Abstract
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.
Highlights
People report feelings of fear, anxiety, dyspnea and panic during CO2 inhalation
When inhaling 35% CO2, the anxiety experienced by healthy people and the panic attacks experienced by panic disorder patients are highly consistent between exposures [4, 5]
In more recent work we found that variation in rat behaviour was consistent between two exposures to CO2, during forced exposure, aversion- and approach-avoidance testing and we found that rats that consistently showed higher responses to CO2 forced exposure were consistently less tolerant of CO2 when tested in aversion-avoidance [15]. These results suggest that variation in rat responses to CO2 is linked to consistent individual differences in CO2 sensitivity; i.e. like humans, rats may vary in the emotional experience elicited by CO2
Summary
People report feelings of fear, anxiety, dyspnea and panic during CO2 inhalation (for a review see [1]). This emotional response to CO2 inhalation varies among individuals. When inhaling 35% CO2, the anxiety experienced by healthy people and the panic attacks experienced by panic disorder patients are highly consistent between exposures [4, 5]. This between subject variability in the subjective emotional experience is often referred to as variation in CO2 sensitivity [1]
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