Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

This thesis investigates the involvement of the non-neuronal cholinergic system in endothelium-dependent relaxations and the impact of hypertension on the function of this system. In Study1 the contribution of nicotinic receptors (nAChRs) to endothelium-dependent relaxations evoked by acetylcholine was examined. Both muscarinic (mAChRs) and nAChR were expressed in the aortic endothelium of spontaneously hypertensive (SHR)and Wistar-Kyoto rats (WKY). However, isometric tension measurements showed that, the muscarinic antagonist atropine abolished the relaxations to acetylcholine in WKY aortae, but only partially inhibited those in SHR aortae. While the nicotinic antagonist mecamylamine inhibited the remaining response in SHR aortae, it did not significantly affect the response solely in either SHR or WKY preparations. Hence, nAChRs mediate endothelium-dependent relaxations to the acetylcholine only in the SHR aorta and only when mAChRs are inhibited. Nicotine, the prototypical nicotinic agonist, also induced endothelium-dependent relaxations in both SHR and WKY aortae which were due to activation of α7-nAChRsbut not by mecamylamine-sensitive α3-nAChR. The acetylcholine-induced, atropine-insensitive relaxations and that to nicotine both involve the PI3K pathway. Thus, activation of nAChRscan contribute to acetylcholine-induced endothelium-dependent relaxations via PI3K signaling pathway in aortae of hypertensive animals. Study 2 examined the involvement of non-neuronal cholinergic system in endothelium-dependent relaxations. Isometric tension measurements showed that mild hypothermia (37℃–31℃) induced endothelium-dependent relaxations, which were reduced by atropine, tubocurarine, acetylcholinesterase (enzyme responsible for acetylcholine degradation), bromoacetylcholine (inhibitor of acetylcholine synthesis), hemicholinium-3 (inhibitor of choline uptake) and vesamicol (inhibitor of acetylcholine release) in SHR but not in WKY aortae, indicating that the non-neuronal cholinergic system is involved in mild hypothermia-induced endothelium-dependent relaxations. Compared with WKY, SHR preparations expressed similar levels of acetylcholinesterase and choline acetyltransferase, but lesser vesicular acetylcholine transporter, located mainly in the endothelium. A choline/acetylcholine assay showed that, mild hypothermia increased the uptake of choline by the endothelium of SHR,but not WKY, aortae from extracellular environment for acetylcholine production. To define possible different mechanisms employed by SHR and WKY endothelial cells, the involvement of transient receptor potential (TRP)channels in mild hypothermia-induced response were examined using selective pharmacological inhibitors of different subtypes of TRP channels, namelyAMTB (TRPM8 antagonist),HC-030031 (TRPA1 antagonist)and HC-067047 (TRPV4 antagonist).The results suggest that both TRPM8 and TRPA1 play a role in the response to mild hypothermia in the WKY aorta; however, in the SHR aortaTRPV4,but not TRPA1, channels are activated by mild hypothermia. Moreover, the observation that the mild hypothermia-induced increases in cyclic guanosine monophosphate (cyclic GMP)and choline uptake were inhibited by HC-030031 in WKY but by HC-067047 in SHR aortae further indicate that in the hypertensive strain compensatory TRPV4 activation can make up for the loss of TRPA1-mediated NO production, and that the endothelial cells of the hypertensive animal utilize TRPV4 channels to activate the production of endogenous acetylcholine in response to mild hypothermia. Taken in conjunction, the results reported in this thesis together suggest that hypertension alters the function of the non-neuronal cholinergic system (e.g. n-AChR sensitivity or acetylcholine production) to modulate endothelium-dependent relaxations. / published_or_final_version / Pharmacology and Pharmacy / Doctoral / Doctor of Philosophy

Alcoholism is a complex disease that exists as a specific set of behaviors, such as the preoccupation with obtaining alcohol and compulsive alcohol drinking. Currently, more than 18 million adults in the United States suffer from alcohol abuse or alcoholism. This disease poses serious medical and economic consequences for society. Identifying the neurobiological mechanisms that underlie alcohol drinking, specifically the transition from initiation to binge drinking is critical for improved treatments for alcoholics and the vulnerability for relapse in those recovering. Many studies have identified brain regions and molecular mechanisms that underlie various stages of alcohol abuse; however few have investigated the role of specific cell types within these areas. The overarching hypothesis of the studies in this dissertation is that cholinergic interneurons of the nucleus accumbens (NAc) are key neural substrates that underlie alcohol drinking, and as drinking continues; neuroadaptations within these cells then facilitate such behaviors as compulsive alcohol drinking. More specifically, these studies tested whether 1) cholinergic cell ablation in the NAc causes a decrease in alcohol drinking in C57BL/6J mice, 2) neuroadaptive changes in dopamine (DA) D2 receptor and cyclin dependent kinase 5 (Cdk5) occur within these cells following initiation alcohol drinking, and to a greater extent following binge alcohol drinking in C57BL/6J mice, and 3) neuroadaptive changes in DA D2 receptor and Cdk5 also occur in brain regions that have been implicated in the rewarding and reinforcing effects of alcohol in inbred alcohol-preferring (iP) rats. The present findings report a causal role for accumbal cholinergic neurons in binge alcohol drinking and identify DA D2 receptor and Cdk5 neuroadaptations following initiation and binge alcohol drinking. These studies identify the involvement of cholinergic interneurons in binge drinking and reveal alcohol-induced region- and cell-specific receptor and molecular changes that occur with continued drinking. These findings contribute to the understanding of the neurobiological mechanisms that underlie alcohol drinking, and provide the basis for cholinergic targeted treatments designed to attenuate binge drinking. These data also provide the groundwork for future studies aimed to examine receptor and intracellular molecular changes that occur with compulsive alcohol drinking, craving, and relapse.

This thesis examines the movement cues underlying human kinesthesia, using a combination of psychophysical methods and an analyticrrl framework for math<'1l1aticHI and statistical modelling of functional aspects of underlying physiological sensory mechanisms. Using an innovative psychophysical paradigm, the first experiment examines whether people are more sensitive to the occurrence of movement than to movement direction. Contrary to previous investigations, the findings are that the underlying sensitivity for movement detection and direction discrimination is the same. An analytical tool for investigating what are the sensory cues for movement detection is developed as a physiologically plausible model of movement perception. The model accounts for performance in terms of displacement and velocity sensitive directionally tuned channels and probability summation over time. Statistical analysis of optimized model parameters indicates that the dominant cue for movement detection is velocity and that the contribution of displacement information is insignificant. An extended version of a previous movement detection model based on temporal integration is also applied to data from experiment l. Derived estimates of this model's parameters suggest that displacement information does make a significant contribution to movement detection. The conflict between the two models is resolved in favour of the probability summation model, based on statistical comparisons regarding model accuracy and parsimony, and an analysis of the physiological plausibility of underlying assumptions. A second experiment investigates whether manipulation of movement acceleration affects movement detection. The probability summation model is extended to account for processing of acceleration. Estimates of the model's parameters reveal that acceleration information does not contribute significantly to velocity based movement detection.

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