Abstract
Peripheral nerve injury produces increments of the primary afferent activity with an abnormal pattern at the early period after injury, and a reorganization of the large diameter nerve fiber terminals that occurs at later period, which is manifested as allodynia. This primary afferent discharge and reorganization of large diameter nerve fiber terminals in the central nervous system following peripheral nerve injury may occur in a wide area of the spinal cord, beyond the area innervated by the injured nerve. We established a trigeminal nerve injury model and analyzed the neuronal activity in order to clarify the response properties of nociceptive neurons in the trigeminal spinal nucleus caudalis (Vc) of rats with inferior alveolar nerve (IAN) transaction or infraorbital nerve (ION) ligation. The escape threshold from mechanical stimulation applied to the whisker pad area ipsilateral to the transection or ION ligation were significantly lower than that for the contralateral and sham-operated whisker pad. Background activity and mechanically evoked responses of WDR neurons on the ipsilateral side relative to the injured nerve were significantly increased after the operation. We did not observe any modulation of the thermal responses of WDR and NS neurons following IAN transection or ION ligation. The present findings suggest that the increment of neuronal activity of WDR neurons in the Vc following IAN transection or ION ligation may play an important role in the development of the mechano-allodynia in the trigeminal region. [J Physiol Sci. 2007;57 Suppl:S37]
