As well as being expressed in the gastrointestinal tract, mGluR5 expression is predominant in areas of the mammalian brain involved in emotional processes, such as the dentate gyrus regions within the hippocampus, regions of the basal ganglia (striatum and nucleus accumbens) and in the dorsal horn of the spinal cord, suggesting a role for these receptors in affective disorders such as anxiety and depression.14, 15 The mGluR5 is also implicated in central pain processing pathways in the trigeminal nucleus caudalis and spinothalamic tract. Here, GRM5 is linked to major depressive disorder.