James F. Reger

Studies on the fine structure of normal and denervated neuromuscular junctions from mouse gastrocnemius

The fine structure of normal and denervated motor end-plates of gastrocnemii from albino mice was examined in this study. Changes following nerve section are described and include a decrease in the number of synaptic vesicles and axonal terminal retraction from subsynaptic sarcolemma. Counts on the number of synaptic vesicles and the degree of axonal terminal retraction in terms of percentage of total sub-neurilemmal cross-sectional area were made with the aid of a compensating polar planimeter. The events (decrease in the number of synaptic vesicles and axonal terminal retraction) observed here are compared with previously reported loss of neuro-muscular transmission in cat gastrocnemius and decrease in acetylcholine concentration in the distal portion of sectioned popliteal nerves (12). It is suggested from this study that causes for neuromuscular transmission failure following denervation are multiple and due as much to retraction of axolemma from the subsynaptic sarcolemma as to any other single factor.

Spermiogenesis in the tick, Amblyomma dissimili, as revealed by electron microscopy.

Observations on the endoplasmic reticulum (ER), nucleus, and acrosome of developing spermatids in the tick Amblyomma dissimili are reported. In early spermatids the ER consists of branching, tubule-shaped cisternae. In later stages the ER lacks attached particles and takes the form of spheroid cytomembranes, which eventually become flattened and arranged as whorls around mitochondria of mature spermatozoa. in early spermiogenesis the nucleus comes to lie at one pole of the cell where an acrosomal vesicle becomes situated. As acrosome formation proceeds, nuclear chromatin aggregates into electron dense chromatin threads that eventually fill the entire nucleus. The acrosomal vesicle becomes flattened between the nucleus and cell membrane in early spermatids and expands as a flat, dise-shaped acrosome. As spermatids elongate, the acrosome is pulled in upon itself into a U-shaped structure. In the mature spermatozoon the acrosome and nucleus are situated in the tail. Comparisons of these findings are made with respect to the early light microscope studies on spermiogenesis in ticks and with recent electron microscope studies of spermiogenesis in other forms.

A fine-structure study on spermiogenesis in the tick Amblyomma dissimili, with special reference to the development of motile processes

Tick spermiogenesis has been studied with the aid of the electron microscope to observe the development of motile processes. During the second maturation division a series of thimble-shaped, subsurface cisternae appear in dividing spermatocytes. Each cisterna encloses a finger-shaped cytoplasmic process. The cisternae are initially equally distributed around the entire surface of the cell but become aggregated at one side as spermiogenesis progresses. During this period the cisternae fuse, resulting in a single cisterna within which multiple cellular processes are now located. The spermatid next elongates into a long, tubule-shaped cell and the intracisternal cellular processes become aggregated at one end of the tube. At this time electron-dense regions appear within each cellular process which eventually give rise to two hollow filaments 60–90 A in diameter and spaced 100–125 A apart. These resulting processes are the motile structures of tick spermatozoids. These findings are compared with the early light microscope investigations on tick spermiogenesis and with other types of motile process fine structure.

The fine structure of the fibrillar network and sarcoplasmic reticulum in smooth muscle cells of Ascaris lumbricoides (var. suum)

The fibrillar network and sarcoplasmic reticulum of Ascaris smooth muscle cells have been examined with the electron microscope. The fibrillar network, first described in Ascaris smooth muscle cells by Apathy (3), is seen to consist of a three-dimensional network of filaments that are 70–80 A thick, show a 360 A periodicity, and extend throughout the entire smooth muscle cell. This network extends between myofibrils and is here in close association with membranes of the sarcoplasmic reticulum. The sarcoplasmic reticulum is composed of regularly repeating, sarcolemmal infoldings that penetrate between myofibrils in the form of transverse sarcotubules. The sarcotubules come in contact with cisternae to form triads and dyads. Sarcotubular and cisternal membranes are triple layered, 75–80 A thick membranes. The morphology of the sarcoplasmic reticulum and associated fibrillar network in this smooth muscle is compared to the sarcoplasmic reticulum of fast striated muscles.

The fine structure of spermatids from the tick, Amblyomma dissimili

Spermatids of the tick, Amblyomma dissimili , were examined by electron microscopy. Evidence presented here shows that they are elongate, tubule-shaped cells, closed at one end, open at the other. At the closed end an inner plasma extension (“inner cord”) extends from the tubule-shaped “outer sheath.” The plasma membrane of the free tip end of the “inner cord” gives rise to cellular processes which extend helically the length of the spermatid, closely investing the “inner cord” and just beneath the plasma membrane of the “outer sheath.” These processes contain within their center two hollow, longitudinally directed, electron-dense, filaments which are 60–90 A in diameter and are spaced 100–125 A apart. The cellular processes are motile structures ( 3 ) which propel the mature spermatozoids of ticks, performing the same function as flagella in flagellate sperm. A comparison is made between the similarity in subunit structure of these filaments with the paired central filaments of cilia.

