Gap junctions and septate-like junctions between neurons of the opisthobranch molluscNavanax inermis

Hall, David H.; Spray, David C.; Bennett, Michael V. L.

doi:10.1007/bf01258154

Cited by 16 publications

(8 citation statements)

References 26 publications

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“…The dramatic change in strength of coupling associated with these two patterns of firing is attributable to shunting of intercellular current by activation of inhibitory chemical synapses (110). Although a change in resistance of the junctional membrane has not been totally ruled out, the morphological localization of chemical synapses near the site of coupling and the changes in input and transfer resistances recorded in the two states are consistent with uncoupling due solely to changes in nonjunctional resistances (54,110). This sort of uncoupling may also occur in the inferior olive in the mammalian CNS (109).…”

Section: Introduction To Physiological Studies Of Couplingsupporting

confidence: 52%

Physiology and Pharmacology of Gap Junctions

Spray¹,

Bennett²

1985

Annu. Rev. Physiol.

437

164

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Section: Introduction To Physiological Studies Of Couplingsupporting

confidence: 52%

Physiology and Pharmacology of Gap Junctions

Spray¹,

Bennett²

1985

Annu. Rev. Physiol.

437

164

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“…Because the coupling between the cells of Portunus is large (Tazaki & Cooke, 1979a), it could be argued that the small size of the appositions makes them unlikely candidates for these electrical synapses; however, this argument has no validity. As shown by Hall et al (1983), small, scattered clusters of intercellular channels can account for large electrical coupling, provided that they are present in sufficient numbers.…”

Section: Electrical Junctions Between Large Cellsmentioning

confidence: 98%

“…If the coupling between the large cells occurs primarily through a diffuse network of small junctions sited on the fine terminal arborizations of their collaterals, as suggested by our data, their low-pass filtering characteristics could be readily explained (Bennett, 1966), since these processes, being located at some distance from the zone of spike initiation, interpose a load capacitance between the site of intercellular current spread and that of the excitable membrane. It is interesting to note that the junctions between the giant neurons of Navanax, which are ruade up by numerous but small patches of intercellular channels (Hall et al, 1983) between fine neuronal processes, also act as a low-pass filter (Levitan et al 1970).…”

Section: Electrical Junctions Between Large Cellsmentioning

confidence: 99%

Structure and localization of synaptic complexes in the cardiac ganglion of a portunid crab

et al. 1987

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The cardiac ganglion of Portunus sanguinolentus exhibits spontaneous rhythmic activity when isolated. The ganglion contains five large and four small intrinsic neurons and is innervated by three pairs of fibres originating in the thoracic ganglia. We have identified the processes of the large neurons in electron micrographs by injecting these cells with two electron-dense markers, horseradish peroxidase (HRP) and Procion Rubine (PR). In addition we have studied the processes of the four smaller neurons by light microscopy serial reconstructions and by electron microscopy of selected regions. Both markers were found only in neuronal processes and not in glial cells nor in the extracellular space, except close to the soma of the injected cell. We found contacts between the small secondary (collateral) processes of the large cells but not between their somata or their primary processes (axons and dendrites). Two specialized structures present at the contacts between the collateral processes were small membrane close appositions, possibly the site of electrotonic junctions, and chemical synapses. Contacts between processes marked by HRP and those marked by PR were common, as were contacts between processes marked by either HRP or PR and those of the other intrinsic neurons. Adjacent processes stained by PR could contain PR deposits of different densities, but it is unclear whether this finding was due to intercellular diffusion of the dye or to its diffusing at different rates into branches of the same process. Identified processes of all the intrinsic neurons contained the same type of vesicles, which were different from those found in processes of the extrinsic fibres. Chemical synapses were present at contacts between processes of the extrinsic and intrinsic neurons, as well as at contacts between processes of the intrinsic neurons. The axons of three small cells made a series of contacts at which extensive arrays of membrane close appositions, but not chemical synapses, were found. These three axons also formed contacts, either directly or through their collateral branches, with processes of the large cells, at which both membrane close appositions and chemical synapses were present. The axon of the fourth small cell could not be followed in our series.

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“…In addition, through the use of HRP labelling, this is the first report of gap junctions connecting the axon collaterals of two identified molluscan neurons (R19, L19) which are known to be electrically coupled (Bulloch, 1985b). Previous ultrastructural studies of molluscan ganglia found it difficult to identify unambiguously gap junctions in thin sections and have relied primarily on freeze fracture (Hall et al, 1983(Hall et al, , 1984Kaczmarek et al, 1979;Roubos et al, 1985). The use of hypertonic fixatives, en bloc uranyl acetate, and a goniometer tilting stage in this study, however, were found greatly to facilitate the detection of gap junctions in thin plastic sections.…”

Section: Gap Junctionsmentioning

confidence: 70%

Chemical synapses, particle arrays, pseudo‐gap junctions and gap junctions of neurons and glia in the buccal ganglion of Helisoma

Berdan¹,

Shivers²,

Bulloch³

1987

Synapse

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The nervous system of the snail, Helisoma trivolvis, has been utilized for a wide range of studies of neuronal plasticity; however, the ultrastructural features of this tissue were previously unknown. The present study examined the nature of synaptic interactions of neurons and glia and considered several plasma membrane specializations of these cells. The symmetrical pair of buccal ganglia consisted of a ring of unipolar neurons surrounding a central neuropil. The neurons were separated by two morphologically distinct types of glia: type I were most numerous and possessed an electron-dense homogeneous cytoplasm, whereas type II glia were of lower electron density, possessed a heterogeneous cytoplasm, and appeared to be phagocytic. Gap junctions were abundant between glia and were occasionally found between neuronal processes, including those of neurons 19 injected with horseradish peroxidase (HRP). Comparison of neuron and glial gap junction widths (16.4 and 17.6 nm, respectively) in thin sections and their intramembrane particle diameters (13.1 and 13.7 nm, respectively) by freeze fracture, did not elucidate significant differences. A heterogeneous population of putative chemical synapses, similar to those reported in other molluscs, was also observed between axonal collaterals in the neuropil. Additionally, examination of freeze-fractured neuropil revealed rhombic arrays of particles localized on neuronal membranes; these arrays do not appear to form intercellular junctions but may represent postsynaptic receptor sites. Freeze fracture also revealed small, square arrays consisting of 7-9 nm diameter particles on glial membranes which may correspond to pentalaminar membrane contacts (pseudo-gap junctions) seen in thin sections between glia situated around dilated extracellular spaces (lacunae).

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Gap junctions and septate-like junctions between neurons of the opisthobranch molluscNavanax inermis

Cited by 16 publications

References 26 publications

Physiology and Pharmacology of Gap Junctions

Physiology and Pharmacology of Gap Junctions

Structure and localization of synaptic complexes in the cardiac ganglion of a portunid crab

Chemical synapses, particle arrays, pseudo‐gap junctions and gap junctions of neurons and glia in the buccal ganglion of Helisoma

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