A comparison of the antinociceptive effects of voltage-activated Na+ channel blockers in two rat models of neuropathic pain

The pain-relieving effects of various voltage-activated Na+ channel blockers have been evaluated in two rat models of neuropathic pain; the photochemically induced nerve injury model (Gazelius) and spared nerve injury model. Lidocaine (up to 40 mg/kg, i.p.) and lamotrigine (up to 60 mg/kg, i.p.) had no effect on mechanical or cold allodynia in either model. However, lamotrigine (10, 30 and 60 mg/kg) significantly attenuated mechanical hyperalgesia in the spared nerve injury model, while mexiletine (25 and 37.5 mg/kg, i.p.) attenuated mechanical allodynia in the Gazelius model. Tocainide (50, 75 and 100 mg/kg, i.p.) significantly reduced all types of pain behaviour measured. The present results show that these voltage-activated Na+ channel blockers have broadly similar aminociceptive effects in these two models of neuropathic pain. They also show that these drugs can have markedly different effects on distinct neuropathic pain-related behaviours within models. (C) 2002 Elsevier Science B.V. All rights reserved.