UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    HARMFUL ALGAL BLOOM STRESSORS ALTER BEHAVIOR AND BRAIN ACTIVITY IN THE KILLIFISH, FUNDULUS HETEROCLITUS.
    (2005-04-15) Salierno, James D; Kane, Andrew S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Harmful algal bloom (HAB) events are increasing in severity and frequency worldwide, and are known to severely impact fish populations. Impacts of HABs on fish, as well as other organisms, occur through toxic and physical stress. Behavioral and central nervous system (CNS) alterations can have direct consequences to the fitness and survival of individuals and populations. This study investigated and characterized alterations in social and swimming behaviors and brain activity in mummichog (Fundulus heteroclitus) exposed to HAB stressors. The mummichog is an ecologically important estuarine fish species exposed to a variety of HAB events in the wild. A behavioral analysis system was developed to study swimming and social behavior of fish and an immunohistochemistry technique was used to investigate alterations in neuronal activity as evidenced by c-Fos protein expression. HAB stressors included excitatory (domoic acid, brevetoxin) and inhibitory (saxitoxin) neurotoxic agents as well as direct exposures to the dinoflagellate Pfiesteria shumwayae and the diatom Chaetoceros concavicornis. P. shumwayae and C. concavicornis are HAB species that are known to induce mortality through physical trauma to fish. Brevetoxin exposure increased swimming and social behaviors whereas saxitoxin decreased these behaviors. The effects of saxitoxin on swimming and social behaviors were consistent with exposure to a fish anesthetic, MS-222. Similarly, it was found, through c-Fos expression, that the excitatory HAB neurotoxins brevetoxin and domoic acid, increased neuronal activity while saxitoxin decreased activity. Exposure to P. shumwayae and C. concavicornis, resulted in significant dose related increases in neuronal activity. Stressor-specific neuronal activity was greatest in the optic lobe, but was also found in the telencephalon with physical stressors increasing activity greater than chemical stressors. Results demonstrate that sublethal exposures to HAB neurotoxins can alter swimming and social behavior in mummichog and exposures to both neurotoxins and algae can alter neuronal activity. Alterations in brain activity, and knowledge of specific regions within the brain activated during stress, can provide insights into the control of fish behavior. Ultimately, HAB exposure related changes in neuronal signaling may alter behaviors, resulting in individual and population level alterations during HAB events.
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    Neuronal Activation Following Cohabitation in the Prairie Vole (Microtus ochrogaster)
    (2004-04-29) Hazelton, Julie Louise; Ottinger, Mary A; Hoffman, Gloria E; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sexually naïve female prairie voles require exposure to a novel male to activate the neural circuits involved in the formation of stable pair bonds and to stimulate sexual receptivity. The objective of our study was to investigate the neural pathways involved in the formation of pair bonds. Cushing et al. (2003) studied neuronal activation in selected brain regions, as expressed by c-Fos immunoreactivity (ir), during the first hour of cohabitation in prairie voles. In the present study, we extend the findings of this study to examine neuronal activation associated with cohabitation to include 2, 6 and 12 hr. In addition, we examined the potential colocalization of luteininzing hormone releasing hormone (LHRH) and c-Fos to determine if this is a system activated during the initial stages of pair bond formation. The selected time periods include the initiation of sexual activation of the female and pair bond formation. Expression of c-Fos as analyzed in three regions that play a role in early social encounters. These areas included: (1) the sociosexual behavior circuit, (2) the reward pathway, and (3) nuclei whose peptides regulate the actions of those networks. Based on the previous data, increased c-Fos expression was predicted in the social behavior circuit, including the medial amygdala, bed nucleus of the stria terminalis, medial preoptic nucleus, and ventromedial nucleus of the hypothalamus. The lateral septum was examined due to its role in the social behavior circuit and in the process of pair bond formation. Next, we predicted that increased c-Fos activity would be observed over time in regions that did not show increases during initial contact, but are involved in pair bond formation. These regions include two components of the reward pathway: the nucleus accumbens and the ventral pallidum. Finally, nuclei known to regulate both the social behavior and reward circuits were examined and included the supraoptic nucleus and the pariventricular nucleus, which produce oxytocin and vasopressin. These neuropeptides are critical in social behavior and the formation of pair bonds. Immediately following the period of cohabitation (0, 1, 2, 6 or 12 hour in length) animals were separated and brains fixed. Fixed brains were sectioned at 30μm and stained with c-Fos and LHRH antibodies using double label immunocytochemistry (ICC) (Berghorn et al., 1994). Significant colocalization of LHRH and c-Fos was not observed in the first twelve hours in either sex of cohabitated prairie voles. Additionally there was no difference in number of LHRH ir neurons between sex or treatments. LHRH ir neurons in male and female prairie voles were predominantly located in the diagonal band of broca, preoptic area, lateral hypothalamus and supraoptic decussation. Individual LHRH neurons that did express c-Fos were predominantly located in the POA and LH. We observed a sexually dimorphic temporal pattern in c-Fos ir in the circuitry involved in pair bond formation in prairie voles. This pattern suggests that incoming information is first sorted through the social-sexual circuit and continues to be processed as information is received by nuclei of the reward pathway a short time later in both sexes. An increase in immediate early gene (ieg) immunoreactivity in the social behavior network is reported concurrently with peak activation of the reward circuit. During the same time period, an increase in c-Fos ir is reported in the nuclei involved in the endocrine control of partner preference and pair bond formation. Together these data suggest that in prairie voles, both the social and reward circuits interact early in cohabitation prior to reproductive activation to establish a heterosexual bond and that both circuits may be regulated by neuropeptides produced by the PVN and SON. This research was conducted by funding from the following: NSF IBN-9817024 (MAO), NIH HD 38490 (CSC, GEH, BSC, MAO) and MH 01992 (BSC). Subject Category: Neuronendocrine Activation following cohabitation Keywords: LHRH, social behavior, reward pathway, c-Fos, neuronal activation