Long-term exposure of mice to 890 ppm atmospheric CO 2 alters growth trajectories and elicits hyperactive behaviours in young adulthood.

Atmospheric carbon dioxide (CO ₂ ) levels are currently at 418 parts per million (ppm), and by 2100 may exceed 900 ppm. The biological effects of lifetime exposure to CO ₂ at these levels is unknown. Previously we have shown that mouse lung function is altered by long-term exposure to 890 ppm CO ₂ . Here, we assess the broader systemic physiological responses to this exposure. Mice were exposed to either 460 or 890 ppm from preconception to 3 months of age, and assessed for effects on developmental, renal and osteological parameters. Locomotor, memory, learning and anxiety-like behaviours of the mice were also assessed. Exposure to 890 ppm CO ₂ increased birthweight, decreased female body weight after weaning, and, as young adults, resulted in reduced engagement in memory/learning tasks, and hyperactivity in both sexes in comparison to controls. There were no clear anxiety, learning or memory changes. Renal and osteological parameters were minimally affected. Overall, this study shows that exposure of mice to 890 ppm CO ₂ from preconception to young adulthood alters growth and some behaviours, with limited evidence of compensatory changes in acid-base balance. These findings highlight the potential for a direct effect of increased atmospheric CO ₂ on mammalian health outcomes. KEY POINTS: Long-term exposure to elevated levels of atmospheric CO ₂ is an uncontrolled experiment already underway. This is the first known study to assess non-respiratory physiological impacts of long-term (conception to young adulthood) exposure of mice to CO ₂ at levels that may arise in the atmosphere due to global emissions. Exposure to elevated CO ₂ , in comparison to control mice, altered growth patterns in early life and resulted in hyperactive behaviours in young adulthood. Renal and bone parameters, which are important to balance acid-base levels to compensate for increased CO ₂ exposure, remained relatively unaffected. This work adds to the body of evidence regarding the effects of carbon emissions on mammalian health and highlights a potential future burden of disease.
(© 2021 The Authors. The Journal of Physiology © 2021 The Physiological Society.)