Influence of orofacial pain, in superficial and deep tissue, on the anxiety levels in rats

Abstract

Purpose: The present study aimed to determine the influence of orofacial pain in superficial and deep tissue on anxiety levels in male Wistar rats. Methods: Orofacial pain was induced by injecting 50 μL of 1% formalin in the lip (superficial tissue) and in the temporomandibular joint (TMJ) (deep tissue) of male Wistar rats. The anxiety level was measured by the elevated plus maze (EPM) test. The standard measures (number of entries into open and enclosed arms, and time spent in opened ones), were recorded. The three measures of plus-maze behavior calculated were the percentage of entries into the open arms (% EOA) (100 X open/total), the percentage of time spent in the open arms (% TSOA) (100 X open/total) and the number of entries into the closed arms (NECA). Data were analyzed with ANOVA and Tukey’s tests. Results: The formalin injection in the lip and in the TMJ region significantly increased the anxiety level as measured by the percentage of time spent inside and the number of entries in the open arms of the EPM test, but did not increase the general activity measured by the number of entrances in the closed and opened arms. Anxiety response was significantly reduced by Diazepam® administration (1 mg/kg) before the formalin injection to lip/TMJ. Conclusion: The results suggest that the orofacial nociceptive response induced by the injection of 1% formalin in the lip or TMJ region increases the anxiety level in rats and that Diazepam® can reduce it.