The effects of anaesthesia on cortical stimulation in rats: a functional MRI study

The purpose of this study was to investigate the affects of equithesin and isoflurane on cortical activation in the rat using fMRI. Eight healthy male Sprauge-Dawley rats were anaesthetised separately with isoflurane and equithesin following a week in between. Functional EPI images were acquired in axial and sagittal orientations on a Bruker 47/30 Biospec system. Each experiment included repetitive air puffs over the right face region and was divided into 4 OFF (no stimulation) and 3 ON (repeated air puffs) periods. Changes in the BOLD-fMRI signal response were analysed using a box-car response function (SPM99) correlated against each voxel to determine regions of activation (p Corrected <0.0001, Z score>3.54). Neural activation was not detected when equithesin was used except in one rat compared to consistent activation with isoflurane in all 16 functional EPI scans. Equithesin appears to have effectively reduced brain activity in response to sensory stimuli. Isoflurane anaesthesia (1.6%) showed consistent, robust neural activations. It is therefore recommended that equithesin should be further investigated with other functional modalities or behavioural tests prior to consider it as an anaesthetic agent for future functional MRI studies.