Long‐term exposure of mice to 890 ppm atmospheric CO₂ alters growth trajectories and elicits hyperactive behaviours in young adulthood

Abstract

Atmospheric carbon dioxide (CO2) levels are currently at 418 parts per million (ppm), and by 2100 may exceed 900 ppm. The biological effects of lifetime exposure to CO2 at these levels is unknown. Previously we have shown that mouse lung function is altered by long‐term exposure to 890 ppm CO2. 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 CO2 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 CO2 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 CO2 on mammalian health outcomes. Key points Long‐term exposure to elevated levels of atmospheric CO2 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 CO2 at levels that may arise in the atmosphere due to global emissions. Exposure to elevated CO2, 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 CO2 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.

Developing in a polluted atmosphere: A link between long‐term exposure to elevated atmospheric CO2 and hyperactivity

“…Surprisingly, no pathological changes were observed in kidney structure at adulthood following exposure to the high CO 2 environment for 3 months (i.e. from gestation to young adulthood) or using measures of renal function (Wyrwoll et al 2022). Nor were differences in bone structural density identified, as would be expected if substantial physiological compensation was occurring.…”

“…Further exploration is needed to determine how elevated CO 2 may affect pregnancy, ageing and the mechanisms underlying behavioural change. It is unclear from the study by Wyrwoll et al (2022) whether the reported hyperactivity is a result of changes in brain structure and function. Elucidating both behaviours and their neurological basis in this paradigm will not be trivial.…”

“…The study by Wyrwoll et al (2022) makes the case that global rising CO 2 levels could confer a risk similar to other components of air pollution. High life-time CO 2 exposure produced significant differences in dopamine receptors in the brain of adult offspring (Wyrwoll et al 2022). Increased expression of the dopamine receptor D1 (DRD1) was found in males, whereas DRD2 expression decreased in females.…”

“…This reduction is probably a result of altered neuronal excitability, a phenomenon that could affect brain development, where neural activity is essential for co-ordinating normal developmental events. The study by Wyrwoll et al (2022) makes the case that global rising CO 2 levels could confer a risk similar to other components of air pollution. High life-time CO 2 exposure produced significant differences in dopamine receptors in the brain of adult offspring (Wyrwoll et al 2022).…”

“…In this issue of The Journal of Physiology, Wyrwoll et al (2022) address this timely question, exploring both systemic and neurological outcomes of a life lived in a high CO 2 environment. Comparing life-time exposure to current atmospheric CO 2 (460 ppm) with the higher CO 2 level of 890 ppm, a level predicted to occur by the year 2100, Wyrwoll et al (2022) showed that mice exposed to elevated CO 2 during gestation had a higher birth weight than their control counterparts. Abnormal birth weight can increase risk of later morbidity, although, in this case, weight normalised over the postnatal period and developmental milestones, such as righting reflex or eye opening, were not delayed.…”