NelsonSeasonality - The Journal of Neuroscience May 4 2005...

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Behavioral/Systems/Cognitive Short Photoperiods Impair Spatial Learning and Alter Hippocampal Dendritic Morphology in Adult Male White-Footed Mice ( Peromyscus leucopus ) Leah M. Pyter, Brenda F. Reader, and Randy J. Nelson Departments of Neuroscience and Psychology and Institute of Behavioral Medicine Research, Ohio State University, Columbus, Ohio 43210 Although seasonal changes in brain morphology and function are well established in songbirds, seasonal plasticity of brain structure and function remain less well documented in mammals. Nontropical animals display many adaptations to reduce energy use to survive winter, including cessation of reproductive activities. Because of the high energetic costs of brain tissue, we hypothesized that male white-footed mice ( Peromyscus leucopus ) would reduce brain size in response to short days as well as regress their reproductive systems. Because short days may decrease hippocampal volume and impair spatial learning and memory in rodents and because of the potential for seasonal plasticity in the hippocampus, we hypothesized that photoperiod alters hippocampal morphology to affect spatial learning and memory. Mice housed in either long or short days for 10 weeks were examined for performance in a water maze; brains were then removed and weighed, and hippocampal volumes were determined. We also measured dendritic morphology and spine density in the CA1, CA3, and dentate gyrus. Short days decreased brain mass and hippocampal volume compared with long days. Short days also impairedlong-termspatiallearningandmemoryrelativetolongdaysbutdidnotaffectsensorydiscriminationorothertypesofmemory. Short days decreased apical (stratum lacunosum-moleculare) CA1 spine density, as well as increased basilar (stratum oriens) CA3 spine density. Results from this study suggest that photoperiod alters brain size and morphology, as well as cognitive function. Understanding the mechanisms mediating these photoperiod-induced alterations may provide insight for treatment of seasonal cognitive and affective disorders. Key words: seasonality; photoperiod; spatial learning and memory; hippocampus; spine density; dendritic complexity Introduction Photoperiod (day length) is a reliable cue by which organisms determine the time of year and coordinate adaptations to sea- sonal changes in their environment (Goldman, 2001). In non- tropical environments, energy-conserving, adaptive adjustments occur among individuals in response to decreasing day lengths that are believed to promote survival during the harsh conditions of winter (Bronson, 1985). For example, short days decrease re- productive system size and function in white-footed mice ( Pero- myscus leucopus ) (Whitaker, 1940; Ruf et al., 1997). In addition to reproductive involution, individuals of several
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NelsonSeasonality - The Journal of Neuroscience May 4 2005...

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