The VIP-IRES-Cre transgene decreases vasoactive intestinal polypeptide (VIP) expression in proportion to copy number in an age-related manner. (A) Representative, thresholded images of VIP expression in the SCN of Vip+/+, Vipcre/+, and Vipcre/cre mice collected at P10 or in adulthood. (B) The VIP-IRES-Cre transgene causes an age-related decrease in regional VIP levels in the SCN. (C) The VIP-IRES-Cre transgene reduces the number of VIP+ cells in the SCN of adult Vipcre/cre mice but not in adult Vipcre/+ mice. (D) The VIP-IRES-Cre transgene does not reduce DAPI-labeled cells in the ventral SCN. Italicized numbers below the abscissa indicate sample size. *Differs from Vip+/+, Tukey’s HSD, p < 0.05.