UBC Theses and Dissertations

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UBC Theses and Dissertations

Understanding individual variation in rat responses to carbon dioxide Améndola Saavedra, Lucía


Carbon dioxide (CO₂) is commonly used to kill laboratory rats, but the humanness of this method remains controversial. Cumulative evidence indicates that CO₂ elicits negative emotions in rats. However studies using inescapable exposure (forced exposure) have shown contrasting results. Understanding individual differences could allow for stronger inferences regarding rat experiences when exposed to CO₂. The main aim of this thesis was to determine if CO₂ sensitivity is variable between rats. In Chapter 2, I described rat active and passive behaviours during CO₂ forced exposure and assessed consistency of individual differences in rat response to CO₂. Results from Chapter 2 confirmed that rats do not express passive behaviours when exposed to gradually increasing concentrations of CO₂, showed that the individual rat is an important source of variation in the behavioural responses to CO₂, but this variation was not related to individual differences in coping strategies. In Chapter 3, I investigated consistency and stability of rat individual thresholds of aversion to CO₂ across repeated exposures, and I assessed whether other situational-dependent personality traits could account for the variation in response to CO₂. My results suggest that individual differences in rat thresholds of aversion are not related to other personality traits but to sensitivity to CO₂. In Chapter 4, I assessed the effects of an anxiolytic on the individual thresholds of aversion to CO₂. I found that rats experience anxiety when exposed to lower CO₂ concentrations and variation in rat CO₂ sensitivity is driven by individual differences in the onset of these feelings. Collectively these studies suggest that the emotional experience of rats exposed to CO₂ varies among individuals, likely due to differences in the onset of CO₂-induced anxiety. In these studies using aversion tests, all rats avoided CO₂ before losing consciousness, even less sensitive rats when treated with an anxiolytic. Indicating that CO₂ concentrations required to render rats unconscious elicit negative affective states. Further research is necessary to determine what type of emotions, in addition to feelings of anxiety, are experienced by rats at higher concentrations (e.g. intense air hunger or panic), and whether these experiences also vary between individuals.

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