Isoflurane prevents transitions to tonic and burst firing modes in thalamic neurons

We used patch-clamp whole-cell techniques to assess the effects of a volatile anaesthetic on thalamic firing modes in rat brain slices. Isoflurane application in clinical concentrations (0.5-2%) reversibly prevented voltage-dependent transitions to repetitive spike and burst firing modes in ventrobasal neurons. In voltage-clamp studies, isoflurane increased leak conductance, which shunted tonic and burst firing. Isoflurane also blocked the low-threshold Ca(2+)-current underlying the burst mode of firing, by increasing leak current and depressing membrane Ca(2+)-channel activity. We suggest that the mechanism of anaesthesia is distinct from sleep, although both states critically involve excitabilities of thalamic neurons.