Investigation into the effect of the general anaesthetic etomidate on local neuronal synchrony in the mouse neocortical slice.

How general anaesthetic drugs cause unconsciousness is a topic of ongoing clinical and scientific interest. It is becoming increasingly apparent that they disrupt cortical information processing, but the effects appear to depend on the spatial scale under investigation. In this study we investigated whether the intravenous anaesthetic etomidate synchronises neuronal activity on a sub-millimetre scale in mouse neocortical slices. In slices generating no-magnesium seizure-like event (SLE) field activity, we analysed the morphology of field potential activity recorded with 50µm extracellular electrodes. The analysis was based on the understanding that the amplitude and sheerness of field potential oscillations correlates with the synchrony of the underlying neural activity. When recorded from the region of the slice initiating SLE activity, etomidate consistently increased both population event amplitude (median(range) 85(24-350) to 101(30-427) µV) and slope 16.6(1.5-106.2) to 20.2(1.7-111.1) µV/ms (p=0.016 and p=0.0013, respectively). The results are consistent with an increase in neuronal synchrony within the receptive field of the recording electrode, estimated to be a circle diameter of 300µm. In conclusion, the neocortical slice preparation supports in vivo data showing that general anaesthetics increase neuronal synchrony on a local scale and provides an ideal model for investigating underlying mechanisms.