The two isoforms of dopamine D2 receptor, D2 short (D2s) and D2 long, are generated by alternative splicing of premessenger RNA and differ in the length of their third cytoplasmic loop. Expression of these two isoforms has not yet been studied at the level of the peripheral arterial chemoreflex pathway. Using reverse transcriptase-polymerase chain reaction, we evaluated the relative abundance of dopamine D2 receptor mRNA by amplifying a common segment between both D2 receptor mRNA isoforms which reflects the total D2-receptor mRNA and the two isoforms in the carotid bodies, the petrosal ganglia, and the superior cervical ganglia of 1-, 10-, and 25-day-old and adult rabbits, GH4C1 cell line, which does not express D2 receptors, was used as negative control, whereas GH4C1 19 cell line, which expresses only the D2s mRNA and the striatum of each age, were used as positive controls. Both D2-receptor mRNA isoforms were found to be expressed in all organs studied of newborn and adult rabbits. The expression of total D2 receptor mRNA in 10- and 25-day-old and adult rabbits was found to be 3-, 5-, and 1.5-fold more, respectively, compared with 1-day-old rabbits for all organs studied. Our data suggest that the expression of D2-receptor mRNA is modulated with age at the level of the peripheral arterial chemoreflex pathway.