Receptor tyrosine kinase involved in the development and the maturation of the central and peripheral nervous systems through regulation of proliferation, differentiation and survival of sympathetic and nervous neurons. High affinity receptor for NGF which is its primary ligand, it can also bind and be activated by NTF3/neurotrophin-3. Upon dimeric NGF ligand-binding, undergoes homodimerization, autophosphorylation and activation. Recruits, phosphorylates and/or activates several downstream effectors that regulate distinct overlapping signaling cascades driving cell survival and differentiation. In absence of ligand and activation, may promote cell death, making the survival of neurons dependent on trophic factors. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] The pro-survival signaling effect of NTRK1 in neurons requires its endocytosis into signaling early endosomes and its retrograde axonal transport. Exists in a dynamic equilibrium between monomeric (low affinity) and dimeric (high affinity) structures. Homodimerization is induced by NGF dimer binding (By similarity). Interacts with PTPRS (PubMed:17967490). Internalized to endosomes upon binding of NGF or NTF3 and further transported to the cell body via a retrograde axonal transport. Localized at cell membrane and early endosomes before nerve growth factor (NGF) stimulation. Recruited to late endosomes after NGF stimulation. Colocalized with RAPGEF2 at late endosomes. 2 isoforms are produced. Expressed in the condensing dorsal root ganglia at embryonal day 3, and in the primary sympathetic chain ganglia at embryonal day 4. Ligand-mediated auto-phosphorylation. Ubiquitinated. Undergoes polyubiquitination upon activation; regulated by NGFR. Ubiquitination regulates the internalization of the receptor. Belongs to the protein kinase superfamily. Tyr protein kinase family. Insulin receptor subfamily.