Neural Mechanisms Underlying Trigeminal Neuropathic Pain Following Inferior Alveolar Nerve Transection

More than half of the inferior alveolar nerve(IAN) fibers were regenerated 14 days after IAN transection. The escape threshold following mechanical stimulation of the mental skin innervated by the transected IAN was significantly reduced but that of heat nocifensive behavior was not reduced at this time period, indicating that mechano-allodynia occurred but not heat hyperalgesia after IAN regeneration. Neuronal excitability of the myelinated primary afferent and trigeminal spinal subnucleus caudalis(Vc) neurons were significantly enhanced 14 days after IAN transection. However, heat evoked responses of primary afferent and Vc nociceptive neurons were not enhanced after IAN regeneration. These findings suggested that changes in excitability of the primary afferent and Vc nociceptive neurons were involved in mechano-allodynia but not in heat hyperalgesia in the cutaneous region innervated by the regenerated IAN.