Individual differences in rat sensitivity to CO2.

Feelings of fear, anxiety, dyspnea and panic when inhaling carbon dioxide (CO2) are variable among humans, in part due to differences in CO2 sensitivity. Rat aversion to CO2 consistently varies between individuals; this variation in aversion may reflect CO2 sensitivity, but other personality traits could also account for individual differences in aversion. The aims of this study were to 1) assess the stability of individual differences in rat aversion to CO2, 2) determine if individual differences in sweet reward motivation are associated with variation in aversion to CO2, and 3) assess whether variation in aversion to CO2 is related to individual differences in motivation to approach gains (promotion focus) or maintain safety (prevention focus). Twelve female Sprague Dawley rats were exposed multiple times at three different ages (3, 9 and 16 months old) to CO2 in approach-avoidance testing to assess motivation to avoid CO2 against motivation to gain sweet rewards. Rats were also tested for motivation to find hidden sweet rewards, and for their motivation to approach rewards or darkness. Tolerance to CO2 increased with repeated exposures and was higher at older ages. Individual differences in aversion to CO2 were highly repeatable but unrelated to motivation for sweet rewards or the strength of promotion and prevention focus. These results indicate that individual differences in aversion to CO2 reflect variation in CO2 sensitivity.