Changes in nitric oxide synthase isoforms in the trigeminal ganglion of rat following chronic tooth pulp inflammation

Nitric oxide (NO) possibly plays an important role in the events resulting in hyperalgesia. NO synthase (NOS) is a key enzyme in the production of NO. Changes in NOS expression in primary sensory neurons may be involved in the persistent sensory abnormalities that can be induced by inflammation. To assess the possible roles of NOS in trigeminal sensory system, we studied changes in the expression of NOS isoforms in the trigeminal ganglion (TG) following chronic inflammation after pulp exposure (PX) in rats. The neurons innervating injured tooth in the TG were labeled by fluoro-gold (FG). Immunohistochemical staining was used to reveal the presence of NOS. The results showed that within the FG-labeled population, neuron counts revealed a significant increase in the proportion of NOS neurons following PX, in which the frequency of iNOS and nNOS-positive neurons started to increase at 3 and 7day, respectively, and peaked at 28day. There was no eNOS expression observed in the control group and PX-treated groups. The results demonstrate that PX-induced chronic pulpal inflammation results in significant increase of nNOS and iNOS in the TG. It suggests that nNOS and iNOS could be involved in mediation of peripheral processing of nociceptive information following chronic tooth pulp inflammation.