Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Neuroendocrine mechanisms underlying paternal experience-induced plasticity of the hippocampus(2016) Hyer, Molly Melissa; Glasper, Erica R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Evidence suggests that males, like females, undergo altered structure and function of the hippocampus postpartum, a brain region that regulates certain aspects of emotion, learning, and memory. These behaviors are beneficial for successful parenting. In maternal rodents, offspring contact contributes to postpartum hippocampal plasticity in both mothers and offspring. Fathers do not undergo pregnancy, parturition, or lactation, therefore, the impact of offspring on hippocampal plasticity is less clear. California mouse (Peromyscus californicus) fathers are highly paternal, making this monogamous species a good model of paternal care. In this species, between postnatal days 15 and 21 paternal behavior becomes more active (i.e. increased pup retrievals) to care for pups that are beginning to explore outside of the nest. I observed reduced anxiety-like behavior in fathers specifically within this temporal window. Concomitant with attenuated anxiety-like behavior, I found that fathers maintain survival of adult born neurons in the dentate gyrus of the hippocampus. Enhanced hippocampal plasticity is not restricted to adult neurogenesis, as dendritic spine density in the dentate gyrus is increased in fathers at this same time – an effect that lasts until weaning. When permanently separated from their offspring, fathers show increased passive stress coping and reduced spine density in the DG. Taken together, these data suggest that the degree of active father-offspring interaction significantly alters hippocampal plasticity in the father. Estradiol and its receptors have been implicated in alterations to anxiety and adult neurogenesis in both males and females. I observed that estrogen receptor β (Erβ) mRNA expression was elevated in whole hippocampal homogenates at PND 16 in fathers. Similarly, circulating estradiol was elevated at both PND 2 and PND 16. After inhibition of Erβ with the drug tamoxifen, the number of surviving adult born neurons was suppressed in fathers alone. Taken together, these data suggest that in fathers, hippocampal plasticity occurs concomitantly with active father-offspring contact and that this plasticity, at least structural, is driven by activation of Erβ. Understanding paternal experience-induced plasticity and the mechanisms that drive it, may help to prevent deficits in paternal behavior that can disrupt offspring development and contribute to emotional dysregulation in fathers.Item REGULATION OF THE INHIBITORY DRIVE IN THE OLFACTORY BULB(2013) Nunez-Parra, Alexia Francisca; Araneda, Ricardo C; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Animals are exposed to a variety of odor cues that serve as environmental guides for their exploratory and social behaviors. Two distinct but complementing pathways process chemosensory cues: the Main and the Accessory olfactory System (AOS). Sensory neurons send their axons to the olfactory bulb (OB), specifically to the main and the accessory olfactory bulb (MOB and AOB, respectively) where they synapse onto principal neurons, the mitral (MCs). The OB is the only relay center between sensory neurons and cortical and limbic structures and therefore important aspects of odor processing occur in this region. Specifically, a distinctive mechanism used for olfactory processing is a strict regulation of MCs output by inhibitory neurons called granule cells (GCs). Importantely, inhibition of MCs is a dynamic process; it is regulated by the constant addition of new GCs to the OB circuit throughout life, in a process known as adult neurogenesis. Little is known, however, about the contribution of adult born neurons to the processing of olfactory cues, known as pheromones. Detection of pheromones by the AOS is critical for proper display of social behaviors such as hierarchical dominance and mate recognition. Here, we studied how the integration of new-born neurons could be regulated. We found that the arrival of new neurons into the adult AOB increases after animals are exposed to aggression and mate cues, suggesting that these newly arrived neurons can add important plasticity to the AOB circuitry and modify olfactory processing under different behavioral contexts. In addition, GCs mediated inhibition in the OB is precisely controlled by an extensive centrifugal innervation. For example, cortical feedback projections and neuromodulatory afferents originating in the midbrain and basal forebrain excite GC, inhibiting MCs' and decreasing their output. Regulation of of GCs by inhibition has also been reported, however, the source of this inhibition and its relevance to olfactory processing is not known. Here we characterized inhibitory inputs onto GCs and show that GCs receive extensive inhibition from GABAergic neurons in the HDB/MCPO and from neighboring GCs. Moreover, we show, for the first time, that inhibition onto GCs is required for proper olfactory discrimination.