A Simple Exsanguination Method That Minimizes Acute Pre-anesthesia Stress in the Mouse: Evidence Based on Serum Corticosterone Concentrations.

: Enormous variability exists among published values for serum corticosterone concentration of mice. Exsanguination of mice is widely used and has been little-tested, but is a likely variable to affect corticosterone concentrations. Exsanguination may impose unrecognized and unnecessary distress on mice used in research. Male and female C57BL/6J mice that were 25 to 30 days old were housed separately, and blood samples were obtained between 9 and 10 a. m. Methoxyflurane and CO2 were each used to induce anesthesia. Mice were anesthetized in the housing room (to minimize environment- and transport-related stress) or in an adjacent room after a transport procedure that required 30 seconds or less. Mice were accustomed to transportation in their cages while in the housing room, and CO2 anesthesia involved placing the entire cage in a chamber flushed with CO2. Serum corticosterone concentrations, determined by radioimmunoassay, were 32 6 17, 113 6 37, 103 6 32, and 97 6 34 ng/ml (mean 6 SEM, n = 10 mice/group) for mice in anesthesia groups housing room/CO2, housing room/methoxyflurane, transport stress/CO2, and transport stress/methoxyflurane, respectively. Values for the housing room/CO2 group differed significantly (P < 0.05, two-way ANOVA; least-squares means) from values for the other groups and appeared to define the serum corticosterone concentration of quiescent laboratory mice. A subsequent study yielded a serum corticosterone concentration of 31 6 5 ng/ml (mean 6 SEM) in 16 adolescent C57BL/6J mice exsanguinated in the same manner. Finally, exsanguination of 4 groups of 5 young adult C57BL/6J mice, each group in timed sequence, by means of the housing room/CO2 procedure indicated that distress communicated by the mice did not disturb adjacent mice in the room (i. e., mice used subsequently in each sequence), as determined on the basis of the serum corticosterone concentration. Use of CO2 to induce anesthesia coupled with a familiar routine and environment constitutes an important procedural refinement in terms of reduction in acute distress preceding anesthesia in the mouse.