The fine structure of spermatozoa from the isopod Asellus militaris (Hay)

Mature spermatozoa of Asellus militaris (Hay) have been examined with the light and electron microscope. Spermatozoa from the male vas deferens are found grouped in bundles of up to a hundred sperms per bundle. When observed vitro each sperm is seen to be a nonmotile, elongate, threadlike cell approximately 400–500 μ long and 0.5 μ wide. The nucleus extends as a whip-like appendage from the anterior end of a relatively inflexible tail. When observed in the electron microscope the sperm is seen to consist of a nucleus, a mid-region which lacks mitochondria, and a cross-striated, tubelike tail. The nucleus contains filaments, which are arranged in a tightly packed, longitudinally oriented pattern in some areas. The mid-region contains a myelin figure composed of parallel membranes, which are spaced approximately 80 A apart, and the rostral extension of the tail. The tail is cross-striated at major repeating intervals of 750–800 A and minor repeating intervals of 125–150 A. The tube-shaped tail contains a central, electron-dense core which is cross-linked with the hollow tube in the mid-region at intervals of approximately 150 A. On the basis of the observed lack of motility in vitro, the absence of mitochondria in the mid-region, and the unusual fine structure of the tail, it is concluded that this sperm may be nonmotile in vivo and should be classified as nonflagellate.

The fine structure of neuromuscular junctions and contact zones between body wall muscle cells of Ascaris lumbricoides (var. suum)

SummaryNeuromuscular junctions and close membrane apposition between body wall muscle cells of Ascaris lumbricoides (var. suum) have been examined with the light and electron microscopes. It was found that the body wall muscle cells send out elongate processes from their basal, myofibril containing portion to terminate on dorsal and ventral nerves. When observed with the aid of the electron microscope the neuromuscular junctions were seen to consist of several muscle cell processes in apposition to a single axon. The intersynaptic cleft was approximately 350–500 Å wide. Both the axolemma and sarcolemma were triple layered membranes which were 75–80 Å thick. Electron dense patches were observed at intervals on the apposed membranes which were due to increased thickness of the inner membrane leaflets of axolemma and sarcolemma. Muscle cell membranes, at the level of the neuromuscular junction, were in “close” apposition resulting in an apparently five-layered membrane complex which was 170–210 Å thick. The sarcolemmata in these regions were separated by 10–50 Å. Presynaptic axons contained mitochondria, microtubules which were 180–270 Å in diameter, and two, morphologically distinct types and sizes of synaptic vesicles. One was 200–600 Å in diameter, with a single, triple-layered membrane bounding a center of low electron density. The other was 600–1200 Å in diameter, with a single, triple-layered membrane bounding a central, electron dense granule of 500–800 Å size.The functional significances of the “close” membrane appositions between body wall muscle cells and of the two types of synaptic vesicles found at the neuromuscular junctions of Ascaris lumbricoides were discussed with respect to their possible role in neuromuscular physiology.

Renal pathology in paroxysmal nocturnal hemoglobinuria: An electron microscopic illustration of the formation and disposition of ferritin in the nephron

Abstract The pathologic changes seen on light and electron microscopy of the kidney in paroxysmal nocturnal hemoglobinuria are described in two cases, one at autopsy and the other at biopsy. Intense hemosiderosis of the kidney is the most characteristic pathologic change in paroxysmal nocturnal hemoglobinuria although not specific for this disease. There is no apparent structural or functional reaction to the hemosiderosis. The intensity of ferritin accumulation at various points in the nephron is correlated with current concepts of hemoglobinuria, hemoglobin and ferritin metabolism and large molecule transport.

The fine structure of human hemoglobinuric kidney cells with particular reference to hyalin droplets and iron micelle localization

Two human kidney biopsy specimens were obtained by needle biopsy from a patient with classical clinical and laboratory evidence of paroxysmal nocturnal hemoglobinuria. Iron, in the form of hemosiderin granules and iron micelles 50–60 A in size was found at all levels of the nephron. The visceral and parietal epithelial cells of Bowmans capsule contained individual 50–60 A iron micelles, and membrane-limited masses of closely packed iron micelles (hemosiderin granules). The proximal convoluted tubule cells contained hyalin droplets, hemosiderin granules, and 50–60 A iron micelles. The hyalin droplets were membrane-limited, spheroid, structures which contained peripherally located electron-dense masses. The hemosiderin granules, sometimes membrane-limited, consisted of tightly packed 50–60 A iron micelles. Iron micelles were also observed in the basement membranes underlying parietal epithelial cells, proximal convoluted tubule cells, and in the peritubular capillary endothelium and lumen. The iron micelles were similar in sub-unit structure throughout all regions of the kidney, consisting of sub-units 15–20 A in size spaced 15–20 A apart, and indistinguishable from the iron micelles of ferritin. A comparison is made between the morphology of the hyalin droplets, and hemosiderin granules observed here and elsewhere, and the localization of iron micelles is discussed with respect to ferritin transport.