Co-expression of cholecystokinin mRNA and tyrosine hydroxylase mRNA in populations of rat substantia nigra cells; a study using a combined radioactive and non-radioactive in situ hybridization procedure.

Improvements in the sensitivity of non-radioactive in situ hybridization histochemistry methods for detection of mRNA now make it feasible to combine the use of non-radioactive and radioactive in situ methods to visualize two mRNAs on the same tissue section. The method reported here allows the simultaneous detection of two mRNAs in one cell and therefore is ideally suited to the studies of co-expression. Here we demonstrate the co-expression of tyrosine hydroxylase (TH) mRNA and cholecystokinin (CCK) mRNA in the ventral mesencephalic dopaminergic neurones of the rat. The distribution of dopaminergic neurones containing both TH and CCK transcripts suggests, on the basis of earlier anatomical studies that these CCK/TH-containing doubled-labelled cells project mainly to the striatal matrix. Dopamine neurones believed to project to the patch compartment did not contain CCK mRNA.