Anoxic depolarization of rat hippocampal slices is prevented by thiopental but not by propofol or isoflurane

Background. There is strong evidence to suggest that anoxic depolarization (AD) is an important factor in hypoxia/ischaemia-incluced neural damage. Treatments that prevent the occurrence of AD may be useful in providing neuronal protection against hypoxia. The current study was designed to determine whether general anaesthetics which have been suggested to 'induce prophylaxis' against hypoxia can attenuate the incidence of AD. Methods. The effects of anoxia (3 min) on evoked extracellularly recorded field potentials of CA1 neurons in rat hippocampal slices were assessed in the absence and presence of the i.v. general anaesthetics thiopental and propofol and the volatile anaesthetic isoflurane. Results. In the absence of anaesthetics, AD occurred in 81% of the preparations tested. Thiopental (2×10^-4 M) significantly reduced the incidence of AD (16%, P=0.0006). In comparison, propofol (2×10^-4 M) and isoflurane (1.5 vol%) were ineffective (69% and 60%, respectively). Furthermore, in the presence of thiopental, the population spike amplitude recovered with and without AD (90% and 94% of pre-anoxic value, respectively) following 3 min anoxia. Conclusion. The prophylactic effect of thiopental against hypoxia might be induced, in part, by preventing the generation of AD.