TRIGEMINAL GANGLION NEURONAL-ACTIVITY AND GLIAL FIBRILLARY ACIDIC PROTEIN IMMUNOREACTIVITY AFTER INFERIOR ALVEOLAR NERVE CRUSH IN THE ADULT-RAT

Nerve injury to the mandibular division of the trigeminal nerve has be en shown to cause satellite cell reactions that extend beyond the mand ibular division of the trigeminal ganglion into the maxillary and opht halmic divisions. The goal of this study was to determine whether any physiological abnormalities correlated with this dispersal of satellit e cell reaction, We investigated the electrophysiological and satellit e cell glial fibrillary acidic protein immunoreactivity (GFAP-IR) chan ges that occur within the trigeminal ganglion 3, 10 and 59 days after a crush injury of the inferior alveolar nerve (IAN). At 3 days after I AN crush, there were no mechanically-evoked responses to ipsilateral s timulation of the skin and intraoral structures (e.g., mandibular inci sor, lower lip and rostral mandibular gingiva) innervated by the IAN. However, the peripheral representations of the auriculotemporal, myloh yoid, lingual and maxillary nerve were intact and no abnormal response s to mechanical stimulation were detected to stimulation of tissue inn ervated by these nerves. By 10 days after the IAN crush, mandibular ne urons responded to mechanical and electrical stimuli of the peripheral receptive field of the IAN, but with slower conduction velocities and higher electrical thresholds compared to control values. These abnorm al electrophysiological response characteristics persisted 59 days fol lowing nerve injury. At 3, 10 and 59 days after IAN crush, 3-4% of the recorded mandibular neurons displayed spontaneous activity that was n ever observed in rats without nerve injury. Spontaneous activity was a lso never observed in neurons recorded in the maxillary or ophthalmic divisions of the trigeminal ganglion. Intense GFAP-IR in satellite cel ls was observed surrounding a mean of 131.7 neurons/section within the mandibular division of the trigeminal ganglion 3 days after nerve inj ury and around 50.3 neurons/section at 10 days. GFAP-IR was also prese nt surrounding 16.5 and 10.3 neurons/section in the maxillary division of the trigeminal nerve at 3 and 10 days, respectively. At 59 days af ter IAN crush, GFAP-IR satellite cells were found around 22.9 neurons/ section in the mandibular division of the trigeminal nerve, but were n ot found elsewhere in the trigeminal ganglion. The more extensive dist ribution of neurons encircled by satellite cell GFAP-IR compared to th e trigeminal ganglion region containing abnormal electrophysiological responses demonstrates that abnormal neuronal signaling may not be cha racteristic of trigeminal ganglion neurons that are surrounded by GFAP injury reactions. However, the persistence of GFAP-LR 59 days after n erve injury suggests that satellite cell GFAP is involved in the long- term recovery of injured neurons. (C) 1997 International Association f or the Study of Pain. Published by Elsevier Science B.V.