Neurotoxic effect of dermally-applied chlorpyrifos and cypermethrin in Wistar rats

The aim of the study was to evaluate the neurotoxic effect of a dermally-applied mixture of chlorpyrifos and cypermethrin in rats based on cognitive function, activity of the blood cholinesterase and brain acetylcholinesterase, as well as histologic brain examination. Nurelle D 550 EC (500 g of chlorpyrifos and 50 g of cypermethrin) was used in the study. The application liquid was in the form of a water solution. The investigation covered eight groups of animals: six experimental groups and two control groups, of 15 rats each. Experimental groups received 5.6 mg/cm2 chlorpyrifos and 0.5 mg/cm2 cypermethrin, or 27.8 mg/cm2 chlorpyrifos and 2.7 mg/cm2 cypermethrin dermally, for one day, one week and four weeks, except for Saturdays and Sundays. The preparations examined were applied to the tail skin of rats. The animals were anaesthetized at the end of exposure period. Plasma cholinesterase and brain acetylcholinesterase activities were determined. The brain for histological examination was perfused with a solution of methanol, formalin and glacial acetic acid, and the sections stained by the Nissel method. The behaviour of the animals was evaluated in the open field test four times: before exposure, and after one, two and four weeks of the experiment. The results of the study showed that chlorpyrifos and cypermethrin applied in a mixture caused an inhibition of cholinesterase and acetylcholinesterase activity and elicited the pycnosis of brain neurocytes.