A model for evaluation of gastric sensitivity in awake rats

We developed a model for the evaluation of gastric sensitivity to distension in awake rats. A balloon made from a latex condom was chronically placed in the stomach and three stainless steel electrodes were implanted in the neck muscles. Isobaric distensions were performed with a barostat by step of 5 mmHg with 10 min inflation and 2 min deflation. Gastric pressure, integrated neck electromyogram (EMG) and gastric volume were continuously monitored on a potentiometric recorder. Gastric distension at 15 or 20 mmHg induced a typical posture associated with contractions of the neck muscles. Pain threshold was defined as the pressure inducing an increase of integrated neck EMG greater than 100%. The mean pain threshold was 18.5 +/- 0.7 mmHg and was not modified 2, 4 and 7 days after the first experiment. However, gastric volumes were significantly higher on the 4th and the 7th days. Morphine at the doses of 0.4 and 4 mg kg-1 i.p. significantly increases the pain threshold. At the doses of 0.04 and 0.4 mg kg-1, morphine significantly increased gastric volume for the distending pressure of 10 mmHg. Naloxone (2.5 mg kg-1 i.p.) reversed the effects of morphine. In conclusion, our model permits simultaneous evaluation of pain threshold and gastric compliance associated with gastric distension in conscious rats.