Involvement of nitric oxide in re-innervation of rat molar tooth pulp following transection of the inferior alveolar nerve

Abstract

The aim of this study was to elucidate whether nitric oxide (NO) is involved in re-innervation of rat molar tooth pulp following transection of the inferior alveolar nerve. The inferior alveolar nerves (IAN) of rats were transected unilaterally under anesthesia with chloral hydrate. The animals received horseradish peroxidase (HRP) application to mandibular molar tooth pulps on both sides and were fixed by transvascular perfusion. The average number of labeled cells on each side of the trigeminal ganglion was not significantly different [101±11 (mean±S.E.M.; n=6, left) and 89±11 ( n=6, right)]. With HRP application on postoperative day 3, the ratio of the number of labeled neurons in the transected vs. non-transected (contralateral) sides was 31.5±5.8% ( n=11). The i.p. administration of N ω -nitro- l-arginine methyl ester ( l-NAME; 100 mg/kg, once a day for a period of 4 days), but not d-NAME, significantly decreased the ratio of the number of labeled neurons (10.1±7.0%, n=10). l-Arginine (300 mg/kg, i.p., once a day for a period of 4 days) slightly increased the number of labeled neurons on the transected side. Clonidine (25 μg/kg, i.p., once a day for a period of 4 days) failed to exhibit any significant effect on nerve regeneration. In the trigeminal ganglion ipsilateral to the transected IAN on postoperative day 4, NADPH-diaphorase (NADPH-d)-positive neurons had significantly increased. On the other hand, no changes in NADPH-d were observed in the superficial layers of the subnucleus caudalis of the spinal trigeminal nucleus from where primary neurons innervating the mammalian tooth pulp project. These results suggest that NO is involved in several mechanisms related to neuronal regeneration.