Dopamine D3 receptor is selectively and transiently expressed in the developing whisker barrel cortex of the rat

The rodent primary somatosensory cortex (SI) contains a map of the body surface, the most conspicuous part of which are "barrels," neuronal aggregates in layer IV that receive somatotopic projections from whiskers on the rodent's snout. We report that the D-3 dopamine receptor (D3R) is selectively and transiently expressed in SI during the first 2 weeks of postnatal development. D3R binding sites and mRNA overlap completely and are limited to layer IV of SI. D3R/mRNA are organized in a pattern corresponding to somatotopic representations of the body (e.g., whiskers, jaws, paws, etc.) with the highest expression in the barrel field. D-3 mRNA is first detected at postnatal day (P)4, increases rapidly until P7-10, and sharply decreases after P14. D3R binding sites are detectable at P6, peak at P14, and decline afterwards. D-1, D-2, D-4, or D-5 mRNAs display dissimilar expression pattern. D-1 mRNA is mostly confined to infragranular layers throughout the cortex. D-4 mRNA expression in layer TV rises by 4 weeks postnatal, when D3R expression is virtually undetectable. Quantitative analysis of D-3 mRNA expression demonstrates that the proportion of D-3 mRNA-positive cells decreases between P7 and P14, whereas mRNA concentration per cell remains stable. Moreover, D3R number continues to rise, whereas mRNA levels begin to decline. Thus, a process limiting D3R expression to fewer cells may occur that also induces changes in post-transcriptional regulation of D3R expression in remaining cells. These findings indicate that dopamine acting via D3R may play an important role in the development or function of the SI. J. Comp. Neurol. 420:35-51, 2000. (C) 2000 Wiley-Liss, Inc.