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Brain slices are well-established tools in neuroscience research. In the last decade scientists succeeded in isolating viable brain slices from many different regions of the mammalian central nervous system. The brain slice preparation was introduced by Henry MacIlwain in the 1950s.40 45 46 Milestones in the development of this technique are listed in Table 1. Brain slices can be viewed as intact local microcircuits, lacking synaptic inputs from other parts of the central nervous system. In using this type of preparation, drug actions on specific types of neurones have been investigated on the network, cellular, and molecular level. Studies on brain slices provided interesting insights into the mechanisms by which general anaesthetics affect cortical neurones. In the last decade, brain slices also proved to be helpful for analysing patterns of neuronal activity, observed during the anaesthetic state in experimental animals. There is increasing interest in uncovering the contribution of specific local microcircuits to the overall changes in neuronal activity evoked by general anaesthetics. Electroencephalographic (EEG) recordings have shown that anaesthetic agents dramatically alter the firing mode of cortical neurones, even when applied in a range of rather low concentrations.20 68 As well as compound-specific actions, almost each anaesthetic that has been investigated transfers high-frequency low-voltage EEG activity, present during the awake state and rapid eye movement (REM) sleep, into low-frequency high-voltage activity. The latter is commonly taken as evidence for the presence of a hypnotic, delta sleep-like state. However, interpretation of EEG recordings turned out to be rather difficult, as they provide a complex correlate of the summed synaptic activity of neurones located in the upper layers of the cerebral cortex.53 As yet, the physiological mechanisms that underlie EEG activity during anaesthesia remain largely unknown. Recent imaging studies on human subjects demonstrated that, besides altering synchronized activity, some general anaesthetics strongly depress cortical metabolism and blood flow.1 2 4 5 24 Again, the physiological processes underlying these phenomena remain to be elucidated. In this article, anaesthetic actions in brain slices are discussed. Experimental findings will be related to recent work on living animals and human subjects.
