CREB1 and depressive symptom measurement: Interestingly, in Aplysia, serotonin rapidly and robustly regulates miRNA-124.72 MiR-124 responds to serotonin by de-repressing CREB and thereby enhances serotonin-dependent long-term facilitation.72 In future, it will be interesting to examine whether manipulation of miR-124 can lead to depression phenotype.