The intrathecal injection of fenvalerate, a sodium channel activator, at do
ses of 0.01 to 3 mug, dose-dependently induced the duration of a characteri
stic behavioral syndrome mainly consisting of reciprocal hind limb scratchi
ng directed towards caudal parts of the body and biting or licking of the E
nd legs in mice. Fenvalerate-induced behavior was inhibited by morphine (1
- 10 mg/kg, i.p.). The characteristic behavior was also inhibited by mexile
tine, a sodium channel blocker; MK-801, a N-methyl-D-aspartate ion-channel
blocker; and GR82334, a neurokinin-1-receptor antagonist. Calphostin C (3 p
mol, i.t.), a protein kinase C inhibitor, inhibited fenvalerate-induced beh
avior. On the other hand, phorbol-12, 13-dibutyrate (50 pmol,i.t.), a prote
in kinase C activator, markedly enhanced the fenvalerate-induced behavior.
The present results also showed that fenvalerate produced thermal allodynia
and hyperalgesia in the tail-flick test. Furthermore, fenvalerate-induced
thermal allodynia and hyperalgesia were inhibited by the pretreatment with
calphostin C. These results suggest that the intrathecal administration of
fenvalerate induces a marked nociceptive response and thermal allodynia/hyp
eralgesia, and they suggest that tetrodotoxin-resistant sodium channels may
play an important role in this effect.