Definition
Brain-derived neurotrophic factor is a member of the neurotrophin family of growth factors. It is synthesised as a precursor, proBDNF, and cleaved to mature BDNF, which binds the tyrosine kinase receptor TrkB to promote neuron survival, neurite growth and synaptic plasticity, including long-term potentiation in the hippocampus. ProBDNF can signal through the p75 receptor with opposing effects. BDNF expression is regulated by neuronal activity, and altered levels have been associated with several conditions in observational studies, though causality is unclear. Because BDNF itself crosses the blood–brain barrier poorly, researchers study small molecules and peptides that may influence its expression. Semax and selank have been reported to alter BDNF expression in rodent studies.