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Metabotropic glutamate receptor 6, mGluR6, interacts with scaffold proteins and Gβγ subunits via its intracellular C-terminal domain (CTD). The mGluR6 pathway is critically involved in the retinal processing of visual signals. We herein investigated whether the CTD (residues 840-871) was necessary for mGluR6 cell surface localization and G-protein coupling using mGluR6-CTD mutants with immunocytochemistry, surface biotinylation assays, and electrophysiological approaches. We used 293T cells and primary hippocampal neurons as model systems. We examined C-terminally truncated mGluR6 and showed that the removal of up to residue 858 did not affect surface localization or glutamate-induced G-protein-mediated responses, whereas a 15-amino acid deletion (Δ857-871) impaired these functions. However, a 21-amino acid deletion (Δ851-871) restored surface localization and glutamate-dependent responses, which were again attenuated when the entire CTD was removed. The sequence alignment of group III mGluRs showed conserved amino acids resembling an ER retention motif in the CTD. These results suggest that the intracellular CTD is required for the cell surface transportation and receptor function of mGluR6, whereas it may contain regulatory elements for intracellular trafficking and signaling.

Visual cortical neurons generate synchronous oscillations depending on the coherent features in the visual field. This property may serve to bind the distributed neuronal activities into a unique representation. By applying a plannar multielectrode array to the retina isolated from the frog eye, we recorded light-evoked spike discharges from multiple OFF-sustained ganglion cells (dimming detectors) and demonstrated the presence of synchronous oscillations with the correlation analysis (~30 Hz [1]). In the present study, we examined the stimulus dependence of synchronous oscillations and their neural basis. The time domain of the stimulus intensity was sinusoidally modulated at 0.25 Hz while its spatial domain was kept constant.