Dendro-dendritic and reciprocal synapses in the primate motor cortex

1978 ◽  
Vol 203 (1150) ◽  
pp. 23-38 ◽  
Keyword(s):  
Motor Cortex ◽  
Synaptic Vesicles ◽  
Postsynaptic Membrane ◽  
Presynaptic Membrane ◽  
Membrane Specialization ◽  
Single Axon ◽  
Deep Layers ◽  
Presynaptic Dendrites ◽  
Symmetrical Type ◽  
Dense Projections

Dendro-dendritic synapses have been observed infrequently in the deep layers of the motor cortex. The presynaptic dendrites are of a varicose type and themselves receive a considerable density of synapses both of the asymmetric and symmetrical type. The ultrastructure of the dendro-dendritic synapse itself shows the typical arrangement of presynaptic and postsynaptic membrane densities, often with presynaptic dense projections, and the membrane specialization is of the symmetrical type. There is the usual cleft containing electron-dense material between the presynaptic and postsynaptic profiles. The synaptic vesicles occur in a small cluster confined to a region close to the presynaptic membrane specialization; some of the vesicles are flattened and were shown by tilt analysis to be of the discoid type. Two examples were found of reciprocal dendro-dendritic synapses, both components being of the symmetrical type. A single axon terminal may make a synapse on to both dendrites involved in a dendro-dendritic synapse.

scholarly journals The Lobster Optic Lamina

1966 ◽  
Vol 1 (2) ◽  
pp. 257-269
Author(s):  
J. HÁMORI ◽  
G. A. HORRIDGE
Keyword(s):  
Ganglion Cell ◽  
Synaptic Vesicles ◽  
Ganglion Cells ◽  
Postsynaptic Membrane ◽  
Retinula Cell ◽  
Secretory Vesicles ◽  
Presynaptic Membrane ◽  
Cell Axon ◽  
Sharp Distinction ◽  
Ganglion Cell Axon

The following interpretations are based on the assumption that the vesicles are presynaptic. Synapses between retinula cells are symmetrical contacts, with cisternae attached to both thickened membranes and the cleft is 8-10 mµ wide. Synapses from retinula terminal bags to the numerous invaginating spines of the ganglion cell axon have presynaptic ribbons and filaments but few vesicles; the cleft is 7.5-13 mµ wide. Synapses from retinula cell bags to secretory horizontal fibres have postsynaptic spines, typical vesicles one side and thickened presynaptic membrane (cleft Io-17 µ wide). Synapses from retinula fibres to empty (long) transverse fibres are similar. Synapses from secretory or empty transverse fibres to ganglion cell axons are axon-to-axon contacts; there are vesicles one side but both membranes are thickened; the cleft is 11-13 mµ wide. Between empty transverse fibres the synapses are similar but symmetrical; from empty to secretory transverse they have vesicles one side. Synapsesfrom secretory fibres to each other (symmetrical) or to empty transverse fibres (vesicles on one side and with only the postsynaptic membrane thickened) reveal a sharp distinction between synaptic vesicles and secretory vesicles. Serial synapses occur (a) from empty transverse fibre to secretory fibre to another empty transverse fibre, and (b) from retinula cell to secretory fibre to ganglion cell fibre. On account of its curious structure the optic cartridge probably has complex synaptic properties. Retinula terminals are probably inhibitory. Their light mitochondria, contrasting with the dense ones of the ganglion cells, are interpreted as aged.

Gap junctions between dendrites and somata of neurons in the primate sensori-motor cortex

1978 ◽  
Vol 203 (1150) ◽  
pp. 39-47 ◽  
Keyword(s):  
Motor Cortex ◽  
Gap Junctions ◽  
Plasma Membranes ◽  
Stellate Cells ◽  
Electrical Transmission ◽  
Cell Soma ◽  
Deep Layers ◽  
Sensory Cortices ◽  
A Cell ◽  
Presynaptic Dendrites

Gap junctions have been found infrequently between two dendrites or a dendrite and a cell soma in the deep layers of both the motor and somatic sensory cortices of the primate. At these junctions the outer leaflets of the plasma membranes of both profiles are intimately apposed with a gap of 2 nm between them which shows a structure of hexagonal subunits in tangential sections. These gap junctions occur mainly between the dendrites or dendrites and somata of large stellate cells but are also associated in some examples with a dendro-dendritic synapse and thus occur between large stellate dendrites and presynaptic dendrites; a desmosome may also occur in association with a gap junction and dendro-dendritic synapse. Gap junctions have been identified as sites of electrical transmission between cells in a number of sites and it is therefore suggested that some neurons in the sensori-motor cortex are electrotonically coupled.

