Comparison of Scotopic and Photopic Mouse ERGs (Electroretinogram) Under Isoflurane and Ketamine Anesthesia

Abstract

Purpose: : Rodent ERGs are generally studied under ketamine anesthesia. We have met difficulties while using ketamine in our studies of mutant mouse strains, including hypersensitivity (unexplained sudden death) and hyposensitivity (lack of anesthetic action). Moreover, since ketamine acts by blocking the ion channel of NMDA receptors, we were concerned that this action might alter ERG waveforms in the mouse strain under investigation. We have shown previously (ARVO 2004) that isoflurane may be a useful alternative as an anesthetic agent for recording mouse ERGs. In this study, we compare mouse ERGs collected under isoflurane or ketamine anesthesia.

Methods: : Scotopic and photopic ERGs were performed on C57BL/6J mice anesthetized with either the standard dose of subcutaneous ketamine cocktail, or with inhaled isoflurane (2%). Male (8) and female (8) mice were divided equally into ketamine or isoflurane groups. The ERG studies in these mice were repeated at 3–4 week intervals between the ages of 46 to 184 days, with a two day gap between scotopic and photopic ERGs. A Ganzfeld apparatus with a temperature–regulated platform was used, and the ERGs were recorded via a contact lens electrode with an embedded platinum wire (200 µm). Light intensities used for these studies were varied over a range of –3.04 to +0.80 cd–s/m².

Results: : In mice 12 to 20 weeks of age, typical ages used for mouse ERG studies, we found no appreciable differences in the b–wave amplitudes for either scotopic or photopic ERGs. Moreover, there were no gender differences, or any appreciable age related decline in these amplitudes during this interval. Studies are ongoing to look for effects in older animals. Recovery from isoflurane was rapid (<2 min) compared to ketamine (∼43 min). Five male mice in the ketamine group died during the course of the studies and were replaced by 4 age–matched males. There were no losses in the isoflurane groups or the female ketamine group.

Conclusions: : Isoflurane is a safe and useful anesthetic alternative to ketamine for mouse ERGs. The advantages of isoflurane include a constant level anesthesia for as long as required and a rapid post–anesthetic recovery. In contrast, the level of anesthesia under ketamine is difficult to control and may differ with different mutant strains. Our data suggest that the results of ketamine and isoflurane ERGs in mice 12 to 20 weeks of age are comparable and that ERGs gathered under isoflurane can be directly compared to those in the literature gathered under ketamine anesthesia.

Keywords: electroretinography: non-clinical • electrophysiology: non-clinical • pharmacology