Scanning and transmission electron microscopic study on the cerebral arterial endothelium of experimentally hypertensive rats fed an atherogenic diet

In order to clarify the roles of hypertension and hypercholesterolemia in atherogenesis, the cerebral arterial endothelium of experimentally hypertensive female rats fed an atherogenic diet were investigated by scanning and transmission electron microscopy. The hypertension was induced by constriction of the bilateral renal arteries. In both hypertensive groups, group I (hypertension + hypercholesterolemia) and group III (hypertension), many endothelial cells covered with numerous microvillous projections were observed. Pinocytotic vesicles and caveolae were also increased in these endothelial cells. On the other hand, in group II loaded with only hypercholesterolemia, microvillous projections on the endothelial cells tended to be increased, but its grade seemed to be lower than those of the hypertensive groups. These findings suggest that hypertension appears to be more effective than hypercholesterolemia in the cause of the increase of microvilli on the endothelial cell surfaces and the increase may be related to increased permeability in the cerebral arteries.     

Light and electron microscopic studies on rat arterial lesions induced by experimental arterial contraction

Summary Experimental contraction was produced in the rat mesenteric arteries and the arterial segments were studied morphologically. When the rat mesenteric artery was exposed in physiological saline solution at 37° C and 2–3 mg of methoxamine hydrochloride (10 mg/ml) was dripped onto it, intense contraction was observed for about 30 min but elevation in blood pressure was slight. During the contraction, numerous vacuoles were seen in the medial smooth muscle cells of the arterial segments, and these vacuoles were shown electron microscopically to have double unit membranes, indicating that they were formed by herniation of a part of the adjacent smooth muscle cell body. In the arteries 1–6 h after the end of the contraction, cellular, nuclear and vacuolar membranes and myofilaments of the medial muscle cells were partially lost. 12–24 h after the contraction the arteries exhibited necrosis and desquamation of endothelial cells and platelet adhesion. In the media, smooth muscle cells were completely deprived of cell membranes, myofilaments, nuclei, intracytoplasmic organelles other than mitochondria, and vacuolar membranes. The cytoplasm was filled with fine granular and granulo-vesicular material, and fibrin insudation was observed in these severely damaged cells. Arterial contraction may be an important factor in the induction of arterial lesions.     

An electron microscopic study of plasmatic arterionecrosis in the human cerebral arteries

Summary An electron microscopic study of the intracerebral arteries from 9 hypertensive cases was performed in order to elucidate the morphogenesis of the plasmatic arterionecrosis which was considered to be the direct cause of hypertensive intracerebral hemorrhage. In the preceding stage of the arterial lesions, marked necrosis of medial smooth muscle cells and increase of basement membrane-like substance in the intima and media were observed. The lumina of these arteries were slightly dilated. The dilatation and hemodynamic factors were supposed to cause endothelial injury resulting in blood plasma insudation into the intima through the opened spaces between endothelial cells. The insudated blood plasma dispersed and dissolved the basement membrane-like substance, collagen and elastic fibers in the arterial wall, leading to the development of the plasmatic arterionecrosis.This study was supported by a Grant-in-Aid for Scientific Research of the Japanese Ministry of Education (No. 857052).     

Thalamic arterial pattern: An endocast and scanning electron microscopic study in normotensive male rats

Rat cerebral vasculature serves as a model for study of the pathophysiology of stroke in humans. Human thalamic anteries show a high incidence of stroke. The objective is to describe the thalamic arterial vascular pattern in normotensive male rats as the initial step for quantitative histochemical studies of enzyme activities in the walls of these vessels. Intracardiac injections of methyl methacrylate monomer provide detailed vascular endocasts. The thalamic vascular bed defined by in situ dissection, serial reconstruction, and light and scanning electron microscopy of endocasts contained four groups of vessels: (1) ventral medial thalamic arteries, (2) thalamic branches from the posterior cerebral artery, and (3) ventral lateral and (4) ventral anterior thalamic arteries. Thalamic vessels are muscular arterioles that, after three to four bipinnate branches, feed into a continuous capillary bed (no loops). The parent vessels and their subsequent branches have been evaluated in terms of their mean internal diameters, mean interbranch intervals, and branch angles. The arterial patterns to rat and human thalami are very similar, with the exception of the anterior choroidal artery which is missing in the rat. The branches supplying the thalamus in both the rat and human are closely associated with the circle of Willis; however, the constituent parts of the circle in rat vary from the pattern in human brain. The rat thalamic arteries show morphological features similar to those seen in the stroke-prone ganglionic arteries in the human basal ganglia.     

