Aberrant Light‐Induced Depression is Associated with Decreased Adult Hippocampal Neurogenesis in Mice

In today's world of constant activity, people are frequently exposed to light outside of the natural daytime hours. This leads to a disruption in the endogenous circadian rhythm resulting in various mood disorders in humans (Bedrosian and Nelson 2013). In mice, it has been shown that aberrant light is sufficient to induce a depressive‐like phenotype; however, there is no clear explanation of the neurological basis for this phenomenon except light input is transmitted by intrinsically photosensitive retinal ganglion cells (Legates et al 2012). In other mouse models of depression, adult hippocampal neurogenesis (AHN) has been shown to be decreased (Mahar et al 2014). This study tested whether aberrant light‐induced depression was associated with decreased AHN in mice. Adult male C57B/6 mice were housed in standard light conditions (12:12 hours (T24) LD) or aberrant light conditions (3.5:3.5 hours (T7) LD) for at least three weeks prior to testing. Mice were assayed for a depressive‐like phenotype using a two‐bottle sucrose preference test over four days. Mice exposed to T7 LD showed significant reductions in sucrose preference compared to mice on T24 LD. Immunohistochemical fluorescent labeling for the cell proliferation marker Ki‐67 was then used to quantify AHN in the dentate gyrus. Mice under T7 LD had significant reduction of AHN compared to mice on T24 LD. These parallel observations of decreased sucrose preference and decreased AHN resulting from chronic exposure to aberrant light (T7 LD) suggest that AHN may provide the neurological basis for aberrant light‐induced depression. Support or Funding Information APS Undergraduate Summer Research Fellowship and NIH RO3NS094419