The release of vasopressin (VP) from magnocellular neurosecretory cells (MNCs) of the supraoptic (SON) and paraventricular (PVN) nuclei is essential to hydromineral homeostasis. This release is controlled by several physiological stimuli, including changes in the osmotic pressure of the extracellular fluid, and in core body temperature. The osmotic control of VP release is mediated by specific and highly sensitive 'osmoreceptors'. Indeed, VP-releasing neurons in the SON are directly osmosensitive, and this osmosensitivity is mediated by stretch-inhibited cation channels. The molecular identity of these channels, however, remains unknown. The thermal control of VP release, on the other hand, is largely unexplained. In this thesis, we demonstrate that the mouse SON is a valid model for investigating the molecular basis of osmotransduction. We show that hyperosmotically-induced increases in membrane conductance are blocked by ruthenium red (RR), a non selective blocker of TRPV channels. In addition, SON neurons were found to express an N-terminal splice variant of TRPV1, but not full-length TRPV1. Unlike their wild-type counterparts, SON neurons in Trpv1 knockout (Trpv1-/-) mice could not generate RR-sensitive increases in membrane conductance and depolarizing potentials in response to hyperosmotic stimulation. Moreover, Trpv1-/-mice showed a pronounced serum hyperosmolality under basal conditions and severely compromised VP responses to osmotic stimulation in vivo. These results suggest that the Trpv1 gene may encode a central component of the osmoreceptor. Furthermore, we demonstrate that VP neurons are intrinsically thermosensitive. In these neurons, thermal stimuli spanning core body temperatures activate a RR-sensitive non selective cation current. Interestingly, VP neurons isolated from Trpv1 -/-mice are significantly less thermosensitive. These results suggest that channels encoded by the Trpv1 gene can confer thermosensitivity in the physiological range. Overall, these data suggest that products of the Trpv1 gene in VP neurons may represent a molecular point of convergence for the detection of osmotic and thermal stimuli.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.111867 |
| Date | January 2007 |
| Creators | Sharif Naeini, Reza. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002598576, proquestno: AAINR32383, Theses scanned by UMI/ProQuest. |
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