DISTRIBUTION OF MUSCARINIC RECEPTORS ON THE ENDOTHELIUM OF CORTICAL VESSELS IN THE RAT-BRAIN

Functional and pharmacological studies have suggested that there are m uscarinic receptors (mAChRs) on the endothelial cells of major cerebra l arteries, while recent immunological studies indicate that there are no mAChRs on the endothelium of brain capillaries. This difference ma y be because the distribution of mAChR on the endothelium varies with the type of vessel. This paper examines the distribution of mAChR on t he vascular endothelium along intraparenchymal blood vessels in the ra t brain by immunolabelling and laser confocal microscopy. Sections wer e immunostained by combinations of an anti-mAChR antibody (M35) with a ntibodies to endothelial (anti-GLUT1), or to smooth muscle markers (an ti-actin). Antibody labellings were detected with fluorescent second a ntibodies. Most of the penetrating vessels bore mAChR immunolabelling which coincided over almost all the vessel surface with endothelial la belling. The mAChR immunolabelling was less widespread over the endoth elium on the medium sized vessels (diameter < 50 mu m) and only 50% of these vessels had mAChR staining on the endothelium. There was no mAC hR immunostaining on the endothelium of the capillaries. in contrast w ith the basilar artery, there was no mAChR immunolabelling on the smoo th muscle layer of the intracortical vessels. These data indicate that the intensity of mAChR immunolabelling decreases along the vascular t ree from large conducting vessels to capillaries. (C) 1997 Elsevier Sc ience B.V.