Objective: We aimed to investigate the role of K_v7 potassium channels in the morphine-induced antinociception in both acute and neuropathic pain models.

Methods: Neuropathic pain was induced by partial ligation of the right sciatic nerve. For intracerebroventricular (i.c.v.) injections, each rat was equipped with a permanent cannula. The response to painful thermal stimuli was assessed by the tail-flick test. In sciatic nerve-ligated rats, thermal hyperalgesia was assessed by paw withdrawal latencies in the plantar test and the mechanical hyperalgesia was determined by rigid von Frey filaments.

Results: Rats received morphine (2, 5, 20 µg/10 µl; i.c.v.) or saline (10 µl; i.c.v.) 15 min before the tests. In all tests, morphine produced significant antinociceptive effect. When a K_v7 potassium channel blocker, linopirdine (0.1, 1, 10 µg/10 µl; i.c.v.) was administered 15 min before morphine, the effect of i.c.v. morphine in the tail-flick test and plantar test but not in the test with von Frey filaments were prevented.

Conclusions: K_v7 potassium channels contribute to the effect of i.c.v. morphine on acute pain induced by thermal stimulation. In the sciatic nerve-ligated rats, these channels play role in the effect of morphine on thermal hyperalgesia, but not on mechanical hyperalgesia.