GRM5 and depressive symptom measurement: In young subjects (n=3, average age=30.3), 40% of caudate nucleus neurons expressed mGluR5 receptors, compared with 80% in elderly subjects (n=6, average age=78.2).18 However, a recent in vivo PET study reported no statistically significant association between age and [11C]ABP688 binding.19 To our knowledge, no study has examined mGluR5 in elderly depression.