Trait anxiety affects the orofacial nociceptive response in rats

Abstract

The aims of the present study were to assess the influence of: a) trait anxiety on orofacial pain; and b) orofacial pain on state anxiety. Fortyfour rats were initially exposed to the free-exploratory paradigm for the evaluation of their anxiety profi les. In accordance to the parameter "Percentage of time in the novel side", the animals were considered as presenting high or low levels of trait anxiety when presenting values below the 1st quartile, or above the 3rd quartile, respectively. A week later, formalin-1.5% was injected into the upper lip of each animal. The behavioural nociceptive response, characterized by increased orofacial rubbing (OR), was quantifi ed for 30 minutes, as follows: Total time OR (0-30 minutes: total pain), 1st phase OR (0-6 minutes: neurogenic pain), and 2nd phase OR (12-30 minutes: inflamatory pain). Immediately after this test, but still under the effect of formalin, the rats were submitted to the Elevated Plus-maze test (EPM). The results showed that the high trait anxiety individuals presented higher frequency of OR than the low trait anxiety ones, except during the neurogenic pain period. However, no correlation was found between OR frequency and levels of state anxiety presented on the EPM. In conclusion, the animals presenting higher anxiety profi les were the most susceptible to orofacial pain, nevertheless, orofacial pain did not infl uence state anxiety.