Spherical Synaptic Vesicles Research Articles

Observations on the fine structure of the central nucleus of the inferior colliculus of the cat.

AbstractThe central nucleus of the inferior colliculus has been examined electron microscopically in the adult cat, particular attention being paid to its ventrolateral division in which the majority of lateral lemniscal afferents end.Two cell types can be recognized: one, which is the equivalent of the spiny principal cell of light microscopy, is distinguished by having its soma and large proximal dendrites covered by axon terminals. More distally situated dendrites have fewer terminals ending mainly on dendritic spines. These spines resemble those of the cerebral cortex and have a modified spine apparatus. The second type of cell is the equivalent of the small multipolar cell of light microscopy. It has spineless dendrites and these and the soma receive relatively fewer axon terminals. It has a very thin axon.Several types of axon terminal can be recognized. Type I terminals are large, contain spherical synaptic vesicles and end by means of asymmetrical synaptic contacts, on the somata and proximal dendrites of principal cells and on the smaller dendrites of multipolar cells. The extracellular space on one or both sides of the synaptic complex is often characteristically widened. Correlative experimental degeneration studies show that these are the terminals of lateral lemniscal fibers. Various forms of smaller terminal also make asymmetrical contacts and have spherical vesicles. One type has a high concentration of large, densecored vesicles as well.Two types of axon terminal end in symmetrical synaptic contacts. One contains large, homogeneously flattened synaptic vesicles; the other, which is more common, contains smaller, irregularly flattened or pleomorphic synaptic vesicles.In the dorsomedial division of the central nucleus, the terminals of corticofugal fiber have spherical synaptic vesicles and end in asymmetrical synaptic contacts upon large dendritic spines.

Structural characteristics of connections between medial descending systems and spinal neurons

Structural and ultrastructural changes in the medial part of the ventral horn were studied in segments of the cat spinal cord following destruction of the ventral column at the level C1–C2. Analysis of results obtained by the Fink — Heimer method showed that degenerating preterminals occur mainly in Rexed's lamina VIII and also in ventromedial zones of lamina VII. Preterminals of descending pathways of the ventral column are also found in the intermediate nucleus of Cajal (central part of lamina VI) and in the ventromedial motor nucleus. Fewer of these preterminals are present in the thoracic and, in particular, in the lumbar segments. Staining by the Hollander — Vaaland method revealed degenerating myelinated axons of small diameter (3–5 µ), evidently collaterals of descending fibers entering the gray matter, in lamina VIII. Degenerative changes in myelinated axons may be manifested either as marked condensation and shrinking or as the appearance of numerous neurofilaments, polymembraneous structures, and cytolysomes. Degeneration also affects axon terminals (axo-dendritic, axo-somatic, and axo-axonal) with spherical or flattened synaptic vesicles. Counting the relative numbers of intact terminals of the various types and their comparison with the corresponding figures for normal animals shows that most connections of descending fibers with spinal neurons are axo-dendritic in character. No degenerating terminals were found on the soma of the "dark" neurons or their processes.

Cell and neuropil architecture of the intermediolateral (sympathetic) nucleus of cat spinal cord

A Golgi study of the neuronal elements in the thoracic intermedio-lateral nucleus (preganglionic sympathetic neuronal column) is presented, with some additional electron microscopic observations. The dendrites of the sympathetic neurons are strictly longitudinally oriented; their axons can be traced along the border between the ventral horn and the lateral funiculus directly into the ventral rootlers. No initial collateral of the axons can be observed. The neuronal population of the intermedio-lateral nucleus is entirely homogeneous and little contaminated by dendrites of other cells. The axonal neuropil of the nucleus is also longitudinally oriented and is fed mainly from collaterals of the lateral funiculus. The synaptic arrangement between the axonal and dendritic arborizations is mainly of the ‘climbing type’. Three different kinds of synaptic terminals can be recognized in the electron microscope picture: (1) terminals containing an unusually large number of large osmiophilic vesicles and apparently clear ordinary vesicles; (2) terminals (often axo-somatic) containing characteristic flattened vesicles; and (3) axo-dendritic terminals containing clear spherical synaptic vesicles.

On the significance of cross-bridges between microtubules and synaptic vesicles.

Observations on the fine structure of synaptic and non-synaptic axoplasm in the spinal cord of the lamprey ammocoete ( Petromyzon marinus ) are described. Previous studies on this material revealed a close association between spherical vesicles and axoplasmic microtubules near central synapses, and observations were consistent with the suggestion that synaptic vesicles become detached from oriented microtubules in the focal clusters adjoining the presynaptic membrane across which transmitter release takes place. These observations have been extended to include axons containing non-spherical or ellipsoidal vesicles— possibly containing a transmitter chemically and functionally distinct from that in spherical synaptic vesicles. Structural cross-bridges between both microtubules and vesicle populations are now described; these are found not only in the vesicle concentrations bordering synaptic foci, but also in non-synaptic axoplasmic regions where sparsely distributed vesicles are found in association with microtubules. It is suggested that the bridging between vesicles and microtubules may reflect a mechanism for transport of the former—a possibility in accord with cumulative evidence of involvement of microtubules in rapid intracellular translocation in a variety of cells. It is proposed that arrival of excitation at a synaptic site is not only coupled with transmitter release across the axon plasma membrane, but that events at the cell membrane may in turn be coupled with a means of supplying vesicles to the synaptic locus. This hypothesis suggests that the synapse may rely on distant parts of the neuron, perhaps including the cell body, for materials involved in synaptic transmission.

