Neurotrophin-4 (NT-4) is a member of the nerve growth factor family which includes neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), all of which promote the differentiation, growth, and survival of peripheral and central nervous system neurons (Eide et al.). NT-4 binds and activates tropomyosin receptor kinase B (TrkB) at the cell surface; in doing so, it acts as a survival factor for certain populations of sensory neurons (Berkemeier et al.; Skaper). It has been shown that NT-4, together with BDNF, promotes neurite extension and maturation, as well as maintenance of differentiated cerebellar granule cells (Gao et al.).