Antibody specificity. The CB1, CB2, NAPE-PLD and FAAH antibodies demonstrated specific staining to first trimester trophoblast. CB1 specific staining was visible in the syncytiotrophoblast (sy), cytotrophoblast (ct) and fibroblast (f) cell cytoplasm and to a lower intensity in the cytoplasm of the fetal endothelial cell (ec). Perinuclear and nuclear CB1 immunoreactivity was also observed in the cytotrophoblast layer, but only in the occasional syncytiotrophoblast (sy). CB2 immunoreactivity was also observed to be cytoplasmic, with immunopositive cells observed within the fetal blood vessels (bv), whereas NAPE-PLD immunoreactivity appeared almost exclusively in the nuclei of immunoreactive cells. FAAH immunoreactivity was both nuclear and cytoplasmic with differential expression of nuclear staining within the cytotrophoblastic layer. Photomicrographs are representative images taken from surgical terminations at weeks 7 and 8 of gestation. All images were captured at 400× magnification; bar = 50 μm. Respective rabbit IgG isotype or rabbit serum controls at equivalent concentrations are shown in the left panels.