Fish brain and muscle acetylcholinesterase activity in vivo and in vitro related to water pollutants and other chemicals

Acetylcholinesterase, the enzyme which normally functions in inactive acetylcholine, the neurotransmitter at the motor end plate of skeletal muscles and at cholinergic types of synapse in the central nervous system and autonomic nervous system, is now being developed abroad as a biosensor for the detection and assay of toxic chemicals, particularly of pesticides. The electric enzyme is currently being prepared for practical use in environmental monitoring. The present study aims to test the sensitivity of the tilapia fish enzyme, although still in cruder brain and muscle extracts, for its possible eventual use also in environmental monitoring. The knowledge obtained from the experiment contribute to our understanding of fish acetylcholinesterase and the importance of in vivo and in vitro approaches in the assessment of existent and potential detrimental effects of environmental degradation. Brain and muscle acetylcholinesterase activity in vivo in Oreochromis mossambicus was assayed using the Ellman colorimetric procedure following the exposure of the fish to sublethal levels of three kinds of pesticides, copper sulphate, zinc chloride, and mercuric chloride at 24, 28, 72, and 62 hours. Likewise, assays were done on O. niloticus fish that were exposed to sublethal doses of lead nitrate, cadmium chloride, and a commercial detergent. Reduction in brain and muscle acetylcholinesterase activity was generally observed with in vivo exposures to carbofuran, chlorpyrifos, and the deltamethrin. To a certain extent, enzyme inhibition, particularly in the muscle, was observed. Among the metal salts, lead nitrate and zinc chloride demonstrated some activating effects. Exposure to detergent initially caused enzyme activation which was abolished at 48 hours of exposure onwards. When brain and muscle acetylcholinesterase activity of O. niloticus was tested in vitro using field samples of river and marine waters, there were indications that the procedure could be applied to a certain extent