The neurophysiological pathways associated with beat-to-beat regulation of mean arterial pressure are well known. Less known are the control dynamics associated with short term maintained of arterial blood pressure about a homeostatic set point.The baroreflex (BRx), the most rapid and robust of neural reflexes within the autonomic nervous system, is a negative feedback controller that monitors and regulates heart rate and blood pressure. By leveraging the parasympathetic and sympathetic divisions of the autonomic nervous system, the BRx can change blood pressure within a single heart beat. To better understand these controller dynamics, a classic BRx reflexogenic experimental preparation was carried out. This thesis reconfirmed previous observations of an electrically-evoked sexually-dimorphic peak depressor response in the BRx of Sprague-Dawley rats and verified that these functional reflexogenic differences carry over to sustained electrical paradigms. Further, it uncovered interesting recovery dynamics in both blood pressure and heart rate. The rat aortic depressor nerve was used as an experimental target for electrical activation of the parasympathetic-mediated reduction in mean arterial pressure. The duration, frequency, and patterning of stimulation were explored, with emphasis on differences between sexes. By measuring the normalized percent decrease in mean arterial pressure as well as the differences in beats per minute during rest and during stimulation,the null hypothesis was rejected.<br>

Many signaling pathways which are classically understood for their roles in early development are also known to be involved in tissue maintenance and adult energy homeostasis. Furthermore, dysfunction of these signaling pathways results in human diseases such as cancer. An in depth understanding of how developmentally important signaling pathways function in the adult will provide mechanistic insights into disease and potential new therapeutic targets. Herein Chapter 1, the Wnt, fibroblast growth factor (FGF), and Hedgehog (Hh) signaling pathways are discussed and examples of their relevance in development, adult homeostasis, and disease are provided. Wnt signaling provides an example of this concept as it has well described roles during both development and adult metabolism.<div><br></div><div> Work included in Chapter 2, investigates the regulation of adult energy homeostasis by a member of the endocrine FGF family, FGF19. The three endocrine FGFs, FGF19 (FGF15 in mice), FGF21, and FGF23 have well described roles in the regulation of metabolic processes in adults. While FGF23 is primarily involved in the regulation of phosphate and vitamin D homeostasis,FGF19 and FGF21 have shown similar pharmacological effects on whole body metabolism. Here, the importance of adaptive thermogenesis for the pharmacological action of FGF19 is explored. UsingUCP1KO animals we show that whole-body thermogenesis is dispensable for body weight loss following FGF19 treatment.<br></div><div><br></div><div>Finally, the potential involvement of Hh signaling in mediating the hyperphagia driven obesity observed in certain ciliopathies is explored in Chapter 3. Emerging evidence suggests cilia play an important role in the regulation of feeding behavior. In mammals, the hedgehog pathway is dependent on the primary cilium as an organizing center and defects in hedgehog signaling share some clinical symptoms of ciliopathies. Here, we characterized the expression of core pathway components in the adult hypothalamus. We show that neurons within specific nuclei important for regulation of feeding behavior express Hh ligand and members of its signaling pathway. We also demonstrate that the Hh pathway is transcriptionally upregulated in response to an overnight fast. This work provides an important foundation for understanding the functional role of Hh signaling in regulation of energy homeostasis. In its entirety, this work highlights the emerging clinical relevance of developmentally critical pathways in diseases associated with dysfunction of adult tissue homeostasis, such as obesity.<br></div>

<div>Hydrocephalus is a debilitating disease characterized by an increase in cerebrospinal fluid (CSF) in the brain, leading to increases in pressure that can ultimately result in death. Current treatments for hydrocephalus include only invasive brain surgery. Therefore, the need for a pharmaceutical therapy is great. In order to develop a suitable treatment, we first must be able to study the disease and the mechanisms by which it develops. By characterizing appropriate in vivo and in vitro models, we are better able to study this disease. In this thesis, the Wpk rat model and the PCP-R cell line are described as such appropriate models. In addition to suitable models, we also require a target for drug treatment. Transient Receptor Potential Vanilloid 4 (TRPV4) is a non-selective cation ion channel present in the main CSF-producing organ in the brain, the choroid plexus (CP). Preliminary data suggest this channel plays a role in the development of hydrocephalus. In the following work, some of the mechanisms by which TRPV4 functions in the brain are also described, including through calcium-sensitive potassium channels and inflammation. From this research, we are able to achieve a better understanding of the function of TRPV4 and how it can affect the development and progression of hydrocephalus.</div>

<p>  </p> <p>Cilia are cell appendages that sense our environment and are critical in cell-to-cell communication. Dysfunction of cilia can result in several disease states including obesity. While cilia in the brain are known to be important for feeding behavior, it is unclear how they regulate energy homeostasis. Classically, cilia coordinate signaling through surface receptors called G-protein coupled receptors (GPCRs). For example, cilia mediated GPCR signaling is critical for both our senses of vision and smell. How cilia regulate the signaling of GPCRs in other areas of the body including the brain is only now emerging. To answer cell biology questions around cilia mediated GPCR signaling in neurons, we developed a system for primary neuronal cultures. We discovered that the cilia mediated hedgehog pathway influences the ability of neurons to respond to GPCR ligands. For the first time, this result highlights the role of the hedgehog pathway in neurons. We continue to explore how cilia integrate the hedgehog pathway and GPCR signaling in the central nervous system, and the potential connections to energy homeostasis. We discovered that hedgehog pathway activity in feeding centers of the brain changes based upon feeding conditions like fasting. We also learned that activating the hedgehog pathway in these brain regions is sufficient to cause obesity in mice. These novel results highlight an unrecognized role for the hedgehog pathway in the regulation of feeding behavior. Overall, this work provides a better understanding of ciliopathy associated obesity and may reveal more common mechanisms of obesity in the general population. In addition, this work implicates the hedgehog pathway in regulating behaviors and new modes of cell-cell communication within the central nervous system.</p>

