Carbon Dioxide Production by Individual Mice as an Index of Behavioral and Metabolic Activity

Carbon Dioxide Production in Individual Mice as an Index ofBehavioral and Metabolic Activity. BUSHNELL, P. J., EVANS, H.L., AND PALMES, E. D. (1985). Fundam. Appl. Toxicol.. 5,962-970.A noninvasive method for simultaneous real-time determinationof spontaneous locomotor activity (LA) and CO₂ production (asminute volume expired CO₂, or _ECO₂) in miceis described. As an apical measure of overall metabolic activity,_ECO₂ proved sensitive to changes in manyphysiological processes, including behavioral activity. In normalmice, LA (as photobeam breaks) and _ECO₂ werepositively correlated (r = 0.73), and stable over repeated dailytests. Food deprivation for 18 hr overnight increased LA whiledecreasing _ECO₂. Stimulation of peripheralsympathetic activity, either by exposure to cold air or by injectionof epinephrine, increased _ECO₂ without affectingLA. Intoxication with pentobarbital produced a biphasic changein both measures: anesthetic doses increased LA and _ECO₂ during induction and recovery, and reduced themduring the period of anesthesia itself. These results characterize_ECO₂ as an easily quantifiable, compositeindex of behavioral and metabolic activity in mice. This measure,along with its covariation with LA, may provide better informationabout toxic effects than any single screening test.