BDNF (brain-derived neurotrophic factor) is a neurotrophin, i.e. a target-derived growth factor, which is expressed in the brain predominantly in the hippocampus.
It acts through its tyrosine kinase receptor, trkB, which after ligand activation induces phosphorylation of intracellular signalling proteins on tyrosine residues.
BDNF expression is suppressed by stress hormones, and increased by antidepressants through a yet unknown mechanism.