Patterns of physiological electrical activity in the central nervous system (CNS) cause longlasting changes in gene expression that promote neuronal survival. These changes can be mediated by signalling pathways activated by Ca2+ influx through synaptic N-methyl DAspartate receptors (NMDARs). Identification and study of these, and other neuroprotective signalling pathways of the CNS, is invaluable; as this may one day lead to therapeutic strategies against the deleterious effects of CNS injury or degeneration. The data presented in this thesis focuses on activity-dependent neuroprotection and how it interacts with other signalling pathways to protect against apoptotic and oxidative insults. A previously unobserved role of activity-dependent neuroprotection in mediating the effects of the neuropeptide PACAP is demonstrated. By promoting cAMP/PKA signalling PACAP triggers neuronal firing activity, which is essential for the neuroprotective effects mediated by PACAP. This firing activity cooperates with direct signalling by PKA in promoting longlasting CREB-mediated gene expression. The molecular events associated with PACAP mediated stimulation of CRE-dependent gene expression are presented. Investigation of the control of neuronal antioxidant defences by neuronal activity, both on its own and in cooperation with astrocyte-derived support, was also investigated. Neuronal activity is demonstrated to strongly increase the capacity of the antioxidant glutathione (GSH) system, through a program of coordinated transcriptional events. The utilisation, biosynthesis and recycling of GSH is enhanced in neurons, leading to increased resistance against oxidative insults. Since several GSH pathway enzyme genes are regulated by the transcription factor Nrf2, the ability of CDDO-F3, a small molecule activator of Nrf2, to mimic the effect of firing activity on neuronal GSH levels was examined. CDDO-F3 sustains neuronal GSH levels and confers neuroprotection against oxidative insult. These actions are dependent on the presence of astrocytes; whereas Nrf2 mediated regulation of GSH pathway genes is essentially inactive in neurons. Neuronal activity and activation of the astrocytic Nrf2 pathway can cooperate, maintaining neuronal GSH levels and protecting neurons against strong oxidative insults. Collectively this work expands our knowledge as to the molecular mechanisms of activity-dependent neuroprotection, and how such signals may synergise with other protective pathways to promote neuronal health.

NCA-1 (putative nematode calcium channel) and NCA-2 are two cation channel-like proteins in Caenorhabditis elegans that function redundantly to regulate locomotion through unknown mechanisms. A recent study from our lab showed that in vivo Ca2+ imaging analyses of egg-laying neurons in nca-1 loss- and gain-of-function mutants implicate that NCA channels regulate Ca2+ flux at synapses, without affecting Ca2+ dynamics in neuron somas. Furthermore, we observed that NCA-1 localizes to non-synaptic region along axons, strongly suggesting that NCA channels propagate electrical signals from cell bodies to synapses. To identify molecular components that function in the nca-1 genetic pathway, I performed a genetic suppressor screen that led to the identification of behavioral suppressors of nca-1 gain-of-function mutant. Possible NCA auxiliary subunits, UNC-79 (uncoordinated) and UNC-80, were identified from this screen. Molecular characterization of other suppressors will help to identify other regulators and downstream signaling components through which NCA channels transmit electrical signals.

NCA-1 (putative nematode calcium channel) and NCA-2 are two cation channel-like proteins in Caenorhabditis elegans that function redundantly to regulate locomotion through unknown mechanisms. A recent study from our lab showed that in vivo Ca2+ imaging analyses of egg-laying neurons in nca-1 loss- and gain-of-function mutants implicate that NCA channels regulate Ca2+ flux at synapses, without affecting Ca2+ dynamics in neuron somas. Furthermore, we observed that NCA-1 localizes to non-synaptic region along axons, strongly suggesting that NCA channels propagate electrical signals from cell bodies to synapses. To identify molecular components that function in the nca-1 genetic pathway, I performed a genetic suppressor screen that led to the identification of behavioral suppressors of nca-1 gain-of-function mutant. Possible NCA auxiliary subunits, UNC-79 (uncoordinated) and UNC-80, were identified from this screen. Molecular characterization of other suppressors will help to identify other regulators and downstream signaling components through which NCA channels transmit electrical signals.

Coupling the small GTPase Rab3 to the Synaptic Vesicle Cycle

No description available.

