acase@tulane.edu

Involutions and fixed-point-free involutions arise naturally as representatives for certain Borel orbits in invertible matrices. Similarly, partial involutions and partial fixed-point-free involutions represent certain Borel orbits in matrices which are not necessarily invertible. Inclusion relations among Borel orbit closures induce a partial order on these discrete parameterizing sets. In this dissertation we investigate the associated order complex of these posets. In particular, we prove that the order complex of the Bruhat poset of Borel orbit closures is shellable in symmetric as well as skew-symmetric matrices. / acase@tulane.edu

The current set of experiments was designed to test the hypothesis that there is a sex difference in impulsivity and in brain areas associated with impulse control in prepubertal and adult rats, such that females have greater inhibitory control than do males. Preliminary studies established that neonatal testosterone exposure is able to masculinize and increase impulsive behavior in prepubertal female rats. In the current study, male and female prepubertal rats exposed to treatments that resulted in either neonatal androgen or estrogen receptor activation made more impulsive choices than did control females and their performance mirrored that of control males. Assessment of impulsivity in adult rats indicated that impulsive choice behavior was similar in males and females whereas impulsive action behavior was greater in males than in females. Analysis of protein levels of markers of dopaminergic and noradrenergic reuptake in the orbital frontal cortex (OFC) and dorsal striatum (dSTR), two brain areas important for impulse control, revealed no differences between male and female prepubertal or adult rats, whereas analysis of protein levels of markers of myelination in the OFC and dSTR revealed similar levels between the sexes in prepubertal rats but increased myelin levels in the OFC but not dSTR of adult female rats as compared to males. Furthermore, analysis of the projections from the OFC to dSTR discovered that the strength of these projections was significantly greater in adult females as compared to males. However, inactivation of the OFC during an impulsive action task in adult rats failed to have an effect on impulsive action responding. Collectively, these results demonstrate for the first time that there is a sex difference in impulsive choice control in prepubertal rats that is organized neonatally by actions of both androgens and estrogens, this sex difference subsides in adulthood, but a sex difference in impulsive action control is present in adulthood. Furthermore, the novel discovery that adult female rats have increased levels of myelination within the OFC and increased strength of projections from the OFC to dSTR as compared to males establishes a molecular sex difference that could underlie the enhanced impulse control in females. / acase@tulane.edu

In India, ranked 132nd out of 148 countries in the United Nations Gender Inequality Index (2013), females face numerous challenges that pose a threat to their sexual health and psychological well-being. This paper focuses specifically on adolescent unmarried females living in an urban slum, a particularly vulnerable segment of the population that is important to empower in order to effect change. With the ultimate aim to better understand how to design effective and accessible interventions for adolescent females, this paper explores sexual health and its relation to psychological well-being from the perspectives of multiple stakeholders: adolescent girls, mothers of adolescent girls, and service providers who work with adolescent girls. To understand the unique and shared perspectives of the stakeholders regarding the constructs of psychological well-being, gender roles, and sexual health, the author utilized focus group and interview data. Through the use of the deductive-inductive coding process, the author identified overall themes and differences in perspective that elucidated the perspectives of the population. The findings revealed that there is great overlap in the three constructs studied, and each is influenced by and impacts the other. Additionally, the findings showed a trend of girls, mothers, and service providers understanding the importance of girls having access to sexual health information and openness towards mothers potentially sharing this information with daughters. Other implications, future research directions, and limitations are discussed. / acase@tulane.edu

The stress response is an evolutionarily conserved mechanism critical for survival that requires orchestration of different systems in the body. Corticotropin-releasing hormone (CRH) neurons of the hypothalamic paraventricular nucleus (PVN) represent the final common pathway leading to HPA axis activation in response to stress. Noradrenergic inputs to CRH neurons in the PVN provide a powerful drive to activate the HPA axis. Previous anatomical studies have shown that noradrenergic afferents synapse directly on CRH neurons, but electrophysiological analyses indicate that the noradrenergic activation of CRH neurons is mediated primarily by the stimulation of presynaptic glutamatergic neurons. Here, using whole cell patch clamp recordings in identified CRH neurons, I demonstrate that norepinephrine (NE) stimulates excitatory synaptic inputs by activating postsynaptic α1 adrenergic receptors in CRH neurons and inducing the release of the retrograde messenger nitric oxide, which drives upstream glutamate neurons to elicit spike-dependent synaptic glutamate release onto the CRH neurons. Notably, the NE effect is dependent on ATP transmission and astrocytic function, suggesting that astrocytes serve as an intermediary in the retrograde activation of glutamateregic synaptic inputs to the CRH neurons. In addition, I also show that the NE-induced excitation of CRH neurons is stress-status sensitive and corticosterone dependent, in that stress-induced corticosterone causes internalization of membrane α1 adrenergic receptors to desensitize the CRH neurons to NE. Taken together, my findings provide evidence that NE excites CRH neurons in a stress state-dependent manner by a retrograde NO stimulation of local glutamate circuits that is dependent on glial activation. This retrograde trans-neuronal-glial regulation of excitatory synaptic inputs to CRH neurons by NE provides a mechanism for the NE activation of the HPA axis in the early stage of stress response. The stress-/corticosterone-induced desensitization of CRH neurons to NE modulation by the internalization of α1 adrenergic receptors confers a stress state-dependent resistance of the CRH neurons to repeated noradrenergic activation, which provides a mechanism for the negative feedback regulation of the CRH neurons and the HPA axis by stress and glucocorticoids, and a means to restore neuroendocrine homeostasis after stress exposure. / acase@tulane.edu

