VEGF mRNA expressed in microvessels of neonatal and adult rat cerebral cortex

We measured mRNA levels of vascular endothelial growth factor (VEGF) and its Flk-1/KDR receptor in isolated cerebral cortical microvessels and in the cerebral cortex of neonatal (1 week) and adult (11 week) rats using reverse transcription-polymerase chain reaction (RT-PCR). Cerebral microvessels were isolated by density centrifugation, mesh filtration and passage through glass bead columns. The dominant cell types in this preparation are endothelial cells and pericytes. Among the four isoforms of VEGF mRNA expressed in these tissues, VEGF(165) was dominant (67% higher than VEGF(189) or VEGF(206)). All isoforms of VEGF were higher in adult cortical microvessels than in cortical homogenates. In isolated microvessels, VEGF mRNA for all isoforms combined was 70% higher in the neonate than in the adult. VEGF receptor Flk-1/KDR mRNA was also present in cortical microvessels and was higher in neonatal than in adult microvessels. The results suggest that VEGF is normally expressed in cerebral microvessels of both neonates and adults. Whether the source of VEGF is the endothelial cell or pericyte, will determine if VEGF has autocrine or paracrine actions. The results also support the hypothesis that microvascular cell turnover continues in the adult brain.