In muscularis externa of mouse small intestine, cells with ultrastructural features of macrophages were invariably observed in three layers: in the subserosal layer, between the circular and longitudinal muscle layers, and in association with the deep circular plexus. These macrophage-like cells (MLC) had a single indented nucleus, perinuclear Golgi complex, smooth and rough endoplasmic reticulum, many pits (coated and uncoated) in the plasma membrane, coated vesicles, light vesicles, and primary lysosomes, but rather few heterogeneous lysosomal vacuoles. MLC were partially enveloped by processes of interstitial cells of Cajal. FITC-dextran used in combined fluorescence stereo microscopy, fluorescence microscopy, and electron microscopy was employed as a tracer to study the endocytic qualities of the MLC. The mice were killed 5, 15, 30, and 60 min, 1 day, and 4 days after dextran administration. By fluorescence microscopy after 1 or 4 days MLC were observed as a constant cellular population with a strikingly regular distribution. By electron microscopy dextran-containing vacuoles were conspicuous after 1 h or more. MLC of the subserosal layer and between the circular and longitudinal muscle layers could be distinguished with respect to general appearance, pattern formation, and apparent dextran contents.
Coupling fluorescein-isothiocyanate to dextrans (FITC-D) extends the usefulness of the dextrans as electron microscopic tracer particles by permitting preceding fluorescence stereo microscopy and high-power light microscopy of the tissue specimens. The fate of the tracer may thus be studied in vivo during the experiment, during fixation, and during the succeeding tissue processing. A study of some simple physicochemical characteristics of the tracer, and the influence, if any, of the fixing agent are also made possible. FITC-D was found to be uncharged in the pH range from 6.5 to 8.5, more rapidly precipitated by acetone than by alcohol, and to react with glutaraldehyde and osmium tetroxide in an unknown way during tissue fixation. FITC-D with molecular weights 70,000 and 150,000 showed no signs of diffusion during tissue preparation with the methods reported in the paper, whereas FITC-D 40,000 did so to a slight degree, when the tissue was kept for several days in the fixative vehicle. Securing the preservation of the lower molecular weight FITC-Ds during tissue fixation and preparation is more difficult and the described methods are not adequate. Dextrans provoke an anaphylactic reaction in most rat strains, but are well tolerated by Wistar Furth rats. The introduction of FITC into the dextran molecule might alter the biological reactions, but was also well tolerated by Wistar Furth rats. Combined fluorescence stereo microscopy, fluorescence microscopy of sections, light microscopy of strained sections and electron microscopy made it possible to follow a particular microcirculatory area, selected in vivo, to the final study in the electron microscope.
In the continuously growing upper incisor of 100 g rats about 25 arterioles arise from an artery outside the tooth and pass through the apical foramen to run parallel to one another in the central part of the pulp, each supplying a well-defined sector of the migrating odontoblast layer. The arterioles pass through a cycle of proliferation, growth, remodeling, regression and decay, phase displaced in relation to each other. Proliferative and degenerative processes occur in the arteriole wall throughout the cycle, but vary considerably in intensity at different phases. Proliferation takes place by mitosis in the endothelium and the innermost smooth muscle cells. The degenerative process consists of reduction in size of smooth muscle cells by partial autodigestion and by cell death. When the odontoblasts reach the incisal extremity of the tooth, they die, and the associated regressed arteriole disappears. The system of pulpal arterioles has remarkable spatio-temporal features and each of its vessels appears to be in a state of sensitive structural equilibrium.
K E Y WORDS. Perfusion fixation, fixation, vascular reactions.Vascular reactions to fixation with a 2.5",', wjv glutaraldehyde fixative were studied in a Constant flow perfusion system on isolated rabbit intestines and hind limb preparations. Reactions induced by the fixative were compared to reactions induced by noradrenaline in each single preparation. Changes in vascular resistance were assessed from continuous recordings of arterial and venous pressures and perfusion flow. Changes in vascular filtration and macromolecular permeability during fixation were approximated from recordings of flow and measurements of concentrations of dextran in the perfusate at the arterial inlet and at the venous outlet.Our results indicate that the vascular bed of the preparations studied can be reliably fixed in a high resistance state of smooth muscle activity induced by noradrenaline as well as in a low resistance state in the absence of noradrenaline, provided that hydrodynamic parameters are strictly controlled. The vascular filtration decreases during fixation. In optimally perfused preparations 5-10 min are required to fully saturate the binding capacity of the tissue for glutaraldehyde.Data on viscosity and colloid osmotic pressure of Tyrode solution containing dextran T-70 in various concentrations, and of various aldehyde-containing fixatives in 0.1 M sodium phosphate buffer with and without dextran added, are given. 0 1983 The Royal Microscopical Society 123 * Abbreviations used in the text: NA: noradrenaline; GA: glutaraldehyde; FA: formaldehyde. * The analyses were performed by B. S .
The ultrastructure of intestinal submucosal arterioles in rats with angiotensin-induced hypertension was examined. Dilated arteriolar segments showed focally localized severe changes ("patches") with gaps in the endothelial cell layer and with discontinuities in the endothelial basement membrane, the internal elastic lamina and the luminal basement membrane of media. Through the discontinuities, plasma, formed elements of the blood and injected carbon particles penetrated into the arteriolar wall. In the patches, severe injury and slighter degenerative changes were observed in all layers of the vascular wall. Lesions were most extensive in the media and showed a gradient in severity of changes from the centre to the marginal zone of the patches. The observed changes were results of smooth muscle cell necrosis and plasma insudation.
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