Gate for photic resetting of intrinsic rhythmicity of the rat suprachiasmatic nucleus under a long photoperiod.

In rats maintained under a long photoperiod and then released into darkness, the time interval enabling photic resetting of the intrinsic rhythmicity of the suprachiasmatic nucleus (SCN), namely of the rhythm in the light-induced c-Fos production, was similar to the previously reported time interval enabling high c-fos photoinduction in the SCN (Sumová, A., Trávnícková, Z., Peters, R., Schwartz, W.J. and Illnerová, H., The rat suprachiasmatic nucleus is a clock for all seasons. Proc. Natl. Acad. Sci. USA, 92 (1995) 7754-7758). The data indicate that both intervals may represent the same window for the photic sensitivity of the SCN pacemaking program.