Behavioral and biochemical alterations following in utero exposure to methylmercury

Behavioral changes induced in utero by methylmercury (MeHg) were studied with a non-invasive measure of patterns of effects in 1 to 35 day old rats. Lipid peroxidation (LP) and acetylcholinesterase (AChe) activity were used to compare effects in four different brain regions. MeHg (0, 2 or 6 mg/kg) was administered (PO) at day 6, 7, 8 and 9 of gestation. Rats were videotaped on day 10, 12, 20 and 34 and sacrificed on day 1, 13, 21 and 35. No changes in body or brain weights or other ancillary measures of growth and development occurred between 1-35 days. Cellular injury in brain regions as measured by LP was not altered by MeHg. AChe activity decreased in the anterior cortex and cerebellum on PN12. Frequency, dispersion and interactions of behavioral elements were determined. Frequency of grooming mode elements was decreased at 10, 12 and 34 days for 6 mg/kg, and at 12 and 34 days for 2 mg/kg pups. The frequency of exploratory mode elements increased at days 10 and 12 for 6 mg/kg, days 12 and 20 for 2 mg/kg pups. MeHg increased activities in the attention mode on PN12 at both doses. Behavior patterns were altered on all days observed, but these were not dose related. PN12 was observed to be the beginning of patterning (56 possible interactions). The 6 mg/kg group demonstrated a delay of pattern development at PN12 with a recovery to an altered array of behaviors at PN20. MeHg generally decreased interaction values (Chi2).(ABSTRACT TRUNCATED AT 250 WORDS)