Figure 4-4 The effects of halothane (left) and isoflurane (right) on three excitatory synaptic pathways in the rat hippocampal slice. The potential recordings were produced from stimulation of three discrete regions of the hippocampal slice: the stratum radiatum (RAD), the stratum oriens (OR), and the perforant path (PP) fibers. Each superimposed series of records shows control (C) responses before (solid line) and after washout (dotted line) together with two or three concentrations of anesthetic (numbers refer to volume percent). The horizontal calibration bar represents 20 msec, and the vertical calibration bar represents 2.0 mV. These studies demonstrate that the ability of inhaled agents to depress or enhance neuronal excitability depends on the anesthetic, the anesthetic concentration, and the particular brain region examined. (From Maclver MB, Roth SH: Inhalation anaesthetics exhibit pathway-specific and differential actions on hippocampal synaptic responses in vitro. Br J Anaesth 60:680, 1988.)