Per R. Flood

Structure of the segmental trunk muscle in amphioxus

SummaryLight and electron microscopy of the segmental trunk muscle in amphioxus demonstrate at least two types of muscle fibre or muscle lamella.One kind of lamella is narrow and located just beneath the lateral surface of the muscle. It contains mainly irregular myofibrils, mitochondria and glycogen particles and is in cytoplasmic continuity with the so-called thin ventral root fibres. The other kind of lamella is very wide and extends from the lateral to the medial surface of the myotome. It contains mainly myofilaments and is in cytoplasmic continuity with the so-called thick ventral root fibres. These two kinds of lamella probably correspond to sarcoplasma-rich (i. e. slow) and sarcoplasmapoor (i. e. fast) muscle fibres of higher chordates.Some other muscle lamellae are tentatively identified as a third, intermediate, type. These are intermediate between the above mentioned two kinds of lamella in size and structure and probably join the thick ventral root fibres.

Myasthenia gravis patients with a thymoma have antibodies against a high molecular weight protein in sarcoplasmic reticulum

Our purpose was to investigate whether components of the sarcoplasmic reticulum (SR) are relevant antigens in myasthenia gravis (MG). Using enzyme-linked immunosorbent assay (ELISA), 75 MG sera and 120 control sera were examined for IgG antibodies against SR prepared from rabbit skeletal muscle. 16/30 thymoma MG patients had IgG antibodies that reacted with SR. 1/30 MG patients with thymic hyperplasia and 3/15 MG patients with thymic atrophy had SR antibodies in low concentrations. Control sera were negative. Using immunoblot, SR antibodies were detected in the thymoma group only. 14/30 sera from thymoma patients reacted with a protein of 320 kDa relative molecular weight. The only reported SR protein with similar electrophoretic mobility is the subunit of the spanning protein which links junctional SR to sarcolemma and functions as a calcium-release channel.

Substructure of solitary cilia in mouse kidney

SummaryRecent scanning electron microscopic studies confirm the presence of solitary cilia on most epithelial cells along the mammalian nephron and collecting ducts.By transmission electron microscopy we have found that the axonemata of such cilia consist of a maximal number of 9 doublet and no singlet filaments. 10% of the cross-sectioned cilia contain 9 doublets arranged in a peripheral ring (9+0 pattern). 30 % of the cross-sections contain 8 or 7 doublets in peripheral ring and 1 or 2 doublets in the central region (8+1 and 7+2 patterns). Serial sections and goniometer tilt reveal the central doublets to originate as dislodged peripheral doublets. 60% of the sectioned cilia contain filament numbers between 8 and 4. In patterns of 5 and 4 filaments single microtubules predominate.The functional significance of these atypical cilia is discussed.

Early morphological changes in rat cerebellum caused by a single dose of methylmercury

A single dose of 10 mg methylmercury chloride per kg body weight was given to 30 days old rats and to adult rats (180–200 g). This resulted in brain levels of 1.4–2.2 μg Hg/g wet weight. In the young rats electron microscopic morphometry showed swelling of the granule cells. The extent of changes was more pronounced in the cerebellar hemispheres than in the vermais and flocculus. At 7 days after giving the methylmercury the granule cells appeared to have returned to normal. Methylmercury produced both light and electron microscopic changes in cerebellar neurons of adult (180–200 g) rats 3 days after dosing. 2.5–10% of the granule cells appeared dark and condensed in toluidine blue stained semithin sections of perfusion fixed and plastic embedded material. In control animals the comparable percentage never exceeded 1. By electron microscopic morphometry the dark cells proved to be shrunken to 70%, whereas the remaining light granule cells were swollen to 130% of the normal cell volume. The heterochromatin and mitochondrial volumes per cell remained constant in both dark and light cells from methylmercury treated animals.In the Purkinje cells from both young and adult rats, geometrical changes in the cisternae of the granulated endoplasmic reticulum were evident. The swelling and shrinkage of the granule cells is supposed to be due to impaired electrolyte control and the disorganized granulated endoplasmic reticulum of the Purkinje cells may be related to the deleterious effects on protein synthesis.

The connection between spinal cord and notochord in Amphioxus (Branchiostoma lanceolatum)

SummarySilver impregnation of nerves, histochemical reactions for acetylcholinesterase, and electron microscopy reveal an efferent innervation of the notochord in amphioxus. Extensions of the notochordal lamellae end in groups (the “notochordal horns”) just below the ventro-lateral surface of the spinal cord where they are opposed to large nerve terminals originating as short collaterals of axons running longitudinally in the nerve cord. This neurochordal junction resembles an ordinary neuro-muscular junction in several respects and is interpreted as a part of the muscular system found in the notochord itself.

The ultrastructure and vascular supply of the different fibre types in the axial muscle of the sturgeon Acipenser stellatus, Pallas

SummaryThe ultrastructure and vascular supply of the different fibre types in the lateral muscles of the sturgeon Acipenser stellatus were studied by light- and electron microscopy and morphometry. Three fibre types form separate layers without intermingling. The red fibres are superficial, the white fibres deep and the intermediate fibres between them. From morphometric analyses, the mitochondrial volume fraction in red fibres is 30%, in intermediate fibres 3.7% and in white fibres 0.7%. Z lines are most fuzzy in the red fibres. Triads of the sarcotubular system are always situated at the level of the Z discs. In red fibres the three elements are arranged in a series along the myofibrils, whereas in white fibres they are arranged transversely and in the intermediate fibres they are aligned obliquely. The number of capillaries surrounding each fibre is 2.3, 0.9 and 0.2 for the red, intermediate and white fibres, respectively. In red fibres 16% of the surface is directly covered by capillaries. The corresponding percentages for intermediate and white fibres are 5 and 1, respectively. Per unit volume of the fibre, the directly vascularised fibre surface in red fibres is about ten times larger than that of white fibres.The degree of vascularisation of the fibre types is directly related to the volume fraction of mitochondria, and thus to their aerobic capacities.

