Daniel Levanon

Permeability of blood vessels in experimental gliomas: uptake of 99mTc-glucoheptonate and alteration in blood-brain barrier as determined by cytochemistry and electron microscopy.

Experimental gliomas were induced in rats by prenatal exposure to ethyl nitrosourea. Changes in the blood-brain barrier were determined by the uptake of a water-soluble compound, 99mTc-glucoheptonate. Increased uptake of 99mTc-glucoheptonate was measured in intact tumors and in various sectors of dissected tumors. The extent of 99mTc-glucoheptonate uptake greatly varied among different tumors and among different sectors of the same tumor. Ultrastructural and cytochemical analysis of the capillary endothelial wall revealed major alterations in tight junctions, which became permeable to horseradish peroxidase. In brain tissue around the tumors, uptake of 99mTc-glucoheptonate and ultrastructure of tight junctions were comparable to normal brain capillaries. The results of the present study indicate that altered endothelial tight junctions may provide the main route of transport of 99mTc-glucoheptonate through the endothelial wall.

Effects of UV-A irradiation on lens morphology and optics

Epidemiological studies have indicated that ultraviolet radiation (UVR) is one of the main factors leading to senile cataract formation. We investigated morphological changes in the eye lens caused by UVR-A. Twenty three pairs of lenses obtained from 23 one-year-old calves were used for this study. For each pair, one lens was exposed to 44 J/m(2) UVR in the 365 nm wavelength region while the contralateral lens was not exposed and served as a control. The lenses were placed in specially designed organ culture containers for pre-incubation. Lenses were exposed to UVR after one day in culture. After irradiation, lens optical quality was monitored throughout additional 15 days of the culture period and lenses were taken for morphological analysis by scanning electron microscopy. Damage to lens optical quality was evident as early as day 8 after the irradiation and increased with time in culture. We found irregularity of fiber morphology in lenses exposed to UV-A irradiation (but not in control lenses), similar to that reported previously for aged lenses. At the end of the culture period (day 16), lens fiber membranes also showed holes in fiber membranes. We conclude that UVR-A caused damage to cell membranes of the lens and alterations in lens optics, which may subsequently lead to senile cataract formation.

Horseradish peroxidase as a cytochemical marker of blood-brain barrier integrity in oxygen toxicity in the central nervous system

The ultrastructural integrity of endothelial tight junctions in cerebral microvessels of the rat exposed to hyperbaric oxygen was examined to find whether or not there are alterations of the blood-brain barrier in the initial phase of central nervous system oxygen toxicity. Rats were pre-implanted with cortical electrodes for continuous EEG and provided with two polyethylene cannulae inserted into the common carotid artery. HRP was administered to unanesthetized rats through a cannula directed into the brain, before the onset of O2 pressurization. As soon as the early electrical discharges of oxygen toxicity were recorded (20 to 30 min), the animal was killed by injection with saturated KCl into the heart. Examination of small blood vessels in both LM and EM did not support the possibility that the blood-brain barrier is altered prior to the first electrical discharge appearing in central nervous system oxygen toxicity.

Articular cartilage of the rabbit knee after synovectomy: a scanning electron microscopy study

We sought to study the effect of synovectomy on the surface morphology of articular cartilages of the rabbit knee using scanning electron microscopy (SEM). Fifteen rabbits were surgically synovectomised and allowed to regenerate their synovia during time intervals ranging from 3 to 44 wk. Cartilage specimens were shaved from 5 distinct articular sectors of synovectomised, contralateral and sham‐operated knees and prepared for SEM using tannic acid. Applying structural reinforcement by tannic acid was found to secure the in vivo surface morphology of the cartilages and thus production of surface irregularities during preparation was excluded. The surface morphology of cartilages both from the synovectomised and contralateral joints was found to differ from that of intact healthy rabbits. A ‘chaotic’ nature of the altered cartilaginous morphology persisted as late as 44 wk postsynovectomy. Cartilages from sham‐operated joints did not differ detectably from normal cartilages.

The synovial lining of the rabbit knee : a scanning electron microscopy study of specimens reinforced structurally with tannic acid

SummaryMedial and lateral synovial linings of the rabbit knee, structurally reinforced with tannic acid during fixation, were studied in the scanning electron microscope. Low-resolution micrographs revealed, in both linings, gross architecture of four types: accordion-like, lobe-like, fatty areolar, and flattened areas. In high resolution, both cellular and acellular surfaces were recorded. A novel, ‘bubble-like’ appearance, of unknown nature and origin, accounted for 70% of both linings. No definite correlation between anatomical location, gross type, or microarchitectural pattern was noted.

Quantitative analysis of chondroitin sulphate retention by tannic acid during preparation of specimens for electron microscopy

SummaryThe ability of tannic acid to enhance binding of glycosaminoglycans to purified collagen was analysed in an in vitro system using amino sugar analysis on an amino acid analyser, transmission electron microscopy, and scanning electron microscopy. Collagen was purified by digestion with trypsin, papain, and hyaluronidase. Purified collagen was incubated with hyaluronic acid or with chondroitin sulphate glycosaminoglycan and then treated with tannic acid. Tannic acid was found to enhance retention during preparation for electron microscopy of either of the glycosaminoglycans onto collagen fibres. The ability of tannic acid to enhance binding of collagen and glycosaminoglycans might explain, at least in part, its structural reinforcement effect on resected synovial joint-apposing surfaces during preparation for scanning electron microscopy.

Tannic acid and thiocarbohydrazide as structural reinforcement agents in the preparation of rabbit knee articular cartilage for the scanning electron microscope.

Samples from seven sectors of the rabbit knee articular cartilage were shaved and prepared for the scanning electron microscope using either tannic acid, thiocarbohydrazide or nothing (control). Surface morphology was found to be more typical to a given sector and less so to a specific preparation procedure. Rough areas were recorded from load-bearing sectors, while smooth areas appeared on load-free ones. However, fibrillations were discerned on control load-bearing sectors only, and pits and humps were never detected. Tannic acid and thiocarbohydrazide may have exerted their structural reinforcing effect on the tissue preservation by enhancing the binding of osmium tetroxide to it, possibly along with that of other soluble tissue constituents.