An electron microscopic study of dendritic degeneration in the cerebral cortex resulting from laminar lesions

Summary The morphological characteristics of dendrites in layers of the cerebral cortex above laminar lesions induced by ionizing particle irradiation have been studied in the striate field of rat at various survival times. Within two weeks following irradiation an increasing number of dendrites display unusual alterations inferred to be signs of degeneration.Degenerating dendrites can be characterized by a dense cytoplasmic matrix, disruption of mitochondria, presence of dense bodies, irregular outline and a marked alteration of the plasmalemma in its dimensions and staining properties. Some degenerating dendrites possess a large accumulation of dense subsynaptic material and are contacted by synapses with enlarged and altered synaptic clefts. A few dendrites contain extensive membranous whorls. Engulfment by reactive astrocyte processes is a common feature and often includes the presynaptic axonal knob, but only the degenerating dendrite has been observed within glial cytoplasm. The inference that the majority of degenerating dendrites in this material are apical dendrites of pyramidal cells suggests that either shaft synapses are common for these cells, protuberances may retract during degeneration, or spines are lost due to loss of afferent terminals.Supported by research grants from the United States Public Health Service, NB-4578 and NB-6594.     

高血压大鼠大脑中动脉内膜超微结构观察

目的:观察高血压大鼠大脑中动脉内膜的超微结构变化。方法:双肾双夹法建立肾血管性高血压大鼠模型,分别于7d、30d、90d处死动物,取大脑中动脉始段,用透射电镜观察。结果:高血压组7d内皮细胞肿胀明显,细胞膜呈虫蚀样改变,胞质内空泡明显增多,线粒体肿胀,呈大小不等的圆球状,内弹力膜肿胀,可见较多的空泡,局部增厚,与内皮细胞之间的边界模糊不清,核周隙增宽;30d内皮细胞和内弹力膜的变化与7d相似,肿胀略有减轻,但内皮细胞伸出伪足伸入内弹力膜形成的肌内皮细胞样连接多见;90d内皮细胞肿胀较7d、30d减轻,但线粒体肿胀更加明显,而且数量增多,可见散在的糖元颗粒,另外,内皮细胞间连接破坏明显,失去正常的形态,内弹力膜肿胀减轻,但仍可见空泡样改变,而且局部变薄,内皮下间隙增宽。结论:高血压大鼠脑动脉内膜结构的改变存在从水肿、肿胀减轻到结构性破坏的变化过程,这种变化可能是其在高血压晚期发生脑卒中的病理学基础。     

An electron microscopic study of uterine arteries during pregnancy

The mesometrial arteries of pregnant guinea pigs are not mere blood conducting channels. Instead they are dynamic in nature. The cells forming the intima and media exhibited significant structural modifications during pregnancy. The endothelial cells became hypertrophied and attenuated. Their cytoplasm showed an increase in the amount of ribosomes, rough endoplasmic reticulum and lysosome-like bodies during pregnancy. Dense bodies that were often closely associated with the Golgi apparatus were seen in pregnant animals. These bodies exhibited a graduation in size within each cell and were thought to be the precursors of the lysosome-like bodies. Similar structures were also seen in smooth muscle cells of the mesometrial arteries of pregnant animals. The endothelium of these arteries was often discontinuous in full term pregnant animals. In that case, the underlying smooth muscl4 cells provided the lining surface. Irrespective of which type of cells formed the lumen of these arteries, they became coated with a “fuzzy” layer which specifically stained intensely with phosphotungstic acid, suggesting that this layer might be a mucoprotein. The smooth muscle cell of the arterial media also became hypertrophied during pregnancy. The cytoplasm exhibited a gradual increase in free ribosomes and rough endoplasmic reticulum, mitochondria and microtubules throughout pregnancy. During the latter half of pregnancy many smooth muscle cells developed extensive amounts of smooth endoplasmic reticulum whose vesicles often were filled with an electron opaque secretory material. It is suggested that the development of unusually large quantities of smooth endoplasmic reticulum might be associated with steroid metabolism. Unusually thick basement membranes were formed around the modified smooth muscle cells of full term pregnant animals and the surfaces of these cells often exhibited large numbers of microvilli. The microvilli seemed to disrupt the continuous patterns of the basement membrane.     

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.     

An electron microscopic study of varicella skin lesions

Summary The skin lesions of varicella were studied by electron microscopy. Singlemembrane particles were the only type of viral particles present in the nucleus. Two modes of viral envelopment were observed; budding from the inner nuclear membrane, and budding from vacuole membranes of the cytoplasm. Tubular, filamentous structures, probably an aberrant form of the virus, were often observed in affected nuclei. Nuclear bodies were frequently found and showed abnormal structures in the nuclei of cells near the intraepidermal vesicles. Strands, inclusion-like structures, probably composed of degenerated nuclear materials, were seen in some instances in the cytoplasm. Virions were frequently included in phagosomes of epidermal or dermal macrophages.     

