Expression of rat striatal D1 and D2 dopamine receptor mRNAs: ontogenetic and pharmacological studies

The developmental characteristics of D1 and D2 dopamine receptor mRNA levels were determined by Northern blot analyses. Striatal D1 and D2 receptor mRNAs of male Fischer 344 rats were about 60% of adults levels at postnatal day 1 and reached their highest measured levels at day 30 (126-139% adults levels) and then decreased by day 120 (100%). D1 and D2 receptor densities at day 30 were about 8-fold higher than at day 1, while mRNA levels showed only a 2-fold increase. The highest level of D2 receptor mRNA in midbrain as reached at day 14 (195% adult level) while levels at day 1 were 31% higher than dose at day 120. Treatment with selective D2 receptor antagonist, haloperidol (0.5 mg/kg/day, s.c., for 2 h, 7, 14, 21 days or 21 days + 3 days withdrawal) had no effect on Sprague-Dawley rat striatal D2 receptor mRNA levels in spite of significant increases in receptor density at the later time points. However, the selective D1 receptor antagonist, SCH 23390 (0.5 mg/kg/day, s.c.) produced increases in striatal D1 receptors and mRNA levels after treatments of 7, 14 and 21 days + 3 days withdrawal.