Thesis (Ph. D.)--University of Missouri--Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 189-210). Also available on the Internet.

Diversos estudos demonstram que o aumento da osmolaridade é capaz de causar simpatoexcitação e aumento da pressão arterial, estando o núcleo paraventricular do hipotálamo (PVN) envolvido em tal resposta. Evidências recentes demonstraram um papel da VP modulando a atividade de neurônios do PVN envolvidos com o controle da atividade simpática. Deste modo, o objetivo deste estudo foi investigar o papel da vasopressina, por meio de sua ação no PVN, sobre as alterações na atividade simpática em situações de hiperosmolaridade. Nossos resultados demonstraram que a VP microinjetada bilateralmente no PVN foi capaz de promover um aumento significativo NA ansl. O antagonismo bilateral dos receptores V1a no PVN em animais submetidos à sobrecarga de sal promoveu uma queda significativa na ANSL, a qual não foi observada em animais normohidratados. O conjunto dos resultados nos permite afirmar que a VP agindo diretamente em neurônios do PVN é capaz de alterar a atividade simpática, participando da resposta simpatoexcitatória observada durante aumento da osmolaridade. / Diverse studies demonstrated that osmorality increase is able of causing simpatoexcitação and increase in arterial pressure, with paraventricular hypothalamic nucleus (PVN) involved in this response. Studies showed an role of VP modulating the activity of neurons in the PVN involved in the control of sympathetic activity. In this way, the aim of this study was to investigate the role of the vasopressina, through it\'s action in the PVN, over the alterations in the sympathetic activity induced by hiperosmolality.The results showed that bilateral microinjection of VP into the PVN is able of increase significatively the lumbar sympathetic nerve activity. Moreover, the bilateral block of the V1a receptors into PVN of animals subjected to osmotic stimulus showed a decrease in sympathetic activity not observed in normohydrated animals. Overall, the results allow to assert that the centrally released VP plays an important role in the development of the simpatoexcitation raised by increased osmolarity, through an action on the PVN neurons.

One of the main components underlying drug addiction is the emergence of tolerance. Although its development is a complex issue, and is believed to have both psychological and physiological connotations, it is clear that some physiological change must occur that would enable an organism to withstand drug concentrations lethal to a naïve system. The purpose of this thesis was to identify and study a physiological mechanism, whose characteristics were altered due to chronic exposure to ethanol. Vasopressin (AVP), whose primary function is to control water balance, release from the neurohypophysis is suppressed by an acute ethanol challenge. Therefore, I hypothesized; 1) that chronic ethanol exposure would reduce the normal suppression of AVP release during an acute ethanol challenge and 2) that the ion channels that are acutely sensitive to ethanol, involved in the control of AVP release, would exhibit a change in their ethanol sensitivity and characteristics. To study the hypothesis, I utilized the neurohypophysis from rats chronically exposed to ethanol and yoked controls to determine whether chronic exposure would modify the acute ethanol sensitivity of the neurohypophysial vasopressin release mechanism. I examined whether the long-term ethanol exposure affected the suppression of vasopressin release from either or both the intact neurohypophysis and the isolated neurohypophysial terminals. In addition, I investigated how chronic exposure affected two types of potassium channels, the ethanol sensitive large conductance Ca+2-activated (BK) channel and the fast inactivating (IA) channel known to be insensitive to physiologically relevant concentrations of ethanol. I was able to establish that chronic ethanol exposure reduced the suppression of vasopressin release by an acute ethanol challenge from both the intact neurohypophysis and the isolated neurohypophysial terminals. In addition, I discovered that oxytocin release was affected similarly. I concluded from this data that chronic exposure to ethanol affected a general mechanism, which controlled hormone release from the neurohypophysis, and that this mechanism could be isolated to the neurohypophysial terminals. I also used electrophysiological techniques to study ion channel characteristics of both the BK and IA potassium channels. I found that in naïve rats, BK channels were potentiated and IA channels insensitive to physiological relevant concentrations of ethanol. But in chronic ethanol-exposed rats the BK channels exhibited a reduced sensitivity to ethanol while IA channels were inhibited. In addition, the current density of the BK channel was significantly reduced. These results show that at least one characteristic of each potassium channel has been modified. This suggests that chronic exposure can not only modify the ethanol sensitivity of ion channels known to be ethanol-sensitive, but also those believed to be relatively insensitive. Therefore, since modifications in these channels have previously been shown to alter the duration and frequency of action potentials, I conclude that these ethanol-induced modifications play a role in the modified hormone release patterns observed in the chronically exposed rats.

