Comparison of the effects of four anaesthetic agents on somatosensory evoked potentials in the rat

Electrophysiological techniques provide an objective and non-invasive measure of neurological function. In order to undertake detailed evoked potential studies in rats on repeated occasions, it is necessary to find an appropriate anaesthetic agent which has minimal and reproducible effects on the parameters to be studied and also has a minimal effect on the general welfare of the animals. In this study we compared the effects of four common anaesthetic agents (ketamine-xylazine, medetomidine, isoflurane and fentanyl/fluanisone-midazolam) on somatosensory evoked potentials (SEPs) in rats following electrical stimulation of the fore- and hind-paw. Fentanyl/fluanisone-midazolam was found to be well tolerated by the animals and to have, in general, the least deleterious effect on SEPs. For example, the response recorded at the level of the somatosensory cortex (P1), following forelimb stimulation, appeared on average 1.80 ms earlier with fentanyl/fluanisone-midazolam than with the other agents and the peak-to-peak amplitude (CI to CII) of the response recorded at the cervical (C3) level was on average 5.86 microV greater with fentanyl/fluanisone-midazolam. Fentanyl/fluanisone-midazolam is, therefore, recommended as the anaesthetic of choice for longitudinal studies of SEPs in the rat.