Immunocytochemical localization of the dopamine transporter in human brain

The dopamine transporter (DAT) was localized in normal human brain tissue by light microscopic immunocytochemistry by using highly specific monoclonal antibodies. Regional distribution of DAT was found in areas with established dopaminergic circuitry, e.g., mesostriatal, mesolimbic, and mesocortical pathways. Mesencephalic DAT-immunoreactivity was enriched in the dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. Staining in the striatum and nucleus accumbens was dense and heterogeneous. Mesocortical DAT immunoreactivity in motor, premotor, anterior cingulate, prefrontal, entorhinal/perirhinal, insular, and visual cortices was detected in scattered varicose and a few nonvaricose fibers. Varicose fibers were relatively enriched in the basolateral and central subnuclei of amygdala, with sparser fibers in lateral and basomedial subnuclei. Double-labeling studies combining DAT and tyrosine hydroxylase (TH) immunostaining in the ventral mesencephalon showed two subpopulations of dopaminergic neurons differentiated by the presence or absence of DAT-immunoreactivity in the A9 and A10 cell groups. In other dopaminergic cell groups (All, A13-A15), TH-positive hypothalamic neurons showed no detectable DAT-immunoreactivity. However, fine DAT-immunoreactive axons were scattered throughout the hypothalamus, particularly concentrated along the medial border, with more coarse axons present along the lateral border. These findings demonstrate that most mesotelencephalic dopamine neurons of human brain express high levels of DAT throughout their entire somatodendritic and axonal domains, whereas a smaller subpopulation of mesencephalic dopamine cells and all hypothalamic dopamine cell groups examined express little or no DAT. These data indicate that different subpopulations of dopaminergic neurons use different mechanisms to regulate their extracellular dopamine levels.