THE EFFECT OF ISOFLURANE ON EXCITATORY SYNAPTIC TRANSMISSION IN THE RAT HIPPOCAMPUS

The purpose of this investigation was to study the effect of isoflurane on excitatory synaptic transmission. Rat hippocampal slices maintained in vitro were used as a model. Isoflurane caused a dose-dependent reduction of the excitatory postsynaptic potential (EPSP); 1.5% isoflurane reduced the EPSP by 35 +/- 9% (mean +/- s.d.) and 3% by 57 +/- 11%. Neither spontaneous nor potassium-stimulated efflux of the glutamate analogue D-(H-3)aspartate was changed, but the content of D-(H-3)aspartate in slices loaded during isoflurane was reduced to 83 +/- 12% of control (P < 0.05). The intracellularly recorded response to direct application of glutamate increased by 37 +/- 20% during isoflurane (3%) and 50 +/- 5% during halothane (2%). Isoflurane (3%) enhanced the response to the glutamate receptor agonist quisqualate by 44 +/- 19%, whereas the N-methyl-D-asparate response was unchanged. Isoflurane enhanced the tetanic depression of the population spike. The present results suggest that isoflurane reduces excitatory synaptic transmission by a presynaptic mechanism.