The vascular supply of three fibre types in the parietal trunk muscle of the Atlantic hagfish (Myxine glutinosa, L): A light microscopic quantitative analysis and an evaluation of various methods to express capillary density relative to fibre types

Abstract Each segment of the parietal trunk muscle of Myxine is organized in myomeric units that contain a ventral and lateral layer of red muscle fibres, two or three dorsal layers of white fibres, and some intermediate fibres scattered in between. India ink-injected samples reveal that each myomer is supplied and drained by its own arterial and venous branch of the segmental vessels and, as might be expected from the histochemical and electrophysiological properties of the fibres, that 97% of the capillaries are located next to the red fibres and 53% of the white fibres lack contact with capillaries. Although the mean numbers of capillaries around the three fibre types are 2.76 for red, 1.95 for intermediate, and 0.69 for white fibres, the different sizes of the fibres make the surface fractions directly covered with capillaries 31, 14, and 0.4% for red, intermediate, and white fibres, respectively. Likewise, the mean portions of the fibre circumference served by one capillary are 53, 103, and 362 μm, respectively; the mean fibre volumes served by a 1-μm length of capillary are 580, 1385, and 6812 μm 3 , respectively; and the mean vascularized surface areas per unit volume of fibre are 0.029, 0.011, and 0.0002 μm 2 /μm 3 , respectively. Based on these and other results, it is concluded that the vascular supply to distinct fibre types in a mixed muscle is adequately vizualized by some new counting methods whereby “pure” fibre contacts (i.e., capillaries found between fibres of the same type) are selected or whereby the probable “active” partner in any capillary-mixed fibre type contact (i.e., the fibre type to which the capillary owes its presence) may be judged. The results obtained by these methods, however, are difficult to relate in a quantitative way to other structural or functional parameters. For such purposes, the rather laborious morphometrical measurements mentioned above are better to use.

Rod-shaped accumulations in cisternae of the endoplasmic reticulum in root cells of Lepidium sativum seedlings

SummaryUltrathin sections through the median plane of norm al, 48-hrs-old seedling roots of cress, showed the presence of accumulations of a finely fibrillar material. These inclusions were confined to the cisternae of the granular endoplasmic reticulum of surface cell layers of the root tip and the root-hair zone. The rod-shaped structure and random orientation of these inclusions were clearly seen in 3-dimensional reconstructions of serial ultrathin sections.

The sarcoplasmic reticulum and associated plasma membrane of trunk muscle lamellae in Branchiostoma lanceolatum (Pallas)

SummaryThe trunk muscle lamellae of Amphioxus is made up of cross-striated lamellae about 1 μm thick. Transverse tubules are absent, but numerous subsarcolemmal vesicles are found in both tissue blocks and minced samples after aldehyde and osmium fixation, embedding and sectioning.The vesicles contain a granular matrix, range in diameter from 30 to 200 nm and constitute about 3 to 6% of the muscle fibre volume. 8 out of 10 vesicles are found above the Z and I-bands. In the presence of oxalate, electron dense precipitates form within the vesicles. Energy-dispersive X-ray microanalysis reveals the presence of Calcium in these precipitates.The area of the plasma membrane is about 2 μm2/μm3 muscle fibre volume. The corresponding area of sarcoplasmic membrane is ca. 1 μm2/μm3. About 20% of the plasma membrane is directly overlaid and coupled to the sarcoplasmic vesicles.A thin surface coat is present all over the lamellae, but ruthenium red staining indicates that the coat is slightly concentrated above the sarcoplasmic vesicles.Freeze-fracture replicas reveal tightly packed coarse granular material in the vesicular membrane and less concentrated and smaller particles in the plasma membrane. The latter particles are seen somewhat less commonly above the vesicles than on the rest of the plasma membrane. Likewise, direct replicas of lamella spread on glass slides and freeze-dried, reveal a distinct pattern in the surface coat or its underlying structures, corresponding to the Z and I-bands.In the scanning electron microscope the general arrangement of the sarcoplasmic vesicles could be examined. In addition, numerous defects in the plasma- and vesicular membranes indicate a strong adhesion between the two.It is concluded that the trunk muscle lamellae of Amphioxus have a sarcoplasmic reticulum consisting of subsarcolemmal vesicles with calcium sequestrating properties at Z and I-level. Further that the plasma membrane and its surface coat is probably specialized above the vesicles as compared to the rest of the surface.

Graph-directed modelling from serial sections

We propose a general 3D-surface reconstruction technique for objects defined in terms of contours in a stack of serial sections. It is built around a data structure, in which the topology of the objects is represented as a set of disconnected graphs. The basic idea is to let the topological information direct the reconstruction process. There are several advantages with this approach. The alignment of the stack of sections is computed automatically. This operation does not depend on artificial reference points, such as fiduciary marks introduced by laser-beam penetration of a biological sample prior to sectioning. Furthermore, the unknown surfaces between successive sections can be created automatically, even though the sections contain a large number of arbitrarily shaped contours that are clustered or perhaps partly overlapped. If present, 3D irregularities in the surface model can be reduced in a controlled manner.