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Organophosphate (OP) and carbamate (C) have replaced organochlorine pesticides because of their rapid breakdown in water and their low environmental persistence. However, these insecticides used in intensive agricultural production can reach the aquatic environment either via seepage of chemicals from the soil or directly due to the spraying against pests (Castillo et al. 1997). These compounds may become concentrated in the organs of aquatic organisms, especially those at the top of the food chain. The main mechanism of action of organophosphate and carbamate insecticides involves the inhibition of cholinesterase (ChE). There are two distinct types of enzymes capable of acetylcholine hydrolysis. The acetylcholinesterase or "true cholinesterase" (AChE EC.3.1.1.8) predominantly associated with nervous tissue and erythrocytes, and the pseudo cholinesterase (ChE EC: 3.1.1.7) which is found in the serum, muscle and ganglia (Fossi et al. 1995; Harel et al. 1992; Vigny et al. 1978). These two enzymes, AChE and ChE can be distinguished not only by their distribution but also by their substrate specificity and their sensitivity to certain selective inhibitors (Augustisson and Nachmanshon 1949; Davison 1955; Toutant et al. 1985; Vigny et al. 1978). Both AChE and ChE are inhibited by eserine but only AChE is inhibited by 1.5-bis(4-allyl dimethyl amino phenyl)pentan-3-one dibromide (BW284C51) and by an excess of substrate, for example acetylthiocholine chloride (ACh) (Augustisson and Nachmanshon 1949; Vigny et al. 1978). These enzymes may be soluble, linked to the basal lamina via a collagen tail or to membrane via a glycolipid or via a hydrophobic peptide (Bon et al. 1979; Massoulie and Bon 1982). The toxicity of OP and C insecticides toward AChE has been extensively studied both in insects and vertebrates (Bocquene et al. 1995; Coppage and Mathews 1974; Haubruge and Toutant 1997; Sharma et al. 1993). The accepted mode of action of these insecticides is to phosphorylate or carbamilate AChE enzyme (Fleming and Grue 1981). This results in the increase of acetylcholine levels at the nerve synapse causing continual stimulation of the fibers and eventual failure of nerves to repolarize. Moreover, some pesticides are used in fish farming. Those applications cause great damage to fish populations (Bocquene et al. 1995). Acetylcholinesterase, the primary enzymatic target of OP and C is commonly used to detect their impacts (Bastos et al. 1991; Fossi et al. 1995; Westlake et al. 1981a; Westlake et al. 1981b). In order to use AChE as an insecticide pollution biomarker, it is necessary to characterise this enzyme. We are interested in validating in vitro methods, which will predict in vivo toxicity. We study teleostean brain AChE, particularly in common carp, because of its great geographical distribution throughout the world (Billard 1995). Previous investigators have characterised AChE in common carp using different extraction techniques and inhibitors (Szabo et al. 1992; Szegletes et al. 1995). The objectives of this paper were: firstly to extend the observations of Szabo et al. (1992) by investigating the common carp brain AChE, secondly to determine the type of inhibition induced by carbofuran (C) in chlorfenvinphos (OP) on the common carp brain AChE, and finally to determine the in vivo required time for the recovery of brain AChE activity of the common carp after inhibition by these two insecticides.

Recovery of Acetylcholinesterase Activity in the Common Carp ( Cyprinus carpio L.) After Inhibition by Organophosphate and Carbamate Compounds