Important signaling molecule that activates signaling cascades downstream of NTRK2 (PubMed:27457814). During development, promotes the survival and differentiation of selected neuronal populations of the peripheral and central nervous systems. Participates in axonal growth, pathfinding and in the modulation of dendritic growth and morphology. Major regulator of synaptic transmission and plasticity at adult synapses in many regions of the CNS. The versatility of BDNF is emphasized by its contribution to a range of adaptive neuronal responses including long-term potentiation (LTP), long-term depression (LTD), certain forms of short-term synaptic plasticity, as well as homeostatic regulation of intrinsic neuronal excitability (PubMed:8139657, PubMed:15486301, PubMed:17023662, PubMed:27457814, PubMed:29909994). Important signaling molecule that activates signaling cascades downstream of NTRK2 (PubMed:27457814). Activates signaling cascades via the heterodimeric receptor formed by NGFR and SORCS2 (PubMed:24908487, PubMed:29909994). Signaling via NGFR and SORCS2 plays a role in synaptic plasticity and long-term depression (LTD) (PubMed:27457814). Binding to NGFR and SORCS2 promotes neuronal apoptosis (PubMed:24908487). Promotes neuronal growth cone collapse (PubMed:24908487, PubMed:27457814). Monomers and homodimers (PubMed:7957235). Binds to NTRK2/TRKB (By similarity). Can form heterodimers with other neurotrophin family members, such as NTF3 and NTF4 (in vitro), but the physiological relevance of this is not clear (By similarity). BDNF precursor form: interacts with the heterodimer formed by NGFR and SORCS2. Mature BDNF has much lower affinity for the heterodimer formed by NGFR and SORCS2 (PubMed:24908487). A proportion of BDNF is secreted as immature precursor (proBDNF). Expressed in the dorsal root ganglion and the spinal cord (at protein level) (PubMed:28111162). Detected in brain, especially in brain cortex, hippocampus, midbrain and cerebellum (PubMed:2369898, PubMed:8139657). Expression oscillates in a circadian manner in the suprachiasmatic nucleus (SCN) of the brain (PubMed:23785138). Expressed at higher levels during the dark period and at lower levels during the light period (PubMed:23785138). Up-regulated after sciatic nerve injury (PubMed:28111162). Contrary to mature BDNF, the propeptide is N-glycosylated and glycosulfated. Mature BDNF is produced by proteolytic removal of the propeptide, catalyzed by a FURIN family member. In addition, the precursor form is proteolytically cleaved within the propeptide, but this is not an obligatory intermediate for the production of mature BDNF (By similarity). Can be converted into mature BDNF by plasmin (PLG) (PubMed:15486301). Mutant mice are smaller than wild-type littermates, and most die during the second week after birth. They exhibit impaired motor coordination and balance, head bobbing and tilting, and spinning during perionds of hyperactivity. Mutant mice display a strongly reduced number of neurons in the dorsal root ganglion, trigeminal ganglion, mesencephalic trigeminal nucleus, vestibular ganglion and nodose ganglion. Cell death of vestibular ganglion neurons is strongly increased 14 days after birth. The number of facial motor neurons and sympathetic superior cervical ganglion neurons are not decreased. Mutant mice display defects in the innervation of the inner ear, but respond to auditory stimuli. Tne inner ear from mutant mice has fewer nerve fibers that enter the sacculus, utricle and ampulla of the semicircular ducts, and axons fail to contact their target cells and terminate in the connective tissue adjacent to the sensory epithelia of the sacculus. Belongs to the NGF-beta family.