Effects of decreased BDNF expression in the mouse SCN on light-induced phase shifts (ΔΦ) of the rhythm in wheel-running activity. A, Representative activity records in DD of wild-type mice (WT:bdnf+/+) and mice heterozygous for the BDNF null mutation (HET:bdnf+/−) exposed to a 20 min light pulse (LP) at CT 14 (top) or 22 (bottom). Actograms are double-plotted over a 48 hr period, and shadedcircles on each record indicate the day and time during which light pulses were administered. A thin shaded bar has been fitted through the activity onsets for 6 d before each light pulse to facilitate visualization of the phase shifts in the activity rhythm. B, Mean (±SEM) phase shift (ΔΦ) in hours of the activity rhythm induced by light pulses at CT 6, 14, and 22 in wild-type andbdnf+/− mice. For each treatment group, the sample size is designated in parentheses. Phase delays are indicated by negativevalues, and advances are denoted bypositivevalues. Light-induced phase delays at CT 14 (*p < 0.05) and advances at CT 22 (**p < 0.01) were significantly decreased in mutant bdnf+/− mice compared with those in wild-type mice.