Thomas S. Leeson

The mammalian testicular capsule and its muscle elements

This study of the testicular capsule of rat, dog, cat and human has confirmed the presence of three layers, viz., the tunica vaginalis, the tunica albuginea proper and an innermost tunica vasculosa. Smooth muscle cells are present in the tunica albuginea of all four species and are more prominent at the posterior pole of the testis where the capsule merges with the mediastinum testis. In the rat and the dog, a few striated muscle fibers also are present.

Fine Structure and Possible Secretory Mechanism of Rat Palatine Glands

Electron microscopic studies of the soft and hard palates of adult male rats, removed before and after stimulation, have been used in the study of possible mechanisms of elaboration and discharge of mucin by the tubuloacinar glands within the palate. Results suggest that both the endoplasmic reticulum and the Golgi apparatus are directly involved in the elaboration of the secretory product.

T-tubules, couplings and myofibrillar arrangements in rat atrial myocardium

Myocardial cells of rat atria have been studied using standard fixation and tannic acid mordanting. Cells were arranged in bundles or fascicles with little connective tissue. Fiber size varied, with complex cell junctions and in many fibers, particularly those of small diameter, no T-tubules or internal couplings were seen. Most cells, however, contained T-tubules, mainly coupled as triads at Z-lines but showing considerable variation in morphology. Direct continuity of T-tubules with the sarcolemma was demonstrated. Apparently unrelated to T-tubules and internal couplings, all cells showed the presence of peripheral couplings between sarcoplasmic reticulum and sarcolemma and, often, the subsarcolemmal element of reticulum was observed to pass internally in the sarcoplasm from a peripheral coupling. Also present were subsarcolemmal caveolae. The occasional presence within a single cell of myofibrils orientated in different planes was noted also. The findings are discussed in relation to the role of T-tubules and couplings in excitation-contraction.

Comparative electron microscope studies of the myocardium in adult rats fed on normal and cholesterol diets

Abstract In young adult rats which were fed on cholesterol diet for four weeks, moderate morphological changes occurred within the myocardium, as compared to the myocardium in rats of the same age which were fed on normal rat diet only. After a period of ten weeks on the cholesterol diet, further changes or degenerations of the heart wall were observed. In general, the primary changes were thickening of the basal laminae of the endothelial layer of the endocardium and of the capillaries. In the extracellular spaces, numerous membrane-bound bodies or vacuoles were present. Within the myocardial cells, swelling of mitochondria occurred as well as their conversion into myelin bodies. Large numbers of formed myelin structures were present within the sarcoplasm which lead to a disruption in the normal relations of the myofibrils, the sarcoplasmic reticulum, and the transverse tubular system. Increased complexity (jigsawpattern) of the intercalated discs, and formation of an electron dense zone inside the apposed plasma membranes occurred. Eventually the intercellular gap of the intercalated discs became enlarged and irregular and finally adjacent myocardial cells became completely separated.

Lanthanum as an intracellular stain for electron microscopy

SummaryResults obtained after the normal aldehyde fixation of duodenal enterocytes for electron microscopy have been compared with results obtained when 0.1% Malachite Green or 10mm lanthanum chloride had been added during aldehyde fixation. Sections were examined without further staining, and after counterstaining with lead citrate and uranyl acetate. In unstained sections, lanthanum-treated material showed improved contrast when compared to results from the other two methods. Also, after counterstaining, areas showing excellent contrast were much more frequent and more readily detected in the lanthanum-treated material. In the microvilli of enterocytes fixed in the presence of lanthanum, the plasmalemma-glycocalyx was defined more clearly and the results were more pleasing subjectively. When Malachite Green was present in the fixative, good contrast was observed more frequently than in routinely fixed tissues, but less often than in those treated with lanthanum. It is suggested that the addition of lanthanum chloride or Malachite Green to the fixative may prove useful in many ultrastructural studies.

Postnatal Development of Sarcolemmal Invaginations in Right Atrial Myocardium of the Rat

Postnatal development of the sarcolemmal invaginations of right atrial cells of the rat has been studied using standard fixation combined with tannic acid mordanting. T tubules were seen to form at Z lines as simple tubular invaginations starting at the 14th postnatal day. T tubules were present in most cells by the 18th postnatal day but, as in the adult, were restricted to peripheral regions. Also, between the 16th and 18th postnatal day a proliferation of caveolae was seen, both as single vesicles and as complexes with up to a dozen caveolae sharing the same neck. The caveolar complexes persisted in the adult and did not seem to contribute significantly to the formation of the T tubules. Dyadic couplings were seen to become more abundant as T tubules and caveolae proliferated. These findings are discussed in relation to transsarcolemmal Ca2+ movements and excitation-contraction coupling during postnatal development.

The Fine Structure of Snake Myocardium

Snake myocardium has been studied using standard methods and tannic acid mordanting. In both atria and ventricle, cells were arranged in fascicles with little connective tissue, up to 20 cells per fascicle, and few differences between cells of atria and ventricle. Cell (fiber) size varied from 8 to 12 micrometers in the nuclear area with a few cells up to 14 micrometers in ventricle, and cells generally were spindle-shaped, tapering toward the extremities where relatively simple intercalated discs were seen. Few myofibrils per cell were present and poorly delineated. Transverse tubules were absent and sarcoplasmic reticulum was poorly developed and, apparently, even absent from some cells. All cells contained micropinocytotic vesicles associated with the surface plasmalemma and subsarcolemmal caveolae. In addition to intercalated discs, intercellular junctions showed spot desmosomes, small and sparse gap junctions and fasciae adherentes of two types, one associated with Z-bands, one independent of Z-bands. Nerve fibers and nerve endings were numerous, particularly in atrium. These findings are discussed in relation to the structure of mammalian myocardium.

Non-myofibrillar filamentous material in right atrial myocardial cells of the rat

Abstract Cytoplasmic filaments of indeterminate length, but longer than either thin or thick myofilaments, and of 9 to 11 nm diameter, are present in a few right atrial cells of the rat myocardium. They apparently form tubular elements of approximately 45 nm overall diameter that show a regular cross-bridging by fine filaments of 4 to 5 nm diameter at a periodicity of about 30 nm when sectioned longitudinally. Some of the elements appear helical. In transverse section, they form a square grid pattern of similar dimensions. In both planes of sections they are seen to occur both singly and in lateral aggregations. Although many of the filamentous elements are parallel to myofilaments, or nearly so, their orientation varies not only from cell to cell but also within a single cell. Occasionally, the filaments appear to intermesh with thin myofilaments but always on transverse section they are seen around and between myofibrils. The amount of the filamentous material within a cell varies from a few, even a single tubular element, to masses of material virtually filling the cell. Their nature and function is unknown but they may be related to the special conducting fibers known to exist in the right atrium.