NGF and major depressive disorder: Early adverse experiences in humans, for instance, maternal deprivation, are linked to an increased risk of mental illnesses such as anxiety and MDD, and data from Cirulli et al. showed that NGF was a potential candidate for adverse events in brain dysfunction and a neuroendocrine marker for the different responses of male and female rhesus monkeys suffering from maternal deprivation (Cirulli et al., 2009).