Fritiof S. Sjöstrand

Ultrastructure of retinal rod synapses of the guinea pig eye as revealed by three-dimensional reconstructions from serial sections.

The structure of the synaptic bodies of the retinal receptors of the guinea pig eye and the synaptic connections of these receptors have been studied on three-dimensional reconstructions from serial sections. Series with up to forty ultrathin sections (average thickness 250 A) were examined. Two types of synaptic bodies belonging to the α- and the β-cells respectively can be distinguished. Both types contain the same basic structural components: the synaptic granules or vesicles, the synaptic vacuoles and the synaptic ribbon. The α-cells are in synaptic contact with dendrites presumably belonging to two different bipolars. The dendrites end inside an invagination of the plasma membrane of the synaptic body at its vitreal pole and make contact with two synaptic vacuoles forming a pair of vacuoles which are in mutual contact. Extensions from three to four synaptic bodies belonging to the β-cell type enter into contact relation to each α-cell and the dendrites which are synaptically connected to the α-cell. These contacts are interpreted as synaptic contacts. It is proposed that this extensive system of interreceptor contacts might exert inhibitory effects on the transmission between α-cells and bipolars.

Structure of the nerve endings on the external hair cells of the guinea pig cochlea as studied by serial sections.

The nerve endings about the external hair cells of the organ of Corti in the guinea pig have been studied by means of serial sections, and plastic reconstructions. Three kinds of nerve endings were found most often. Type 1 is small ending, containing a few or a moderate number of vesicles. A dense osmiophilic rod with vesicles about it is often found in the hair cell cytoplasm, adjacent to this ending. Type 2 is a large ending, filled with vesicles and mitochondria. A pair of membranes is always found in the hair cell cytoplasm covering the synaptic membrane adjacent to the Type 2 ending. Type 2a is similar in size and cytoplasmic contents to Type 2, but it only touches the hair cell, whereas it has wide contact with other neural structures. Other endings, not conforming to the above, are less frequently found. Two types of hair cells, classed according to the distribution of these endings, are present. Type A shows Type 1 and Type 2 endings in approximately equal numbers, the total number being less in the basal turn. Type B shows a few Type 2 and Type 2a endings, and many Type 1 endings. These hair cells are found in an orderly arrangement along the basilar membrane. Only Type A cells were observed in the first turn of the cochlea. The second turn showed Type B cells in the third row. The third and fourth turns showed Type B cells in the second and third rows.

The Ultrastructure of Cells as Revealed by the Electron Microscope

Publisher Summary The development of ultrathin sectioning techniques has made possible a systematic study of the ultrastructural organization of cells. As a result a great number of electron microscope studies on various cellular components are presented. This chapter discusses all the basic problems of electron microscopy as applied to the study of tissue cells. The chapter focuses on the type of work that has aimed at providing the description of the ultrastructural components of the cells. Between these studies, in which the resolving power of the electron microscope has been used to its limit, and the old light microscopic studies, there are all kinds of intermediate levels. Several new structural components are revealed by the electron microscope as compared with the classical light microscope studies. In most cases the electron microscopes contribution presents a detailed analysis of the geometrical morphology of already well-known components of the cells.

The ultrastructure of the intercalated discs of frog, mouse and guinea pig cardiac muscle

The intercalated discs of cardiac muscle of the frog, mouse and guinea pig consist of transversally oriented cell boundaries and of about 0.1 μ broad zones of dense cytoplasm associated with the plasma membranes at these boundaries. The plasma membranes are represented by an opaque osmiophilic layer, the o-layer, which in certain regions appears triple-layered. The two o-layers of the two cells at the boundary are separated by a less osmiophilic interspace, the l-space. This space varies in thickness in different parts of the boundary and in different species. It is interpreted as representing the lipid layers of the two plasma membranes in close contact. This arrangement is assumed to ensure a mechanically firm contact between the cells. It is possible structurally to distinguish between interfibrillar and intersarcoplasmic regions along the disc. The density of the cytoplasm in the interfibrillar regions is due to a dense network that connects the I-band part of the myofilaments with the o-layer of the plasma membrane. In the intersarcoplasmic regions, zones of dense cytoplasm contribute to the differentiation of specialized regions of cellular contact, the S-regions according to the terminology used here.