Neurotransmitter release mechanisms and microtubules

1983 ◽  
Vol 218 (1211) ◽  
pp. 253-258 ◽  
Keyword(s):  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Ordered Structure ◽  
Presynaptic Membrane ◽  
Vesicle Membrane ◽  
Ordered Arrays ◽  
The Central Nervous System ◽  
Active Zones ◽  
Dense Projections ◽  
Regular Arrays

The morphological mechanisms involved in translocation of the synaptic vesicle to the presynaptic membrane, release of transmitter from the vesicle and recycling of the vesicle membrane are still far from understood. However, there is strong evidence that vesicles move along the surfaces of a specific set of highly labile presynaptic microtubules that direct the vesicles to the active zones. These microtubules are focused in a precise geometrical array, which is in register with and in contact with presynaptic dense projections of the central nervous system synapse or presynaptic dense bars of the motor endplate. These dense complexes constitute the presynaptic grid or active zones. The regular arrays of dense projections or bars are in turn coincident with rings or chains of synaptic vesicles mobilized at release sites on the presynaptic membrane (having arrived at these precise points by microtubule translocation). Thus it is suggested that the presynaptic microtubules not only translocate synaptic vesicles, but because of their ordered arrays determine, in ontogeny, the ordered structure of the presynaptic grid.

scholarly journals The Fine Structure of Synapses in the Ciliary Ganglion of the Chick

1960 ◽  
Vol 7 (1) ◽  
pp. 31-36 ◽  
Author(s):  
A. J. de Lorenzo
Keyword(s):  
Fine Structure ◽  
Synaptic Vesicles ◽  
Ganglion Cells ◽  
Single Cells ◽  
Synaptic Cleft ◽  
Structural Features ◽  
Ciliary Ganglion ◽  
Single Axon ◽  
Electron Microscopes ◽  
Electron Microscope Image

Ciliary ganglia of chick embryos and newly hatched chicks were examined in the light and electron microscopes. Particular attention was given to the fine structure of calyciform synapses, which are characteristically found in ciliary ganglia of birds. The calyciform endings are characterized by large expansions of the presynaptic axons upon ganglion cells, and the terminal processes extend over a considerable area of the cell surface. Often, indeed they appear to envelop the cell. In the electron microscope image, the appositional membranes are separated by a space about 300 to 400 A wide; i.e., the synaptic cleft. At irregularly spaced regions, the appositional membranes show areas of increased density. The presynaptic processes contain clusters of synaptic vesicles, localized at these dense regions. Thus the fine structure complex typical of other synapses is evident. The unique structural features of this synapse are as follows: (a) The calyx or presynaptic terminal derives from a single axon, does not arborize, and terminates upon a single ganglion cell. Thus, unlike the classical bouton terminal, this represents an anatomical device for firing single cells by single axons. (b) The surface area in contiguity, i.e., the area of appositional membranes, is far more extensive than the bouton terminal. The fine structure of this synapse is compared with others, for example, the classical boutons terminaux and purely electrical synapses, in an attempt to correlate fine structure with function.

G protein is coupled to presynaptic glutamate and GABA receptors in lobster neuromuscular synapse

1990 ◽  
Vol 63 (1) ◽  
pp. 173-180 ◽  
Author(s):  
A. Miwa ◽  
M. Ui ◽  
N. Kawai
Keyword(s):  
G Protein ◽  
Gaba Receptors ◽  
Neuromuscular Synapse ◽  
Postsynaptic Membrane ◽  
Gabab Receptors ◽  
Resting Membrane Potential ◽  
Gamma Aminobutyric Acid ◽  
Presynaptic Membrane ◽  
Axonal Membrane ◽  
K Channels

1. We have examined the effects of L-glutamate and gamma-aminobutyric acid (GABA) on the presynaptic membrane of spiny lobster by the use of intra-axonal recording near the nerve terminals. 2. Application of glutamate to the synaptic region produced hyperpolarization in the presynaptic membrane but depolarization in the postsynaptic membrane. The presynaptic glutamate potential (PGP) is generated by an activation of K+ channels, as evidenced by its dependence on external K+ concentration. 3. The PGP was not affected by a spider toxin (JSTX), which blocks the postsynaptic glutamate receptor. By contrast, pertussis toxin (IAP) effectively blocked the PGP without affecting the resting conductance channels or action potentials in the presynaptic membrane. 4. Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), a hydrolysis-resistant analogue of GTP, blocked the PGP, suggesting the involvement of a G protein in the generation of K+ current. 5. Application of GABA induced depolarization or hyperpolarization in the presynaptic axon depending on the resting membrane potential. By reducing external Cl-, GABA-induced hyperpolarizations were converted to depolarizations, indicating that they are mainly mediated by Cl-. 6. In contrast to GABA, baclofen consistently induced hyperpolarization in low Cl- solution as well as in normal solution. Baclofen-induced hyperpolarization was blocked by IAP, indicating the mediation of G protein. 7. These results suggest that the presynaptic membrane of lobster neuromuscular synapse has entirely different types of amino-acid receptors from those in the postsynaptic membrane. Both the excitatory and the inhibitory axonal membrane have glutamate ("glutamateB") and GABAB receptors, which activate K+ channels via G protein.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Determinants of synaptic strength vary across an axon arbor

