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-ind uced c-Fos production, was similar to the previously reported time interval enabling high c-fos photoinduction in the SCN (Sumova, A., Travnickova, Z. , Peters, R., Schwartz, W.J. and Illnerova, H., The rat suprachiasmatic nuc leus 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. (C) 2000 Elsevie r Science Ireland Ltd. All rights reserved.