1.1.7) and butyrylcholinesterase (BChE, EC 18.104.22.168). The enzymatic functions of both enzymes include hydrolysis of acetylcholine ACh8(Lane and He, 2013). At the nerve synapses, AChE
terminates nerve impulse transmission by hydrolyzing this neurotransmitter. On the other hand, BChE acts as a backup for AChE and as a scavenger for poisons that might inhibit AChE activity (Masson and Lockridge, 2010). These enzymes have been very rapidly distinguished and subject of considerable research (Massoulié and Millard, 2009). AChE and BChE are well-known for their multiple Sirolimus molecular forms (Chen et al., 2011). Polymorphism is achieved by certain combinations of alternative gene splicing, and AZD5363 by the attachment of non-catalytic structural subunits. In mammals, AChE is encoded by a single gene. However, alternative splicing at the C-terminus of AChE mRNA generates three different isoforms. Conversely, one BChE transcript has been identified so far (Johnson and Moore, 2012). The presence of ChEs in tissues that are not cholinergically innervated provides the most compelling evidence that both AChE and BChE might have functions, other than the termination of cholinergic neurotransmission (Jaganathan and Boopathy, 2000).In fact, the human placenta contains an active cholinergic
system which was associated to the amino acid uptake, the release of human placental chorionic somatotropin and prostaglandin production (González-García et
al., 2008) and to the modulation of nitric oxide effect (Bhuiyan et al., 2006). The concentrations of AChE and BChE are considerably lower in the placenta than in the nervous system (Sastry, 1997). The analysis by electron microscopy of cross sections from term placenta, cytochemically pheromone stained for ChEs activities, showed thatterm placenta syncytiotrophoblast cells produce primarily AChE. On the other hand,epithelial cells that surround the inner part of blood vessels, as well as hematopoietic cells present in them, all intensely stained for both AChE and BChE activities (Sternfeld et al., 1997). In accordance with these observations, it was reported that both AChE and BChE activities were detectable in cultured explanted villous of term placenta (Hahn et al., 1993). Depending on the experimental conditions used, dissimilar OP effects on placental AChE activity have been reported. Gestational exposure of rats to oral doses of the OP chlorpyrifos cause no inhibition of AChE activity (Lassiter et al., 1999), while a single cutaneous dose of OP in pregnant rats decreased AChE activity (Abu-Qare et al., 2000). Nevertheless, we previously reported increased ChE activity in human placenta associated to OP environmental exposure (Souza et al., 2005). Considering that AChE up regulation was induced post OP-treatment in rodents brain (Evron et al.