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Biomedical subjects

E G Gray

Publications and source records attributed to E G Gray.

14 recordsLinked to original sources
PubMed1979

Marginal bundles of axoplasmic microtubules at nodes of Ranvier within muscle.

Using a special albumin technique, nodes of Ranvier have been examined within frog skeletal muscle, sciatic nerve and rat and frog cerebrum. Initial segments have been examined in cerebrum of frog and rat. Mictotubules usually run longitudinally through these regions, but within the bare area of the intramuscular node of Ranvier, annular or helical bundles of microtubules run in a marginal band at right angles to the more centrally placed longitudinal microtubules. These nodal bare areas show a pronounced convexity and it is suggested that the annular microtubules serve to maintain this convexity during muscle contraction.

Animals↗
PubMed1979

Ultrastructure of the Mauthner axon collateral and its synapses in the goldfish spinal cord.

The ultrastructure of the synapses formed by the Mauthner axon collateral (MAC) was examined in the goldfish spinal cord. All such collaterals form axo-dendritic chemical synapses with dendrites of motor and interneurons. Besides these chemical synapses, contacts have been found between some MAC and axons of interneurons, which can be characterized as gap junctions with presumed electrical transmission. All cellular processes contacted by the MAC contain 'dense bands' of material in their cytoplasm. These 'dense bands' are absent from other parts of the fish C.N.S. These observations and the peculiar synaptic pattern are discussed and correlated with electrophysiological results.

Animals↗
PubMed1979

Aggregations of synaptic vesicles on the exposed inner membrane of presynaptic mitochondria in brain.

Fragments of rat cerebral cortex have been incubated under various conditions. When divalent cations are present, patches of the external membrane of some mitochondria are disassembled leaving the inner mitochondrial membrane exposed to the cytoplasm. Sometimes the entire external membrane is missing. In presynaptic bulbs the synaptic vesicles are attracted and adhere to the exposed outer face of the inner mitochondrial membrane. The mode of attraction and adhesion of the vesicles is discussed. Possibly this could serve as a model for further investigation of the attraction of vesicles to the active zone of the presynaptic membrane.

Animals↗
PubMed1978

Synaptic vesicles and microtubules in frog motor endplates.

Motor endplates of the cutaneous pectoris skeletal muscle of the frog have been examined by electron microscopy using a new technique. This involves pretreatment with an albumin solution, followed by fixation with 4% unbuffered tetroxide. A small proportion of the endplate axonal ramifications show microtubules clothed in synaptic vesicles and focused on the presynaptic membrane, in particular on the active zones. The microtubules run in the presynaptic cytoplasm either parallel to or across the active zones. These two sets of microtubules cross each other at the active zones, which lie opposite the dips in the post-junctional folds. The possibility that the microtubules are involved in the translocation of synaptic vesicles to the active zone is discussed.

Albumins↗
PubMed1978

On T-tubule openings at the sarcolemma of white fast-twitch muscle fibres in fish and frog.

In "white" muscle fibres of a teleost fish T-tubule openings may occur regularly at all Z-disc levels between adjacent peripheral myofibrils, the T-tubule openings thus occurring at a density of ca. 0.9 micrometer-2. In frog "white" fibres, T-tubule openings are infrequently seen in material fixed like the fish material. In material prepared according to the albumin method of Gray (1975, 1976 a, b) which renders the muscle fibres swollen, straight tubules or sometimes chains of vesicles instead are seen opening at the sarcolemmal surface. Such tubules occur at a higher density than expected from experiments with local activation of contraction. Lability and dynamics within the T-system normally and during fixation are discussed.

Animals↗
PubMed1977

The effects of different methods of fixation on central nervous system synaptic pinocytotic vesicles.

Synaptic pinocytotic vesicles (invaginating from the surface membrane) and coated vesicles inside rat mossy fiber endings were counted after the use of different kinds of fixatives. Significantly greater numbers of pinocytotic vesicles and coated pinocytotic vesicles per unit length of membrane were found when osmium was used as the first fixative. A high positive correlation was found between these values and the number of coated vesicles per unit area of mossy fiber ending profiles. The results emphasize the need for caution when considering the theory that in vivo synaptic vesicle recycling involves a coated vesicle invagination of the surface membrane followed by internalisation and loss of coat of the vesicle.

Animals↗
PubMed1977

Microtubules associated with postsynaptic 'thickenings'.

