Native metabotropic glutamate receptor 4 depresses synaptic transmission through an unusual Gα transduction pathway.

In cerebellar cortex, mGlu receptors located on parallel fibers play an essential role in normal motor function, but the molecular mechanisms involved are not yet completely understood. Using a strategy combining biochemical and electrophysiological approaches in the rodent cerebellum, we demonstrate that presynaptic mGlu receptors control synaptic transmission through an atypical activation of Gα proteins. First, the Gα subunit, PLC and PKC signaling proteins present in cerebellar extracts are retained on affinity chromatography columns grafted with different sequences of the cytoplasmic domain of mGlu receptor. The i2 loop and the C terminal domain were used as baits, two domains that are known to play a pivotal role in coupling selectivity and efficacy. Second, in situ proximity ligation assays show that native mGlu receptors and Gα subunits are in close physical proximity in cerebellar cortical slices. Finally, electrophysiological experiments demonstrate that the molecular mechanisms underlying mGlu receptor-mediated inhibition of transmitter release at cerebellar Parallel Fiber (PF) - Molecular Layer Interneuron (MLI) synapses involves the Gα-PLC signaling pathway. Taken together, our results provide compelling evidence that, in the rodent cerebellar cortex, mGlu receptors act by coupling to the Gα protein and PLC effector system to reduce glutamate synaptic transmission.