In an animal study, Martin et al. discovered that insulin (i) directly inhibits the activity of serotoninergic neurons in the dorsal raphe nucleus (DRN) via 5-HT1A autoreceptor dependent mechanism, (ii) exerts its anxiolytic-like effects due to modulation of serotoninergic transmission, (iii) in animal models of T2D-related depression serotoninergic neurons in DRN are no longer sensitive to insulin, (iv) in animal models of depression addition of insulin to fluoxetine potentiated the antidepressant action of the drug [23▪▪]. Here, INS is linked to major depressive disorder.