Figure 9:  Dopamine receptor-ADO receptor neuromodulation in the basal ganglia.
(A) The Indirect Pathway:  Activation of A2A receptors, both pre-synaptically and post-synaptically modulate the functional activation of D2 receptors on striatopallidal neurons.  The mechanism for this interaction is not yet well understood, but appears to represent a ADO-mediated transmembrane conformational change in the state of the D2 receptor.  Presynaptically, A2A receptor activation leads to increased acetylcholine release resulting in a potentiation of post-synaptically regulated GABA release.
(B) The Indirect Pathway:  Activation of A1 receptors, both both pre-synaptically and post-synaptically modulate the functional activation of D1 receptors on striatonigral-striatoentopeduncular neurons. Presynaptically, A1 receptor activation leads to decreased dopamine and acetylcholine  release resulting in a potentiation of post-synaptically regulated GABA release. The mechanism for these dopamine-ADO receptor-receptor interactions is not yet well understood, but appears to represent a ADO-mediated transmembrane conformational change in the state of the D2 receptor.

Adapted from 30.
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published 2000