BDNF and neurodegenerative disease: In addition to neurodegenerative diseases, alterations in BDNF and TrkB levels have been implicated in psychiatric diseases such as depression (Castrén and Monteggia, 2021) and the action of many antidepressant drugs have been linked to the regulation of TrkB signaling (Casarotto et al., 2021) suggesting that direct activation of TrkB receptors could be a new approach to treat major depression in humans.