D1 and D2 dopamine receptor gene expression in the rat striatum: Sensitive cRNA probes demonstrate prominent segregation of D1 and D2 mRNAS in distinct neuronal populations of the dorsal and ventral striatum

TLDR

Dopamine’s postsynaptic actions in the striatum are mainly mediated by D1, D2, and D3 receptors, with D1 and D2 being the most abundant and traditionally thought to occupy distinct neuronal populations, though some studies report extensive colocalization. The study aimed to map D1 and D2 receptor gene expression across striatal efferent populations to resolve their cellular localization. Highly sensitive digoxigenin‑ and 35S‑labeled cRNA probes were employed to detect D1 and D2 mRNAs in rat striatal neurons. D1 and D2 mRNAs were segregated into substance P and enkephalin neurons in the caudate‑putamen, accumbens shell and core, and olfactory tubercle, with only a very small fraction of neurons coexpressing both genes, confirming distinct populations. © 1995 Wiley‑Liss, Inc.

Abstract

Abstract The postsynaptic effects of dopamine in the striatum are mediated mainly by receptors encoded by D1, D2, and D3 dopamine receptor genes. The D1 and D2 genes are the most widely expressed in the caudate‐putamen, the accumbens nucleus, and the olfactory tubercle. Several anatomical studies, including studies using in situ hybridization with oligonucleotide and cDNA probes, have suggested that D1 and D2 receptors are segregated into distinct efferent neuronal populations of the striatum: D1 in substance P striatonigral neurons and D2 in enkephalin striatopallidal neurons. In contrast, on the basis of several in vivo and in vitro studies, other authors have suggested the existence of an extensive colocalization of D1 and D2 in the same striatal neurons. Our study was undertaken in order to analyze in detail the expression of the D1 and D2 receptor genes in the efferent striatal populations, with special reference to the various striatal areas, and to yield insights into the question about D1 and D2 mRNA localization in the striatum. We have, therefore, used highly sensitive digoxigenin‐and 35 S‐labeled cRNA probes to address this question. The present results demonstrate that the D1 and D2 receptor mRNAs are segregated, respectively, in substance P and enkephalin neurons in the caudate‐putamen and accumbens nucleus (shell and core) and in the olfactory tubercle (for their largest part). A very small percentage of neurons may coexpress both genes. These results confirm that the D1 and D2 receptor genes are expressed in distinct populations of striatal efferent neurons in the normal adult rat. © 1995 Wiley‐Liss, Inc.