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Title: Oxygen Sensing in Lymnaea: from Behaviour to Central Pattern Generators
Author: Janes, Tara Adele
Advisor: Syed, Naweed I.
Keywords: Animal Physiology;Neuroscience
Issue Date: 2-Feb-2016
Abstract: From invertebrates to humans, the regulation of cellular O2 levels within narrow physiological limits represents a significant challenge, but one that is necessary for survival. This essential task of O2 homeostasis is controlled by the nervous system so as to meet metabolic O2 demands in the face of ever-changing environments or injury/disease. The process by which the nervous system exercises such precise control over systemic O2 levels is termed respiratory behaviour. Specialized neural circuits termed respiratory central pattern generators (rCPG’s) produce the basic rhythmic motor output underlying respiratory behaviour. In turn, rCPG activity is subject to extensive neuromodulation, which allows respiratory behaviour to be adapted to changing environments or during various disease states. However, the fundamental mechanisms by which rCPG networks collect and integrate sensory information about the O2 environment and orchestrate a diversity of adaptive behavioural responses remains poorly understood. Specifically, data characterizing the effect of graded hypoxia on respiratory behaviour, locomotion and breathing pattern have not been described for many invertebrate taxa. These data are important as they aid our understanding of fundamental network mechanisms in metazoan respiratory control. Furthermore, while O2 chemoreceptors have been shown to be critical for rCPG modulation and adaptation to hypoxia, the mechanisms of hypoxic signal transduction and O2-sensing, as well as the functional relationship between multiple peripheral and central chemoreceptors remains uncertain. This thesis has sought to fill these gaps in our knowledge using the Lymnaea stagnalis model system wherein the neural correlates of aerial respiratory behaviour have been previously defined. Here, I demonstrate how graded environmental hypoxia produces adaptive changes in Lymnaea aerial respiratory behaviour by altering respiratory parameters, breathing pattern and plasticity. Moreover, I have identified a distributed peripheral O2 chemoreceptive network, which provides significant modulation of rCPG activity. Finally, I have defined the ability of central hypoxia to modulate rCPG activity and connectivity. Taken together, these studies fill significant gaps in fundamental knowledge vis-à-vis the mechanisms by which highly plastic respiratory neural networks collect and integrate information about the O2 environment in order to produce adaptive respiratory behaviour.
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