Morphology of cerebral arteries

A comparison of the major cerebral arteries between humans and rats shows many similarities, including anomalies in their general organization, the structure of these vessels at the light and electron microscope levels and their morphological changes associated with cerebral vascular diseases. The general organization of the major cerebral arteries shows the following main differences between humans and rats. In rats, the internal carotid arteries have become an integral part of the circle of Willis. In the anterior cerebral arteries, a common variation in humans is the underdevelopment of one of the two arteries, whereas in rats, buttonhole-like structures are common in one or both arteries. The anterior communicating artery present in humans is absent in rats. The olfactory artery is prominent in rats, but absent in humans. The posterior communicating artery in humans is the most variable component of the circle of Willis, being asymmetric in its origin, diameters and branches. Similarly, the posterior cerebral arteries in rats often exhibit asymmetrical origin from the basilar artery. There was some confusion in the literature regarding the name of the posterior cerebral arteries in rats, but this was caused mainly by misquotations and incorrect interpretations of the papers. In humans, most aneurysms occur in the anterior half of the circle of Willis, and the incidence is higher in females than males; the middle cerebral artery is most often the one to become occluded, and the vertebral arteries are common sites for thrombosis. The various channels that constitute collateral circulation in humans provide a margin of safety, so that in case of cerebral occlusion due to thrombosis, atherosclerosis, or vasospasm related to hemorrhage, blood supply to the affected area can be maintained through these collaterals. Collateral circulation is also present in rats. However, in rats, information on the presence of various types of aneurysms, their location and frequency in normal and experimental models of hypertension and stroke is still lacking. Cerebral arteries from humans and rats are characterized by the absence of external elastic lamina, as compared with systemic arteries. A type of multipolar cell resembling the interstitial cell of Cajal is present in the cerebral arteries of humans. Its function is unknown. Earlier reports of cerebral valves have been shown to represent intimal cushions near the branching points of the cerebral arteries. Intravascular bridges present in human cerebral arteries, have not been reported in rats. Finally, the presence of vascular remodeling, as found in the cerebral arterioles of hypertensive rats, remains to be established in the cerebral arterioles of human hypertensives.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasculature to the germinal matrix in rabbit pups

The authors report a study of the cerebral vasculature of premature rabbits pertaining to the germinal matrix (GM). A pigmented silicone material (Microfil) was injected into the carotid artery of anesthetized rabbits. Methyl methacrylate vascular casts of a similar group of premature rabbits were examined by scanning electron microscopy. The GM is supplied by arteries from both the basal and convexity surfaces of the brain. Vessels could be identified as arteries or veins by their typical patterns of branching and by the characteristic impressions made on the methyl methacrylate casts by endothelial nuclei. Specific evidence of structural weaknesses in the vasculature, which could be a site of predilection for GM bleeding, was not observed. The similarities in basal ganglia vasculature between premature rabbits and humans justifies using the rabbit model to study vascular aspects of the GM and intraventricular hemorrhage.

Scanning electron microscopic study of arterial cushions in rats: a novel application of the corrosion-replication technique

The morphology and organ distribution of arterial cushions were studied in adult rats (body weight ranging from 200 to 500 gm) by scanning electron microscopic (SEM) observation of corrosion casts. Scanning electron microscopic observations of renal vascular casts were correlated with SEM views of the luminal surfaces of similarly fixed vessels; there was a striking similarity in shape, organ distribution, and dimensions between fixed arterial cushions and indentations at the surfaces of casts. Application of this technique to 11 different organs, some of which had never been studied by SEM before, revealed the occurrence of indentations at branching sites similar to those found in kidneys (and hence they were termed "cushions"). Our findings are in generally good agreement with previous light and transmission electron microscopic studies on rats. Our results support the view that arterial cushions are present throughout the vasculatures of the rat. A quantitative morphologic study of replicated branching sites related to "cushions" showed a great variability of the parent-to-daughter luminal diameter ratio (range 0.87-16.38) and of branching angles. A fruitful application of this technique to other laboratory animals may be anticipated.

Ultrastructural observations on bifurcations in rat cerebral arteries. 2. Rats with long-term hypertension

The bifurcation pads ("valve-like projections") in the anterior cerebral arteries of rats with long-term hypertension were studied electron microscopically. The rats ranging in age from 2 to 10 months were sacrificed after bilateral renal artery constriction at 5-week-old. In the bifurcation pads (intimal pads) of hypertensive rats, smooth muscle cell damage first appeared in the roots of the pads as well as underlying media in the form of granular, vesicular, and somewhat tubular structures (200-1500 A in diameter). Thereafter, with a lapse in time after the operation, these abnormal substances increased around the smooth muscle cells which were arranged in the marginal zones of the pads. Deeply arranged intimal smooth muscle cells which were embedded in an abundance of ground substances were only damaged in rats with very long-term hypertension. The medial smooth muscle cells beneath the pads manifested lesions which were more marked and diffuse than in the intima. These smooth muscle cells were bizarrely atrophied and abnormal substances which might be derived from necrotic smooth muscle cells were found around them. Basement membrane-like substances, either thick or multilaminated, were also present around them.

Valvular structure at the branching portion of the human aorta

The Valvular structure developing at the site from which an artery was given off was examined. The valvular structure consisted mainly of smooth muscle cells, and was found at the openings of such small arteries as the intercostal and lumbar arteries. It was a crescent membrane-like structure extending from the peripheral edge of the opening to the downstream edge. This structure was indistinct in newborn infants, became gradually distinct in infants and stood out in teen-agers. It became rather thick and rounded in human beings more than 20 years of age. With further advance in age, the smooth muscle cells became degenerated and hyalinized with some disappearing eventually. In the valvular structure smooth muscle cells running longitudinally in the same direction as the blood stream were arranged in such a manner as a Venetion blind. This arrangement seemed to suggest that the valvular structure might have some function to adjust the blood stream at the branching portion of the aorta.