Studies of cholecystokinin messenger RNA in rat lingual epithelium

Cholecystokinin (CCK) is - a multifunctional peptide hormone that is widely distributedthroughout the body. Initially discovered as a gut hormone, CCK is important in integrating many digestive functions. In the nervous system cholecystokinin functions as a neurotransmitter or neuromodulator. It is also considered by many to be a naturally occurring satiety factor, important for the termination of a meal. Recently, our lab has identified the presence of CCK-like immunoreactivity in taste receptor cells of Sprague-Dawley rats. Preliminary in situ hybridization experiments appeared to demonstrate that the mRNA for cholecystokinin may also be expressed in the lingual epithelium and the taste cells of the circumvallate and foliate papillae of the rat tongue. To provide confirrnatory evidence for the presence of CCK in taste epithelium and to investigate its role in taste receptor cells, we further examined the expression of cholecystokinin mRNA in rat lingual epithelium using Northern blot analysis and RT-PCR. Northern analysis proved to be difficult using standard non-radiographic techniques and small oligonucleotide (35 bp) probes. Generating a 535 by radio-labeled probe with random primed labeling, Northern analysis demonstrated positive bands in control tissue (cerebral cortex and duodenum) but failed to demonstrate binding to lingual tissue. Since expression of CCK mRNA in taste cells could be below the level of detection of Northern analysis, the more sensitive technique of RT-PCR was employed. Similar results were obtained with RT-PCR PCR products were observed in cortical and duodenal tissues, but not in gustatory tissue. Therefore immunocytochemical and in situ hybridization results appear to be in conflict with those obtained with Northern and RT-PCR techniques. There remain many caveats in the collective interpretation of these results and further experimentation, particularly with probes designed to hybridize with differing regions of the CCK gene, will be required to more fully understand the putative presence and processing the CCK mRNA in taste receptor cells.Department of BiologyThesis (M.S.