Adenosine receptor expression in murine fetal thymocytes. Adenosine receptor expression was analyzed by RT-PCR with RNA from day-15 fetal thymocytes (T). Brain tissue (B) was used as a positive control. RT-PCR was also performed with primers specific for β-actin. PCR products were visualized by EtBr staining after separation on a 2% agarose gel. The molecular-weight markers are a HaeIII digest of φX174 DNA.