BDNF and major depressive disorder: Of note, given the delicate homeostatic balance between BDNF and proBDNF expression, as well as the important roles these proteins play in the function of the nervous system and development of neurologic disease (including depression,88 Parkinson disease,89 dementia,90 and schizophrenia91), agents to block BDNF signaling, such as NTRK inhibitors, could potentially carry the risk of neurological toxicity and additional studies are needed to balance the risks and benefits of targeting the BDNF pathway.