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D.–A.M. Pillers, J. Grose, B. Malmin, S. Hurst, J. Pang, R.G. Weleber, W.R. Woodward; Mouse ERG (Electroretinogram) Is Not Affected by Use of Isoflurane versus Ketamine Anesthetic . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3086.
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© ARVO (1962-2015); The Authors (2016-present)
The traditional agent of choice for the rodent ERG is ketamine, a dissociative anesthetic. In studying mutant mouse strains, we have found different levels of sensitivity to ketamine (including resistance to its anesthetic effects), and that some strains are susceptible to sudden death. In addition, the mechanism of action of the drug by blockade of NMDA receptors for the neurotransmitter glutamate makes ketamine an undesirable option when abnormalities in this pathway may be inherent in the strain being studied. We have shown previously (ARVO 2004) that isoflurane may be a useful alternative as an anesthetic agent for the mouse ERG. In this study, we sought to determine whether there are any significant differences in the ERG data obtained with isoflurane or ketamine cocktail.
Scotopic and photopic ERGs were performed on C57BL/6J mice anesthestized with either the standard dose of subcutaneous ketamine/xylazine cocktail, or with inhaled isoflurane 2%. Male (11) and female (8) mice were studied in discrete groups exposed to either ketamine or isoflurane. Mice were studied serially from ages 46 to 184 days. A Ganzfeld apparatus with a temperature support platform and a platinum wire electrode embedded in a contact lens was used. Studies included a range of light intensities (–3.04 to +0.80 cd–s/m2), with the rod–isolated response being determined with neutral density filter set at 2.8.
During the typical interval for study of mouse ERGs, 12 to 20 weeks of age, there were no appreciable differences in the scotopic or photopic b–wave amplitudes. There were no differences based upon sex, nor any appreciable decline in the amplitude during this interval. Studies are ongoing to look for effects at more advanced ages. Recovery from isoflurane was rapid (average of <2 vs 43 min for ketamine). Four male mice in the ketamine group expired during recovery, resulting in a loss of 1 in 3 of the ketamine–exposed animals. There were no losses in the isoflurane group.
Isoflurane is a safe and useful alternative to ketamine for the mouse ERG. Advantages include steady–dosage of isoflurane as opposed to the peak and trough effect with bolused ketamine dosing, enhanced survival of study subjects, and rapid recovery from anesthesia thereby simplifying animal handling needs. Our data suggest that the results of ketamine and isoflurane ERGs in the interval from 12 to 20 weeks of age may be compared directly, making observations in the current literature relevant to future studies using isoflurane.
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