Long day lengths increase brain weight and DNA content in the meadow vole, Microtus pennsylvanicus

Male voles reared in long (spring) day lengths had heavier brains with greater total DNA content than did males housed in short (fall) day lengths; these effects were not observed in female littermates kept in the two photoperiods. Male brains were heavier than female brains in long but not in short photoperiods. Day length affected brain mass during early postnatal development, but not when treatments were initiated in adulthood. Seasonal differences in brain development, including the numbers of neurons and glia, may reflect different metabolic and behavioral demands faced by males born in spring and fall, respectively.