ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the ameliorative effect of melatonin on sub-chronic chlorpyrifos (CPF) and cypermethrin (CYP)-evoked cognitive changes in male Wistar rats.</p><p><b>METHODS</b>Fifty adult male Wistar rats, divided into five groups of ten rats each, were used for the study. Groups 1 and II were given distilled water and soya oil (2 mL/kg) respectively. Group III was administered with melatonin at 0.5 mg/kg only. Group IV was administered with CPF [7.96 mg/kg (1/10th LD50)] and CYP [29.6 mg/kg (1/10th LD50)], and Group V was administered with CPF [7.96 mg/kg (1/10th LD50)] and CYP [29.6 mg/kg (1/10th LD50)] 30 min after melatonin (0.5 mg/kg). The regimens were administered by gavage once daily for 12 weeks. Thereafter, cognitive performances were determined and the brain was evaluated for malonaldehyde concentration.</p><p><b>RESULTS</b>CPF and CYP induced cognitive deficits and increased brain malonaldehyde concentration, which were all ameliorated by melatonin.</p><p><b>CONCLUSION</b>Cognitive deficits elicited by CPF and CYP was mitigated by melatonin due to its antioxidant property.</p>