HTR2A and psychiatric disorder: However, MAOA is also involved in the breakdown of other neurotransmitters including serotonin and norepinephrine, and MAOA variants are implicated in psychiatric disorders.62 Serotonin released in the substantia nigra by dorsal raphe serotonergic fibres results in activation of 5-HT2 receptors and subsequent inhibition of dopamine neuron firing.63 Therefore, more MAOA synthesis/activity in the midbrain in schizophrenia could lead to increased serotonin breakdown and reduced inhibitory modulation of dopamine neurons by serotonin, thus contributing to the dopamine dysregulation.