Interaction of gamma-radiation and methyl mercury during a critical phase of neonatal brain development in mice exacerbates developmental neurobehavioural effects.

In our environment, mammals (including humans) are exposed to various types of ionizing radiation and both persistent and non-persistent toxic chemicals. It is known that ionizing radiation, as well as methyl mercury, can induce neurotoxicological and neurobehavioural effects in mammals. These developmental neurotoxic effects can be seen following exposure during gestation. There is a lack of knowledge concerning the effects and consequences of low-dose exposure during critical phases of perinatal and/or neonatal brain development, and of the combination of ionizing radiation and environmental chemicals. A recent study has indicated that low doses of ionizing radiation to the human brain during infancy influence cognitive ability in adulthood. In the present study, 10-day old neonatal male NMRI mice were exposed to a single oral dose of MeHg (0.40 or 4.0 mg/kg bw). Four hours after the MeHg exposure the mice were subjected to (60)Co gamma-radiation on one occasion at doses of 0.2 and 0.5 Gy. The animals were then subjected to a spontaneous behaviour test at 2 and 4 months, and a water maze test at the age of 5 months. Neither the single dose of MeHg (0.4 mg/kg bw) nor the radiation dose of 0.2 Gy affected their spontaneous behaviour, whereas the co-exposure to external gamma-radiation and MeHg caused developmental neurotoxic effects. The study shows that gamma-radiation and MeHg can interact and significantly exacerbate developmental neurotoxic effects, as manifested by disrupted spontaneous behaviour, lack of habituation, and impaired learning and memory functions.