Research

Alteration of primary afferent activity following inferior alveolar nerve transection in rats

Kazuharu Nakagawa¹ , Mamoru Takeda² , Yoshiyuki Tsuboi^3,4 , Masahiro Kondo^3,4 , Junichi Kitagawa⁵ , Shigeji Matsumoto² , Azusa Kobayashi⁶ , Barry J Sessle⁷ , Masamichi Shinoda^3,4 and Koichi Iwata^3,4,8

¹  Department of Dysphagia Rehabilitation, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan

²  Department of Physiology, School of Dentistry at Tokyo, Nippon Dental University, 1-9-20 Fujimi-cho, Chiyoda-ku, Tokyo, 102-8159, Japan

³  Department of Physiology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan

⁴  Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan

⁵  Division of Oral Physiology, Department of Oral Biological Science, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Chuo-ku, Niigata, 951-8514, Japan

⁶  Department of Oral diagnosis, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan

⁷  Department of Oral Physiology, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario, M5G 1G6, Canada

⁸  Division of Applied System Neuroscience Advanced Medical Research Center, Nihon University Graduate School of Medical Science, 30-1 Ohyaguchi-Kamimachi, Itabashi-ku, Tokyo, 173-8610, Japan

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Molecular Pain 2010, 6:9doi:10.1186/1744-8069-6-9

Published:	3 February 2010

Abstract

Background

In order to evaluate the neural mechanisms underlying the abnormal facial pain that may develop following regeneration of the injured inferior alveolar nerve (IAN), the properties of the IAN innervated in the mental region were analyzed.

Results

Fluorogold (FG) injection into the mental region 14 days after IAN transection showed massive labeling of trigeminal ganglion (TG). The escape threshold to mechanical stimulation of the mental skin was significantly lower (i.e. mechanical allodynia) at 11-14 days after IAN transection than before surgery. The background activity, mechanically evoked responses and afterdischarges of IAN Aδ-fibers were significantly higher in IAN-transected rats than naive. The small/medium diameter TG neurons showed an increase in both tetrodotoxin (TTX)-resistant (TTX-R) and -sensitive (TTX-S) sodium currents (I_Na) and decrease in total potassium current, transient current (I_A) and sustained current (I_K) in IAN-transected rats. The amplitude, overshoot amplitude and number of action potentials evoked by the depolarizing pulses after 1 μM TTX administration in TG neurons were significantly higher, whereas the threshold current to elicit spikes was smaller in IAN-transected rats than naive. Resting membrane potential was significantly smaller in IAN-transected rats than that of naive.

Conclusions

These data suggest that the increase in both TTX-S I_Na and TTX-R I_Na and the decrease in I_A and I_k in small/medium TG neurons in IAN-transected rats are involved in the activation of spike generation, resulting in hyperexcitability of Aδ-IAN fibers innervating the mental region after IAN transection.