Effects of carbon dioxide exposure on early brain development in rats.

The developing brain is vulnerable to environmental factors. We investigated the effects of air that contained 0.05, 0.1 and 0.3% CO2 on the hippocampus, prefrontal cortex (PFC) and amygdala. We focused on the circuitry involved in the neurobiology of anxiety, spatial learning, memory, and on insulin-like growth factor-1 (IGF-1), which is known to play a role in early brain development in rats. Spatial learning and memory were impaired by exposure to 0.3% CO2 air, while exposure to 0.1 and 0.3% CO2 air elevated blood corticosterone levels, intensified anxiety behavior, increased superoxide dismutase (SOD) enzyme activity and MDA levels in hippocampus and PFC; glutathione peroxidase (GPx) enzyme activity decreased in the PFC with no associated change in the hippocampus. IGF-1 levels were decreased in the blood, PFC and hippocampus by exposure to both 0.1 and 0.3% CO2. In addition, apoptosis was increased, while cell numbers were decreased in the CA1 regions of hippocampus and PFC after 0.3% CO2 air exposure in adolescent rats. A positive correlation was found between the blood IGF-1 level and apoptosis in the PFC. We found that chronic exposure to 0.3% CO2 air decreased IGF-1 levels in the serum, hippocampus and PFC, and increased oxidative stress. These findings were associated with increased anxiety behavior, and impaired memory and learning.