title: Physiological, Behavioral, and Histological Responses of Male C57BL/6N Mice to Different CO2 Chamber Replacement Rates.
abstract: Rodent euthanasia with CO2 by using gradual displacement of 10% to 30% of the chamber volume per minute is considered acceptable by the AVMA Panel on Euthanasia. However, whether a 50% to 100% chamber replacement rate (CRR) of CO2 is more painful or distressful than 10% to 30% CRR is unclear. Therefore, we examined physiological and behavioral parameters, corticosterone and ACTH levels, and lung histology of mice euthanized at CRR of 15%, 30%, 50%, or 100%. Adult male C57BL/6N mice were euthanized at different CO2 CRR as physiological parameters were recorded telemetrically. Video recordings were reviewed to determine when the mouse first became ataxic, when it was fully recumbent (characterized by the mouse's nose resting on the cage floor), and when breathing stopped. Overall, CO2 euthanasia increased cardiovascular parameters and activity. Specific significant differences that were associated with 50% to 100% compared with 15% to 30% CO2 CRR included an increase in systolic blood pressure per second from initiation of CO2 until ataxia, a decrease in total diastolic blood pressure until ataxia, and a decrease in total heart rate until ataxia, immobility, and death. All physiological responses occurred more rapidly with higher CRR. Activity levels, behavioral responses, plasma adrenocorticotropic hormone and corticosterone levels, and lung pathology were not different between groups. We found no physiological, behavioral, or histologic evidence that 15% or 30% CO2 CRR is less painful or distressful than is 50% or 100% CO2 CRR. We conclude that 50% to 100% CO2 CRR is acceptable for euthanizing adult male C57BL/6N mice.
authors.affiliation: Department of Pathology, Wright State University, Dayton, Ohio, USA; Departments of Veterans Affairs Medical Center, Cincinnati, Ohio, USA. gregory.boivin@wright.edu.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Boivin
authors.affiliation: Department of Mathematical and Microbiologic Sciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Bottomley
authors.affiliation: Department of Pathology, Wright State University, Dayton, Ohio, USA.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Dudley
authors.affiliation: Department of Psychology, Wright State University, Dayton, Ohio, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Schiml
authors.affiliation: Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio, USA.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Wyatt
authors.affiliation: Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University, Dayton, Ohio, USA.
authors.forename: Nadja
authors.initials: N
authors.lastname: Grobe
mesh_terms: D000328:Adult; D000827:Animal Welfare / Q000592:standards; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D002245:Carbon Dioxide / Q000008:administration & dosage*; D003345:Corticosterone / Q000097:blood; D037901:Euthanasia, Animal / Q000379:methods*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D059408:Pain Management / Q000662:veterinary
chemical_list: D002245:Carbon Dioxide; D003345:Corticosterone