Effects of a constant light environment on hippocampal neurogenesis and memory in mice.
Because the environmental light-dark cycle is a key factor involved in modulating circadian rhythm in mammals, disruption of cyclic light conditions has a variety of effects on physiology and behavior. In the hippocampus, neurogenesis, which continues to occur throughout life, has been reported to exhibit circadian variation under cyclic light-dark conditions. In the present study, we examined whether a constant light environment affected hippocampal neurogenesis in mice. Half of the animals were exposed to continuous light conditions (L/L group), while the other half remained under normal cyclic light-dark conditions (L/D group). In the L/L group, the number of BrdU-labeled cells (proliferating cells) and that of BrdU and class III β-tubulin double-labeled cells (newborn neurons) in the granule cell layer were significantly decreased compared with the L/D group. Because hippocampal neurogenesis is involved in memory and learning, we also investigated the effects on performance in water maze tasks to assess spatial learning. Exposure to L/L treatment for 3 weeks impaired spatial learning task performance, although there was no difference in the open field behaviors between the groups. These findings demonstrate that the constant light conditions impaired hippocampal neurogenesis as well as cognitive performance, and suggest an important role for the cyclic light-dark environment in appropriate maintenance of the hippocampal system.
Department of Emergency and Critical Care Medicine, Yamaguchi University Graduate School of Medicine, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan. tfujioka-ygc@umin.ac.jp
Aya
A
Fujioka
Takashi
T
Fujioka
Ryosuke
R
Tsuruta
Tomonori
T
Izumi
Shunji
S
Kasaoka
Tsuyoshi
T
Maekawa
D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D018891:Dentate Gyrus / Q000166:cytology* / Q000528:radiation effects; D005106:Exploratory Behavior / Q000528:radiation effects; D008027:Light; D008297:Male; D018782:Maze Learning / Q000528:radiation effects; D008568:Memory / Q000528:radiation effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D055495:Neurogenesis / Q000528:radiation effects*; D009474:Neurons / Q000528:radiation effects*; D013997:Time Factors; D014404:Tubulin / Q000378:metabolism
D014404:Tubulin; D001973:Bromodeoxyuridine