Axonal transport of VR1 capsaicin receptor mRNA in primary afferents and its participation in inflammation-induced increase in capsaicin sensitivity

Capsaicin receptors are expressed in primary sensory neurons and excited by heat and protons. We examined the inflammation-induced changes of the leve l of VR1 capsaicin receptor mRNA in sensory neurons and the sensitivity of primary afferents to capsaicin. Carrageenan treatment induced axonal transp ort of VR1 mRNA, but not that of preprotachykinin mRNA, from the dorsal roo t ganglia to central and peripheral axon terminals. The sensitivity of cent ral terminals to capsaicin, which was estimated by measuring the capsaicin- evoked release of glutamate from the dorsal horn, was increased by peripher al inflammation, and such an increase was suppressed by inhibiting the RNA translation in the dorsal horn with cycloheximide and an intrathecal inject ion of VR1 antisense oligonucleotides. Thus, peripheral inflammation induce s the axonal transport of VR1 mRNA, which may be involved in the hypersensi tivity of primary afferents to capsaicin and the production of inflammatory hyperalgesia.