Thesis title: Exposure to Neurodevelopmental Disruptors: Assessing the Effects of a Combination of Chemical and Biological Stressors in a Rodent Model
The developing brain is particularly vulnerable to environmental factors, including chemical and biological stressors. Widely diffused chemical pollutants such as toxic metalloids including lead (Pb) and manganese (Mn) may cause various adverse health outcomes, especially affecting foetuses and children through interference with neurodevelopmental mechanisms. Foetus/infant vulnerability to the adverse effects of chemicals on neurodevelopment might also depend on the gene background as well as on the concomitant exposure to other stressors, such as maternal infections in pregnancy. Therefore, it is vital to investigate the effects of these metals as a mixture, as well as to consider the inclusion of other possibly hazardous factors in the scenario. This thesis aimed to investigate in a mouse model the short- and long- term effects of developmental exposure to toxic metalloids such as lead (Pb) and manganese (Mn), alone and in combination, mimicking human exposure scenarios as for selection of doses and longitudinal extension of the exposure itself (from premating to weaning of the offspring). Our study also assessed the effects on behaviour of combined exposure to chemicals and a biological stressor represented by maternal immune inflammation (MIA).
To this aim, firstly, we determined the neurodevelopmental effects of single exposure to low level Pb by mimicking the real-life scenario of human Pb exposure by exposing mice to two different, low-level Pb concentrations in drinking water throughout periconceptional stage, gestation and lactation. Behavioural and biochemical outcomes were monitored in dams and offspring revealing Pb-dependent impairments on motor, anxiety, olfactory and cognitive endpoints. We evidenced a greater vulnerability of males to Pb adversity. Pb monitoring showed an elevated, dose-dependent fashion in blood, brain and bone up to six months after termination of exposure. Furthermore, Pb females had a higher Pb accumulation in bones in comparison to males.
Based on the data confirming the impact of low Pb concentrations on behavioural maturation, as the second step, we applied a real-life longitudinal exposure scenario and investigated the behavioural effects of developmental exposure to low, environmentally relevant levels of Pb and Mn as single metals and in combination. We also challenged the animals exposed to the Pb and Mn mixture with maternal immune activation (MIA) induced via polyinosinic:polycytidylic acid [poly(I:C)] application during gestation. Behavioural and biochemical outcomes were monitored in dams and offspring, confirming the Pb-dependent deficits in the same domains detected in the first step of this thesis. Moreover, we showed sex-specific, robust effects of Mn on recognition memory of a social stimulus at adult age. The coexposure to Pb and Mn failed to exert additive effects on behaviour, and unexpectedly Pb suppressed the effects of Mn on social recognition. Finally, offspring exposed to Pb-Mn combination plus MIA had altered early motor responses, enhanced anxiety and increased social exploration selectively in males. Metal biomonitoring in blood and brain at different ages showed a significant exposure to either Pb, Mn or their combination, with levels comparable to those reported in children but with significant accumulation of Pb in the mouse brain at 2 months of age. These findings confirm the health risk of metal exposure and biological stressors in a longitudinal animal model.