Thesis (M. A.)--University of North Texas, May, 2007. / Title from title page display. Includes bibliographical references.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaves 75-79). Also available via the World Wide Web.

The adhesion GPCRs are a poorly understood and evolutionarily ancient family of cell surface receptors, several of which have emerging functions in the development of the nervous system. aGPCRs comprise a large extracellular domain, providing binding sites for a variety of ligands, alongside a seven transmembrane domain characteristic of GPCRs. It has been proposed that aGPCRs may function as "context-recognisers", using their large ectodomains to bind different combinations of ligands depending on the molecular make-up of the environment. However there is a lack of direct evidence for this at a molecular level. The ectodomain of one subfamily of aGPCRs, the Latrophilins (Lphns) has been shown to directly interact with several ligands with roles in synaptogenesis and neural guidance. The best-validated of these interactions are those with Fibronectin Leucine-Rich Transmembrane (FLRT) proteins and the Teneurins. In addition, FLRT proteins, also interact with Uncoordinated5 (Unc5) proteins, mediating cell repulsion. Here I reveal that the FLRT-binding site of Lphn is bifunctional, mediating both cell adhesion and repulsion, and that Unc5 is capable of influencing the functional outcome of this interaction. Biophysics and structural studies show that fragments of the Lphn, FLRT and Unc5 ectodomains interact in an unusual and homologue-dependent stoichiometry. Despite the fact that Teneurin interacts with Lphn at a distinct site, Teneurin seems incapable of interacting with the Lphn-FLRT-Unc5 complex, but can form a ternary complex with Lphn and FLRT in the absence of Unc5. Alongside this I present a crystal structure of a large portion of a Teneurin ectodomain, revealing the ancient evolutionary origins of this receptor. Together these data provide strong molecular evidence for a role of Lphns as context-recognisers, by their abilities to bind diverse ligands in distinct combinations and variable stoichiometries.

In vertebrates the brain superimposes control on fundamental processes such as reproduction and growth. Neuropeptides secreted from the brain initiate a cascade of events that affect these processes. In this thesis three neuropeptides are examined to determine their structures and patterns in the context of vertebrate evolution. Reproduction in vertebrates is controlled by the neuropeptide gonadotropin-releasing hormone, GnRH, a decapeptide belonging to a peptide family of twelve known members. One common theme in vertebrates is that there is usually more than one form of GnRH in the brain of a single species; often each form of GnRH has a separate location in the brain and therefore, an implied distinct function. In this thesis, the brain of Siberian sturgeon, Acipenser gueldenstaedti, initially was examined for GnRH using reversed-phase high performance liquid chromatography, HPLC, and radioimmunoassay, RIA, with specific antisera and was shown to contain mammalian (m)GnRH by chemical sequence analysis and by accurate determination of the molecular mass. In addition, another form of GnRH, termed chicken (c)GnRH-II, was found in the sturgeon brain. This is the first report to show that the primary structure of GnRH is identical in an evolutionarily-ancient fish and in mammals including humans. Further, the second form of GnRH, cGnRH-11, was identified for the first time in the brain of adult stumptail monkeys (Macaca speciosa) as well as in adult and fetal rhesus monkey (Macaca mulatta) brains. This study implies that at least two forms of GnRH are found in the brain of most vertebrate species including mammals. In cartilaginous fish that evolved earlier than sturgeon, the same HPLC and RIA methods were used to demonstrate that regions of the brain and pituitary of skate. Raja canebensis, also contained cGnRH-II but dogfish (df)GnRH rather than mGnRH. By the same criteria, teleost fish like whitefish (Prosopium williamsoni), platyfish (Xiphophorus maculatus), green swordtail (Xiphophorus hellerei) and sablefish (Anoplomia fimbria) were shown to have cGnRH-II and salmon (s)GnRH, as well as one or two more immunoreactive variants of GnRH with novel or seabream (sb)GnRH-like properties, within their brain. The identity of at least three types of immunoreactive GnRH molecules in the brain of these fish species suggests that three forms of GnRH in the brain is an early condition in teleost evolution. Ancestral sturgeon emerged at a branch point between the bony fish lineage and the tetrapod lineage and therefore, it is useful to compare the neuropeptide structures found in their brain with those both in fish and more evolutionarily-advanced vertebrates. Several tetrapod species were examined to determine if the forms of GnRH found in the sturgeon brain had been retained in their evolution. In contrasts to studies in our laboratory and by others showing that most amphibians, reptiles and birds contain two forms of GnRH, the present research shows that the brain of the green anole lizard, Anolis carolinensis, contained only cGnRH-II within its brain. In addition, my HPLC and RIA studies showed that only mGnRH was present in the brain of guinea pig, hamster and rat suggesting that there are some species which function with only one form of GnRH in their brain. Also, there were no distinguishable forms of GnRH in a human placenta, demonstrating that the type(s) of GnRH might be tissue-specific. Two neuropeptides associated with growth also were isolated from the sturgeon brain. A cDNA encoding growth hormone-releasing factor, GRF, and pituitary adenylate cyclase-activating polypeptide, PACAP, was isolated and sequenced using the polymerase chain reaction, PCR, and other molecular biology methods. In contrast to mammals where GRF and PACAP are encoded on separate genes, in sturgeon, GRF and PACAP are encoded in tandem on a single mRNA. In this thesis, I establish the structure of GnRH, GRF, and PACAP in sturgeon, a species that evolved near a critical branching point between bony fish and tetrapods. These structures are used as a focal point for comparison to those of other vertebrates. This comparative evolutionary approach is an important step toward understanding the evolution of these important neuropeptides as well as enhancing our knowledge of general principles in the endocrine systems controlling reproduction and growth. / Graduate

