Herpes simplex viruses (HSV) establish latent infections in sensory neurons of their host and are maintained in this state by little understood mechanisms that, at least in part, are regulated by signalling through nerve growth factor (NGF) and its receptor tropomyosin related kinase, trkA. Previous studies have demonstrated that Zhangfei is a transcriptional factor that is expressed in differentiated neurons and is thought to influence HSV replication and latency. Zhangfei, like the HSV trans-activator VP16 and Luman, binds the ubiquitous nuclear protein host cell factor (HCF) inhibiting the ability of VP16 and Luman to initiate HSV replication. <p>Recently, Brn3a, another neuronal factor thought to influence HSV latency and reactivation was found to possess an HCF-binding domain and could potentially require HCF for activity. The neuronal POU IV domain protein, Brn3a, among its many regulatory functions has been described as an enhancer of the NGF receptor trkA, during development in mouse. I therefore investigated the possible link between Brn3a, TrkA, NGF signaling, HCF, Zhangfei and HSV-1 latency and reactivation. I hypothesized that Zhangfei would also suppress the ability of Brn3a to activate the expression of TrkA and that this would have an impact on NGF-TrkA signaling and, consequently on HSV-1 reactivation from latency.<p>My first study determined which Brn3a/trkA promoter interactions were important for trkA transcription. I constructed a plasmid that contains 1043 base pairs of genomic sequences that extend from 30 nucleotides upstream of trkA coding region. In contrast to previous data, a short 190 bp region that lies proximal to the trkA initiation codon was sufficient for Brn3a trans-activation in NGF-differentiated PC12, Vero and human medulloblastoma cells. At least two portions of the 190 bp fragment bind to Brn3a. In addition, Brn3a increased endogenous levels of trkA transcripts in PC12 cells and initiated trkA expression in medulloblastoma cells, which normally do not express trkA. <p>The second step was to determine the effects of HCF and Zhangfei association with Brn3a on trkA trans-activation. I found that Brn3a required HCF for activating the trkA promoter and that Zhangfei has a suppressive effect over Brn3a-trkA activation in non-neuronal cells. In sympathetic neuron-like NGF-treated PC12 cells, Zhangfei did not suppress the ability of Brn3a to activate the TrkA promoter, however, Zhangfei was able capable of inducing the expression of TrkA in the absence of Brn3a. Both Brn3a and Zhangfei induced the expression of endogenous trkA in PC12 cells.<p>Since Vero and PC12 cells are not from human origin I wanted to examine the ability of Zhangfei to induce trkA transcription in medulloblastoma cells, that because of its tumor nature do not express trkA. TrkA transfections in these cells have shown to drive them to cell arrest or apoptosis. Since Zhangfei is not express in medulloblastoma tumors I then used ONS-76 medulloblastoma cells as a model to determine Zhangfeis envolvement in the NGF-trkA signaling pathway.<p> I show herein that in ONS-76 medulloblastoma cells resveratrol, an inducer of apoptosis and differentiation, increased the expression of Zhangfei and trkA as well as Early Growth Response Gene 1 (Egr1), a gene normally activated by NGF-trkA signalling. ONS-76 cells stop growing soon after treatment with resveratrol and a portion of the cell undergo apoptosis. While the induction of Zhangfei in resveratrol-treated cells was modest albeit consistent, the infection of actively growing medulloblastoma cells with an adenovirus vector expressing Zhangfei mimicked the effects of resveratrol. Zhangfei activated the expression of trkA and Egr1 and caused these cells to display markers of apoptosis. The phosphorylation of Erk1, an intermediate kinase in the NGF-trkA signaling critical for differentiation, was observed in Zhangfei infected cells, supporting the hypothesis that Zhangfei is a mediator of trkA-NGF signaling in theses cells leading either to differentiation or apoptosis. Binding of HCF by Zhangfei did not appear to be required for this effect as a mutant of Zhangfei incapable of binding HCF was also able to induce the expression of trkA and Egr1. <p>In in vivo and in vitro models of HSV-1 latency, the virus reactivates when NGF supply to the neuron is interrupted. Based on the above evidence Zhangfei, in HSV-1 latently infected neurons, would have the ability to prolong a state of latency by inducing trkA expression allowing the activation of NGF-trkA signaling pathway. Since NGF is produced by many cell types it is possible that reactivation is triggered not by a decrease in NGF but by a down-regulation of TrkA expression.Therefore, if Zhangfei expression is suppress the trkA signaling could be interrupted or shifted towards apoptosis signaling, this would allow neuronal HCF-binding proteins like Luman, which can activate HSV IE expression, to initiate HSV IE expression and subsequently viral replication.

