The relationship of brain catecholamine levels to enflurane requirements among three strains of mice with different anesthetic sensitivities

Purpose. It has been reported that brain catecholamines alter the minimum alveolar concentration (MAC) of anesthetics. The extent of the relation between the levels of brain catecholamine and anesthetic sensitivity should be evaluated by excluding several factors. Methods. Anesthetic sensitivity was measured by using loss of the righting reflex in three strains of mice with different sensitivities. The mice were decapitated without any anesthesia, adding on ddN and C57BL/6J mice in 2% enflurane, their brains were divided into three parts, and dopamine and norepinephrine levels were analyzed by high-performance liquid chromatography (HPLC). Results. The values of enflurane requirement (%) were 1.30 ± 0.05 in ddN, 1.10 ± 0.02 in C57BL/6J, and 1.05 ± 0.02 in MSM mice. The values of dopamine (μg·g^-1) in the mesencephalon were 0.23 ± 0.02 in ddN, 0.15 ± 0.02 in C57BL/6J, and 0.12 ± 0.02 in MSM (mean ± SE). No statistical significance in the values in 2% enflurane could be obtained between ddN and C57BL/6J. The stepwise regression line showed a significant correlation: enflurane requirement (%) = -0.89 + 1.60 X (dopamine levels of mesencephalon) (r² = 0.571, P < 0.0001). Conclusion. Dopamine in the mesencephalon seems to play an important role in the production of different anesthetic sensitivities, and the anesthetic mechanism might be related to the regulation of dopamine levels that promote arousal.