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 The functional importance and significance of ecdysteroids in molt-cycle regulation of the blue crab, Callinectes sapidus(2014) Techa, Sirinart; Chung, Sook J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study aims to expand our understanding of how ecdysteroids and neuropeptide hormones (MIH/CHH) regulate molting in crustaceans using the blue crab Callinectes sapidus as a model animal. The hypothesis of this study is that ecdysteroids have a stimulatory effect on MIH/CHH production in eyestalks while generating both positive and negative feedback on ecdysteroidogenesis in Y-organs. Since ecdysteroids exert their signals through an ecdysteroid receptor complex, composed of an ecdysone receptor (EcR) and its partner, the retinoid-X receptor (RXR), the functional activity of ecdysteroids on tissues of interest is examined through EcR expression. Endogenous levels of ecdysteroids as well as expression in EcR, RXR and MIH/CHH are assayed in both embryonic and juvenile molt cycles. Similar patterns of changes in these two cycles suggest that molting control is driven by the same mechanisms in each. During embryonic molt, the correlation of ecdysteroid levels and MIH/CHH expression suggests that ecdysteroids are involved in MIH/CHH production. Using an in vitro system, stimulation of MIH expression occurs in eyestalks incubated with ponasterone A (PoA) and 20-hydroxyecdysone (20-HE) in the ratio found endogenously (3:1) and in ecdysteroid concentrations of 75 and 150 ng/ml. The in vivo response of MIH expression to depletion of ecdysteroid signals was examined by RNAi knockdown of an ecdysone receptor that was found to reduce the levels of MIH to those found by MIH knockdown, providing support for the hypothesis that ecdysteroids stimulate MIH expression through an ecdysone receptor. This study also found evidence suggesting that crustaceans have long-loop feedback for ecdysteroids in the neuroendocrine axis, which is similar to that found in insects.Item EFFICACY OF ESTROGEN TREATMENT IN A MURINE MODEL OF ALZHEIMER'S DISEASE(2012) Schlappal, Anna Elise; Ottinger, Mary Ann; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Clinically, Alzheimer's Disease (AD) presents with cognitive dysfunction, cell death, and amyloid-beta (AB) plaque and neurofibrillary tangle (NFT) formation. Moreover, age and gender are primary risk factors; women are at much higher risk for developing AD compared to men. Estrogens may be neuroprotective; however, clinical use in hormone replacement therapy (HRT) is controversial due to potential adverse effects. Experiments were conducted using the APPswe/PS1dE9 (DTG) and APPswe/PS1M146V/TauP301L (3xTgAD) transgenic mouse models to assess the efficacy of an estrogen pro-drug, estradiol-quinol (E2Q). Treatment groups consisted of vehicle, estradiol (E2), or E2Q in intact and ovariectomized (OVX) DTG females, intact DTG males, and intact 3xTgAD females and males. The objectives of this study were to 1) characterize AD progression in a double transgenic (DTG) murine model and compare the efficacy of treatment with estradiol (E2) or E2Q in ovariectomized (OVX) and intact females, 2) compare the effects of E2Q in males, 3) determine if E2Q affects neurodegenerative disease progression in the triple transgenic (3xTgAD) murine model in both males and females, and 4) assess the effects of the neurodegenerative disease progression on mitochondrial function and determine if E2Q affects these endpoints. E2Q did not stimulate uterine tissue and proved to be an effective intervention; treated DTG mice had better cognitive behavior, decreased amyloid precursor protein (APP), and amyloid beta (AB) protein levels. Taken together, these data suggest that E2Q has potential as a therapeutic for AD patients.Item Proximate mechanisms and ultimate causes of female reproductive skew in cooperatively breeding golden lion tamarins, Leontopithecus rosalia(2011) Henry, MaLinda Dawn; Dietz, James M; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many cooperatively breeding species exhibit high reproductive skew. Delayed dispersal and cooperative breeding may have evolved as a consequence of the limits ecological constraints place on independent breeding. When simultaneous breeding by multiple females reduces the survival of the dominant's offspring, selection should favor dominants able to control subordinate reproduction. Monopolization of reproduction by dominant group members by means of suppression of subordinate reproduction has been documented in several taxa of cooperative breeders. In this dissertation I examine the proximate mechanisms and ultimate causes of reproductive skew in cooperatively breeding golden lion tamarins (Leontopithecus rosalia). In chapter one I combine data from phenological transects with hormonal evaluation of reproductive status to test whether caloric availability limits reproduction by female tamarins. Caloric availability was sufficient to support not only pregnancy polygyny