D2 dopamine receptor gene expression by cholinergic neurons in the rat striatum.

In situ hybridization with D2 receptor probe and immunohistochemistry with choline acetyltransferase (ChAT) antibody performed on adjacent sections demonstrate dopamine D2 receptor gene expression in cholinergic neurons of the rat caudate-putamen and nucleus accumbens. Eighty per cent of cholinergic neurons in the striatum contain detectable D2 receptor mRNA. The other neurons without detectable D2 mRNA do not display specific localization or aspect in the caudate-putamen and nucleus accumbens as compared to the other cholinergic neurons. The absence of detectable D2 mRNA in certain cholinergic neurons can be due to the limited sensitivity of the procedure that would not detect low mRNA levels, or alternatively can reflect the existence of two cholinergic cell populations in the striatum, one of which would not express the D2 receptor gene. The other forebrain cholinergic neurons do not contain D2 mRNA.