Regional distribution of cholecystokinin messenger RNA in rat brain during development: Quantitation and correlation with cholecystokinin immunoreactivity

The regional distribution of CCK-octapeptide (CCK) and CCKmRNA were studied in parallel in rat brain during development in order to characterize changes in gene expression in different structures at different periods of development and to determine whether differential regulation of translation and peptide turnover occurs, by correlating peptide and mRNA levels. CCK was characterized by Northern blot analysis. Methods were developed for quantitation of CCKmRNA by in situ hybridization (ISH) and compared with results obtained by slot blot analysis. Analysis of CCKmRNA by ISH showed that CCKmRNA was abundant in cerebral cortex, hippocampus, dentate gyrus, thalamus, inferior colliculus and periaqueductal grey in keeping with the high concentrations of CCK-like immunoreactivity in cell bodies located in these regions. Quantitation of CCKmRNA by computerized densitometric image analysis by referece to [35S]brain paste standards gave a similar pattern to that obtained by slot blot analysis of regional RNA extracts. Distinctive patterns of CCK development were seen. In cerebral cortex and hippocampus, a marked increase in peptide and mRNA levels was found from day 1 which showed a steady increase up to adult levels. However, in the thalamus, the highest levels of mRNA and peptide were reached at a much earlier stage, generally by 14d. In contrast, inferior and superior colliculus showed a delayed onset of peptide expression.