Fig. 6. Effect of norepinephrine (50 μm) on Aδ-fiber and C-fiber excitatory postsynaptic currents (EPSCs) evoked in substantia gelatinosa neurons in the presence of an α²adrenoceptor antagonist, yohimbine (1 μm). (A  and B ) Aδ-fiber and C-fiber EPSCs, respectively, in the control (left ) and in the presence of norepinephrine together with yohimbine (right ; where control EPSC is superimposed for comparison). Note that norepinephrine had no effects on both EPSCs in the presence of yohimbine. Each of the records is an average of 12 traces of EPSCs; V^H=−70 mV.