The hypothalamo-neurohypophysial model has been studied for many years. Of note, when the axons of the magnocellular, peptidergic neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) are transected or crushed, varying degrees of polydipsia and polyuria ensue as the result of measurable losses of vasopressin (AVP) within the organism's circulation. Following insult, these hypothalamic cells show a remarkable capacity to reorganize themselves within the proximal areas of the infundibular stalk and median eminence and form what has come to be known as a new 'mini neural lobe' . While the surviving neurons sprout new projections toward the level of the external zone, vascular hypertrophy is marked throughout the new neurohypophysis and new neurohemal contacts have been identified (at the ultrastructural level) associated with these vessels. In parallel with this vascular hypertrophy is a measurable re-release of vasopressin into the circulation. This new 'mini neural lobe' now has the morphological and physiological appearance of an intact neural lobe and is capable of releasing AVP in response to changes in water balance. While the ability of these axons to reorganize is more characteristic of the peripheral nervous system (PNS), this model system provides an unique opportunity to study axonal regeneration of the central nervous system (CNS). Not only the mechanisms underlying the restoration of AVP function following axotomy but the extent to which various magnocellular neuron populations are involved in the regenerative process may also be analyzed. Before attempting to identify putative markers associated with this regenerative process, it was necessary to carefully characterize the system following axonal injury. Using Sprague Dawley rats, we repeated previous physiological studies which had examined the intake of water and output of urine following hypophysectomy. In addition, we also correlated the restoration of water balance with the return of AVP release, as measured by radioimmunoassay. These data defined a temporal framework in which magnocellular AVP regeneration occurs. As a result of repeating these physiological studies, we noted several inconsistencies between other previously published work. First, the time course of AVP recovery did not agree with other published results, nor did the first appearance of AVP immunoreactivity . We did not observe a complete recovery of water balance as previously reported and the degree of magnocellular death was inconsistent with other reports. In light of these many conflicting observations between several historical reports and our own results, we did a basic physiological re-characterization of the hypothalamo-neurohypohysial system following hypophysectomy. By means of immunohistochemistry, we also demonstrated the re-appearance of AVP within the new the 'mini neural lobe ' concomitant with the increased appearance of synapsin I, a marker associated with the presence of mature and presumably functioning synapses to be no sooner than 28 days following surgical removal of the hypophysis. Immunocytochemistry was also used in conjunction with retrograde fluorescent labeling to extend the previous studies and include a 2-D analysis of cell survival throughout the PVN and SON following hypophysectomy or neurohypophysectomy. As reported previously, magnocellular neuronal loss is greater within the SON, particularly the hypophysectomized subject, and less so within the PVN; again with the greater loss in the PVN of the hypophysectomized animal. Based upon our observations and other recent reports, we suggest the possibility that some cells of the hypothalamo-neurohypophysial system or some other extrahypothalamic cell population may be capable of expressing vasopressin in response to neurohypophysectomy. We provide initial evidence that glial cells of the third ventricle may indeed be involved. Finally, one of the ultimate goals of using this as a model system of CNS regeneration is to understand the underlying mechanisms and components essential to central nervous tissue regeneration. Toward that end I have been involved with the initial studies to optimize an adenovirus delivery system which will be capable of incorporating various putative neurotransmitter and/or peptide anti-sense messages, being injected into the neurohypophysis and transported back into the cells of the hypothalamo-neurohypophysial system. Once these antisense sequences are expressed by the cells following axotomy, the sequence of expression of various proteins in response to injury may be elucidated.