The extraneuronal monoamine transporter Slc22a3/Orct3 co-localizes with the Maoa metabolizing enzyme in mouse placenta

Monoamine clearance is a combined function of uptake mechanisms in the plas ma membrane with intracellular metabolizing enzymes. Two different uptake m echanisms have been described. Uptake(1) is located in presynaptic neurones , whereas uptake(2) is extraneuronal. Recently, the Slc22a3/Orct3 gene was identified as the extraneuronal monoamine transporter. In mouse embryonic d evelopment Orct3 expression is restricted to the placenta, which is also a site of expression of neuronal transporters. We have used RNA blots and in situ hybridization to examine the expression of Orct3 and other members of the monoamine uptake and metabolizing pathways in mouse placenta. The resul ts show that Orct3 expression overlaps that of the monoamine metabolizing e nzyme Maoa in the labyrinth layer of the placenta with an expression patter n distinct from that of the neuronal transporters Slc6a2/Net and Slc6a4/Ser t. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.