Fig. 5. Effect of a blocker (ZD 7288) 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^hblocker preinjection (60 min) before lidocaine increased the duration of sensory block (  P < 0.05) by an amount similar to that of adding clonidine. Preinjection of the I^hblocker before lidocaine/clonidine did not produce any additional increase in block duration. n = 9–10 rats per dose.