in 83% of tamarin groups, but also the additional group members resulting from multiple litters. The super abundance of calories and the timing of births suggested that competition for allocare rather than for food resources may be the selective force limiting reproduction by subordinate females. In my second chapter I combine hormonal and demographic data to explain reproductive skew in terms of the costs and benefits to subordinate fitness under existing social circumstances. Subordinate females older than 18 months of age ovulated while residing within their natal group, but conceptions were delayed one to two years following reproductive maturity. The likelihood of successful reproduction by a subordinate female doubled with each year of age of the dominant female. Conceptions under incestuous mating conditions were rare (7 of 37 pregnancies). My results provide support for the hypothesis that subordinate adult females under three years old exercise reproductive self-restraint. I speculate that the threat of being evicted from the group and inbreeding avoidance are sufficient to delay attempts at reproduction by young subordinates without the need for costly fighting with the dominant female. In my third chapter I test whether reproduction by subordinate adult female tamarins is limited by dominant females who have incomplete control (incomplete control model, ICM) or complete control (optimal skew model, OSM) over subordinate reproduction. I combine hormonal data with group demography and caloric availability to determine variables useful in predicting a successful pregnancy to a subordinate female. Whereas subordinate females younger than 2.5 years of age ovulated but did not conceive, all females older than 3.9 years of age became pregnant. Reproduction in subordinate adult females was not limited by hormonal suppression of ovulation or conception, but by the failure of 7 of 11 pregnancies to produce live offspring. The likelihood of reproductive success increased 1.7 times with each additional group member. My results suggest that when caloric availability is sufficient to support reproduction by two breeding females and the group members necessary to provide allocare for two litters, subordinate females do not abide by a social contract that would limit their reproduction (OSM). Instead, older subordinates compete with dominant females for reproduction and succeed in producing live young if the dominant female is at least 10 years old, if subordinates conceive while the dominant is heavily pregnant, and if they reside within larger groups (ICM).Item Behavioral and Neuroendocrine Correlates of Sex Change in the Gilthead Seabream (Sparus aurata)(2009) Reyes-Tomassini, Jose J.; Zohar, Yonathan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sequential hermaphroditism is the most radical form of environmental sex determination observed in fish: functional adult males or females retain their ability to change sex even as adults. Among the factors that affect sex change in these species, the least understood is the social environment. Here, I studied the influences of social context on sex change in the Gilthead Seabream, Sparus aurata, by using the individual‟s dominance rank as an indicator of social status. To understand the role that the brain might play in sex change, I also studied the two main neuroendocrine factors that serve as the sexually differentiated axes of neural plasticity in most teleost species: AVT and GnRH. To do this, I first developed a set of tools designed to address the challenges associated with observing the behavior of aquacultured species. Using these tools, I provide the first in-depth study of seabream captive behavior, including the results of size-matched and sex-matched paired encounters. I found that females are more aggressive than males, but this difference is influenced by gonadal developmental status. I also showed that small but young males are more aggressive than bigger but older females. I cloned the AVT mRNA in seabream, and validated a quantitative assay to measure total brain AVT levels together with GnRH-1, GnRH-2, and GnRH-3 levels. I found that AVT and GnRH-3 levels rise during the onset of the hypothesized sex-change window, and drop to pre-quiescent levels until spawning, when all of these factors seem to increase their expression levels again. I also show for the first time, that GnRH-2 and dominance rank are strongly correlated in seabream during the spawning season but not during quiescence. GnRH-1 was strongly correlated to rank during quiescence but not during spawning. Finally, neither dominance rank nor size were a good predictor of the outcome of sex change, which seems to contradict what has been documented in sequential hermaphrodite reef fishes. I provide a model that accounts for this apparent contradiction and conclude that the Gilthead seabream remains true to the size-advantage hypothesis of sex allocation theory, if size and dominance are seen as proximate, rather than ultimate, factors.