Figure 1. Amplitude of the postsynaptic population spike (P.S.) in untreated and thiopental-treated slices. The evoked responses were recorded from CA1 pyramidal cells after stimulation of the Schaffer collaterals and quantified by measuring the amplitude of the first postsynaptic population spike. The amplitude of the population spike is expressed as a percentage of its initial value (designated as 100%). Control group: The slices were maintained normoxic and not subject to any treatment. The population spike remained stable for 6 h after the start of superfusion. Thiopental group: Thiopental (600 micro Meter) was present in the perfusing solution for 35 min and then washed out. The amplitude of the population spike was significantly reduced after 35 min of thiopental exposure and returned to its normal level 50 min after the washout of thiopental.