Differential expression of A(2a), A(1)-adenosine and D-2-dopamine receptorgenes in rat peripheral arterial chemoreceptors during postnatal development

The sensitivity of peripheral arterial chemoreceptors in the carotid body t o hypoxia increases with postnatal maturation. Carotid sinus nerve activity is augmented by adenosine binding to A(2a)-adenosine receptors and attenua ted by dopamine binding to D-2-dopamine receptors. In this study, we used i n situ hybridization histochemistry to determine the change in the levels o f mRNA expression for A(2a) and A(1)-adenosine receptors and D-2-dopamine r eceptors in the rat carotid body. We also investigated the cellular distrib ution and possible colocalization of these receptor mRNAs and tyrosine hydr oxylase (TH) mRNAs during the first 2 weeks of postnatal development. By us ing immunohistocytochemistry, we detected A(2a)-adenosine receptor protein in the carotid body and petrosal ganglion. We found that A(2a)-adenosine re ceptor mRNA and protein are expressed in the carotid body in animals at 0, 3, 6 and 14 postnatal days. The level of A(2a)-adenosine receptor mRNA expr ession significantly decreased by 14, postnatal days (P<0.02 vs. day 0) whi le D-2-dopamine receptor mRNA levels significantly increased by day 3 and r emained greater than D-2-dopamine receptor mRNA levels at day 0 (P<0.001 al l ages vs. day 0). TH mRNA was colocalized in cells in the carotid body wit h A(2a) adenosine receptor and D-2-dopamine receptor mRNAs, A(1)-adenosine receptor mRNA was not expressed in the carotid body at any of the ages exam ined. In the petrosal ganglion, A(1)-adenosine receptor mRNA was abundantly expressed in numerous cells, A(2a)-adenosine receptor mRNA was expressed i n a moderate number of cells while D-2-dopamine receptor mRNA was seen in a few cells in the rostral petrosal ganglion. In conclusion, using in situ h ybridization histochemistry, we have shown that mRNA for both the excitator y, A(2a)-adenosine receptor, and the inhibitory, D-2-dopamine receptor, is developmentally regulated in presumably type I cells in the carotid body wh ich may contribute to the maturation of hypoxic chemosensitivity. Furthermo re, the presence A(1)-adenosine receptor mRNAs in cell bodies of the petros al ganglion suggests that adenosine might also have an inhibitory role in h ypoxic chemotransmission. (C) 2000 Elsevier Science B.V. All rights reserve d.