Using a new albumin technique, microtubules can be seen closely related to or associated with the postsynaptic 'thickening' of mature and immature central nervous synapses. Thus in conventionally fixed synapses (without albumin pretreatment) where microtubules cannot usually be observed running into the postsynaptic dense material, this material could perhaps, in part, consist of the debris of in vivo microtubules. Smooth endoplasmic reticulum (ER) is often seen associated with the microtubules near the postsynaptic 'thickening'. Microtubules, and possibly smooth ER, may have an important role in the initiation of synapse formation and in the maintenance of mature synapses.

Age Factors↗
PubMed1976

Microtubules associated with nuclear pore complexes and coated pits in the CNS.

Using a new albumin prefixation technique, microtubules have been observed in close association with the nuclear pores of neurons and glia. Thus, microtubules may be involved in such phenomena as anchoring, migration or rotation of the nucleus or in chemical messenger transport between nucleus and cytoplasm. Microtubules are also seen running close to the coated pits of dendrites. The implications are discussed.

Animals↗
PubMed1976

Microtubules in synapses of the retina.

Using a new method, microtubules can be seen running up to, and lying in close relationship with, the synaptic ribbons in the outer and inner plexiform layers of the frog retina. In the inner plexiform layer microtubules can be seen running up to the terminal membrane in the non-ribbon synapses. Unlike non-ribbon C.N.S. synapses (frog and rat) processed by the same method. There is no clear association between synaptic vesicles and microtubules in the approach regions.

Animals↗
PubMed1976

Coated-vesicle shells, particle/chain material, and tubulin in brain synaptosomes. An electron microscope and biochemical study.

Coated vesicles (CVs), plain synaptic vesicles (PSVs), and nonvesicular flocculent material were isolated from synaptosomes and examined with goniometry and high-resolution electron microscopy after either negative staining or various biochemical procedures. The flocculent material (i.e. the presynaptic matrix material except CV shells) is largely composed of particulate or elongated (chainlike) structures; some of this material (here referred to as particle/chain material) is attached to PSVs. The results obtained were: (a) the proteinaceous properties of the CV coat (also referred to as CV shell) and the particle/chain material were demonstrated with chymotrypsin; (b) the CV shell, studied with various negative-staining techniques, differs from the particle/chain material since it has no 3-4-nm globular subunits and reacts differently to alkaline pH; (c) the particle/chain material consists of aggregates of 3-4-nm globular subunits, four of which yield 8-10-nm fine particles; and these particles can be further aggregated into chains 8-10 nm wide and up to 30-60 nm long showing a "hollow" core; (d) vinblastine sulfate induced ringlike or helical crystalloid precipitates closely resembling the vinblastine-induced microtubule crystals reported in the literature, but vinblastine had no effect on either the CV shell material or the particle/chain material.

Animals↗
PubMed1975

Synaptic fine structure and nuclear, cytoplasmic and extracellular networks: The stereoframework concept.

When certain intracellular and extracellular localities known to be rich in protein complexes are fixed and processed for electron microscopy, they show a reticulate precipitate which represents three-dimensional framework of material that forms the wall of polygonal lacunae. This is referred to as a stereoframework. Examples of a stereoframework described her include the presynaptic dense projections, cleft substance, postsynaptic density, the cytonet, coats of coated vesicles, reticulosomes, 'microfilamentous' network of growth cones, the glycocalyx of gut microvilli, blood plasma, precipitates of the Golgi apparatus, the chromatin of nuclei and the nuclear pore complex. The stereoframeworkappears most electron-dense when it has a very close mesh, e.g. as in the case of the dense projections. The stereoframework is assumed to have no direct relationship with themolecular architecture of the protein complexes in vivo and so can be regarded as a denaturization and precipitation artifact. This being so, attempts to elucidate the substructure of the above entities simply by inspection are fruitless. Furthermore, evidence is given that stereoframework precipitation can distort or completely obliterate organelles occupying the same locality, for example this could apply to structures such as actin filaments (perhaps running into the locality marked by a dense projection), microtubules(running into the presynaptic bag), smooth ER, tenuous connections between synaptic vesicles and the presynaptic membrane, structures within the nuclear pore complex and chromosome substructures in the nucleus. Finally it is suggested that the flat shape of synaptic vesicles (at inhibitory synapses) may be a distortion effect imposed upon the synaptic vesicles not as a result of osmotic effects, but as a conformation to the shape of a stereoframework which has been precipitated from protein complexes in the vicinity ofthe synaptic vesicles.

Animals↗