Detection of static and dynamic components of mechanical allodynia in rat models of neuropathic pain: are they signalled by distinct primary sensory neurones?

In the present study, chronic constrictive injury (CCI model) of the sciati c nerve or tight ligation of L5 and L6 spinal nerves (Chung model) produced both dynamic and static components of mechanical allodynia in rats. The tw o responses were detected, respectively, by lightly stroking the hind paw w ith cotton wool or application of pressure using von Prey hairs. Animals wi th spinal nerve ligation developed both types of responses at a faster rate compared to animals with the CCI. Morphine (1-3 mg/kg, s.c.) dose-dependen tly blocked static but not dynamic allodynia. In contrast, pregabalin (prev iously S-isobutylgaba and CI-1008) dose-dependently (3-30 mg/kg, p.o.) bloc ked both types of allodynia. In CCI animals, two administrations of capsaic in (100 mu g/50 mu l) into the plantar surface of the ipsilateral paw at 1- h intervals blocked the maintenance of thermal hyperalgesia without affecti ng either static or dynamic allodynia. The similar administration of a furt her two doses of capsaicin into the same animals blocked the maintenance of static allodynia without affecting the dynamic response. These data indica te that thermal hyperalgesia, static and dynamic allodynia are respectively signalled by C-, A delta- and A beta/capsaicin insensitive A delta-primary sensory neurones. It is suggested that pregabalin possesses a superior ant iallodynic profile than morphine and may represent a novel class of therape utic agents for the treatment of neuropathic pain. (C) 1999 International A ssociation for the Study of Pain. Published by Elsevier Science B.V.