Understanding rat emotional responses to CO2

Abstract

The aim of this review is to summarize evidence regarding rat emotional experiences during carbon dioxide (CO 2) exposure. The studies reviewed show that CO 2 exposure is aversive to rats, and that rats respond to CO 2 exposure with active and passive defense behaviors. Plasma corticosterone and bradycardia increased in rats exposed to CO 2. As with anxiogenic drugs, responses to CO 2 are counteracted by the administration of anxiolytics, SRIs, and SSRI's. Human studies reviewed indicate that, when inhaling CO 2 , humans experience feelings of anxiety fear and panic, and that administration of benzodiazepines, serotonin precursors, and SSRIs ameliorate these feelings. In vivo and in vitro rat studies reviewed show that brain regions, ion channels, and neurotransmitters involved in negative emotional responses are activated by hypercapnia and acidosis associated with CO 2 exposure. On the basis of the behavioral, physiological, and neurobiological evidence reviewed, we conclude that CO 2 elicits negative emotions in rats.

Attitudes of laboratory animal professionals and researchers towards carbon dioxide euthanasia for rodents and perceived barriers to change

“…Thus, it is reasonable to infer that many participants who use CO 2 as a primary euthanasia method are not convinced that this method provides a good death. These results are consistent with the ongoing debate within the scientific community where some authors argue that CO 2 euthanasia causes suffering in rodents 11 and others argue there is insufficient evidence to draw conclusions regarding the method. 10 The current study did not assess if the information used by participants to interpret the animals’ experiences came from their knowledge of the scientific literature, personal experience, or information provided by regulatory bodies.…”

“…For example, two recently published literature reviews arrived at contrasting conclusions; Turner and colleagues concluded that there was not enough evidence to determine whether CO 2 killing compromises rodent welfare, 10 while Améndola and Weary concluded that CO 2 inhalation induces negative emotions in rats likely corresponding to fear, anxiety, dyspnea, distress, and panic. 11 Conflict also surrounds alternative methods such as inhalant anaesthetics, with some scholars arguing that that use of CO 2 should continue, 12 and others concluding that alternative methods are more humane. 13 – 15 …”

Comparative Study of the Aftereffect of CO2 Inhalation or Tiletamine–Zolazepam–Xylazine Anesthesia on Laboratory Outbred Rats and Mice

“…CO 2 inhalation in the chamber is a more stressful method and causes a cascade of pathophysiologic reactions reflected in blood, as well as the unnecessary suffering of animals [ 39 , 40 ]. In the condition of hypoxia after CO 2 inhalation, hypercalcemia can be developed, as a consequence of electrolyte balance failure [ 41 ].…”

Hypothesis: Potentially Systemic Impacts of Elevated CO2 on the Human Proteome and Health

“…Exposure to pCO 2 levels > 600 ppm has been shown to lead to the "sick-building syndrome, " resulting in irritation, fatigue, anxiety, headaches, and poor cognitive performance (22,(24)(25)(26)35) and sleep apnea (36), linked to elevated pCO 2 in blood (10). Exposure to elevated CO 2 also leads to the emotional responses of fear and panic in humans, a behavior that has also been experimentally confirmed in rats (37). Elevated indoor CO 2 concentrations, well in excess of 1,000 ppm CO 2 , are also characteristic of farm animal houses [e.g., (38,39)].…”