In male hamsters mating behavior is dependent on sufficient androgens and chemosensory input from the main olfactory and vomeronasal systems, whose central pathways contain cell bodies and fibers of gonadotropin-releasing hormone (GnRH) neurons. Regions of the medial amygdala (vomeronasal amygdala) contain androgen receptors and differentially process chemosignals with different social implications. According to published reports of "categorical" patterns of response, conspecific chemosensory stimuli activate the anterior (MeA) and posterior (MeP) medial amygdala, while heterospecific stimuli only activate MeA, in male hamsters (and male mice). Furthermore, chemosignals with distinct social implications differentially activate the dorsal and ventral subregions of MeA and MeP (MeAd/v, MePd/v). In sexually-naïve male hamsters, lesions of the vomeronasal organ (VNX), but not the main olfactory bulb, impair mating behavior. Intracerebroventricular (icv)-GnRH restores mating in sexually-naïve VNX males and enhances medial amygdala (Me) activation by chemosensory stimulation. In sexually-experienced males, VNX does not impair mating and icv-GnRH suppresses Me activation. Thus, main olfactory input is sufficient for mating in experienced- but not naïve-VNX males. I tested whether GnRH enhances access of main olfactory input to the amygdala using icv-GnRH and either electrical or pharmacological stimulation of the main olfactory bulb (MOB), and then examined immediate early gene (IEG) expression there. Electrical stimulation of the MOB did not significantly activate the ipsilateral main olfactory cortex or amygdala in intact or VNX animals. When the IEG counts from both sides of the brain were averaged together, GnRH appeared to enhance activation in the medial amygdala in naïve-intact males, but appeared to decrease activation in naïve-VNX males. I concluded that electrical stimulation was not a sufficient means of driving main olfactory input to downstream brain regions, possibly due to activation of intra-bulbar inhibitory circuits. To alleviate this possible confound, I pharmacologically stimulated the MOB with a mixture of bicuculline methiodide and d,l Homocysteic acid. In sexually-naïve intact-males, MOB stimulation produced significant activation in MeAv and MePv. MePv activation is also characteristic of chemosensory stimuli from potential competitors and predators. In sexually-naïve VNX-males, in which GnRH facilitates mating, GnRH enhanced activation by MOB stimulation in posterodorsal medial amygdala (MePd), a region known to be rich in androgen resceptors and activated by conspecific reproductive chemosignals. Conversely, in sexually-experienced VNX-males, animals that do not require exogenous GnRH to mate normally after VNX, there is a depression in activation in MePd due to GnRH and stimulation in MePd, similar to its response to natural chemosensory stimulation. There also appeared to be a possible effect of VNX due to the difference in selective activation of GnRH in naïve-intact vs. naïve-VNX animals. MeP is also rich in steroid receptors and many chemosensory behaviors are steroid dependent. Therefore, I also tested the activation of androgen receptor (AR)-containing cells in Me after conspecific or heterospecific chemosensory stimulation. Conspecific and heterospecific chemosensory stimuli significantly activated AR-containing cells in Me and significantly increased the number of AR-positive cells in Me above control. The increase in the number of AR-ir cells produced by conspecific stimuli was also significantly above the numbers of AR-ir cells produced by the heterospecific stimulus. These effects may be due to increases of testosterone in response to chemosignals or circuit activity dependent on steroid levels. Future studies on castrated testosterone-replaced males will test these possibilities. The studies of this dissertation provide important information about the neurohormonal regulation of chemosensory and olfactory input to the medial amygdala. The integration of hormonal and chemosensory factors is vital to mating and other social behaviors, and thus species survival. The amygdala is crucial to this process in many vertebrate species, including the hamsters, which use chemicals to communicate with one another. This dissertation suggests, and provides some evidence for a part of the mechanism by which the amygdala accomplishes this integration. / A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2009. / December 9, 2008. / Olfactory Bulb, GnRH, Androgen Receptor, Vomeronasal, Hamster, Amygdala / Includes bibliographical references. / Michael Meredith, Professor Directing Dissertation; Jon Maner, Outside Committee Member; P. Bryant Chase, Committee Member; Richard Hyson, Committee Member; Zuoxin Wang, Committee Member.

