Effect of midazolam, medetomidine, and butorphanol tartrate combination anesthetic on electroretinograms of mice

Purpose: To evaluate electroretinogram (ERG) responses under anesthesia with midazolam, medetomidine, and butorphanol tartrate (MMB) combination compared with pentobarbital sodium and ketamine/xylazine (KX). Methods: Six-week-old male C57BL/6J mice were divided into MMB-, pentobarbital sodium-, and KX-administered groups. Following overnight dark adaptation, an ERG was performed. The parameters sensitivity (S), log maximum amplitude (R_max), R_max, and time delay to the onset (T_d) of the ERG a-waves were computed based on the Lamb and Pugh model. The parameters light intensity at half maximum amplitude (K), R_max, and n of the ERG b-waves were computed based on the Naka-Rushton equation. The amplitude and the implicit time of oscillatory potentials (OPs) were quantified. Results: The T_d of the dark-adapted a-waves was statistically significantly larger under anesthesia with the MMB combination and pentobarbital sodium compared to KX. The K of the dark-adapted b-waves was statistically significantly larger under anesthesia with pentobarbital sodium compared to the MMB combination. The amplitude of the dark-adapted OPs was statistically significantly larger under anesthesia with the MMB combination compared to pentobarbital sodium. The implicit time of the dark-adapted OPs was statistically significantly smaller under anesthesia with the KX combination compared to pentobarbital sodium. Conclusions: The results suggested that ERG responses, especially in OPs, are greatly affected by the type of anesthetic. It is important to consider the sensitive responses influenced by the selection of anesthetics when ERG is performed.