Gax在肺动脉高压大鼠肺动脉中的表达变化

目的:使用低氧及野百合碱(monocrotaline,MCT)诱导的两种肺动脉高压(pulmonary arterialhypertension,PAH)大鼠模型,观察生长终止特异性同源盒(growth arrest-specific homeobox,Gax)在肺动脉的表达变化。方法:Sprague Dawley大鼠随机分为四组:低氧模型组(n=16)、低氧对照组(n=16)、MCT模型组(n=16)及MCT对照组(n=16)。采用插管法测定大鼠的右心室压力及肺动脉压力。右心室质量除以左心室和室间隔质量,计算右心肥厚指数。采用定量RT-PCR法测定肺动脉主干及肺组织Gax mRNA表达;采用Western免疫印迹法测定肺动脉主干Gax蛋白表达;免疫组织化学染色观测Gax在肺内的分布及表达变化。结果:低氧模型组及MCT模型组大鼠的右心压力、肺动脉压力及右心肥厚指数均显著高于相应对照组(P<0.01),两种模型大鼠的肺动脉血管均出现明显重构。与对照组比较,Gax mRNA在两种模型组大鼠的肺组织表达降低(P<0.05),而在肺动脉主干表达升高(P<0.05)。Gax蛋白在肺内主要表达在微小动脉。与对照组比较,两种模型组大鼠的肺动脉主干和肺微小动脉Gax蛋白表达均升高(P<0.05),而肺组织Gax蛋白表达下降(P<0.05)。结论:Gax主要表达在肺微小动脉,在PAH发生时表达上调。     

Role of lysosomes in mesenteric arterial lesions of renal hypertensive rats

The acid phosphatase activities of arterial cells in the mesenteric arteries of renal hypertensive rats were investigated by both light and electron microscopy. Light microscopically, strongly positive acid phosphatase reactions were confirmed in endothelial cells, intimal cells, medial cells and adventitial cells of the mesenteric arteries, together with considerable deposition of fibrinoid substance in the intima and media in contrast to the appearance in control rats. Electron microscopically, lysosomes with acid phosphatase-positive reaction products were increased in number in endothelial cells, intimal smooth muscle cells, medial smooth muscle cells and adventitial neutrophils or macrophages. The lysosomes in intimal smooth muscle cells and those which were extracellularly discharged were responsible for lysis of the fibrinoid substance. In the media, acid phosphatase-positive lysosomes of medial cells and extracellularly discharged matrix lysosomes with acid phosphatase-positive reactions were also involved in the hydrolysis of necrotic substances and extracellular matrix. These acid phosphatase-positive reactions were diminished both light and electron microscopically in endothelial cells, intimal cells, medial muscle cells and adventitial cells in the regions of healing arteries where fibrinoid substance had been degradated and the intima showed cellulofibrous thickening. The possible role of this acid phosphatase activation for the clearance of cell debris as well as exudative substances in the healing of damaged arterial tissue was discussed.     

Influence of antihypertensive treatment on basal cerebral arteries in spontaneously hypertensive rats. A morphometric study

Spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP) were treated with a combination of a beta 1-blocker (metoprolol) and a calcium antagonist (felodipine) from 1 to 4 or from 4 to 6 months of age. Basal cerebral arteries were fixed by immersion and embedded in plastic. The ratio between media thickness and luminal radius was determined in cross-sectioned arteries for a standardized condition, assuming a smooth and circular internal elastic membrane. The treatment caused a significant decrease in blood pressure and a normalization of m/r ratios in basal cerebral arteries when initiated in young as well as in adult SHR and SHRSP, i.e. the therapy efficiently prevents as well as reverses hypertensive arterial changes. Even though 4-month-old treated rats were still significantly hypertensive, their m/r ratios did not differ from those of normotensive controls. The latter results may indicate that the treatment affects the vessel walls also through other mechanisms than by decreasing the pressure load.     

Light and scanning electron microscopic changes observed in experimental arterial forks of rabbits

Experimental arterial forks were fashioned by anastomosing one common carotid artery to the contralateral vessel by microvascular surgery in rabbits. In one rabbit group the forks were examined histologically by the serial section technique from 5.5 to 25 months postoperatively. The second group was used for scanning electron microscopy of the arterial endothelial surface from 1 to 257 days post-operatively. Intimal proliferation was observed at the lateral angles histologically at sites comparable to those where intimal proliferation occurs spontaneously in human infants. In addition, disruption of the internal elastic lamina with minimal intimal proliferation occurred at the sides of the neo-apex, mostly in the transposed artery. These disruptions corresponded to predominantly transversely orientated tears of the internal elastic lamina from 8 days post-operatively in the scanning electron microscopic study. They were similar to the early atrophic changes preceding berry aneurysm formation in human cerebral arterial forks. The results indicate that both intimal pads (cushions) and elastic tears can be haemodynamically induced.     

Electron microscopic study on the proximal portions of the anterior cerebral arteries in rats with long-term hypertension

Proximal portions of the anterior cerebral arteries in rats with long-term hypertension were electron microscopically studied. The abnormal substances such as granules, vesicles, vacuoles and other membranous structures, relatively homogeneous masses, and basement membrane-like substances were observed around the medial smooth muscle cells. Basement membrane-like substances were increased with advancing age and the majority of these substances are thought to be turned from the granulo-vesicles. Abnormal substances deposited in the media are thought to be "hyalino-fibrous materials". The majority of our materials had a clear-cut border between the media and the adventitia. The subendothelial spaces were slightly distended with fibrillar and/or finely granular substances with age, but neither cellular element nor fibrinoid substance was found in them.     

Delayed intimal lesion development in cerebral arteries versus aortic and carotid arteries of spontaneously hypertensive rats

The development of intimal lesions is delayed in spontaneously hypertensive rats (SHR) in cerebral versus aortic and carotid arteries. The reason for this delayed involvement needs further study.