Thesis (Ph. D.)--Cornell University, 2001. / Vita. Includes bibliographical references (leaves 167-194).

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 100-132).

Thesis (Ph.D.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 177-206.

Repeated exposure to amphetamine (AMPH) induces sensitization to its behavioral-activating effects. The development of sensitization depends on (1) the direct actions of AMPH in the ventral tegmental area (VTA), the cell body region of the mesocorticolimbic DA system, and (2) AMPH-induced glutamatergic neurotransmission in this region. Moreover, sensitization is accompanied by morphological changes in mesocorticolimbic DA circuitry. During development, the DA system is organized, at least in part, by the netrin-1 family of guidance cues. Both netrin-1 and its DCC and UNC-5 receptors continue to be expressed in the mesocorticolimbic DA system of the adult brain. Importantly, netrin-1 receptor deficient mice do not develop sensitization to AMPH, implicating an involvement of netrin-1 signaling in AMPH-induced plasticity of the DA system. To explore this possibility, adult rats were pretreated with repeated AMPH or saline, and DCC and UNC-5 receptor expression was examined in DA cell body and terminal regions using western blot. Striking AMPH-induced increases in the expression of DCC and UNC-5 were observed in the VTA only. Remarkably, these changes depended on NMDA-mediated glutamatergic neurotransmission. This is the first demonstration that repeated AMPH pretreatment regulates netrin-1 receptor expression in the adult brain and suggests that netrin-1 receptor regulation may be involved in the development of AMPH-induced sensitization.

Biological responses to orthodontic forces involve various cell types, these include fibroblasts, endothelial cells, blood vessels and sensory nerves in the periodontal ligament as well as osteoblasts, osteoclasts and cementoblasts in roots and bone surfaces. Neurotrophins are believed to interact with these cells to initiate the process of bone resorption particularly during orthodontic tooth movement. Neuropeptides released from sensory neurons have been shown to modulate the tissue inflammatory responses. In addition, neurotrophins, including nerve growth factor (NGF), play an important role in neural cell differentiation and survival. The exact localization and function of neurotrophins and neurotrophic receptors in the dento-alveolar complex remains unclear. Moreover, the identity and distribution of structures expressing neurotrophins and neurotrophic receptors has yet to be fully determined. It is reasonable to propose that periodontal ligament and alveolar bone remodelling may be influenced by NGF. In addition, anti-NGF may block neurochemical changes and, hence, inhibit orthodontic tooth movement. The aims of this research were to investigate the cells responsible for NGF secretion within the periodontal ligament (PDL), pulp and bone, and the effect that anti-NGF might have on orthodontic tooth movement. 28, 8 week-old, male Sprague-Dawley rats were randomly divided into control and experimental groups. Fourteen experimental animals had anti-NGF injected paradentally. Animals were sacrificed at 7 and 14 days. Sections from an earlier study were examined and stained using TRAP for osteoclast identification and analysed histomorphometrically to enable comparisons between control and experimental groups. The findings of this investigation indicated that injections of anti-NGF did not significantly affect the rate of tooth movement with the use of different tooth movement measurement methods. TRAP staining proved to be a useful and reliable marker of osteoclasts. TRAP-positive osteoclastic cells were detected in both anti-NGF and control groups. However, the TRAP-positive cells were not stained intensely with NGF immunolabelling. On the other hand, cells that were stained intensely with NGF, were TRAP-negative. The results suggested that both sympathetic and nociceptive nerves might function in counter balance to modulate bone resorption, and osteoclasts might not be directly responsible for NGF secretion within the PDL and bone. Further studies to determine the effect of NGF on tooth movement are warranted to more clearly identify the NGF expressing cells within the rat dento-alveolar complex and possible role played by NGF in orthodontic tooth movement. / http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297498 / Thesis (D.Clin.Dent.)-- School of Dentistry, 2007

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2002. / Härtill 6 uppsatser.

Thesis (M.Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 100-132). Also available in print.

Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on July 23, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Cell Biology, University of Alberta." Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 110-138. Also available online.