Figure 7.

Overview of neuronal synthesis of DA and astrocyte metabolism. DA synthesis occurs in a presynaptic neuron (green) and is metabolized or packaged into vesicles and released into the synapse. DA is synthesized from tyrosine by TH to L-DOPA, which is then metabolized to DA via dopa decarboxylase (DDC). DA can then be metabolized by monoamine oxidase (MAO) to DOPAC, which can be exported to astrocytes (blue) for further metabolism into HVA by COMT. If DA is packaged into vesicles by VMAT2, it can be released into the synapse and bind to receptors on the postsynaptic neuron (orange). DA can also be transported back into the axon terminal by DAT. If DA is exported to the astrocyte, it can undergo metabolism by COMT to 3-MT, which then can be metabolized by MAO to HVA. Graphics were adapted from Servier Medical Art (www.servier.com) with a Creative Commons Attribution 3.0 Unported License and edited for use in this figure.