Transient increases and individual variations in preprocholecystokinin gene expression in rat telencephalic regions during postnatal development: a quantitative comparison between preprocholecystokinin mRNA and preproenkephalin mRNA.

Postnatal development of the tissue levels of mRNAs encoding preprocholecystokinin and preproenkephalin in rat telencephalic regions was analyzed by quantitative dot blot hybridization using synthetic RNAs as standards. Preprocholecystokinin mRNA levels per tissue weight showed distinct peaks in the frontal cortex and hippocampus on postnatal days 10 and 20, respectively, while preproenkephalin mRNA levels in these regions showed no apparent peaks. In the striatum, preproenkephalin mRNA abundance linearly increased 8-fold from day 5-43, while a transient increase in the preprocholecystokinin mRNA abundance between days 10 and 20 was noted. Furthermore, the striatal levels of preprocholecystokinin mRNA showed marked individual variations during the early period of postnatal development. These results suggest transient and variable increases in cell density and/or in gene expression of cholecystokinin-synthesizing cells in the developing telencephalon.