Characterization of the dorsal raphe-periaqueductal grey DAT neurons innervating onto the extended amygdala

It has been known that a number of tyrosine hydroxylase (TH)-positive neurons, which are regarded as dopaminergic (DA) neurons, exist in the dorsal raphe (DR). These DA neurons in the DR and periaqueductal gray (PAG) region (DA^DR-PAG neurons) are thought to belong to the A10 cluster, which is known to be heterogeneous. This DA population projects to the central nucleus of the amygdala (CeA) and the bed nucleus of the stria terminalis (BNST) and has been reported to modulate various affective behaviors. The DA transporter (DAT) neurons, which are well overlapping with DA neurons, in the DR-PAG region are also expected to be heterogeneous. However, even though the heterogeneity of DA/DAT^DR-PAG neurons has been suggested, the characteristics of each DA/DAT^DR-PAG neuron subpopulation are not well investigated. In this paper, we summarize the previous reports investigating the heterogeneity of DA/DAT^DR-PAG neurons and the functional importance of DA/DAT^DR-PAG neurons on various affective behaviors and introduce our recent findings that DAT^DR-PAG neurons consist of two subpopulations: TH+/vasoactive intestinal peptide (VIP)-putative DA neurons and TH-/VIP+ putative glutamatergic neurons.