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Mechanisms underlying P2Y1 receptor-mediated excitation of the inspiratory network in vitro; and NPY-induced stress resilience in vitro and in vivo
- Author / Creator
- Miranda Tapia, Ana
The present thesis will discuss the cellular and molecular mechanisms by which neurochemical systems modulate the activity of CNS networks underlying breathing and anxiety. The thesis is divided into two parts. The first part examines the mechanisms by which the neuromodulator/neurotransmitter ATP excites the brainstem network that is responsible for generating inspiratory rhythm, the preBötzinger Complex (preBötC). The biphasic hypoxic ventilatory response (HVR) is an adaptive response in which a fall of arterial oxygen is detected by peripheral chemoreceptors which trigger a rapid increase in breathing that is followed by a centrally-mediated secondary hypoxic respiratory depression (HRD). This HRD is more pronounced in premature mammals and it can be life threatening, bringing breathing below the initial baseline. The dogma that has reigned for the last 30 years holds that the initial increase in ventilation is mediated by peripheral carotid body chemoreceptors, and the secondary depression is mediated through central depressive mechanisms. It is believed that the only role of the CNS in this response is to depress breathing, i.e., there is no mechanism whereby central hypoxia
stimulates breathing. Recent data from our laboratory challenge this dogma. These data suggest
that during hypoxia, astrocytes within the preBötC release ATP, which then activates P2Y1
receptors (P2Y1Rs) on inspiratory preBötC neurons to excite the inspiratory network and increase ventilation. This uncovered a novel mechanism by which hypoxia excites breathing. The purpose of this part of the thesis is to determine the mechanisms by which ATP acts via P2Y1Rs in the preBötC to increase inspiratory frequency.
The second part of this thesis examines the mechanisms by which neuropeptide Y (NPY) modulates behaviour of amygdala circuits that control anxiety-related behaviour. NPY is a potent anxiolytic that acts on a variety of receptor subtypes. The basolateral amygdala (BLA) is the neural substrate of fear and anxiety, and its activation is associated with high fear and anxiety states. When administered acutely into the BLA, NPY reduces anxiety via activation of Y1 receptors (Y1Rs), in part by reducing the excitability of a subpopulation of excitatory BLA principal neurons. Moreover, repeated injection of NPY into the BLA results in a sustained state of anxiolysis, called stress resilience, that long outlasts the period of NPY injection. Recently, NPY-induced stress resilience was attributed to downregulation of the hyperpolarization activated inward current, Ih, and dendritic remodeling (hypotrophy). However, the receptor responsible for this long-term effect is unknown. The purpose of this part of the thesis is to determine the receptor mechanism by which NPY induces a less anxious phenotype and the neural pathways underlying NPY-induced stress resilience. The two components of the thesis are each preceded by an independent literature review to cover the background information necessary to understand their rational and significance. The first chapter begins with a review of relevant topics in central respiratory control including: the organization of the central networks underlying the neural control of breathing; the organization of the brainstem respiratory network; afferent control of breathing; respiratory rhythm generation, and; the role of purinergic signalling in the homeostatic regulation of breathing. This is followed by a brief introduction, and the methods, results and discussion for the initial study that explores the mechanisms underlying the P2Y1R-mediated excitation of the inspiratory network in vitro. This is followed by a review of literature relevant to the second study which examines amygdala networks and their modulation by NPY in relation to understanding the control of anxiety-related behaviors. The literature review is followed by the methods, results and the discussion of the second chapter that examines mechanisms underlying NPY-induced stress resilience in vitro and in vivo.
- Graduation date
- Spring 2021
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.