Expression of neuropeptide Y receptors mRNA and protein in human brain vessels and cerebromicrovascular cells in culture

Neuropeptide Y (NPY) has been suggested as an important regulator of CBF. H owever, except for the presence of Y1 receptors in large cerebral arteries, little is known about its possible sites of action on brain vessels. In th is study, we sought to identify the NPY receptors present in the human cere brovascular bed. Specific Y1 receptor binding sites, localized on the smoot h muscle of human pial vessels and potently competed by NPY, polypeptide YY (PYY), and the selective Y1 receptor antagonist BIBP 3226, were identified by quantitative radioautography of the Y1 radioligand [I-125]-[Leu(31), Pr o(34)]-PYY. In contrast, no specific binding of the Y2-([I-125]-PYY3-36) an d Y4/Y5-(I-125-human pancreatic polypeptide [hPP]) radioligands could be de tected. By in situ hybridization, expression of Y1 receptor mRNA was restri cted to the smooth muscle layer of pial vessels, whereas no specific signal s were detected for either Y2, Y4, or Y5 receptors. Similarly, using revers e transcriptase-polymerase chain reaction (RT-PCR), mRNA for Y1 but not Y2, Y4, or Y5 receptors was consistently detected in isolated human pial vesse ls, intracortical microvessels, and capillaries. In human brain microvascul ar cells in culture, PCR products for the Y1 receptors were exclusively fou nd in the smooth muscle cells. In cultures of human brain astrocytes, a cel l type that associates intimately with brain microvessels, PCR products for Y1, Y2, and Y4 but not Y5 receptors were identified. Finally, NPY signific antly inhibited the forskolin-induced cAMP production in smooth muscle but not in endothelial cell cultures. We conclude that smooth muscle Y1 recepto rs are the primary if not exclusive NPY receptors associated with human bra in extraparenchymal and intraparenchymal blood vessels, where they most lik ely mediate cerebral vasoconstriction.