scholarly journals Neural Organization of the Median Ocellus of the Dragonfly

1972 ◽  
Vol 60 (2) ◽  
pp. 148-165 ◽  
Author(s):  
John E. Dowling ◽  
Richard L. Chappell
Keyword(s):  
Electron Microscopy ◽  
Synaptic Vesicles ◽  
Receptor Cell ◽  
Presynaptic Membrane ◽  
Cell Axon ◽  
Axon Terminals ◽  
Neural Organization ◽  
Dense Cluster ◽  
Median Ocellus ◽  
Ocellar Nerve

Two types of presumed synaptic contacts have been recognized by electron microscopy in the synaptic plexus of the median ocellus of the dragonfly. The first type is characterized by an electron-opaque, button-like organelle in the presynaptic cytoplasm, surrounded by a cluster of synaptic vesicles. Two postsynaptic elements are associated with these junctions, which we have termed button synapses. The second synaptic type is characterized by a dense cluster of synaptic vesicles adjacent to the presumed presynaptic membrane. One postsynaptic element is observed at these junctions. The overwhelming majority of synapses seen in the plexus are button synapses. They are found most commonly in the receptor cell axons where they synaptically contact ocellar nerve dendrites and adjacent receptor cell axons. Button synapses are also seen in the ocellar nerve dendrites where they appear to make synapses back onto receptor axon terminals as well as onto adjacent ocellar nerve dendrites. Reciprocal and serial synaptic arrangements between receptor cell axon terminals, and between receptor cell axon terminals and ocellar nerve dendrites are occasionally seen. It is suggested that the lateral and feedback synapses in the median ocellus of the dragonfly play a role in enhancing transients in the postsynaptic responses.

Presynaptic Afferent Inhibition of Lobster Olfactory Receptor Cells: Reduced Action-Potential Propagation Into Axon Terminals

1998 ◽  
Vol 80 (2) ◽  
pp. 1011-1015 ◽  
Author(s):  
Matt Wachowiak ◽  
Lawrence B. Cohen
Keyword(s):  
Action Potential ◽  
Olfactory Receptor ◽  
Receptor Cell ◽  
Action Potential Propagation ◽  
Cell Axon ◽  
Axon Terminals ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Afferent Inhibition ◽  
Reduced Action

Wachowiak, Matt and Lawrence B. Cohen. Presynaptic afferent inhibition of lobster olfactory receptor cells: reduced action-potential propagation into axon terminals. J. Neurophysiol. 80: 1011–1015, 1998. Action-potential propagation into the axon terminals of olfactory receptor cells was measured with the use of voltage-sensitive dye imaging in the isolated spiny lobster brain. Conditioning shocks to the olfactory nerve, known to cause long-lasting suppression of olfactory lobe neurons, allowed the selective imaging of activity in receptor cell axon terminals. In normal saline the optical signal from axon terminals evoked by a test stimulus was brief (40 ms) and small in amplitude. In the presence of low-Ca2+/high-Mg2+ saline designed to reduce synaptic transmission, the test response was unchanged in time course but increased significantly in amplitude (57 ± 16%, means ± SE). This increase suggests that propagation into receptor cell axon terminals is normally suppressed after a conditioning shock; this suppression is presumably synaptically mediated. Thus our results show that presynaptic inhibition occurs at the first synapse in the olfactory pathway and that the inhibition is mediated, at least in part, via suppression of action-potential propagation into the presynaptic terminal.

scholarly journals Neural Organization of the Median Ocellus of the Dragonfly

1972 ◽  
Vol 60 (2) ◽  
pp. 121-147 ◽  
Author(s):  
Richard L. Chappell ◽  
John E. Dowling
Keyword(s):  
Synaptic Transmission ◽  
Receptor Potential ◽  
Transient Responses ◽  
Slow Potential ◽  
Neural Organization ◽  
Postsynaptic Activity ◽  
Potential Activity ◽  
Median Ocellus ◽  
Ocellar Nerve

Intracellular responses from receptors and postsynaptic units have been recorded in the median ocellus of the dragonfly. The receptors respond to light with a graded, depolarizing potential and a single, tetrodotoxin-sensitive impulse at "on." The postsynaptic units (ocellar nerve dendrites) hyperpolarize during illumination and show a transient, depolarizing response at "off." The light-evoked slow potential responses of the postsynaptic units are not altered by the application of tetrodotoxin to the ocellus. It appears, therefore, that the graded receptor potential, which survives the application of tetrodotoxin, is responsible for mediating synaptic transmission in the ocellus. Comparison of pre- and postsynaptic slow potential activity shows (a) longer latencies in postsynaptic units by 5–20 msec, (b) enhanced photosensitivity in postsynaptic units by 1–2 log units, and (c) more transient responses in postsynaptic units. It is suggested that enhanced photosensitivity of postsynaptic activity is a result of summation of many receptors onto the postsynaptic elements, and that transients in the postsynaptic responses are related to the complex synaptic arrangements in the ocellar plexus to be described in the following paper.

