Fig. 5: Inhibition of GABA release by homodimeric mGlu4 receptors at the synapse between striatal projection neurons of the indirect pathway and neurons of the external globus pallidus.

Through this mechanism, mGlu4 receptor agonists or PAMs may improve motor symptoms in PD and restrain excitotoxic degeneration of nigral neurons (A). Inhibition of glutamate release by heterodimeric mGlu2/mGlu4 receptors in cortico-striatal fibers (B). Whether mGlu2/mGlu4 heteromers are localized in the pre-terminal region of the axon terminal or in the active zone of neurotransmitter release is unknown.