Submitted on July 14, 2007
Accepted on March 3, 2008
Modulation of trigeminal spinal subnucleus caudalis neuronal activity following regeneration of transected inferior alveolar nerve in rats
Kimiko Saito1, Suzuro Hitomi1, Ikuko Suzuki1, Yuji Masuda2, Junichi Kitagawa3, Yoshiyuki Tsuboi4, Masahiro Kondo5, Barry J Sessle6, and Koichi Iwata7*
1 Department of Physiology, Nihon University, School of Dentistry, Tokyo, Japan
2 Division of Oral and Maxillofacial Biology, Matsumoto Dental University, Institute for Oral Science, Nagano, Japan
3 Department of Physiology, School of Dentistry at Tokyo, Nippon Dental University, Tokyo, Japan
4 Department of Physiology, Nihon University, School of Dentistry, Tokyo, Japan; Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan
5 Department of Physiology, Nihon University, School of Dentistry, 1-8-13 Kandasurugadai, Chiyoda-ku, Tokyo, 101-8310, Japan; Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan
6 Faculty of Dentistry, University of Toronto, Tronto, Canada
7 Department of Physiology, Nihon University, School of Dentistry, 1-8-13 Kandasurugadai, Chiyoda-ku, Tokyo, 101-8310, Japan; Division of Applied System Neuroscience Advanced Medical Research Center, Nihon University Graduate School of Medical Science, Tokyo, Japan; Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: iwata-k{at}dent.nihon-u.ac.jp.
In order to clarify the neuronal mechanisms of abnormal pain in the face innervated by the regenerated inferior alveolar nerve (IAN), nocifensive behavior, trigeminal ganglion neuronal labeling following Fluorogold (FG) injection into the mental skin, and trigeminal spinal subnucleus caudalis (Vc) neuronal properties were examined in rats with IAN transection.
The mechanical escape threshold was significantly higher at 3 days and lower at 14 days after IAN transection, whereas head withdrawal latency to heat was significantly longer at 3, 14 and 60 days after IAN transection. The number of FG-labeled ganglion neurons was significantly reduced at 3 days after IAN transection but increased at 14 and 60 days. The number of WDR neurons with background (BG) activity was significantly higher at 14 and 60 days after IAN transection compared to naive rats, and the number of WDR and LTM neurons with irregularly bursting BG activity was increased at these 2 time points. Mechanical-evoked responses were significantly larger in WDR and LTM neurons 14 days after IAN transection compared to naïve rats. Heat and cold-evoked responses in WDR neurons were significantly lower at 14 days after transection compared to naïve rats. Mechanoreceptive fields were also significantly larger in WDR and LTM neurons at 14 and 60 days after IAN transection.
These findings suggest that these alterations may be involved in the development of mechanical allodynia in the cutaneous region innervated by the regenerated IAN.
