The localization of cholecystokinin mRNA in embryonic striatal tissue grafts: further evidence for the presence of non-striatal cells.

We have studied by in situ hybridization histochemistry the mRNA expression of preprocholecystokinin (CCK) in grafts of foetal striatal tissue neurones implanted into the ibotenic acid lesioned adult rat neostriatum. Animals were studied at 30 and 90 days after implantation. Using a 35S-labelled 'antisense' oligonucleotide (45-mer) probe complementary to the rat CCK cDNA we observed a dense hybridization signal for CCK mRNA in the striatal eminence in developing embryos and in all the striatal grafts examined; no CCK mRNA expressing cells were found in the normal neonatal or adult rat neostriatum. However, CCK mRNA was heavily expressed in other areas of the host brain including the somatosensory cortex, the claustrum, primary olfactory cortex and endopiriform cortex. The germinal cell layer of the striatal eminence is the source of origin for these non-striatal cell groups as well as for cells destined to form the neostriatum. The present results suggest that CCK mRNA expression provides an unambiguous marker for many of the non-striatal cells in 'striatal' grafts.