Fig. 4. Changes in the response of NMDA-gated currents to isoflurane in cultured cortical neurons with time in culture. (A ) Inhibition by isoflurane of steady state currents as a function of the concentration of isoflurane in neurons cultured 1–4 weeks. The n for each group is 5 for 1 week, 8 for 2 weeks, 9 for 3 weeks, and 6 for 4 weeks. (B ) Concentration-dependent inhibition of NMDA-gated peak currents by isoflurane. The n for each group is as the same as that in A . (C and D ) Currents activated by 100 μm NMDA alone (control) or 100 μm NMDA + the indicated concentrations of isoflurane (ISO) from two neurons cultured for 1 (C ) or 2 (D ) weeks. The arrows indicate the termination of NMDA or NMDA + isoflurane. Note the hooked tail currents on the termination of NMDA + isoflurane in D .