Cholinergic enhancement of cell proliferation and differentiation in the postnatal neurogenic niche of the intact and demyelinated spinal cord.

Among the heterogeneous central canal (CC) cell population of the adult spinal cord are the normally quiescent endogenous neural stem cells; the ependymal cells (ECs). The naturally latent ECs are activated upon the occurrence of injury, and are capable of robust cell proliferation, migration and differentiation into neurons or glia. Furthermore, in the intact and injured adult spinal cord, oligodendrocyte precursor cells (OPCs) and astrocytes give rise to new progeny. Harnessing these endogenous resources to replace damaged or lost neurons and oligodendrocytes after spinal cord injury or other white matter disorders requires a better understanding of how the microenvironment they reside in modulates their proliferation and differentiation. This project investigates the role that the neurotransmitter acetylcholine (ACh) has on cell proliferation and differentiation in the adult mouse spinal cord. Enhancing the levels of ambient ACh using an acetylcholinesterase inhibitor (AChEI) donepezil decreased the number of proliferating cells (visualised using the thymidine analogue EdU) in the CC in vivo and in vitro compared to control. Potentiating the effect of ACh transmission on α7 nicotinic acetylcholine receptors (α7nAChR) using the positive allosteric modulator PNU-120596 in combination with donepezil resulted in higher numbers of EdU+ cells in the CC, grey and white matter of the intact spinal cord in vivo compared to vehicle treated animals. There was also an increase in the proportion of EdU+ cells that also expressed either the oligodendrocyte marker PanQKI in both the grey and white matter or the neuronal marker HUC/D in the spinal cord grey matter in PNU-120596 + donepezil treated animals. In a lysolecithin (LPC)-induced focal demyelination mouse model, treatment with either PNU-120596 alone or in combination with donepezil significantly enhanced cell proliferation and oligodendroglial differentiation compared to LPC alone treated animals. There was also a significant increase in the extent of remyelination post cholinergic treatment. Spinal cord slice cultures in the presence of donepezil alone or in combination with the muscarinic receptor inhibitor atropine and the non-α7nAChR inhibitor DHβE suggested that cell proliferation is mostly mediated through α7nAChRs. Finally, the calcineurin-nuclear factor of activated T cells (NFAT) calcium signalling pathway downstream of α7nAChR activation plays a role in cell proliferation in vitro. This study provides a potential therapeutic avenue for modulation of ACh through α7nAChRs to aid in spinal cord repair.