2012 ◽  
Vol 107 (9) ◽  
pp. 2430-2441 ◽  
Author(s):  
Xiaoyu Peng ◽  
Thomas D. Parsons ◽  
Rita J. Balice-Gordon
Keyword(s):  
Synaptic Vesicles ◽  
Hippocampal Neurons ◽  
Synaptic Strength ◽  
Pool Size ◽  
Spatial Modulation ◽  
Readily Releasable Pool ◽  
Single Axon ◽  
Individual Vesicle ◽  
Highly Correlated ◽  
Vesicle Pool

We used synaptophysin-pHluorin expressed in hippocampal neurons to address how functional properties of terminals, namely, evoked release, total vesicle pool size, and release fraction, vary spatially across individual axon arbors. Consistent with previous reports, over short arbor distances (∼100 μm), evoked release was spatially heterogeneous when terminals contacted different postsynaptic dendrites or neurons. Regardless of the postsynaptic configuration, the evoked release and total vesicle pool size spatially covaried, suggesting that the fraction of synaptic vesicles available for release (release fraction) was similar over short distances. Evoked release and total vesicle pool size were highly correlated with the amount of NMDA receptors and PSD-95 in postsynaptic specialization. However, when individual axons were followed over longer distances (several hundred micrometers), a significant increase in evoked release was observed distally that was associated with an increased release fraction in distal terminals. The increase in distal release fraction can be accounted for by changes in individual vesicle release probability as well as readily releasable pool size. Our results suggest that for a single axon arbor, presynaptic strength indicated by evoked release over short distances is correlated with heterogeneity in total vesicle pool size, whereas over longer distances presynaptic strength is correlated with the spatial modulation of release fraction. Thus the mechanisms that determine synaptic strength differ depending on spatial scale.

scholarly journals SOME FEATURES OF THE SUBMICROSCOPIC MORPHOLOGY OF SYNAPSES IN FROG AND EARTHWORM

1955 ◽  
Vol 1 (1) ◽  
pp. 47-58 ◽  
Author(s):  
Eduardo D. P. De Robertis ◽  
H. Stanley Bennett
Keyword(s):  
Electron Micrographs ◽  
Nerve Cord ◽  
Synaptic Vesicles ◽  
Sympathetic Ganglia ◽  
Synaptic Membrane ◽  
Presynaptic Membrane ◽  
Close Relationship

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.

scholarly journals Magnetic susceptibility in the deep layers of the primary motor cortex in Amyotrophic Lateral Sclerosis

2016 ◽  
Vol 12 ◽  
pp. 965-969 ◽  
Author(s):  
M. Costagli ◽  
G. Donatelli ◽  
L. Biagi ◽  
E. Caldarazzo Ienco ◽  
G. Siciliano ◽  
...  
Keyword(s):  
Amyotrophic Lateral Sclerosis ◽  
Magnetic Susceptibility ◽  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Deep Layers ◽  
Lateral Sclerosis

scholarly journals Morphological changes in the neuritic growth cone and target neuron during synaptic junction development in culture.

1976 ◽  
Vol 68 (2) ◽  
pp. 240-263 ◽  
Author(s):  
R P Rees ◽  
M B Bunge ◽  
R P Bunge
Keyword(s):  
Growth Cone ◽  
Synaptic Vesicles ◽  
Morphological Changes ◽  
Postsynaptic Density ◽  
Postsynaptic Membrane ◽  
Coated Vesicles ◽  
Neuronal Membrane ◽  
Initial Contact ◽  
Thoracic Spinal Cord ◽  
Target Neuron

Our object was to characterize the morphological changes occurring in pre- and postsynaptic elements during their initial contact and subsequent maturation into typical synaptic profiles. Neurons from superior cervical ganglia (SCG) of perinatal rats were freed of their supporting cells and established as isolated cells in culture. To these were added explants of embryonic rat thoracic spinal cord to allow interaction between outgrowing cord neurites and the isolated autonomic neurons. Time of initial contact was assessed by light microscopy; at timed intervals thereafter, cultures were fixed for electron microscopy. Upon contact, growth cone filopodia became extensively applied to the SCG neuronal plasmalemma and manifested numerous punctate regions in which the apposing plasma membranes were separated by only 7-10 nm. The Golgi apparatus of the target neuron hypertrophied, and its production of coated vesicles increased. Similar vesicles were seen in continuity with the SCG plasmalemma near the close contact site; their apparent contribution of a region of postsynaptic membrane with undercoating was considered to be the first definitive sign of synapse formation. Tracer work with peroxidase and ferritin confirmed that the traffic of coated vesicles within the neuronal soma is largely from Golgi region to somal surface. Subsequent to the appearance of postsynaptic density, the form and content of the growth cone was altered by the loss of filopodia and the appearance of synaptic vesicles which gradually became clustered opposite the postsynaptic density. As the synapse matured, synaptic vesicles increased in number, cleft width and content increased, presynaptic density appeared, branched membranous reticulum became greatly diminished, and most lysosomal structures disappeared. Coated vesicles continued to be associated with the postsynaptic membrane at all stages of maturation. The incorporation of Golgi-derived vesicles into discrete regions of the cell membrane could provide the mechanism for confining specific characteristics of the neuronal membrane to the synaptic region.

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