INVOLVEMENT OF NITRIC-OXIDE IN RE-INNERVATION OF RAT MOLAR TOOTH-PULPFOLLOWING TRANSECTION OF THE INFERIOR ALVEOLAR NERVE

The aim of this study was to elucidate whether nitric oxide (NO) is in volved 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 hydra te. The animals received horseradish peroxidase (HRP) application to m andibular molar tooth pulps on both sides and were fixed by transvascu lar 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 appl ication on postoperative day 3, the ratio of the number of labeled neu rons in the transected vs. non-transected (contralateral) sides was 31 .5 +/- 5.8% (n = 11). The i.p. administration of N-omega-nitro-L-argin ine 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 la beled neurons on the transected side. Clonidine (25 mu g/kg, i.p., onc e a day for a period of 4 days) failed to exhibit any significant effe ct on nerve regeneration. In the trigeminal ganglion ipsilateral to th e transected IAN on postoperative day 4, NADPH-diaphorase (NADPH-d)-po sitive neurons had significantly increased. On the other hand, no chan ges in NADPH-d were observed in the superficial layers of the subnucle us caudalis of the spinal trigeminal nucleus from where primary neuron s innervating the mammalian tooth pulp project. These results suggest that NO is involved in several mechanisms related to neuronal regenera tion.