A synaptic structure in the hair cells of the guinea pig cochlea

A synaptic structure has been observed in the external and internal hair cells of the guinea pig cochlea. It is a dense osmiophilic rod-like structure, surrounded by vesicles. In the external hair cell it is present only adjacent to the small type 1 nerve endings.

Fixation by freezing-drying for electron microscopy of tissue cells.

Immersion of frozen-dried tissue into methacrylate under high vacuum at a temperature below the boiling point of methacrylate at that pressure makes it possible to obtain a perfect penetration of the methacrylate. The polymerization according to Muller (3) by u.v. light in the cold gives satisfactory results. These techniques for immersion and polymerization prevent an extensive vacuolization of the tissue due to improper embedding. The vacuolization due to ice crystal formation does not interfere in a critical way with the structural organization of the pancreas cells studied so far and represents an easily recognizable artifact. Preliminary observations on frozen-dried pancreas tissue confirm the geometrical structural pattern observed in mitochondria in osmium-fixed material. The basic membrane of the α-cytomembranes also has its counterpart in the frozen-dried material. However, the contrast conditions are such that the picture appears as the negative of that of osmium-fixed material. The opaque 150 A particles (“RNA particles”), or any component that would correspond to them, have not been observed.

The Ultrastructure of the Retinal Receptors of the Vertebrate Eye

The development of refined techniques for preparing ultrathin sections (100–200 A thick or even less) has made it possible to make use of almost the whole maximum resolving power of modern electron microscopes (6–8 A) for the analysis of the structure of tissue cells. These technical advances have drastically widened the field of ultra-structure research by allowing a study of the elementary components of living matter by direct observation. These components are within the range of dimensions of macromolecules. They consist, however, mostly of a number of molecules organized into a supramolecular unit. Careful measurements of the dimensions of these units and the indirect indications of molecular orientation obtained by polarization optical and X-ray diffraction studies make it possible to propose interpretations of the observed structural patterns in terms of the molecular architectonic of the units.

The Structure and Innervation of the Cochlear Hair Cells

(1954). The Structure and Innervation of the Cochlear Hair Cells. Acta Oto-Laryngologica: Vol. 44, No. 5-6, pp. 490-501.

The ultrastructure of the skeletal muscle myofilaments at various states of shortening.

The ultrastructure of the myofilaments of skeletal muscle has been studied at various degrees of shortening and stretch of the muscle fibers. The material consisted of frog and mouse muscle. The relation of the A- and I-band widths to the sarcomere length is fundamentally different when examining sarcomere lengths above and below the resting length. The increase of the sarcomere length when stretching above resting length is associated with a corresponding increase of the I-band width, the A-band width remaining fairly constant. Shortening below resting length is associated with a decrease of the A-band as well as the I-band width. The mean diameter of the myofilaments within the different bands varies with the degree of shortening. The difference between stretched and shortened sarcomeres was 2.5–3 times (from 50–60 A to 150 A within the H-band). Within the H- and M-bands the mean diameter is proportional to the A-band width. In the opaque part of the A-band extending between the H-band and the I-band the myofilaments can be split into several branches. A substructure in the myofilaments has been observed. It appears as about 20 A thick and about 100 A long rodlets which seem to form parts of subfilaments arranged in a helical fashion. When shortening the orientation of the substructural components changes from a roughly longitudinal to a transversal. An interpretation of the observations is presented according to which the shortening is due to a folding of the subfilaments representing cables of supercoiled α-helices.

Macrocrystalline patterns of closely packed poliovirus particles in ultrathin sections

Purified preparations of poliovirus MEF 1 (Type II) were spun down into a pellet by means of ultracentrifugation. The virus particles became closely packed and showed macrocrystalline patterns on sectioning. At least two well differentiated patterns were observed. The average spacing was 200–220 A and the virus particles consisted of osmiophilic, opaque centres which have average diameters of 160 A. These centres are surrounded by approximately 30 A thick, less osmiophilic zones.