Some past work indicates that sexual minorities may experience impaired social relationship outcomes relative to heterosexuals. However, a number of limitations of the extant literature imply the need for further work on potential social relationship disparities. Furthermore, if potential disparities are indeed confirmed, researchers should begin to investigate etiologic mechanisms, including both risk and protective factors. The primary aim of Study 1 was to gauge potential disparities in social relationship outcomes (i.e., social network size, loneliness, relationship strain and social capital) based upon sexual orientation among adults in the United States. Consistent with hypotheses, across each of these measures sexual minorities reported impaired social relationship outcomes relative to heterosexuals. Study 1 also explored whether perceived discrimination and structural discrimination may be involved in producing these disparities. Confirming hypotheses, controlling for perceived discrimination attenuated disparities across three of the four social relationship outcomes. Furthermore, among sexual minorities structural discrimination moderated the association between perceived discrimination and both social relationship strain and loneliness. The primary aim of Study 2 was to test both risk and protective factors stemming from the experience of social devaluation that may be tied to social relationship outcomes among sexual minorities. Specifically, indirect paths from perceived discrimination to social relationship strain through emotional suppression, chronic inflammation and group identification were examined. Study 2 built upon Study 1 by explicating stigma-related variables that potentially exacerbate (suppression, inflammation) and attenuate (group identification) social relationship disparities for sexual minorities. Partial support for the proposed model was found in Study 2. While the pathway through emotional suppression was supported, there was mixed support for the pathway through chronic inflammation and poorer support for the pathway through group identification. Finally, results from these two complementary studies are synthesized and implications for public policy, programmatic interventions and efforts to build resilience among sexual minorities are discussed. / acase@tulane.edu

The Wax Lake Delta (WLD) is one of the few areas of land gain in coastal Louisiana and provides an analog for a naturally developing subdelta created by a river diversion. This study examined the spatial and temporal variability of benthic respiration to broaden our current understanding of the biogeochemical functioning of diversion-created estuarine systems. Spatial and seasonal benthic respiration rates were quantified during distinct periods of discharge and water temperature conditions, which included a spring period of peak river discharge (May 2012, 2013), a summer period of low discharge and maximum seasonal water temperatures (August/Sept, 2012), and an autumn period of low discharge and intermediate water temperatures (October 2013). Benthic respiration rates for the Wax Lake Delta ranged from 4.4 – 46.8 and averaged 16.7 (± 1.5) mmol O2 m-2 d-1 . Atchafalaya Bay sites ranged from 10.3 - 26.5 and averaged 17.1 (± 1.5) mmol O2 m-2 d-1 across all sites and seasons. Benthic respiration generally increased along two spatial gradients: 1) with distance offshore from the delta into Atchafalaya Bay, and 2) toward the interior of a mouth bar island. These patterns were related to similar increases in sediment OC and N content, which were derived from a mix of terrigenous and marine sources and varied with season. Sediment organic (OC and N) content and water temperature were identified as main drivers influencing benthic respiration in the Wax Lake Delta estuary. Seasonal changes in riverine discharge and wind-driven sediment resuspension events were likely to influence the seasonal variability of benthic respiration by governing water temperature and organic matter supply to the sediments. Benthic oxygen consumption rates in the Wax Lake Delta were most sensitive to increases in water temperature during low discharge conditions (< 2,000 m3 /s) of the MI-AR system. In context of coastal restoration, results from this study suggest that opening a sediment diversion during spring peak discharge conditions will have less of an effect on benthic oxygen consumption rates than during warmer low flow conditions. / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

In this dissertation I evaluated the ecological and evolutionary mechanisms that promote the spread of non-native parasites infecting novel hosts under contemporary and future climate conditions. Thorough assessment of the impact of introduced parasites and an understanding of the potential effects of climate change on parasite distributions and densities will promote effective conservation of native aquatic biodiversity. The spread of an introduced nematode parasite, Camallanus cotti, infecting the native Hawaiian stream fish, Awaous stamineus, across the Hawaiian Islands provided an opportunity to examine how biotic (densities of introduced & native hosts, individual host traits, genetic diversity) and environmental (land-use, water chemistry) factors promote novel host-parasite interactions. In addition to completing archipelago-wide surveys of parasite distributions and densities in native fish hosts, I characterized geographic patterns of genetic variation in C. cotti to assess gene flow, identify likely conduits of introduction and spread of the parasite across the archipelago. Finally, I utilized a natural precipitation gradient across the Hamakua coast on the island of Hawai`i, as a natural analog to conditions predicted by climate change, to assess the relationship between precipitation and infection of A. stamineus by C. cotti. I found the distribution C. cotti has become decoupled from that of the non-native hosts and that the parasite infects native fishes in remote, relatively pristine watersheds. The abundance, intensity, and prevalence of C. cotti infecting A. stamineus are influenced by a suite of factors, but notably parasitism increases with decreasing precipitation. This finding suggest that infection of native Hawaiian fishes by introduced parasites will increase if climate conditions change as expected. Genetic analysis indicates that C. cotti has spread across the archipelago following an initial introduction on O'ahu with subsequent dispersal to Maui and then underwent stepwise dispersal to other islands in the archipelago. Significant genetic structure also was detected across islands, suggesting that dispersal potential is constrained, which in turn suggests that remediation efforts focusing on invasion hotspots or areas of concern could be effective at reducing parasites loads in native fishes. / acase@tulane.edu