Neuritis can cause
pain hypersensitivities in the absence of axonal degeneration. Such
hypersensitivities are reputed to be maintained by ongoing activity into the spinal cord, which, in the
neuritis model, is mainly generated from intact C-fiber neurons. The hyperpolarization-activated
cyclic nucleotide-gated (HCN) family of
ion channels has been implicated in nerve injury-induced
pain hypersensitivities. The present study has examined the role of these channels in the development of heat and mechanical
hypersensitivities in the
neuritis model. The systemic administration of the HCN-specific blocker
ZD7288 produced a reversal of heat but not mechanical
hypersensitivity within one hour post-administration. Recordings from C-fiber neurons were performed to determine whether
ZD7288 acts by inhibiting ongoing activity.
ZD7288 (0.5mM) caused a 44.1% decrease in the ongoing activity rate following its application to the
neuritis site. Immunohistochemical examination of the
HCN2 channel subtype within the L5 dorsal root ganglia revealed an increase in expression in neuronal cell bodies of all sizes post-
neuritis. In conclusion, HCN channels contribute to the development of
neuritis-induced heat
hypersensitivity and ongoing activity. Drugs that target HCN channels may be beneficial in the treatment of
neuropathic pain in patients with nerve
inflammation.