Fig. 6. N -methyl-d-aspartate (NMDA) receptor component of solitary tract (ST) synaptic transmission of some capsaicin-resistant medial NTS neurons. In a representative neuron, ST activation evoked a synaptic current (I^NMDA) that ketamine potently inhibited. Slowly developing inward synaptic currents were observed in a subset of capsaicin-resistant neurons, and this component increased in zero-Mg external solutions (A ). The selective NMDA receptor antagonist AP5 (100 μm) reversibly blocked these slow currents (A ). The synaptic I^NMDAwas inhibited by 10–100 μm ketamine with only modest effects on the fast, non–NMDA-mediated components (B ). The fast component of evoked excitatory postsynaptic current (eEPSC) was blocked by NBQX (20 μm), and the slower component was blocked by AP5 (C ). NBQX in combination with AP5 blocked the entire synaptic current. All effects were reversible on washing. Responses displayed are to a train of five ST shocks, with only the initial EPSC (to the first shock of the train) displayed to the left and the last EPSC (to the fifth shock of the train) displayed to the right. Note that the responses to the fifth shock are plotted on a greatly amplified y-axis compared to the first shock responses. Each current trace represents the averaged current of 11 consecutive traces. All traces were recorded from the same cell.