Active site (1); Alternative sequence (8); Beta strand (21); Binding site (1); Chain (1); Disulfide bond (6); Domain (5); Glycosylation (11); Helix (17); Modified residue (5); Natural variant (11); Nucleotide binding (1); Region (1); Repeat (2); Signal peptide (1); Site (3); Topological domain (2); Transmembrane (1); Turn (4); Trk also stands for tropomyosin-related kinase since the first Trk was isolated as an oncogenic protein which was the result of a fusion between the tropomyosin gene TPM3 and NTRK1.; Widely expressed in fetal brain. {ECO:0000269|PubMed:7936202}.; Isoform TrkB is expressed in the central and peripheral nervous system. In the central nervous system (CNS), expression is observed in the cerebral cortex, hippocampus, thalamus, choroid plexus, granular layer of the cerebellum, brain stem, and spinal cord. In the peripheral nervous system, it is expressed in many cranial ganglia, the ophthalmic nerve, the vestibular system, multiple facial structures, the submaxillary glands, and dorsal root ganglia. Isoform TrkB-T1 is mainly expressed in the brain but also detected in other tissues including pancreas, kidney and heart. Isoform TrkB-T-Shc is predominantly expressed in the brain. {ECO:0000269|PubMed:11798182, ECO:0000269|PubMed:7936202}.