INS and metabolic disease: Ohta et al., 2011 have previously revealed as there is a converge in insulin and serotonin producing cells that can lead to metabolic diseases (diabetes) and mood disorders.65 The products of the insulin-producing cells (beta-islet cells) are involved to express the genes that synthesize serotonin, and serotonin also plays a role in the synthesis of insulin in the beta-islet cells.65