Mice that are homozygous for both of the targeted mutations are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. The donating investigator reports that the double mutants have a combined phenotype.
No CCKBR receptor function was detected in competition binding assay of brain (cerebral plasma) membranes. When compared to wildtype, gastric pH in homozygotes is higher, pH 5.2, after overnight fast. Histological analysis reveals diminished parietal cell, enterochromaffin-like cell and antral comatostatin-producing D cell densities. An increase in the number of gastrin-producing G cells is observed. There is an increased number of H+, K+ -ATPase immunoreactive negative cells and abnormal distribution of parietal cells in oxyntic glands. Circulating gastrin levels are 10-fold higher in homozygotes.
No CCKAR receptor function was detected in competition binding assay of pancreatic membranes. Homozygotes do not exhibit decreased food intake due to peritoneal injection of cholecystokinin. Baseline food and water intake and body weight is normal in mutant mice. These mutant mice have larger gallbladder volumes and are more likely to develop spontaneous gallstones than wildtype controls. Gastric function is impaired due to diminished intestinal lipid feedback response. Small-intestine transit time is increased in mutant mice. When fed a lithogenic diet, mutant mice have an increase in biliary cholesterol secretion rates, when compared to the wildtype. Although the total number of olfactory-gonadotropin-releasing hormone-1 neuroendocrine (GnRH-1)neurons is the same in embryonic day 14.5 aged mutant and wildtype mice, more GnRH-1 neurons are found in the forebrain of the mutant than in the wildtype. This mutant mouse strain may be useful in studies of the neuroendocrine and gastrointestinal systems, lipid metabolism, gastric differentiation, hypochlorhydria and hypergastinemia.
