Effects of low doses of atrazine on the neurobehavioural development of mice

Recent studies suggest that atrazine (ATZ), a triazine herbicide widely used and frequently detected in ground and surface water, is able to affect estrogen production by inducing aromatase, the enzyme that converts androgen into estrogen, an essential transformation occurring at the CNS level for maturation and expression of behaviour. In the present study we evaluated the effects of environmentally relevant doses of ATZ on somatic growth and early behavioural ontogeny, a crucial stage in shaping future behaviour. For this purpose we observed mice born to mothers exposed to 1 or 100 µg/kg ATZ during pregnancy and lactation. We studied, between postnatal day 2 to 15, the righting reflex, cliff aversion, forepaw grasping, auditory startle, eyelid and ear opening, and ultrasound vocalizations. In both sexes ATZ effects were evident, on body weight at birth, on the maturation of righting and grasping reflexes, and on the rate of emission and the spectrographic characteristics of ultrasound vocalizations. Dosage level appeared to be particularly relevant because, in some cases, the lower ATZ exposure was more effective than the higher one in modifying behavioural response. The latter finding suggests that this compound, similarly to many others endocrine disruptors, does not follow a linear dose-response curve, and that, as a consequence, its effects should be studied carefully at very low doses. Our results, compatible with ATZ properties, suggest caution in the use of a chemical agent that may, even at low doses, interfere with brain development and differentiation, inducing alterations of the developmental trajectories of behaviours. © 2007 Taylor & Francis Group, LLC.