Developmental effects of fractionated low-dose exposure to gamma radiation on behaviour and susceptibility of the cholinergic system in mice

Purpose: To investigate whether neonatal exposure to fractionated external gamma radiation and co-exposure to radiation and nicotine can affect/exacerbate developmental neurotoxic effects, including altered behavior/cognitive function and the susceptibility of the cholinergic system in adult male mice. Materials and methods: Neonatal male Naval Medical Research Institute (NMRI) mice were irradiated with one 200 mGy fraction/day and/or exposed to nicotine (66 mu g/kg b.w.) twice daily on postnatal day (PND) 10, 10-11, 10-12 or 10-13 (nicotine only). At 2 months of age the animals were tested for spontaneous behavior in a novel home environment, habituation capacity and nicotine-induced behavior. Results: Fractionated irradiation and co-exposure to radiation and nicotine on three consecutive days disrupted behavior and habituation and altered susceptibility of the cholinergic system. All observed effects were significantly more pronounced in mice co-exposed to both radiation and nicotine. Conclusions: The fractionated irradiation regime affects behavior/cognitive function in a similar manner as has previously been observed for single-dose exposures. Neonatal co-exposure to radiation and nicotine, during a critical period of brain development in general and cholinergic system development in particular, enhance these behavioral defects suggesting that the cholinergic system can be a target system for this type of developmental neurotoxic effects.