycle (12:12-h) was abruptly changed to dissociate the dorsomedial SCN (DMSCN) and ventrolateral SCN (VLSCN). As a result, the phase shifting of the gate corresponded well with that of the DMSCN. The finding suggested that the DMSCN determines the phase of the gate.