Bmal1 expression in SCN rescues circadian rhythms and light entrainment in Bmal1−/− mice. Representative body temperature (Tb) records (double-plotted actigrams) and period analyses for (A) Bmal1+/−, (B) Bmal1−/−, and (C) Bmal1−/− mice with AAV-BMAL1 injections into the SCN under both light-dark (LD) and constant darkness (DD) conditions with AL access to food. The power spectrum for period (right panel) shows a dominant frequency at 23.7 hours for both Bmal1 heterozygous littermates and mice with AAV-BMAL1 rescue in the SCN, and the lack of a ~24-hour harmonic in the Bmal1−/− mice. (D to F) Bmal1 mRNA expression (by in situ hybridization) in the SCN in (D) Bmal1+/− mice, (E) Bmal1−/− mice, and (F) after AAV-BMAL1 rescue by injection into the SCN (all ZT18). Scale bar, 100 μm.