A, U-69593 (U69, 300 nm) produced a nor-BNI (300 nm)-sensitive outward current and met-enkephalin (ME, 10 μm) produced no currents in a primary neuron. B, met-enkephalin but not U-69593 produced an outward current in a secondary neuron. Nociceptin (Nocic, 300 nm) produced an outward current in both primary (A) and secondary (B) neurons. Nocistatin (Nstat, 1 μm) and prepronociceptin154-181 (ppOFQ, 300 nm) produced no currents in the secondary neuron (B). Nalx, naloxone (1 μm).