Activation of spinal orexin-1 receptor produces anti-allodynic effect in the rat carrageenan test.

Orexin-A and orexin-1 receptors are found in the dorsal root ganglion cells and the spinal dorsal horn and this suggests that orexin-A is involved in the spinal nociceptive transmission. The authors examined the effect of intrathecally administered orexin-A on the level of mechanical allodynia and thermal hyperalgesia induced by paw carrageenan injection in the rat. Intrathecal injection of 0.3 and 3 nmol of orexin-A suppressed the level of mechanical allodynia, but not that of thermal hyperalgesia, and the effect of orexin-A on mechanical allodynia was antagonized by the pretreatment of 1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl urea hydrochloride, SB-334867, a selective orexin-1 receptor antagonist. These data suggest that the activation of spinal orexin-1 receptor modulates the mechanical information transmission, but not thermal information transmission, in the spinal cord during carrageenan test.