Fig. 1. Two classes of medial NTS neurons were identified based on blockade of afferent synaptic transmission by capsaicin (CAP). Solitary tract (ST) shocks (filled circles) reliably, and at nearly invariant latency, activated evoked excitatory postsynaptic currents (eEPSCs). Each panel shows five consecutive, unaveraged eEPSC traces for responses to trains of five ST stimuli (100 Hz) in these two representative neurons (A  and B ). The horizontal broken line represents the mean level of the holding current before capsaicin treatment at a V^Hof −70 mV. (A ) In capsaicin-sensitive neurons, ST eEPSCs were blocked following 5 min in 200 nm capsaicin. After capsaicin (A, right ) these neurons showed increased spontaneous EPSCs not aligned with ST stimuli. (B ) In capsaicin-resistant neurons, eEPSC responses were unaltered after 5 min of capsaicin (200 nm) treatment.