Figure 3.

Schematic representation of the extrasynaptic transmission in the local circuits around the striatal glutamate synapse of the striato-pallidal GABA neurons. Focus on the glutamate, adenosine, and dopamine signal and the postulated A_2A-D₂, A_2A-D₂-mGluR5, and D₂-NMDA receptor heteromers. Different cell types (microglia, astrocytes) can release both adenosine triphosphate (ATP) and adenosine. In the nervous system the extracellular concentration of adenosine raises as a function of the neuronal activity and acts as an energy-dependent neuromodulator through combined presynaptic and postsynaptic actions through VT.