Neurotransmitter phenotypes and the master transcription factors that determine them. The essential transcription factors are shown under each neuron. The proteins whose genes are known to be regulated by the essential transcription factors are indicated. AADC, amino-acid decarboxylase; D2R, dopamine receptor D2; DAT, dopamine transporter; TH, tyrosine hydroxylase; TPH, tryptophan hydroxylase; VMAT2, vesicular monoamine transporter. ASIC-1, TRP-4, DAT and SERT are membrane transport or channel proteins. The neutrotransmitter-synthesis pathway is indicated in red inside each nerve terminal. Dopamine (DA) is synthesized from tyrosine (Tyr) via the intermediate Dopa. Serotonin (5-HT) is synthesized from tryptophan (Trp) via the intermediate 5-hydroxytryptophan (5-HTP).