COEXPRESSION OF VASOACTIVE INTESTINAL POLYPEPTIDE AND SUBSTANCE-P IN REINNERVATING PULPAL NERVES AND IN TRIGEMINAL GANGLION NEURONS AFTER AXOTOMY OF THE INFERIOR ALVEOLAR NERVE IN THE RAT

The effect of this axotomy on the expression of vasoactive intestinal polypeptide (VIP) in trigeminal ganglion neurones and nerve fibres in the first molar was examined immunohistochemically 3 weeks postsurgica lly in rats. A distinct upregulation of VIP-like immunoreactivity was found in 3 to 4% of the neurones (mean die., 20.9 +/- 0.45 mu m; mean cross-sectional area, 367 +/- 13.2 mu m(2)) in the mandibular region a fter axotomy. An almost complete coexpression was registered in neuron es upregulated for VIP and growth-associated protein 43. Coexpression of VIP and substance P (SP) was found in a small number of the immunor eactive (IR) small-sized neurones, mainly in those in which VIP and SP were both weakly immunoreactive. In the uninjured ganglion, weakly la belled VIP-positive granules were frequently traced at high magnificat ion in the cytoplasm of small neurones. No VIP-IR fibres were found in the control molar pulp, except for a few in the root pulp near the ap ex. However, 3 weeks after axotomy, a number of VIP-containing nerve f ibres were found in the molar pulp and apical periodontium. Coarse VIP -IR fibres directed towards the odontoblast layer were a common findin g. In some of these fibres VIP was shown to colocalize with SP. These results indicate that VIP is clearly expressed and transported in rege nerating primary afferent neurones after axotomy of the inferior alveo lar nerve. (C) 1998 Elsevier Science Ltd. All rights reserved.