 Evidence supports increased MAO activity in people with MDD, and it may even be a trait marker (not changed by response to treatment).Muscarinic receptor binding appears to be increased in depression, and, given ligand binding dynamics, suggests increased cholinergic activity.Four meta analyses on receptor binding in depression have been performed, two on serotonin transporter (5-HTT), one on 5-HT1A, and another on dopamine transporter (DAT).