Fig. 6. Effect of the enhancers, forskolin (  A ) or 8-Br-cAMP (  B ), of the hyperpolarization-activated cation current (I^h) on the duration of sensory nerve block (pinprick withdrawal) of 1% lidocaine with or without clonidine. All injections were into the sciatic notch. I^henhancer preinjection (10 min) before lidocaine alone or with clonidine decreased the duration of sensory block (  P < 0.05). n = 9–10 rats per dose.