(a) TACs derived from the rat brain PET images [18F]3. (n = 7) (b) mGlu4 blocking studies demonstrated reduced uptake in the brain regions by 10-20%, while mGlu5 blocking agents displayed minimal blocking effect indicating good selectivity to mGlu4. Tissue uptake was calculated as area under TAC expressed as % dose/cc × min. Str = striatum, Hipp = hippocampus, Thal = thalamus, Cort = cortex, Cereb = cerebellum, WB = whole brain. Baseline studies (n = 7), mGlu4 (2) blocking studies (n = 4), mGlu5 (MTEP) blocking studies (n = 3) (c) Percentage of [18F]3 in the plasma over time. (n = 2)