Neurotrophin-3 (NT3) is a growth factor found in many body tissues includ-ing the heart, intestines, skin, nervous system and in skeletal muscles includ-ing muscle spindles (Murase et al., 1994). NT3 is required for the survival, correct connectivity and function of sensory (proprioceptive) afferents that innervate muscle spindles; these neurons express receptors for NT3 including tropomyocin receptor kinase C. These proprioceptive afferents are important for normal movement (Boyce and Mendell, 2014) and signals from muscle spindles are important for recovery of limb movement (e.g., after spinal cord lateral hemisection) (Takeoka et al., 2014). The level of NT3 declines in most tissues during postnatal development; its level is low in adult and elderly humans and other mammals (Murase et al., 1994). Elevation of NT3 has been shown to improve outcome in various animal models of neurological disease and injury. For example, many groups have shown that delivery of NT3 directly into the central nervous system promotes recovery after spinal cord injury but this often involved invasive routes or gene therapy (Boyce and Mendell, 2014; Petrosyan et al., 2015; Wang et al., 2018).