Author's personal copy PHOTOPERIOD-MEDIATED IMPAIRMENT OF LONG-TERM POTENTION AND LEARNING AND MEMORY IN MALE WHITE-FOOTED MICE

Abstract—Adult mammalian brains are capable of some structural plasticity. Although the basic cellular mechanisms underlying learning and memory are being revealed, extrinsic factors contributing to this plasticity remain unspecified. White-footed mice (Peromyscus leucopus) are particularly well suited to investigate brain plasticity because they show marked seasonal changes in structure and function of the hippocampus induced by a distinct environmental signal, viz., photoperiod (i.e. the number of hours of light/day). Com-pared to animals maintained in 16 h of light/day, exposure to 8 h of light/day for 10 weeks induces several phenotypic changes in P. leucopus, including reduction in brain mass and hippocampal volume. To investigate the functional con-sequences of reduced hippocampal size, we examined the effects of photoperiod on spatial learning and memory in the Barnes maze, and on long-term potentiation (LTP) in the hippocampus, a leading candidate for a synaptic mechanism underlying spatial learning and memory in rodents. Exposure to short days for 10 weeks decreased LTP in the Schaffer collateral–CA1 pathway of the hippocampus and impaired spatial learning and memory ability in the Barnes maze. Taken together, these results demonstrate a functional change in the hippocampus in male white-footed mice in-duced by day length. © 2011 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: photoperiod, LTP, spatial learning and memory, melatonin. One important goal of neuroscience is to understand the mechanisms underlying brain plasticity. Toward that end, substantial research has been conducted using in vivo and ex vivo chemical and genetic manipulations of standar