Fig. 4.
Representative monosynaptic and mutlisynaptic apical dendritic excitation in hippocampal CA1 after different concentrations (% volume) of isoflurane (ISO). (A) Average evoked potentials in CA1 was recorded after low- (40 μA) and high-intensity (120 μA) stimulation of str. radiatum in one rat (CM13), with responses after 0.5 and 1.5% isoflurane overlaid on baseline responses. High-intensity stimulation resulting in population spike (PS) near str. pyramidale (pyr) in column; the PS was inferred to propagate to str. oriens (dotted, slanted, vertical arrow). The population excitatory postsynaptic potential (pEPSP), measured by the slope E1, and PS were more strongly decreased by 1.5% than 0.5% isoflurane. (B) Depth profile of current source density (CSD, in units of mV/mm2; sink is negative) at the time of the dotted vertical line in part A, showing an apical dendritic excitatory sink, and its decrease with 0.5 and 1.5% isoflurane. (C) Average evoked potentials in CA1 after 120 μA paired-pulse (50-ms interval) stimulation of the medial perforant path (MPP), and trisynaptic (~10 to 15 ms latency) pEPSP, measured as slopes triE1 and triE2 after the first and second pulse, respectively. The trisynaptic response was suppressed by isoflurane in a dose-dependent manner.