Visceral hyperalgesia in transgenic mice induced by visceral stimulation of acetic acid or magnesium sulfate. A-B. The onset (A) and the total number of writhes (B) during a period of 15 minutes were determined after i.p. injection of 0.3%, 0.6%, 1% acetic acid (n = 7-10). 0.6% acetic acid resulted in a shorted onset and increased number of writhes in transgenic (Tg) mice. C. Induction of visceral pain induced by magnesium sulfate (12 mg/k g, i.p.). Tg mice displayed an increase of writhes in response to magnesium sulfate during a period of 10 minutes (mean ± s.e.m., n = 10, *p < 0.05, **p < 0.01, ***p < 0.001).