Early expression of D3 dopamine receptors in murine embryonic development

In order to determine whether the D2 and D3 dopamine receptors may have a role in prenatal development, we have studied the mRNA expression and distribution of these receptors during murine embryonic development. Using RT-PCR on RNA from embryos taken at progressive stages of development, we have shown that the D3 receptor is expressed significantly earlier than the D2 receptor, being detectable at day 9.5 post-conception (p.c.) compared with day 13.5 p.c. for the D2 subtype. We have also examined the mRNA distribution of the two receptors by whole mount in situ hybridisation. In agreement with the PCR assays, the D3 receptor was expressed earlier than the D2 subtype. D3 receptor transcripts were first detected at day 9.5 p.c. in the ventral aspect of the anterior neural tube, whereas D2 receptor transcripts first appeared a day later. By day 10.5-11.5 p.c. both D3 and D2 receptor transcripts were present in the developing forebrain, and later also in the branchial arches and along the prospective vertebral column. The early appearance of the D3 subtype in murine development and its predominance over the D2 subtype suggest that the D3 receptor may have a functional role in prenatal development.