Ultrastructure of tri-ortho-cresyl phosphate poisoning in the chicken. II. Studies on spinal cord alterations.

Electron-microscopic investigations of the spinal cord in adult chickens poisoned with TOCP (Tri-Ortho-Cresyl Phosphate) show pathological alterations as early as the first day after appearance of the clinical symptoms. Of the same qualitative order as in the peripheral nervous system, they refer to the nerve fibres in the white matter in form of primarily diseased axons, with proliferation of the endoplasmic reticulum and disintegration of the neurofilaments. In the grey substance of the anterior horn, in particular, one sees severe structural alterations in the boutons terminaux while the motoneurons are hardly modified. The most striking finding already in the early stage is a massive swelling of the spherical synaptic vesicles in the boutons of theS-type, attributed to axo-somatic synapses.

Morphological variations in the dendritic spines of the neocortex.

ABSTRACT The structural variations which occur in the dendritic spines of pyramidal neurons of the somatic sensory cortex of the cat are described, particular attention being paid to spines attached to different parts of the dendritic tree. Spines may be recognized particularly by the absence of neurotubules and the common presence of a spine apparatus, and they can be considered as pednnculated or sessile, depending upon the presence or absence of a narrow pedicle. Within these 2 categories spines may be rounded, cup-like or prismatic, can be large or small, and may show various degrees of inversion of the surface receiving a synaptic contact. While spines of every size and shape may be attached to dendrites of all diameters, there is a definite tendency for the largest spines to occur on the smallest dendrites and vice versa. Furthermore, the smallest dendrites possess the spines with the longest pedicles. Every dendritic spine receives 1 axon terminal containing spherical synaptic vesicles and ending in an asymmetrical synaptic contact. In addition, 10–20 % of the spines receive a second terminal, which in some cases may contain spherical vesicles and terminate asymmetrically but in others contains small, flattened or pleomorphic vesicles and ends in a symmetrical contact. The additional terminal may end on the pedicle of the spine or on the parent dendrite near the attachment of the pedicle. In the latter site, asymmetrical synapses are commonly associated with an additional spine apparatus.

Electrophysiological and electron microscopic studies on the neuromuscular junction of the crayfish stretch receptors.

1. Investigations on the inhibitory neuromuscular junction of crayfish stretch receptor muscles were performed electrophysiologically and electron microscopically.2. Fast receptor muscles responded to direct stimulation with a transient depolarization which exhibited the property of a propagated action potential, but did not show any overshoot. On the other hand, slow muscles did not generate an action potential but showed excitatory junction potentials of 10-30mV in amplitude. EJPs of fast receptor muscles were summated by repetitive stimulation until all-or-nothing spikes were generated.3. When a nerve bundle was carefully isolated and one of the isolated filaments were stimulated, inhibitory junction potentials could be obtained from fast stretch receptor muscles by the microelectrode inserted near the receptor neuron. They had a reversal potential approximately at-60mV. Inhibitory junction potentials completely inhibited excitatory junction potentials and spikes when inhibitory nerves were stimulated at high frequency of 100c/s for several seconds.4. Application of GABA of 10-4-10-5M showed similar effects to stimulation of inhibitory nerves. It's effect was due to the increase of postsynaptic membrane conductance.5. Two different types of synapses were identified electron microscopically at fast stretch receptor muscles. The one contained spherical synaptic vesicles, the other ellipsoidal ones. The latter was observed within the limit of the vicinity of the neuron soma. From UCHIZONO'S (1965, 1966) previous studies and the present electrophysiological experiments, it was concluded that the latter was the terminal of inhibitory neuromuscular junctions.

Observations on the abdominal stretch receptor and the fine structure of associated axo-dendritic synapses and neuromuscular junctions in homarus.

AbstractThe abdominal stretch receptor of lobster has been examined. Fine structural details of the receptor nerves are presented and neurophysiological correlations are suggested. Both axo‐dendritic synapses and neuromuscular junctions were examined. Axo‐dendritic synapses are of one type only, possessing elongated, or flattened, presynaptic vesicles approximately 200 Å in diameter and 400–600 Å long. In contrast two distinct types of neuromuscular junctions were observed. The first possesses spherical synaptic vesicles 500–900 Å in diameter. The second possesses synaptic vesicles of dimensions similar to those of axo‐dendritic synapses. It is suggested that synapses, both axo‐dendritic and neuromuscular, with elongated or flattened vesicles, are inhibitory, and that neuromuscular junctions with spherical vesicles are excitatory.