As described in the introductory section
As described in the introductory section, the rotifer nervous system would be capable to transmit GW3965 in throughout its neural pathways. In addition, Clément and Amsellem (1989) and Kotikova et al. (2001) suggested acetylcholine to be important for the functioning of rotifer muscles and their contraction during swimming behavior. Regarding the physiological response of rotifers upon chlorpyrifos exposure, swimming speeds of rotifer B. calyciflorus and B. plicatilis were significantly altered by several neurotoxic insecticides/pesticides (Charoy and Janssen, 1999; Garaventa et al., 2010). Based on chlorpyrifos-triggered AChE inhibition in B. koreanus, our results would have an explanation for altered rotifer swimming speed as a response to neurotoxic chemicals. We assume that rotifers have a primitive neural system and/or neurological responsive mechanism including conserved AChE functions against neurotoxic compounds. Our study is the first report of the pharmaceutical effects of AChE activity in rotifers and its neurophysiology. To analyze the effect of pharmaceuticals on the Bk-AChE activity and its transcript level, we used six pharmaceuticals including analgesics (acetaminophen, ATP), β-blocker (atenolol, ATN), anti-epileptics (carbamazepine, CBZ), and three antibiotics (oxytetracycline, OTC; sulfamethoxazole, SMX; trimethoprim, TMP). Although most pharmaceuticals were detected at nanogram levels (ng/L) (Hernando et al., 2006), several antibiotics were usually detected at a relatively high concentration (up to 6000μg/L level in STP effluent; up to 1900μg/L levels in surface water) in an aquatic environment (Kümmerer, 2009), ultimately causing chronic stress to wild organisms (LeBris and Pouliquen, 2004). Moreover, they are commonly used in aquacultures and also continuously enter aquatic environments from various sources (e.g. domestic, industrial, and hospital wastewater) (Fent et al., 2006). Previously, we reported that several pharmaceuticals inhibited the growth rate and reproduction in this species (Rhee et al., 2012). Regarding one of the molecular clues for the understanding of pharmaceutical-mediated metabolism in this species, rotifer P-glycoprotein (P-gp) was considered as an important pharmaceutical transporter for survival (Rhee et al., 2012). However, the biological effects of pharmaceuticals and their intracellular mechanisms are still unknown in this species. Based on our results, inhibition of growth and reproduction is likely derived from changes in the AChE activity caused by exposure to pharmaceuticals and their metabolites. Although the correlation between AChE inhibition and the physiological consequences has fluctuated over different aquatic animals, AChE inhibition may lead to detrimental effects on behavior and physiology, such as growth, food consumption, energy metabolism, and finally significant mortality (Ansari and Kumar, 1984; Van der Wel and Welling, 1989; Zinklet al., 1991; Cooper and Bidwell, 2006; Xuereb et al., 2009). In our study, Bk-AChE activity was significantly inhibited by ATP, CBZ, SMX, and TMP exposure (100 and/or 1000μg/L) (Fig. 2A, C, E, and F). There is a consensus that pharmaceuticals inhibit AChE activity in aquatic organisms. For example, ATP exposure decreased AChE activity with significance in the gills of the marine mussel, Mytilus galloprovincialis (Solé et al., 2010). In goldfish, Carassius auratus exposed to SMX, AChE activity was significantly inhibited (Li et al., 2012). In our study, ATP and SMX exposure showed a similar result as a previous study of AChE activity but little information is available on the AChE activity and transcript level by exposure to other pharmaceuticals in aquatic organisms. Only the acute and chronic toxic effects of these compounds were updated. Likewise, in B. koreanus, ATP, CBZ, SMX, and TMP exposure were associated with growth retardation at high concentrations (100μg/L) (Rhee et al., 2012). Indeed, ATP induced oxidative stress and mitochondrial impairment results in neurotoxicity in mammals (Ghanizadeh, 2012). CBZ has been known as a neuroactive compound that inhibits voltage-dependent neuronal Na+ channels (Macdonald and Kelly, 1995). SMX is a typical synthetic antibiotic that has been used in aquaculture (Trovó et al., 2009). TMP is a microbicide for bacterial infections. This antibiotic inhibits the enzyme dihydrofolate reductase (Binelli et al., 2009) that is involved in the synthesis of tetrahydrofolate, a precursor for thymidine synthesis, and the inhibition of dihydrofolate reductase detrimentally affects synthesis of macromolecules such as DNA, RNA, and protein (Baccanari, 1995). Consequently, the acute toxic effect of several pharmaceuticals is closely related to inhibition of AChE activity, suggesting that these compounds, particularly ATP, CBZ, SMX, and TMP, have a potent neurotoxic effect.