D2 dopamine receptor gene expression in the rat striatum during ontogeny: an in situ hybridization study.

D2 dopamine receptor (D2R) gene expression in the rat striatum was studied by in situ hybridization throughout the pre- and the postnatal period from gestational day 12 to postnatal day 8. D2R mRNA was detected with 35S-labelled oligonucleotide probes, one that hybridized equally to the two isoforms of the D2R mRNA (D2(415) and D2(444)) and the other that hybridized specifically to the large isoform (D2(444)). D2R mRNA was first detected in the striatal primordium at day 14 of gestation with the probe that recognizes indifferently the two isoforms and with the probe specific for the D2(444) mRNA. At day 16, D2R mRNA was present in the lateral part of the striatum and in the germinal ventricular zone lining the lateral ventricle. At day 18, D2R mRNA was found in neurons of the caudate-putamen, the nucleus accumbens, the olfactory tubercle and the subependymal zone lining the lateral ventricle. The microautoradiographic analysis demonstrated that the labelled cells have a neuroblastic and immature aspect before birth. After birth the topography and aspect of labelled cells was similar to the one observed in the adult animals. D2R mRNA was present in neurons of the caudate-putamen, the nucleus accumbens and the olfactory tubercle. In the caudate-putamen there was a latero-medial gradient of labelling. From postnatal day 2 onward the D2R gene was expressed in two striatal cell types, small neurons probably enkephalinergic, and large-sized neurons with prominent cytoplasm, most probably cholinergic.(ABSTRACT TRUNCATED AT 250 WORDS)