Analysis of dopamine and its metabolite, 3,4-dihydroxyphen- ylacetic acid, with high-performance liquid chromatography: Levels of retinal dopamine and its major metabolite, 3,4-dihy- droxyphenylacetic

genetic manipulation in mice is becoming more feasible and affordable. An important part of mouse husbandry is euthanasia, which should be performed as painlessly and efficiently as possible. There are several ways in which laboratory mice are euthanized, two of which include carbon dioxide (CO2)induced asphyxia and cervical dislocation. CO2 overdose has been favored for euthanasia, because the lowering of pH in the cerebrospinal fluid (CSF) that occurs secondary to CO2 overdose is associated with anesthetic depth and insensibility to pain in humans [1]. Nevertheless, many laboratories regularly utilize cervical dislocation to euthanize laboratory mice. Although humane treatment of laboratory mice is important, the method of euthanasia may have a substantial effect on postmortem measurements of experimental variables and could significantly affect experimental results. Hence, in this study, we tested the hypothesis that CO2 overdose alters the retinal level of dopamine, an important regulator of visual function [2].