Neurotrophin-3 (NT-3) has been well characterized as a survival factor for large proprioceptive DRG neurons. Postnatally, NT-3 expression in skeletal muscle becomes restricted to muscle spindles and likely continues to support proprioceptive neurons. Transgenic mice overexpressing NT-3 in skeletal muscle under control of the myosin light chain promoter (mlc/NT-3 mice) have been used as a model to investigate the neuroprotective effects of muscle-derived NT-3 following peripheral nerve injury. Studies assessing the consequences of nerve crush on retrograde transport, neuronal survival, axonal morphology, muscle spindle innervation, and locomotor performance all suggest that delayed axonal degeneration of proprioceptive neurons may occur in mice that overexpress NT-3 in muscle following sciatic nerve crush (Taylor et al., 2002 SFN 821.1). Moreover, immunohistochemical analysis of the innervation of entire muscle spindles revealed that injured sensory and motor axons retract from and reinnervate intrafusal fi...