Differential Changes in Dopamine D2- and D1-Receptor mRNA Levels Induced by Hypoxia in the Arterial Chemoreflex Pathway Organs in One-Day-Old and Adult Rabbits

This study determined: (1) whether dopamine (DA) D2-receptor (R) and D1-R mRNA levels in the carotid body (CB), petrosal ganglion (PG) and superior cervical ganglion (SCG) are modulated by hypoxia; (2) the role of hypoxia intensity and exposure duration, and (3) whether the pattern of modulation differs between newborn (1-day-old) and adult rabbits. Rabbits were exposed to five FiO2 conditions: 21% (control); 15%/6 h; 15%/24 h; 8%/6 h and 8%/24 h. D2- and D1-R mRNA expression levels were calculated for each hypoxia condition relative to control using RT-PCR analysis. In the CB of 1-day-old rabbits, D2- and D1-R transcript levels increased and decreased after exposure to 15 and 8% O2, respectively. In the adult CB, D2- and D1-R transcript levels decreased independently of hypoxia intensities. Only changes in D1-R mRNA levels were dependent on exposure time. In the PG, both hypoxia intensities decreased the D2-R transcript levels in 1-day-old and adult rabbits; but for the D1-R mRNA levels, hypoxia decreased its level in 1-day-old rabbits and increased it in adults regardless of exposure duration. In the SCG, hypoxia had no determinant effect on the D2-R mRNA levels either in newborn or adult rabbits while it induced a decrease of D1-R transcript levels in 1-day-old rabbits and an increase in adult rabbits. It is concluded that hypoxia affects DA D2- or D1-R mRNA levels in the chemoreflex pathway in an age-dependent and site-specific manner.