PRECAPILLARY PATTERNS AND PERIVASCULAR CELLS IN THE RETINAL MICROVASCULATURE - A SCANNING ELECTRON-MICROSCOPE STUDY

The microvasculature of the rat retina was studied in male Wistar rats in order to examine the features of the precapillary vascular pattern and structure that could affect blood flow regulation. Vascular corro sion casts and partially digested tissue specimens were observed by sc anning electron microscopy. Side branching rather than bifurcation was the predominant microvascular pattern in the arterial tree. Two types of precapillary arteriole were present, one with the characteristic p attern of a preferential channel; the other gave off capillaries as te rminal branches. At the origin of arteriolar side branches, smooth mus cle cells appeared to buckle the endothelial nuclei into the vascular lumen. It is concluded that the rat retinal microvasculature appears t o be characterised by 2 distinctive features: (1) side branching of ar terioles which allows preferential flow in the most superficial layers of the retina; (2) peculiar luminal restrictions of arterioles and ca pillaries which permit fine regulation of blood flow.