PRENATAL EXPOSURE TO METHYLMERCURY ALTERS LOCOMOTOR-ACTIVITY OF MALE BUT NOT FEMALE RATS

In the present study the neurotoxic effects of a low dosage (0.5 mg/kg per day) of methylmercury (MeHg) on the developing nervous system wer e investigated. Pregnant rats were treated with MeHg from day 7 of pre gnancy to day 7 of lactation. Locomotor activity (locomotion, rearing, and motility) and spatial learning ability were tested in the offspri ng at 6 months of age. The expression of tyrosine hydroxylase (TH) was examined by immunohistochemistry and in situ hybridization. A signifi cant decrease in spontaneous motility and rearing was observed only in the MeHg-treated male rats. After administration of a low dose of d-a mphetamine (0.5 mg/kg) no differences could be observed between contro l and MeHg-treated male rats, suggesting that changes in dopaminergic transmission were involved. However, no change in TH messenger RNA exp ression was observed. No changes in spatial learning acquisition or me mory were shown in MeHg-treated rats. Taken together, these findings s how that during development a very low dosage of MeHg exerts neurotoxi c effects detectable in adulthood, and that susceptibility is gender-d ependent.