Compound activity at the rat group III mGluRs was assessed using thallium flux through GIRK channels, a method that has been described in detail in (Niswender et al., 2008 ). These cell lines were grown in Growth Media containing 45% DMEM, 45% F-12, 10% FBS, 20 mM HEPES, 2 mM L-glutamine, antibiotic/antimycotic non-essential amino acids, 700 μg/ml G418, and 0.6 μg/ml puromycin at 37°C in the presence of 5% CO2. Briefly, mGluR4, 7 or 8 GIRK cells were plated into 384 well, black-walled, clear-bottom poly-D-lysine coated plates at a density of 15,000 cells/20 μl/well in Plating Medium and incubated overnight at 37°C in the presence of 5% CO2. The following day, the medium from the cells and 20 μl/well of 1.7 μM concentration of the indicator dye BTC-AM (Invitrogen, Carlsbad, CA) in Assay Buffer was added. Cells were incubated for 1 h at room temperature and the dye was replaced with 20 μl/well of Assay Buffer. For these assays, compounds were added at 2x final concentration and then 2.5 min later either an EC20 or EC80 concentration of glutamate (mGluR4, 8) or L-AP4 (mGluR7) was added using the FDSS 6000. Agonists were diluted in thallium buffer (125 mM sodium bicarbonate, 1 mM magnesium sulfate, 1.8 mM calcium sulfate, 5 mM glucose, 12 mM thallium sulfate, 10 mM HEPES) at 5x the final concentration to be assayed. Five frames of data were collected (excitation, 470±20 nm emission, 540±30 nm) at ½ Hz prior to compound addition. Data collection continued at ½ Hz until 10 seconds prior to agonist addition, when the rate was increased to 1 Hz for 2 min after agonist addition. Data were analyzed as described in (Niswender et al., 2008 ).