Fig. 4. Summary concentration–response relations for ketamine effects on evoked excitatory postsynaptic current (eEPSC) amplitude and failure rate for capsaicin (CAP)-sensitive (n = 11, circles) and capsaicin-resistant (n = 11, squares) medial NTS neurons. (A ) Ketamine decreased the amplitude of eEPSCs in capsaicin-sensitive cells at significantly lower concentrations than capsaicin-resistant cells. An IC50value was estimated from a curve fit of to each set of measured data values using sigmoidal logistic relations (capsaicin-sensitive IC50= 386 μm, broken lines; capsaicin-resistant IC50= 1,111 μm, solid lines). Relations are displayed as solid lines for capsaicin resistant (χ2= 2.09 × 10−3) and broken lines for capsaicin sensitive (χ2= 4.62 × 10−33). (B ) Ketamine increased the synaptic failure rates of eEPSCs. Ketamine blocked eEPSCs at lower concentrations in capsaicin-sensitive cells than in capsaicin-resistant cells. An IC50value was estimated as capsaicin-sensitive IC50= 329 μm and capsaicin-resistant IC50= 1,280 μm. Relations are displayed as solid lines for capsaicin resistant (χ2= 0.693) and broken lines for capsaicin sensitive (χ2= 17.8). Points and bars are mean ± SD. *Significant differences between capsaicin sensitive and capsaicin resistant at single ketamine concentrations.