Brain-derived neurotrophic factor, also known as BDNF, is a protein that, in humans, is encoded by the BDNF gene. BDNF is a member of the neurotrophin family of growth factors, which are related to the canonical nerve growth factor. Neurotrophic factors are found in the brain and the periphery. BDNF was first isolated from pig brain in 1989 by Yves-Alain Barde and Hans Thoenen.