In the adult mammalian brain, stem cells in the ventricular/subventricular zone (V/SVZ) niche are a subset of astrocytes. Quiescent neural stem cell (qNSC) astrocytes enter the cell cycle (become activated) and give rise to the V/SVZ lineage under homeostatic and regenerative conditions, suggesting that they can potentially be harnessed for regenerating the brain after neurodegenerative disease, stroke, or injury. Defining the signaling mechanisms that activate adult qNSCs is essential to understand how to harness these endogenous cells for brain repair, and how they may become deregulated in normal aging and in pathological contexts. Here, I present novel and compelling evidence that cholinergic signaling activates qNSCs in vitro and in vivo. I show that the V/SVZ is innervated by cholinergic axonal fibers in a regionalized pattern: the density of cholinergic axons decreases from anterior to posterior. Interestingly, cholinergic innervation of the V/SVZ arises from both a local, anterio population of interneurons, as well as a posterior, long-range source. Moreover, cholinergic axons presynaptically contact qNSCs. Nicotinic agonists increased the activation of quiescent neural stem cells in vitro. In vivo infusion of a nicotinic agonist increased the proliferation of neural stem cells. Based on these data, I hypothesize that cholinergic signaling mediates the activation of predominantly anterior V/SVZ qNSCs. I will define the ultrastructure of cholinergic synapses on qNSCs using immuno-EM. I will define the effect of cholinergic agonists on the proliferation, survival, and differentiation of FACS purified qNSCs in vitro. I will fate map the progeny of qNSCs activated by cholinergic agonists and determine whether the production of specific subtypes of olfactory bulb neurons is regulated by cholinergic input. Finally, I will specifically ablate cholinergic neuronal nuclei to identify the long-range source of V/SVZ innervation, and determine the effect of losing cholinergic V/SVZ innervation on qNSC activation and neurogenesis. Together, these studies will provide key insights into adult V/SVZ stem cell heterogeneity. Finally, these findings will begin to illuminate the cholinergic circuits that regulte adult neural stem cell quiescence and activation.
Stem cells exist in dormant and actively dividing states in the adult brain, however, the biological mechanisms driving the transition from the resting state to the actively dividing state are unknown. This work will illuminate one possible mechanism of activating dormant stem cells. Potentially, this work will help to develop regenerative therapies for central nervous system diseases, stroke, and traumatic brain injuries.