Changes In Expression Of Voltage-Gated Sodium Changes Na_v1.3,Na_v1.7,Na_v1.8,And Na_v1.9 In Rat Trigeminal Ganglia Following Chronic Constriction Injury

Objective Trigeminal neuralgia (TN) is a form of neuropathic pain. The major pathological changes for TN are axonal loss and demyelination in the trigeminal root. Voltage-gated sodium channels (VGSC), especially the TTX-sensitive Nav1.3 and Nav1.7, and the TTX-resistant Nav1.8 and Nav1.9, have been implicated in acute and chronic neuropathic pain. The aim of this study was to investigate expression of VGSC Nav1.3, Nav1.7, Nav1.8, and Nav1.9 after nerve injury and their roles in development of trigeminal neuralgia (TN). Our study also provides clues of targeted TN therapies.Methods We used the infraorbital nerve-chronic constriction injury (ION-CCI) model of TN in the rat, in which the rostral end of the ION was exposed at the point where it emerged from the infraorbital fissure, and 2 ligatures (4-0 chromic catgut) were tied loosely around the nerve (2 mm apart). Sprague-Dawley male rats (180-220 g) were randomly divided into two groups:ION-CCI group and sham-operated group.The time-course of changes in mechanical pain threshold was examined.Video detection of spontaneous behavior and the organizational change in electron microscopy were observed. In addition, real-time PCR and double immunofluorescence staining of VGSC a subunits were used to evaluate mRNA and protein expression, respectively, in the trigeminal ganglion (TG).Results 1.Behavioral tests showed that the mechanical pain threshold significantly decreased 4-42 days after surgery and reached the lowest observed value by day 12, which was statistically significant difference compared with that in the sham-operated group (P< 0.05). There is an increased frequency of scratching the face in6^2 days after surgery and the maximum value appeared at the same time by day 12, which was statistically significant difference compared with that in the sham-operated group (P< 0.05).2.Nerve demyelinations were observed in trigeminal ganglion in ION-CCI group, while there was no demyelination in sham-operated group.3.Compared with sham-operated controls, we found that TG in rats subjected to ION-CCI showed upregulation of Nav1.3 and downregulation of Nav1.7, Nav1.8, and Nav1.9mRNA levels.4. In the sham group,29/801 (3.62%) NeuN-positive neurons were Nav1.3-positive, 832/927 (89.75%) NeuN-positive neurons were Nav1.7-positive,766/877 (87.34%) NeuN-positive neurons were Nav 1.8-positive, and 551/712 (77.39%) NeuN-positive neurons were Nav1.9-positive. In the ION-CCI group,739/786 (94.02%) NeuN-positive neurons were Nav 1.3-positive,287/869 (33.03%) NeuN-positive neurons were Nav1.7-positive,529/874 (60.53%) NeuN-positive neurons were Nav1.8 positive, and 406/742 (54.72%) NeuN-positive neurons were Nav1.9-positive. Thus, the percentage of neurons expressing the Navl.3 significantly increased in the ION-CCI group compared with sham group (P<0.01). In contrast, the percentage of neurons expressing Navl.7, Navl.8, and Navl.9 subunit protein significantly decreased in the ION-CCI group compared with the sham group (P< 0.01, P< 0.01, and P< 0.05, respectively).Conclusions Our findings suggest that there is a series behavior and pathological changes close to the trigeminal neuralgia in ION-CCI rats. ION-CCI is a kind of relatively stable model of TN, which could used to study the subtypes dysfunction of VGSC and its molecular mechanism in TN. VGSC may participate in regulation of TN. The identification of specific sodium channel subunit isoforms raises the possibility of targeted TN therapies without central nervous system or cardiovascular side effects.