Fig. 5. Tolerance of NMDA-gated currents to repeated application of isoflurane in cultured cortical neurons. (A ) Representative current traces are shown from a cultured cortical neuron with a 3-min interval between ISO1 and ISO2. Note less inhibition during application of ISO2. (B ) Normalized ratios of steady state currents induced by ISO1 to those induced by ISO2. The ratios were normalized by the ratios of steady state currents gated by two presentations of NMDA alone (N1 and N2) at the same intervals of ISO1 and ISO2. The n is 6 for an interval of 15 s; 9 for a 30-s interval, 8 for a 45-s interval, and 4 for a 3-min interval. **P < 0.01.