<p>Cerebral radiation necrosis as a consequence of radiation therapy is often observed in patients several months to years after treatment. Complications include painful headaches, seizures, and in the worst-case death. Radiation necrosis is an irreversible condition with the options available to manage it all having noticeable downsides. As such, there is a critical need for better ways of either preventing the onset of necrosis and/or managing its symptoms. As radiation necrosis cannot be induced in humans for ethical reasons, a mouse model that mirrors the features of radiation necrosis observed in patients would allow for new techniques to be tested before being used in human clinical trials. This thesis will explain how our lab designed a murine model of cerebral radiation necrosis that uses a 320 keV cabinet irradiator to produce radiation necrosis and MRI and histology to evaluate the development of radiation necrosis at multiple time points.</p><p><br></p> <p> </p> <p>Our model required the development of a mouse positioning apparatus that could be used in the cabinet irradiator used as well as the machining of lead shields so that focal semi-hemispheric irradiations could be conducted with other critical structures spared. The MRI scans used as well as the algorithm used to draw radiation necrosis lesions were based off what has been used in previous Gamma Knife models of radiation necrosis. Our initial work showed that since the cabinet irradiator has a relatively flat dose distribution unlike the Gamma Knife, the radiation lesion volumes produced in the former either plateaued or decreased, unlike in the case of the latter where lesion volumes tended to decrease over time. Further work analyzed the effects of fractionation and found minimal sparing using four different fractionation schemes. The effects of strain and sex on the development of radiation necrosis were also analyzed, with strain being found to be a statistically significant parameter while sex was not. Future research should focus on testing the effects of new drugs and techniques for better dealing with radiation necrosis.<b></b></p>

<p>My thesis revolves around neuronal circuit dynamics in health and disease. The first part of the thesis characterized cross-regional synchrony within the visual cortical network following visual perceptual experience in healthy mice. This work for the first time described inter-areal 4-8 Hz superficial layer LFP synchrony across mouse visual cortical regions persisting beyond visual stimulation time window, and revealed that the synchrony was expressed specifically between V1 and the higher-order visual area (HVA) with functional preference matching the entrained spatial frequency (SF) and temporal frequency (TF) content, in mice. The discovery of visual familiarity induced inter-areal 4-8 Hz synchrony extends the previous discovery of the 4-8 Hz oscillation in V1 after visual experience from our lab (Kissinger et al., 2018; Kissinger et al., 2020; Gao et al., 2021), and provided the first pivotal evidence supporting the role of 4-8 Hz oscillation in mediating cross-regional communication. Such 4-8 Hz visual cortical network synchrony has been mostly reported in primate studies in contexts of visual attention and working memory (Liebe et al., 2012; Spyropoulos et al., 2018), while our study extended the visual cortical network synchrony research scope to mouse models and in a new context of visual familiarity. The work is a key step for starting cortical network studies in mice, and for starting predictive coding theory study in the context of oscillations in mouse cortical network in the future. Additionally, unit spiking was more strongly modulated by 4-8 Hz oscillations in V1 and HVAs after visual experience. The visually-locked responsive units in V1 and HVAs exihibted either increased or decreased inter-areal spiking synchrony, while most post-stimulus responsive units in V1 and HVA exhibited higher spiking synchrony. </p> <p>The other parts of my dissertation looked at V1 activity in disease and following a novel CNS therapy. One project looked at recovery of visually evoked response in mouse V1 after ischemia through NeuroD1 mediated astrocyte-to-neuron conversion, where we characterized the formation of cortical laminated structure from the converted neurons, longitudinal recovery of visually evoked responses of unit populations in V1, and units’ selective responses to orientations. Another project looked at altered visual cortical activity in an Auxilin knockout mouse model, which demonstrated overall reduced visually evoked responses, less selective responses to orientations, impaired visual adaptive responses and mismatch responses, as well as slower visual experience induced oscillations. These projects utilized the high-density silicon probe recording technique to 1) characterize visual cortical function recovery following a therapy, which provided evidence for its high efficacy for recovering physiological functions, and to 2) phenotype visual cortical functional impairments in a mouse disease model, which provided more basic understanding in visual cortical physiology of Auxilin related disease.</p> <p>In sum, my dissertation work took advantage of the high-density silicon probe recording technique to probe neuronal circuits in health and disease. The discovery of visual experience induced inter-areal 4-8 Hz synchrony paves the way for studying 4-8 Hz activity in relation to stream-dependent visual processing and predictive coding in health and disease.</p>