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Background: Motor dysfunctions are some of the characteristic symptoms of organophosphate (OP) poisoning and they have been associated with decreased levels of cholinesterase inhibition within motor areas of the brain. Objectives: The current study aims to investigate the potential neuroprotective effects of Nigella sativa oil (NSO) in alleviating chlorpyrifos (CPF) induced toxicity in the cerebella and motor cortices of the rat brains using combined behavioural, biochemical and histochemical methods. Methods: Thirty-two rats were randomly divided into four groups (eight rats per group), exposed to 1ml/kg of normal saline, 14.9 mg/kg of CPF, 14.9 mg/kg of CPF plus 1ml/kg of NSO and 1ml/kg of NSO respectively for 14 consecutive days. The rats were each exposed to a single trial of the Open Field Test (OFT) on day 13 of the experiment. This experimental test measured locomotor activity levels (line crossing frequency (LCF)) and exploratory (rearing frequency (RF)) activities in the rats studied. The rats were euthanized on day 15 of the experiment and the brains were subsequently excised. The cerebella cortices of five brains were removed and homogenised to analyse for total reactive oxygen species (ROS), nitric oxide (NO) levels and acetylcholinesterase (AChE) activity. The motor and cerebella cortices from three other brains in each group were processed for histology (Nissl stain) and proliferative activity (Ki67 immunohistochemistry). Results: Rats exposed to CPF experienced a significant increase in cerebella NO and ROS levels, depletion in AChE activity, neurogenic cells loss and subsequent reduction in locomotor and exploratory behaviours respectively (LCF and RF). However, interventional treatment with NSO depleted markers of oxidative damage (NO and ROS), reduced AChE inhibition, preserved neurogenic (Ki67) cells distribution and motor functions. Conclusion: These results demonstrate the potential efficacy of NSO in OP poisoning and the roles of neurogenic and oxidative functions in the pathophysiology and treatment of motor dysfunction in OP neurotoxicity.

1. The changes of cholinesterase activity in rabbit blood, peripheral tissues and the central nervous system following transfusion of erythrocytes with soman inhibited acetylcholinesterase were demonstrated. 2. After incubation with soman for 0.5 or 24 h, erythrocytes without acetylcholinesterase activity were injected to intact rabbits and cholinesterase activity in the erythrocytes, plasma, diaphragm, liver and various parts of the brain were evaluated 24 h following blood-transfusion. 3. When erythrocytes were incubated with soman for 24 h, no changes of cholinesterase activity in the rabbit following blood-transfusion were observed with an exception of erythrocyte acetylcholinesterase. 4. When erythrocytes were incubated with soman for 0.5 h, a significant decrease in cholinesterase activity in the erythrocytes, plasma, diaphragm and liver following blood-transfusion was found. These data show that soman is able to release from erythrocytes and inhibit cholinesterase activities not only in vitro but also in vivo although the significant inhibition of cholinesterase activities by soman was only observed in the peripheral compartment.

The activity and properties of cholinesterase (ChE) of the motor endplate and its fractions were studied in isolated human skeletal muscle. This preparation was used since the ChE activity of the membrane preparation was localized only in the motor endplate. The endplate ChE was stable in the isolated membrane for 4 weeks at 4 degrees C. The specific activity of the extracted ChE of human muscle membrane was 29.6% higher than that of the original membrane. Studies with specific substrates and ChE inhibitors indicated that most of the ChE of human muscle membrane and its fractions was acetylcholinesterase, and that the minor component was pseudocholinesterase. A Michaelis-Menten constant of 3.82 mM was estimated in the endplate ChE, and 0.88 mM in the extracted ChE of the endplate. The extracted human endplate ChE was separated into three fractions by Sephadex G-200 chromatography, and into two fractions by acrylamide gel electrophoresis.

Cholinesterase activity was localized solely in the motor endplate of the membrane in rate intercostal muscle. The diameter of rat motor endplates in the gradient dimension was 31.9 micrometers. The cholinesterase activity per unit protein of the soluble fraction of rat muscle membrane was 35.6% higher than the original membrane. From studies with specific substrates and cholinesterase inhibitors, the cholinesterase activity of rat muscle membrane and its soluble fraction consists of more than 90% acetylcholinesterase and less than 10% pseudocholinesterase.