NEUROPEPTIDE-Y EXPRESSION IN THE TRIGEMINAL GANGLION AND MANDIBULAR DIVISION OF THE TRIGEMINAL NERVE AFTER INFERIOR ALVEOLAR NERVE AXOTOMY IN YOUNG-RATS

Neuropeptide Y (NPY) is a 36-amino-acid peptide residing in sympatheti c nerve terminals, originating from the superior cervical ganglion in oral tissues. NPY exerts vasoconstrictor action together with noradren alin and has been found to inhibit the release of neurotransmitters fr om primary afferent fibers. During regeneration of the axotomized infe rior alveolar nerve (IAN), NPY-immunoreactive (IR) nerve fibers have b een shown in the odontoblast layer and dentin, an area normally innerv ated by afferent nerve fibers. The dynamic shift in neuropeptide expre ssion in the trigeminal ganglion and in the dental pulp was studied by immunohistochemistry 1, 2, 3, and 8 weeks after IAN axotomy. In the i psilateral first mandibular molar a temporal loss of pulpal sensory ne rves lasting for approximately 1 week was found after axotomy. An upre gulation of NPY was shown in neurons located in the mandibular area of the trigeminal ganglion, concomitant to a reduction in number of neur ons expressing substance P (SP). To study an alternate and possible tr igeminal origin of some of the peripheral nerve fibers IR to NPY in th e dental pulp, double immunofluorescence labeling was performed for NP Y and calcitonin gene-related peptide (CGRP). Coexistence of NPY and C GRP was shown in neurons located in the trigeminal ganglion and in ner ve fibers in the tooth pulp during IAN regeneration. Furthermore, retr ograde tracing with Fluorogold revealed NPY-IR neurons projecting to t he first molar pulp 3 weeks after axotomy. Hence, we conclude that aft er IAN axotomy NPY is produced in trigeminal ganglion neurons and tran sported in afferent regenerating fibers to the dental pulp. These resu lts add further evidence for a plasticity in peptide transcription in sensory neurons after nerve injury and indicate a trigeminal origin of at least some of the pulpal NPY-IR fibers during nerve regeneration. (C) 1996 Academic Press, Inc.