EFFECTS OF MELATONIN ON NEURO AND REPRODUCTIVE TOXICITY INDUCED BY IN UTERO AND LACTATIONAL CO-EXPOSURE TO CHLORPYRIFOS AND CYPERMETHRIN IN MALE WISTAR RATS

ABSTRACT

Organophosphates and pyrethroids are common insecticides used in combination. Their use in agricultural and indoor activities has opened several windows of exposure to vulnerable non-target young animals and humans during pregnancy and breast-feeding, which may adversely affect their physical, reproductive and mental health. Oxidative stress has been implicated in pesticide-induced toxicity.

The aim of the study was to investigate the ameliorative potentials of melatonin (MEL) on neurotoxic and reproductive changes provoked by in utero and lactational co-exposure to chlorpyrifos (CPF) and cypermethrin (CYP) in male Wistar rats. Sixty out of the sixty five pregnant rats obtained following overnight mating of seventy-two sexually-mature female nulliparous Wistar rats with 72 adult males in a 1 : 1 mating scheme were used for the study.

Evidence of mating was assessed in each female animal by the presence of spermatozoa deposit or vaginal plug. Day 1 of gestation was the day copulation plugs/spermatozoa were found in the vagina. The 60 pregnant dams were thereafter divided at random into six 6 groups of 10 animals each. Group I (DW) was given distilled water (2 ml/kg), while group II (S/oil) was given Soya oil only (2 ml/kg). Group III (MEL) was dosed melatonin (0.5 mg/kg) only, while group IV (CC) was co-administered with CPF (1.9 mg/kg; 1/50th of the LD50) and CYP (7.5 mg/kg; 1/50th of the LD50); group V (MCC) was pretreated with MEL (0.5 mg/kg) and then co-exposed to CPF (1.9 mg/kg; 1/50th of the LD50) and CYP (7.5 mg/kg; 1/50th of the LD50), respectively, 30 minutes later.

Group VI (CCM) was co-exposed to CPF (1.9 mg/kg; 1/50th of the LD50) and CYP (7.5 mg/kg; 1/50th of the LD50) respectively, and post-treated with MEL (0.5 mg/kg), 30 minutes later. The regimens were given to the dams by gavages once daily from gestation day 1 (GD 1) to postnatal day (PND) 21.

Weekly monitoring of body weight and clinical signs on the dam were carried out and recorded. The dams were allowed to deliver normally and some developmental/ reproductive/neurobehavioural parameters were evaluated on the FI generation male rats at different time intervals, namely: litter size and weight, number of lives and dead pups, anogenital distance (AGD), crown-rump length (CRL), time of eye and ear opening, time of testicular descent, surface and aerial righting reflex, ability to walk and time pivoting, negative geotaxis, inclined plane, ladder walk, bean walk, excitability score, forepaw grip, forced swimming and cognitive (learning and short-term memory) tests.

At PND 80, F1 male rats were mated to a sexually-matured, untreated nulliparous female in a 1 : 1 mating schedule and the females were observed for reproductive indices, including mating index, live-birth index, sex ratio, viability index, gestational length index, fertility index, pregnancy (gestation) index. At the end of the experiment, the rats were sacrificed by jugular venesection after light chloroform anaesthesia.

The F1 male rats were evaluated for epididymal sperm concentration, sperm motility, sperm live-dead ratio, sperm morphology, and concentrations of sex [follicle stimulating hormone (FSH), luteinising hormone (LH) and testosterone] and thyroid [triodothyronine (T3), thyroxine (T4) and thyroid-stimulating hormones (TSH)] hormones, and tissues‟ biochemical parameters (levels of malondialdehyde [MDA] concentration; activities of superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx] and acetylcholinesterase [AChE], concentration of testicular and epididymal total and free sialic acid, and epididymal fructose).

Post-mortem gross and histopathological examinations of some tissues of rats were also conducted on F1 generation male rats. The results revealed alterations in litter size and weight, number of live/dead pups, anogenital distance (AGD), crown-rump length (CRL), time of eye and ear openings, time of testicular descent, surface and aerial righting reflex, ability to walk and time pivoting, negative geotaxis, inclined plane, ladder walk, beam walk, excitability score, fore-paw grip time, forced swimming and cognition; in the group co-exposed to CPF and CPY.

Mating of F1 generation male rats of dams co-exposed to CPF and CPY with untreated female rats showed alteration in mating index, live birth index, sex ratio, viability index, gestational length index, fertility index, pregnancy (gestation) index.

The F1 male rats of CC group showed decreased epididymal sperm concentration, sperm motility; sperm live-dead ratio, concentrations of sex hormones levels (FSH, LH, and testosterone) and altered sperm morphology. Similarly, there were alterations in the tissue levels of MDA, thyroid hormones (T3, T4 and TSH), testicular and epididymal total and free sialic acid, epididymal fructose, SOD, CAT, GPx and AChE in the F1 male rats.

Pre-and post-exposure treatment with MEL mitigated the pesticide-evoked developmental, reproductive, reflexogenic, neurobehavioural, biochemical, oxidative and histological changes in F1 male rats. However, MEL pretreatment was more beneficial than post-exposure treatment. The mitigation of pesticide-evoked developmental, reproductive, reflexogenic, neurobehavioural, biochemical, oxidative and histological changes by MEL was partly due to its antioxidant and free radical scavenging properties.