Cellular mechanisms of gamma rhythms in rat neocortical brain slices probed by the volatile anaesthetic isoflurane.

In hippocampus slice preparations, the frequency of gamma oscillations (30-80 Hz) is inversely related to the decay time of GABA(A)-mediated inhibitory postsynaptic currents (IPSCs), suggesting a causal relationship [Jefferys, J.R.G., Traub, R.D. and Whittington, M.A., Neuronal networks for induced '40 Hz' rhythms, Trends Neurosci., 19 (1996) 202-207]. We determined the effects of the commonly used volatile anaesthetic isoflurane on IPSCs monitored from neocortical and cerebellar neurons, as well as on gamma oscillations detected in the field potential of neocortical brain slices. At 0.16 mM, the anaesthetic lengthened IPSC-decays by a factor of 1.7 and decreased the frequency of gamma oscillations by 41%. Quantitatively equivalent effects of isoflurane on gamma rhythms were discovered during encephalographic recordings from human patients [Munglani, R., Andrade, J., Sapsford, D.J., Baddeley, A. and Jones, J.G., Br. J. Anaesth., 71 (1993) 633-641].