THE EFFECTS OF SEVOFLURANE ON POPULATION SPIKES IN CA1 AND DENTATE GYRUS OF THE RAT HIPPOCAMPUS IN-VITRO

We studied the effects of sevoflurane on population spikes (PSs) in tw o synaptic pathways in rat hippocampal slices. Stimulating electrodes were placed on Schaffer collateral fibers or perforant path to activat e inputs to CA1 pyramidal neurons or dentate gyrus (DG) neurons, respe ctively. Extracellular glass microelectrodes were used to record PSs. The paired-pulse stimulus was used to induce the paired-pulse facilita tion (PPF). Sevoflurane (0.4-5.0 vol%) significantly decreased the amp litudes of PSs of CA1 and DG in a dose-dependent and reversible manner (25% effective dose values were 4.1 and 0.9 vol%, respectively). The stimulus-response relationships for PS amplitudes revealed that sevofl urane increased the threshold for PS generation in CA1 and DG. Sevoflu rane (2.0 vol%) significantly enhanced PPF from 127%; and 263% to 153% : and 494% in CA1 and DG, respectively. The results imply that the eff ects of sevoflurane on PSs are greater in DG than in CA1 neurons, that sevoflurane enhances the PPF in both CA1 and DG, and that the actions of sevoflurane are not similar to those of other volatile or intraven ous anesthetics previously reported in hippocampal preparations, Impli cations: The volatile anesthetic sevoflurane alters neural excitabilit y of individual pathways in the hippocampus in a manner different From other general anesthetics, The results are consistent with a site-spe cific mechanism of action for general anesthesia.