Behavioral evaluation of visceral pain in a rat model of colonic inflammation.

A new rat model was established up to evaluate the antinociceptive effect of compounds in visceral pain. The test consisted in measuring the performance of rats in an aversive light stimulus avoidance experimental device. Rats with TNBS-induced colitis had a lower number of total active lever pressings and did not discriminate the active lever from the inactive one. Morphine (1 mg/kg, s.c.) and CI-977 (0.001 mg/kg, s.c.) treatment restored the level of pressing activity of animals and their ability to discriminate the active lever from the inactive one. Naloxone treatment antagonized the improvement of performance produced by morphine. The results obtained indicate that this behavioral paradigm may be used to evaluate the antinociceptive potential of compounds.