Fig. 4. Effects of external 500 μm Ba²⁺, 500 μm Cs⁺, and 50 μm baclofen on membrane currents in tonic-firing neurons (TFNs,  A ), adapting-firing neurons (AFNs,  B ), and delayed-firing neurons (DFNs,  C ). (  A1 ) Current–voltage (I-V) curves obtained from one TFN in control solution and after addition of 1 μm DAMGO and Ba²⁺. (  B1 and  C1 ) I-V curves for AFNs and DFNs, respectively, in control, Ba²⁺, and after wash. (  A2, B2 , and  C2 ) Cs⁺exerted a voltage-dependent block in all three groups of substantia gelatinosa neurons. (  A3, B3 , and  C3 ) Reversible increase in membrane currents by baclofen.