Expression of the cholinergic gene locus in the rat placenta.

High amounts of acetylcholine (ACh) and its synthesising enzyme choline acetyltransferase (ChAT) have been detected in the placenta. Since the placenta is not innervated by extrinsic or intrinsic cholinergic neurons, placental ACh and ChAT originate from non-neuronal sources. In neurons, cytoplasmic ACh is imported into synaptic vesicles by the vesicular acetylcholine transporter (VAChT), and released through vesicular exocytosis. In view of the coordinate expression of VAChT and ChAT from the "cholinergic gene locus" in neurons, we asked whether VAChT is coexpressed with ChAT in rat placenta, and investigated this issue by means of RT-PCR, in situ hybridisation, western blot and immunohistochemistry. Messenger RNA and protein of the common type of ChAT (cChAT), its splice variant peripheral ChAT (pChAT), and VAChT were detected in rat placenta with RT-PCR and western blot. ChAT in situ hybridisation signal and immunoreactivity for cChAT and pChAT were observed in nearly all placental cell types, while VAChT mRNA and immunolabelling were detected in the trophoblast, mesenchymal cells and the visceral yolk sac epithelial cells. While ChAT is nearly ubiquitously expressed in rat placenta, VAChT immunoreactivity is localised cell type specifically, implying that both vesicular and non-vesicular ACh release machineries prevail in placental cell types.