D 2 dopamine receptor gene expression in the rat striatum during ontogeny: an in situ hybridization study

Abstract

D 2 dopamine receptor (D 2R) 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. D 2R mRNA was detected with 35S-labelled oligonucleotide probes, one that hybridized equally to the two isoforms of the D 2R mRNA (D 2 415 and D 2 444) and the other that hybridized specifically to the large isoform (D 2 444). D 2R 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 D 2 444 mRNA. At day 16, D 2R mRNA was present in the lateral part of the striatum and in the germinal ventricular zone lining the lateral ventricle. At day 18, D 2R 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. D 2R 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 D 2R gene was expressed in two striatal cell types, small neurons probably enkephalinergic, and large-sized neurons with prominent cytoplasm, most probably cholinergic. D 2R mRNA appeared at the same time as the binding sites for iodosulpiride in the caudate-putamen and two days before the binding sites in the nucleus accumbens and olfactory tubercle. These results demonstrate D 2R gene expression in the rat striatal neurons during ontogeny with features similar or identical to the ones observed in the adult especially the presence of the D 2 444 mRNA isoform.