Effects of halothane on the efflux of [3H]D-aspartate from rat brain slices

The in vitro effects of halothane on the potassium-stimulation-induced efflux of [3H]D-aspartate in rat cerebral cortex slices were studied. The slices were initially incubated with Krebs-Ringer's solution containing [3H]D-aspartate, a putative excitatory transmitter. The slices were then stimulated with high concentrations of K+ in the presence and absence of halothane, and the efflux was measured using a scintillation counter. Halothane, 1% and 2%, had little effect on the potassium-stimulation-induced efflux, but that of 4 and 8% increased the efflux significantly. The spontaneous efflux was unaffected by all concentrations of halothane studied. The control study of pentobarbital, in the concentration of 0.05 to 1.00 mmol/l, reduced the efflux in a dose-related manner. These findings indicate that the release of an excitatory transmitter, aspartate, may not be involved in the mechanism of halothane anaesthesia.