In vitro networks: subcortical mechanisms of anaesthetic action.

There were few presentations at the recent International Conference on Basic and Molecular Mechanisms of Anaesthesia (MAC2001) concerning subcortical anaesthetic actions studied in vitro. In addition to the spinal cord studies from the author's laboratory presented in detail here and the review of the associated literature, there was one other presentation on the spinal cord slice, which will be covered in the appropriate section below (C. Grasshoff and B. Antkowiak, Effect of volatile anaesthetics on action potential ®ring of spinal neurones in organotypic slice cultures). In a study of the effects of general anaesthetics on thalamic slices (E. Puil, Thalamic effects of general anesthetics: similar and dissimilar actions of iso ̄urane and barbiturates), Puil found that iso ̄urane in the medial geniculate body shunts tonic ®ring of both sodium and calcium channelmediated bursts by increasing leak conductance. Similar actions were observed for high concentrations of pentobarbital, but low concentrations enhanced excitation and bursting. Pentobarbital actions were not blocked by bicuculline. These results are relevant to the role of the thalamus in mediating arousal to auditory stimuli and its blockade by anaesthetics. In a study on cerebellar slices (M. Debus, K. Unertl and B. Antkowiak, The potency of general anesthetics to suppress spontaneous neuronal activity in cerebellar acute slices compared to neocortical slice cultures), the authors found that a variety of inhalation agents, ethanol and propofol suppressed mean ®ring rates more potently in neocortical slices than in cerebellar slices by approximately 5-fold, and the potency ratios among the agents were similar for the two preparations. The results are relevant to the actions of anesthetics on locomotion and balance.