Circadian rhythms are the outward manifestation of an internal timing system that measures time in 24-hr increments. The mammalian circadian system is hierarchical, with a pacemaker in the suprachiasmatic nucleus (SCN) synchronizing cell-autonomous oscillators in peripheral tissues. Much of what we know about rhythmicity in peripheral tissues comes from studies monitoring bioluminescence rhythms in PERIOD2::LUCIFERASE knock-in mice. A limitation with this model is that rhythmicity cannot be monitored in specific cells due to widespread reporter expression. To address this shortcoming, we generated a mouse that expresses luciferase from the Dbp locus only after Cre-mediated recombination. I validated this conditional mouse to provide a tool for monitoring circadian rhythms in a tissue/cell-specific manner. Crossing the conditional reporter mice with mice expressing Cre recombinase in various cell types allowed detection of rhythmic bioluminescence in the expected tissues, in vivo and ex vivo, as well as in slice cultures containing the SCN. The phase of bioluminescence rhythms from explants of mouse peripheral tissues indicated that DbpLuc/+ bioluminescence rhythms have an earlier phase than PER2::LUC/+ rhythms. Importantly, we confirmed that editing of the Dbp locus did not alter the period of circadian locomotor activity rhythms and did not alter liver Dbp RNA rhythms. Finally, the reporter mouse allows for monitoring rhythms in specific tissues in ambulatory mice. Thus, this mouse line is useful for studying circadian rhythms in a tissue/cell-type specific manner, which can be used to better monitor phase relationships between tissues at baseline and after environmental perturbations that disrupt circadian rhythms.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / A fundamental aspect of vision is the ability to detect motion and to define its direction. In the retina, directionally selective ganglion cells respond to stimulus motion in a 'preferred' direction but respond little to stimulus motion in the opposite or 'null' direction. However despite nearly forty years of investigation, the precise cellular locus and underlying mechanisms of direction selective encoding have remained largely elusive. Recently, starburst amacrine cells, that are presynaptic to directionally selective ganglion cells, have been shown to provide direction specific inhibitory output to these ganglion cells. Therefore defining the biophysical properties specific to starburst amacrine cell dendrites will provide significant insight into the ability of visual systems to encode the direction of objects moving through an animal's visual field. Using a combination of intracellular filling of starburst amacrine cells and immunohistochemical localization of biophysically relevant molecules, we have examined how individual dendrites compute such motion. In order to define the relative degree and pattern of colocalization of these markers on filled dendrites we developed a new set of image acquisition and data analysis procedures that have allowed us to define the biophysical signature intrinsic to different portions of starburst amacrine cell dendrites. We have found that sodium-potassium-chloride cotransporter (NKCC2) and potassium-chloride cotransporter (KCC2) are expressed and differentially distributed on the proximal and distal dendritic compartments of starburst amacrine cells, respectively. The functional relevance of the anatomical distribution pattern of these cation-chloride-cotransporter types has been confirmed by others using physiological techniques. In summary, our studies provide a fundamental mechanism through which starburst amacrine cells define motion direction and transmit this information to directionally selective ganglions cells. In addition, our illumination of the basic concept of segregation of functional components to different dendritic compartments will likely prove to be an important theme of neuronal function throughout the nervous system. / 2031-01-01

No description available.

Neuroergonomics, the application of neuroscience to human factors and ergonomics, is an emerging science focusing on the human brain concerning performance at work and in everyday settings. The advent of portable neurophysiological methods, including electroencephalography (EEG), has enabled measurements of real-time brain activity during physical tasks without restricting body movements. However, the EEG signatures of different physical exertion activity levels that involve the musculoskeletal system in everyday settings remain poorly understood. Furthermore, the assessment of functional connectivity among different brain regions during different force exertion levels remains unclear. One approach to investigating the brain connectome is to model the underlying mechanism of the brain as a complex network. This study applied employed a graph-theoretical approach to characterize the topological properties of the functional brain network induced by predefined force exertion levels, namely extremely light (EL), light (L), somewhat hard (SWH), hard (H), and extremely hard (EH) in two frequency bands, i.e., alpha and beta. Twelve female participants performed an isometric force exertion task and rated their perception of physical comfort at different physical exertion levels. A CGX-Mobile-64 EEG was used for recording spontaneous brain electrical activity. After preprocessing the EEG data, a source localization method was applied to study the functional brain connectivity at the source level. Subsequently, the alpha and beta networks were constructed by calculating the coherence between all pairs of 84 brain regions of interests that were selected using Brodmann Areas. Graph -theoretical measures were then employed to quantify the topological properties of the functional brain networks at different levels of force exertions at each frequency band. During an 'extremely hard' exertion level, a small-world network was observed for the alpha coherence network, whereas an ordered network was observed for the beta coherence network. The results suggest that high-level force exertions are associated with brain networks characterized by a more significant clustering coefficient, more global and local efficiency, and shorter characteristic path length under alpha coherence. The above suggests that brain regions are communicating and cooperating to a more considerable degree when the muscle force exertions increase to meet physically challenging tasks. The exploration of the present study extends the current understanding of the neurophysiological basis of physical efforts with different force levels of human physical exertion to reduce work-related musculoskeletal disorders.

No description available.