Developmental effects of neonatal fractionated co-exposure to low-dose gamma radiation and paraquat on behaviour in adult mice

Radiological methods for screening, diagnostics and therapy are often used in healthcare; however, it has recently been reported that developmental exposure to low-dose ionizing radiation (IR) causes neurotoxicity. Environmental chemicals also have the potential to affect the developing brain and the concomitant effects caused by IR and chemicals are of high interest today. We therefore aim to investigate if low-dose IR can interact with the known neurotoxicant paraquat to induce neurotoxicity in the neonatal mouse model. Using the same model, we also aim to investigate if fractionated low-dose IR can be as neurotoxic as higher acute doses. Male mice were exposed to a single dose of paraquat (0.2 or 0.02 mg/kg) on postnatal day 10 and 11. Two hours following paraquat exposure, mice were whole body irradiated with 100 or 300 mGy gamma radiation (Cs-137). Behavioural observations were performed at 2 and 3 months of age. Following behavioural testing, we evaluated striatal dopaminergic gene transcription. Animals co-exposed to IR and paraquat generally displayed altered spontaneous behaviour compared to controls and single agent exposed mice. Stronger effects by combined exposure were also observed on adult memory and learning. However, dopaminergic gene transcript levels remained unchanged by treatment. Co-exposure to low-dose IR and paraquat can interact to exacerbate neurotoxic effects and to impair cognitive function. Furthermore, fractionation of the radiation dose was observed to be as potent as higher acute exposure for induction of developmental neurotoxicity.