Neural and vascular ultrastructure of the area postrema in the rat

Abstract

Electron microscopy of the area postrema reveals two types of small blood vessels, a large sinusoidal variety and one of smaller diameter. Both are surrounded by perivascular connective tissue sheaths bounded on both inner and outer aspects by well developed basal laminae. In experimental argyria, dense granules are massively deposited in the basal laminae of the large sinusoidal vessels, and more delicately in the laminae of smaller capillaries. By analogy with the similar massive deposits of silver in renal glomeruli, this suggests an extensive transport of fluid from the sinusoids into the perivascular spaces. Neurons, their processes and endings are present in the perivascular spaces, indicating an endocrine function to this neural structure. Scanning electron microscopy coupled with x‐ray analysis reveals the dense granules in argyric animals to contain both silver and sulfur, thus suggesting that much if not all of the stored silver is in the form of its sulfide.