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Trk receptor POONEH HESHMATI MD Trk receptors are a family of tyrosine kinases that regulates synaptic strength and plasticity in the mammalian nervous system. Trk receptor types and corresponding ligands The three most common types of trk receptors are trkA, trkB, and trkC. TrkA TrkA has the highest affinity to the binding nerve growth factor (NGF). TrkB TrkB has the highest affinity to the binding brain-derived neurotrophic factor (BDNF) and NT-4. TrkC TrkC is ordinarily activated by binding with NT3 and has little activation by other ligands. Ligands of trk receptors The common ligands of trk receptors are neurotrophins, a family of growth factors critical to the functioning of the nervous system. (Found only in fish) Activation pathway Trk receptors dimerize in response to ligand, as do other tyrosine kinase receptors. These dimers phosphorylate each other and enhance catalytic activity of the kinase. Trk receptor signaling When a neurotrophin binds to a trk receptor, the kinase domain is activated resulting in autophosphorylation. Autophoshorylation results in further activation of the kinase domain, leading to activation of three potential signaling cascades: MAPK PI3K PLC-g Axonal Regeneration During PNS regeneration, Schwann cells secrete a variety of neurotrophic and neurotropic factors to support axonal regrowth . Regenerating neuronal growth cones have been shown to express many correspondent receptors. Understanding how these cell surface receptors are regulated in response to injury may lead to know more about PNS regeneration .