Fig. 5. Light-induced c-fos expression in Per1 knock-out mice. (A) In situ hybridization with a c-fos probe on brain cuts from animals entrained on a L12:D12 cycle. At CT14 on the third day in DD, the mice were either subjected to light for 15 min and kept another 15 min in the dark (light) or kept all this time in the dark (basal), before dissection. Only the region of the SCN is shown. (B) Quantification of the results (n = 3 for ‘basal’, n = 4 for ‘light’).