Further characterization of the phenotype of mCry1/mCry2-deficient mice

Mice lacking cryptochromes (mCry1(-/-) mCry2(-/-) ) were kept in a 16h ligh t, 8h dark, light-dark (16:8 LD) cycle and were given additional pulses of light of different brightness, starting 2h after dark onset and lasting for 1h. The suppression of wheel running during these light pulses (i.e., mask ing) was compared to that of wild types. No evidence of any decrement in th e masking response to light was detected. As well as studying masking, mino r bouts of activity occurring in the main light portion of a light-dark cyc le were quantified. One possible explanation of such predark activity is th at some damped endogenous process is spared in mCry1/mCry2 double-knockout mice.