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.

A structural study of the squid synapse after intraaxonal injection of calcium

1978 ◽  
Vol 201 (1145) ◽  
pp. 317-333 ◽  
Keyword(s):  
Electron Microscopy ◽  
Nerve Terminal ◽  
Synaptic Vesicles ◽  
Presynaptic Terminal ◽  
Presynaptic Membrane ◽  
Ground Structure ◽  
Presynaptic Nerve Terminal ◽  
Dense Deposits ◽  
Membrane Bound ◽  
Giant Synapse

The giant synapse of the squid was examined by electron microscopy after ionophoretic injection of Ca 2+ ions into the pre- or postsynaptic axon. The results suggest that there are differences in the Ca-buffering mechanisms in pre- and postsynaptic axons. For instance, after injection of Ca 2+ into the postsynaptic axon, mitochondria were heavily loaded with granular inclusions. In contrast, mitochondria of injected presynaptic terminals did not contain inclusions. In the postsynaptic axon, besides inclusions in mitochondria, dense deposits were found in axoplasmic vesicles and cisterns that appeared locally at the site of injection. Injection of Ca 2+ into the presynaptic terminal produced non-membrane bound dense deposits associated with the filamentous ground structure of the axoplasm. Some calcium may also be bound to the presynaptic membrane which appears dense after injection. In both axons the alterations produced by injected Ca 2+ were confined mainly to the area of injection. After injection of Ca 2+ into the presynaptic nerve terminal, synaptic vesicles disappeared and a large number of coated vesicles appeared. In addition, membrane invaginations developed involving not only the presynaptic membrane but also that of postsynaptic processes and glial cells. After injection of large quantities of Ca 2+ into the postsynaptic axon, electron-dense precipitates were seen also in the presynaptic terminal indicating retrograde transfer of material from post- to presynaptic axons.

Synaptic vesicles and microtubules in frog motor endplates

1978 ◽  
Vol 203 (1152) ◽  
pp. 219-227 ◽  
Keyword(s):  
Electron Microscopy ◽  
Skeletal Muscle ◽  
Small Proportion ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Presynaptic Membrane ◽  
Albumin Solution ◽  
Motor Endplates ◽  
Active Zones ◽  
A New Technique

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.

scholarly journals The structure and function of ‘active zone material’ at synapses

2015 ◽  
Vol 370 (1672) ◽  
pp. 20140189 ◽  
Author(s):  
Joseph A. Szule ◽  
Jae Hoon Jung ◽  
Uel J. McMahan
Keyword(s):  
Spatial Resolution ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Electron Tomography ◽  
Structure And Function ◽  
Presynaptic Membrane ◽  
Axon Terminals ◽  
Active Zones ◽  
And Function

The docking of synaptic vesicles on the presynaptic membrane and their priming for fusion with it to mediate synaptic transmission of nerve impulses typically occur at structurally specialized regions on the membrane called active zones. Stable components of active zones include aggregates of macromolecules, ‘active zone material’ (AZM), attached to the presynaptic membrane, and aggregates of Ca 2+ -channels in the membrane, through which Ca 2+ enters the cytosol to trigger impulse-evoked vesicle fusion with the presynaptic membrane by interacting with Ca 2+ -sensors on the vesicles. This laboratory has used electron tomography to study, at macromolecular spatial resolution, the structure and function of AZM at the simply arranged active zones of axon terminals at frog neuromuscular junctions. The results support the conclusion that AZM directs the docking and priming of synaptic vesicles and essential positioning of Ca 2+ -channels relative to the vesicles' Ca 2+ -sensors. Here we review the findings and comment on their applicability to understanding mechanisms of docking, priming and Ca 2+ -triggering at other synapses, where the arrangement of active zone components differs.

scholarly journals Direction selectivity in retinal bipolar cell axon terminals

Neuron ◽  
2021 ◽  
Author(s):  
Akihiro Matsumoto ◽  
Weaam Agbariah ◽  
Stella Solveig Nolte ◽  
Rawan Andrawos ◽  
Hadara Levi ◽  
...  
Keyword(s):  
Bipolar Cell ◽  
Direction Selectivity ◽  
Cell Axon ◽  
Axon Terminals

Orientation of horizontal cell axon terminals in the streak of the turtle retina

Nature ◽  
1979 ◽  
Vol 280 (5717) ◽  
pp. 60-62 ◽  
Author(s):  
RICHARD A. NORMANN ◽  
HELGA KOLB ◽  
MENACHEM HANANI ◽  
EFREM PASINO ◽  
RICHARD HOLUB
Keyword(s):  
Horizontal Cell ◽  
Cell Axon ◽  
Axon Terminals
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