TPH2 and major depressive disorder: The caudal aspect of the DRD nucleus (cDRD), also referred to as the dorsomedial DR (for a description of nomenclature, see Table 4 in [13], which has strong projections to forebrain systems controlling emotional behavior, is believed to be a key player in controlling anxiety-related defensive behavioral responses in rodents [13, 14, 19, 20] and displays increased expression of TPH2 mRNA, encoding the neuronal isoform of tryptophan hydroxylase, TPH2, in persons with depression who died by suicide [21].