CELLULAR-DISTRIBUTION OF ADENOSINE A(2A) RECEPTOR MESSENGER-RNA IN THE PRIMATE STRIATUM

The cellular expression of adenosine A(2A) receptor mRNA in the adult monkey and human striatum was examined by using single and double in s itu hybridization with ribonucleotide probes. Analysis on adjacent sec tions demonstrated a homogeneous overlapping expression of adenosine A (2A) receptor and preproenkephalin A mRNAs throughout nucleus caudatus , putamen, and nucleus accumbens. By contrast, high expression of prep roenkephalin A mRNA but no expression of adenosine A(2A) receptor mRNA was found in the nucleus basalis of Meynert. Double in situ hybridiza tion demonstrated an extensive colocalization of adenosine A(2A) recep tor and preproenkephalin A mRNAs in approximately 50% of the medium-si zed spiny neurons of the monkey nucleus caudatus, putamen, and nucleus accumbens. A small number of neurons (4-12%) that contained adenosine A(2A) receptor mRNA but not preproenkephalin A mRNA was found along t he ventral borders of the striatum. Virtually all adenosine A(2A) rece ptor mRNA-containing neurons co-expressed dopamine D-2 receptor mRNA, whereas only very few adenosine A(2A) receptor mRNA containing neurons co-expressed dopamine D-1 receptor or substance P mRNAs. In addition, a sub-population of adenosine A(2A) receptor mRNA-expressing neurons that also contained preproenkephalin A mRNA was found in the septum in monkeys. These results demonstrate that there is a high expression of adenosine A(2A) receptor mRNA in the primate striatum that is extensi vely co-localized with dopamine D-2 receptor and preproenkephalin A mR NAs. It is concluded that adenosine A(2A) receptors are likely to be i mportant for the parallel organization of primate striatal neurotransm ission and that these receptors could be a target for drug therapy in Parkinson's disease. J. Comp. Neurol. 399:229-240, 1998. (C) 1998 Wile y-Liss, Inc.