Figure 7.
Total gastrointestinal transit time and colonic motility are accelerated in mice that lack D2 receptors. A, Mean gastrointestinal transit time was measured by using spores of B. stearothermophilus. Transit time in mice lacking D2, D3, or D2 and D3 (double knock-out) was compared with that of wild-type littermates. Relative to wild-type littermates, transit time was reduced (faster) in D2 knock-out and double knock-out animals; however, transit time in D3 knock-out mice did not differ from that of their wild-type littermates. Transit time in double knock-out animals was not different from that in mice lacking only D2. B, Colonic motility was estimated by measuring the time require to expel a glass bead inserted into the rectum for a distance of 2 cm. Relative to wild-type littermates, this time was significantly decreased (faster motility) in mice lacking only D2 or D2 plus D3 but was not different in mice lacking only D3. The time required to expel the bead in double knock-out mice was not different from that in mice lacking only D2. *p < 0.05; †, p is not significant. KO, Knock-out; WT, wild type. The error bars indicate SEM.