The olfactory system is a great model for studying regeneration due to the olfactory epithelium’s regenerative capability which makes it a potential a source of neural stem cells. The olfactory epithelium presents three types of cells: sustentacular cells which provide support and act as glial supporting cells; olfactory sensory neurons that are in charge of detecting odorant molecules in the air; and the stem cells that generated the aforementioned cell types. Olfactory sensory neurons are constantly dying and being replaced by new neurons originating from the stem cells that lie at the base of the olfactory epithelium. We have used an injury model that allows us to remove all the olfactory sensory neurons from the olfactory epithelium, via a single injection of methimazole. Then, at different timepoints after injury we measure the functional recovery of the olfactory epithelium by analyzing the expression of specific synaptic associated markers. Specifically, we analyzed the expression of synaptophysin, tyrosine hydroxylase, vesicular glutamate transporter 1, and vesicular glutamate transporter 2. Simultaneously, we measured glomerular size in order to serve as an indicator of anatomical recovery. Finally, we correlate these findings with previously generated data in the lab associated with functional recovery through behavior.

Les réseaux vasculaires et nerveux présentent des similitudes frappantes (points de branchements, superposition, voies afférentes/efférentes, …) et tous deux interagissent lors du développement ou dans le cadre de pathologies.Dans un premier projet, nous avons voulu déterminer si un facteur pro-angiogénique, c'est-à-dire induisant la formation de nouveaux vaisseaux, peut avoir un effet direct sur le réseau neuronal. Des études menées in vitro ou in vivo chez l’adulte, ont montré une implication directe du Vascular Endothelial Growth Factor (VEGF) sur le système nerveux (survie, prolifération neuronale, croissance axonale, …). Nous avons cherché à savoir si ce facteur a un effet sur le développement ou l’activité des réseaux neuronaux lors de la vie embryonnaire alors que les systèmes vasculaires et nerveux se mettent progressivement en place. Avec une approche électrophysiologique, nous avons focalisé notre attention sur les motoneurones de la moelle épinière de souris entre les stades E13,5 et P0. Nos résultats montrent que le VEGF augmente de façon significative la fréquence des activités synaptiques liées à la libération de GABA et de Glycine pendant une fenêtre temporelle correspondant à la mise en place de ces mêmes activités (E13,5 et E15,5). Cet effet modulateur met en évidence un nouveau rôle du VEGF dans la maturation fonctionnelle des réseaux neuronaux et ouvre de nouvelles perspectives dans l’étude des neurodégénérescences précoces. Dans un second projet, nous nous sommes intéressés au glioblastome, cancer cérébral très invasif. Nous montrons que l’inhibition d’IRE1 (Inositol Requiring-Enzyme 1, senseur du stress du réticulum endoplasmique) dans un modèle d’implantation orthotopique chez la souris induit la formation de tumeurs plus petites, moins vascularisées et plus dispersées avec un meilleur pronostic de survie. Nous observons aussi des altérations du microenvironnement tumoral (matrice extracellulaire, réaction astrocytaire) avec des modifications de l’expression de nombreux facteurs de croissance dont le TGFß. / The nervous and the vascular systems share similarities (branching points, afferent/efferent parts …) and are closely connected during development and pathology.In the first part of this project, we questioned whether the pro-angiogenic key factor VEGF (Vascular Endothelial Growth Factor), which promotes new blood vessels formation, can directly interact with neural networks while nervous and vascular systems are developing. In the present study, using an electrophysiological approach, we focused on the effect of VEGF on embryonic spinal lumbar motoneurons (MNs). Our results demonstrate that VEGF increases the frequency of the GABA/glycinergic events at early developmental stages (E13.5 and E15.5) but not at the perinatal stage E17.5. Our data highlight a new role for VEGF which can control both the maturation of the vascular and neuronal networks and may likely be involved in early MNs degeneration.In the second part, we focused on glioblastoma, the most agressive form of brain cancer. Our results show that inhibition of IRE1 (Inositol Requiring-Enzyme 1, stress sensor of endoplasmic reticulum) leads to formation of smaller, less vascularized, more invasive tumors with a better prognosis. We also observe that tumoral microenvironnement is altered (reactive astrogliosis, extracellular matrix) and expression of several growth factors like TGFß is modified.