A long standing goal of our research is to understand how neuronal growth and sprouting is regulated in the mammalian nervous system during development, adult neuronal plasticity, and following injury (i.e. spinal cord injury, traumatic brain injury, stroke or multiple sclerosis). We pursue a mouse genetic approach to study the function of different classes of proteins that are known to regulate neuronal growth, including members of the Semaphorin family and their cognate receptors (Neuropilins and Plexins), myelin-associated inhibitors and their receptors. The Nogo Receptors NgR1 and NgR2 have been implicated in regulating acute neuronal responses to the myelin inhibitors Nogo/RTN4, Myelin-Associated Glycoprotein (MAG), and Oligodendrocyte-Myelin Glycoprotein (OMgp). We recently identified a novel function for NgR1 in regulating activity-dependent synaptic strength. Ongoing studies are aimed at understanding the mechanisms of how enhanced neuronal plasticity leads to improved functional outcomes following nervous system injury.