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James C Walton dissertation.pdf (2.78 MB)

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Photoperiod, Brain Plasticity, and Behavior

Walton, James C
http://rave.ohiolink.edu/etdc/view?acc_num=osu1364994837

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Neuroscience Graduate Studies Program.
Outside of the tropics, distinctive sets of adaptations have evolved to cope with the unique demands of winter and summer on survival and reproduction. Because these seasonal adaptations often require significant time to develop, individuals rely upon an environmental signal (day length) to alter gene expression in order to produce the suite of season-specific adaptations. Photoperiodism is the ability of plants and animals to measure environmental day length (photoperiod) to ascertain the time of year and engage in seasonally appropriate adaptations; the annual cycle of changing photoperiod provides the environmental switch between seasonal phenotypes. The aim of this dissertation is to describe the influence of photoperiod on phenotype, the distribution of energetically expensive processes across the year, to maximize survival and fitness in males of a small photoperiodic rodent species, white-footed mice (Peromyscus leucopus). In Chapter 1 I provide a review of photoperiodism and an overview of the suite of adaptive responses at multiple levels to changing day lengths in a variety of vertebrate species. Among the adaptive responses in male white-footed mice are reduced brain size, and a marked reduction in hippocampal volume. Given that the hippocampus is critical for spatial learning and memory, I explore the functional outcomes of having a small hippocampus in Chapter 2 utilizing a spatial learning and memory task. I also assess neuronal physiology in the form of long-term potentiation in the hippocampus, the form of neuronal plasticity that is the putative mechanism of how memories are stored in the brain. In Chapters 3 and 4 I explore how photoperiod-mediated changes in hormones alter hippocampal function. Given that mammals use pineal melatonin rhythms to monitor day length, in Chapter 3 I explore the role of melatonin in the functional and structural hippocampal changes described in Chapter 2. Downstream of pineal melatonin signaling, gonadal steroids are also altered in short days in this species, and the role of gonadal steroids in photoperiod-mediated changes in the hippocampus is explored in Chapter 4. Given that the hippocampus is heavily interconnected with other brain structures, it follows that these areas, and behaviors dependent upon them, are altered in short days as well. In Chapter 5 I explore how photoperiod affects the structure and function of the amygdala and alters amygdala-dependent fear behaviors. Whereas Chapters 3-5 explore functional outcomes of reduced brain volume, in Chapter 6 and 7 I explore a potential mechanism by which brain mass and hippocampal volume may be altered. The recruitment and retention of new neurons in the brains of adults may contribute to volumetric and mass changes; thus, I explore the effect of photoperiod on neurogenesis in the two main neurogenic niches of adult brains: the olfactory bulb (Chapter 6) and the dentate gyrus of the hippocampus (Chapter 7). In conclusion, in Chapter 8 I summarize my findings and propose future directions for research in this species into how photoperiod affects brain plasticity and behavior, and how this research can inform us on complex gene-environment interactions that affect phenotypic plasticity, and thus behavior.
Randy Nelson, PhD (Advisor)
258 p.
Endocrinology; Neurosciences

Recommended Citations

Citations

  • Walton, J. C. (2013). Photoperiod, Brain Plasticity, and Behavior [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1364994837

    APA Style (7th edition)

  • Walton, James. Photoperiod, Brain Plasticity, and Behavior. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1364994837.

    MLA Style (8th edition)

  • Walton, James. "Photoperiod, Brain Plasticity, and Behavior." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1364994837

    Chicago Manual of Style (17th edition)

osu1364994837
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This open access ETD is published by The Ohio State University and OhioLINK.