Suppressive effects of Neiting acupuncture on toothache: an experimental analysis on Fos expression evoked by tooth pulp stimulation in the trigeminal subnucleus pars caudalis and the periaqueductal gray of rats

To clarify the antinociceptive mechanism of acupuncture on acute pain, c-fo s protein (Fos) expression induced by tooth pulp stimulation was immunohist ochemically examined in the spinal trigeminal subnucleus pars caudalis (spV c) and the periaqueductal gray (PAG) of rats with or without Neiting acupun cture. The central projection of trigeminal ganglion neurons innervating in the tooth pulp was examined by tract-tracing method with horseradish perox idase-conjugated wheat germ agglutinin (WGA-HRP). Central terminals from th e first maxillary molar tooth were labeled transganglionically in the dorso medial part of spVc with WGA-HRP. Numerous numbers of Fos-immunoreactive (F os-ir) cells were found in the spVc and PAG by stimulation of the tooth pul p with acetic acid or saline. Neiting acupuncture significantly reduced the Fos expression in the spVc induced by tooth pulp stimulation. On the other hand, Neiting acupuncture evoked many Fos-ir cells in the PAG. The present results suggest that Neiting acupuncture activated PAG neurons that sent d escending inhibitory fibers to medullo-spinal nociceptive neurons, and redu ced the number of Fos-expressed neurons in the trigeminal subnucleus pars c audalis mediating noxious information from teeth to the higher central nerv ous system. (C) 2000 Elsevier Science Ireland Ltd and the Japan Neuroscienc e Society. All rights reserved.