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Assessment of chlorpyrifos and lead acetate combination on neurobehavioral aspects in Wistar rats after subchronic dietary exposure

H Krishna, AV Ramachandran

Organophosphorus insecticide, chlorpyrifos, and heavy metal, lead, were studied for their interactive effects on neurobehavioral aspects in Wistar rats when exposed for a period of 90 consecutive days through experimental diet. The tests used for the assessment of neurobehavioral changes were include functional observation battery, grip strength measurement, foot splay measurement and motor activity. The study was designed using two different dose levels of chlorpyrifos and lead acetate and grouped into seven groups including concurrent controls. Neurobehavioral observations were performed at the end of 4 and 13 weeks of exposure and after 4 weeks of recovery period. Repeated dietary exposure at a dose level of 10 ppm of chlorpyrifos (i.e., equivalent to 1mg/kg body weight/day) and in a combination of 10 ppm chlorpyrifos plus 500 ppm of lead acetate (i.e., equivalent to 44.0mg/kg body weight/day) to groups of animals revealed mild cholinergic symptoms and decreased rearing counts at the end of week 4. In addition, combination group animals (Chorpyrifos plus Lead) treated at the low dose level (Chlorpyrisfos-1ppm and lead-50 ppm) also revealed reduction in the vertical movements. The lack of persistence and/or cumulative effects of these changes after 13 weeks of exposure is due to tolerance induced by the chlorpyrifos. The rearing movements measured in the open field are considered to be more indicative of exploratory behaviour and emotional tendencies than of general motor activity. A decrease in rearing counts of combination group animals (Chorpyrifos plus Lead) treated at the low dose level after week 4 was noticeable, irrespective of sex, suggests that even at low dose levels, the combination of chlorpyrifos and lead produces behavioral changes. However, many higher levels of tests for detection of cognitive functions should also be considered. No other behavioral changes were noticed in the studied behavioral tests.