Members of the Tyrosine Kinase Receptor (Trk) family (TrkA, TrkB, and TrkC) of receptor tyrosine kinases act as receptors for the neurotrophin family: BDNF, NGF, NT-3, and NT-4. Trks exhibit selectivity for specific neurotrophins. TrkA, TrkB and TrkC preferentially bind NGF, NT-4 and BDNF, and NT-3, respectively. All Trk family proteins share a common structural organization consisting of an extracellular region with two cysteine-rich domains, a cluster of three leucine-rich motifs, and two immunoglobulin-like domains, and an intracellular region that contains the tyrosine kinase domain. They are best known for their regulation of neuronal survival and axon outgrowth. TrkC is predominantly expressed in the central nervous system.