Adiponectin (ADP) is an adipokine, which acts as an insulin sensitizing hormone. Recent studies have shown that adiponectin receptors (AdipoR1, AdipoR2) are present in the CNS; however, there is some debate as to whether or not ADP crosses the blood brain barrier (BBB). Circumventricular organs (CVO) are CNS sites outside the BBB, and thus represent sites at which circulating adiponectin may act to influence the CNS without having to cross the BBB. The subfornical organ (SFO) is a CVO that is responsive to a number of different circulating satiety signals including amylin, CCK, and ghrelin. We report here that the SFO also shows a high density of mRNA for both adiponectin receptors. These observations support the concept that the SFO may be a key player in sensing circulating ADP. To test the hypothesis that ADP influences the excitability of SFO neurons, we used current-clamp electrophysiology on dissociated SFO neurons to observe changes in membrane potential. ADP (10 nM) application effected the excitability of SFO neurons, where the cells either depolarized (8.9±0.9 mV, 21 of 97 cells) or hyperpolarized (-8.0±0.5 mV, 34 of 97 cells). Using single-cell RT-PCR we found that the majority of the responsive neurons expressed AdipoR1 or R2 and the non-responsive neurons expressed neither.
In view of the recognized role of ADP in the regulation of energy balance, we next examined the effects of food deprivation for 48 hours on ADP signaling in the SFO. Our previous microarray analysis of SFO showed increases in AdipoR2 mRNA, with no significant change in AdipoR1 mRNA. We have also assessed the effects of such changes in receptor expression on ADP signaling in SFO neurons using calcium imaging and patch clamp techniques. In SFO neurons obtained from control animals, ADP induced increases in intracellular Ca2+ were observed in 25% of cells, while following food deprivation 0% of cells showed this response. Furthermore, 77% of neurons from starved animals showed clear depolarization, while no hyperpolarizing responses were observed. The results presented in this study suggest that adiponectin modulates the excitability of SFO neurons and that the response to ADP changes during starvation. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2008-09-17 18:07:35.099
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OKQ.1974/1733 |
| Date | 01 April 2009 |
| Creators | Alim, Ishraq |
| Contributors | Queen's University (Kingston, Ont.). Theses (Queen's University (Kingston, Ont.)) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | 1513108 bytes, application/pdf |
| Rights | This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner. |
| Relation | Canadian theses |
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