Influence of anesthesia and electrode type on dual-eye mouse electroretinogram

Abstract

Purpose : A combination of ketamine and xylazine has been used as the choice of anesthetic to record electroretinogram (ERG) in rodents, however, an increase in the sudden death of animals has been reported in recent years. Replacing xylazine with medetomidine, an α2 agonist reports higher survival rates and isoflurane has also been shown to be a suitable alternative, with a much lower mortality rate. In this study, we aimed to assess the suitability of ketamine/medetomidine and isoflurane on mouse ERG. Furthermore, we aimed to determine the best electrode type to minimize crosstalk while recording from both eyes simultaneously. A new conductive material “Staticot^TM” (polyester/cotton blended with 8 μm stainless steel fibers) was trialed as an ERG electrode and compared to highly conductive platinum electrodes.

Methods : ERGs were recorded from mice anaesthetised with either ketamine (72 mg/kg)/ medetomidine (0.5 mg/kg) or 1.75% isoflurane. Both males and females were used with ages ranging between 12-18 weeks. Electrodes (platinum, staticot^TM) were embedded in contact lenses and placed on both eyes simultaneously. Dark- and light-adapted ERG responses to a range of light stimuli were recorded.

Results : No differences were observed in either a-wave amplitude or implicit time but ketamine/medetomidine injected animals displayed a reduction in b-wave amplitude and a large increase in b-wave implicit time in comparison with the isoflurane cohort in dark and light-adapted ERGs. Overall, isoflurane ERG parameters were more similar to published values for the ketamine/xylazine than ketamine/medetomidine suggesting that medetomidine significantly suppresses second/third order processing. Recovery from ketamine/medetomidine was longer, even following α2 antagonist reversal (atipamezole 1 mg/kg), and the mortality rate was 37.5% (n=8). The isoflurane cohort showed rapid recovery and no mortality (n=9). Recordings conducted using platinum electrodes showed some cross-communication between the electrodes in the dual-eye ERG, while no such crosstalk was observed with staticot electrodes.

Conclusions : Isoflurane is a viable alternative to the traditional ketamine/xylazine combination and displays rapid recovery and enhanced survival of animals. Staticot conductive fiber is a suitable and cost-effective replacement of traditional electrodes for dual-eye ERG recordings.

This is a 2021 ARVO Annual Meeting abstract.