The effect of combined dexmedetomidine and isoflurane anaesthesia on visually evoked responses in rats -- an electrophysiological study

Abstract

The purpose of this study was to pilot an anaesthetic regime with the potential to be used for blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI) of the visual system. We used electrophysiology to explore the effect of an anaesthesia regime, combining dexmedetomidine and isoflurane, on the visual system of female Sprague-Dawley rats. This paradigm is hypothesised to affect neural signalling less than other paradigms, and thus may be suitable for studies using BOLD fMRI. Electrodes were implanted bilaterally in the visual cortex (VC) and superior colliculus (SC) of 16 rats. Visual evoked potentials (VEPs) and steady-state VEPs (SSVEPs) were recorded during 1 Hz and 14 Hz light stimulation, respectively. As a control experiment an exploration of the wash-out of isoflurane was performed. The combined anaesthetic regime showed, that the visually evoked responses were almost completely abolished at the initiation of anaesthesia, but gradually recovered to baseline levels over time in the SC. In contrast, the evoked response in the VC only partially recovered, staying significantly below baseline condition. BOLD fMRI results from a previously published study supports this finding.