GRM5 and depressive symptom measurement: Further, despite potential intersubject variability in glutamate transmission, previous [11C]ABP688 studies in controls have not shown high variance in baseline binding.24, 45 Moreover, [11C]ABP688 has been successfully used previously to detect mGluR5-binding differences in depression, smoking and obsessive-compulsive disorder, and in response to antidepressant treatment.14, 15, 46, 47