As shown, chromic gut suture remains along the infraorbital nerve through the entire experimental time course. There is a mild compression of the nerve caused by the placement of the 2 mm chromic gut suture material between the maxillary bone and the infraorbital nerve. No obvious nerve damage was noted with H&E staining. Compared to the histological appearance of normal nerve bundles, enlarged spaces were evident between axons at the site where the chromic gut suture was adhered, likely caused by the edema and accompanying inflammatory cell infiltration. Chemical nerve injury with other methods may likewise be good regimes as trigeminal pain models. For example, when CFA oxycel was applied to the surface of the infraorbital nerve facial grooming is induced indicative of on-going nociception caused by the edema at the affected nerve site [
14]. In another inflammatory model, injection of coral snake venom into the infraorbital nerve produced persistent ipsilateral mechanical allodynia for 60 days [
15]. Many models of inflammation that induce nerve injury have been applied to other nerves. Sciatic nerve immune cell accumulation at the site of CFA soaked gauze was shown by immunofluorescence of CD11b (OX42), a marker for activated macrophages. Thermal hyperalgesia and mechanical allodynia were both noted with rat hindpaw testing [
16]. Our histology results showed that there is nerve inflammation at the site of the chromic gut suture placement. Along with the edema in the axon bundle, CD68, another marker for macrophages or microglia was positively stained in the spaces among the axons on the serial infraorbital nerve sections. Maves et al. [
8] tested the contribution of the chemical toxicity produced by the chromic gut suture on sensory nerve dysfunction after placing different suture materials adjacent to the sciatic nerve. Immune-mediated response, axonal compression and injury induced by nerve ligation have also been confirmed by other researchers [
17,
18]. Constriction of sciatic nerve with chromic gut suture model has been widely used since 1988 [
3]. This nerve injury is reportedly due to both the constricted epineurial vasculature and the response to the chromic gut suture. In our previous study using chromic gut suture ligation of the infraorbital nerve in rats [
19], a statistically significant decrease in axonal numbers compared to controls was evident.