Organic cation transporter 3 (OCT3) is a high-capacity, low-affinity transporter 
that mediates bidirectional, sodium-independent transport of dopamine, 
norepinephrine, epinephrine, serotonin, and histamine. OCT3-mediated transport 
is directly inhibited by corticosterone, suggesting a potential role for the 
transporter in mediating some of the effects of stress and glucocorticoids on 
monoaminergic neurotransmission. To elucidate the importance of OCT3 in 
clearance of extracellular monoamines in the brain, we used immunohistochemical 
techniques to describe the distribution of OCT3-like-immunoreactive (OCT3-ir) 
cells throughout the rostrocaudal extent of adult male rat brains. OCT3-ir cell 
bodies were widely distributed throughout the brain, with the highest densities 
observed in the superior and inferior colliculi, islands of Calleja, subiculum, 
lateral septum, lateral and dorsomedial hypothalamic nuclei, and granule cell 
layers of the main and accessory olfactory bulbs, the cerebellum, and the 
retrosplenial granular cortex. OCT3-ir cells and/or fibers were also observed in 
circumventricular organs, and OCT3-ir ependymal cells were observed in the 
linings of all cerebral ventricles. The widespread distribution of OCT3-ir cell 
bodies, including regions receiving dense monoaminergic projections, suggests an 
important role for this transporter in regulating extracellular concentrations 
of monoamines in the rat brain and is consistent with the hypothesis that 
corticosterone-induced inhibition of OCT3-mediated transport may contribute to 
effects of acute stress or corticosterone on monoaminergic neurotransmission.