The regulated equilibrium between pro-BDNF and mature BDNF appears to be physiologically relevant as a hippocampus-specific deletion of the serine protease tissue plasminogen activator (tPA), which is involved in the cleavage of pro-BDNF to BDNF extracellularly, increases depression and anxiety-like behaviour in adult mice10. Here, BDNF is linked to depressive symptom measurement.