Serial synapses in Aplysia

Serial synapses occur between small profiles in the neuropil of Aplysia abdominal ganglion. Material was fixed in phosphate buffered OsO₄, embedded in epon, and sections were stained with uranyl acetate and lead citrate. A class of synapses had the following characteristics: (1) synaptic vesicles clustered against the presynaptic membrane, (2) a widened extracellular space of about 20 nm containing electron-dense material, (3) straightening of the pre- and postsynaptic membranes, and (4) no postsynaptic membrane specialization. Some density between the presynaptic membrane and the adjacent synaptic vesicles was occasionally observed. Synapses occurred between small profiles in the neuropil (typical profile diameters were 1–3 m?m). In this sample of approximately 100 synapses, four serial synapses were identified. The serial synaptic profiles were all small. In addition to the finding of serial synapses, 40% of the postsynaptic profiles contained vesicles similar to the synaptic vesicles seen in presynaptic profile. Serial synapses may be the anatomical substrate of presynaptic inhibition and facilitation and of dishabituation.     

Synaptic relationships in the plexiform layers of carp retina

Summary The synaptic contacts made by carp retinal neurons were studied with electron microscopic techniques. Three kinds of contacts are described: (1) a conventional synapse in which an accumulation of agranular vesicles is found on the presynaptic side along with membrane densification of both pre- and postsynaptic elements; (2) a ribbon synapse in which a presynaptic ribbon surrounded by a halo of agranular vesicles faces two postsynaptic elements; and (3) close apposition of plasma membranes without any vesicle accumulation or membrane densification.In the external plexiform layer, conventional synapses between horizontal cells are described. Horizontal cells possess dense-core vesicles about 1,000 Å in diameter. Membranes of adjacent horizontal cells of the same type (external, intermediate or internal) are found closely apposed over broad regions.In the inner plexiform layer ribbon synapses occur only in bipolar cell terminals. The postsynaptic elements opposite the ribbon may be two amacrine processes or one amacrine process and one ganglion cell dendrite. Amacrine processes make conventional synaptic contacts onto bipolar terminals, other amacrine processes, amacrine cell bodies, ganglion cell dendrites and bodies. Amacrine cells possess dense-core vesicles. Ganglion cells are never presynaptic elements. Serial synapses between amacrine processes and reciprocal synapses between amacrine processes and bipolar terminals are described. The inner plexiform layer contains a large number of myelinated fibers which terminate near the layer of amacrine cells.This work was supported by an N.I.H. grant NB 05404-05 and a Fight for Sight grant G-396 to P.W. and N.I.H. grant NB 05336 to J.E.D. The authors wish to thank Mrs. P. Sheppard and Miss B. Hecker for able technical assistance. P.W. is grateful to Dr. G. K. Smelser, Department of Ophthalmology, Columbia University, for the use of his electron microscope facilities.     

Dendro-dendritic and reciprocal synapses in the primate motor cortex.

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.     

Diurnal changes in the fine structure of photoreceptors in an abalone,Nordotis discus

Summary The ultrastructure of the synapses in the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The synapses consist of one presynaptic terminal separated by a uniformly wide synaptic cleft, from one or more postsynaptic elements. The presynaptic terminals are characterized by the presence of paramembranous dense projections and associated synaptic vesicles. The postsynaptic elements while possessing membrane densities, are usually devoid of vesicles.The structure of the synapses in the brain of Gastrocotyle is compared to synapses from other platyhelminths.     

大白鼠脑干听觉中枢的研究下丘中心核内神经突触的特点

1.大白鼠下丘中心核(the Central Nucleus of the Inferior Colliculus,ICCN)内神经末稍以群体的形式有在,神经突触排列的类型主要为系列突触.2.末稍群体(Clustered ending)中轴突终末内含有多种类型的突触小泡.3.ICCN内具有不对称突触与对称突触两种类型的突触结构.4.在ICCN内,突触前终末有大量的突触小泡聚集,并且在突触后常有1—2个大线粒体靠近突触后膜.5.以上结果表明了脑干听觉中枢下丘中心核的结构及其突触连结的模式;突触的结构及其特点,这是频有意义的.     

Ultrastructure of the lateral-line sense organs of the ratfish,Chimaera monstrosa

Summary The ultrastructure of the lateral-line neuromasts in the ratfish, Chimaera monstrosa is described. The neuromasts rest at the bottom of open grooves and consist of sensory, supporting, basal and mantle cells. Each sensory cell is equipped with sensory hairs consisting of a single kinocilium and several stereocilia. There are several types of sensory hair arrangement, and cells with a particular arrangement form patches within the neuromast. There are two types of afferent synapse. The most common afferent synapse has a presynaptic body and is typically associated with an extensive system of anastomosing tubules on the presynaptic side. When the tubules are absent, vesicles surround the presynaptic body. These synapses are often associated into synaptic fields, containing up to 35 synaptic sites. The second type of afferent synapse does not have a presynaptic body and is not associated with the tubular system. The afferent synapses of the second type do not form synaptic fields and are uncommon. The efferent synapses are either associated with a postsynaptic sac or more commonly with a strongly osmiophilic postsynaptic membrane. The accessory cells are similar to those in the acoustico-lateralis organs of other aquatic vertebrates. A possibility of movement of the presynaptic bodies and of involvement of the tubular system in the turnover of the transmitter is discussed. A comparison of the hair tuft types in the neuromasts of Ch. monstrosa with those in the labyrinth of the goldfish and of the frog is attempted.     

Ultrastructural elements of CNS development in the Stage 15 Drosophila (Diptera: Drosophilidae) embryo

The ultrastructural neuroanatomy of the wild-type Drosophila melanogaster (Diptera: Drosophilidae) embryo at Stage 15 was examined with the transmission electron microscope. This particular embryonic stage is an approximate midpoint of neurogenesis. No blood-brain barrier has yet formed in the CNS as illustrated by lanthanum tracer infiltration into the neuropil. First structural signs of axo-axonal synapses, in the embryonic neuropil are seen as electron-dense plaques on the cytoplasmic sides of apposing pre- and postsynaptic membranes. Very few clear synaptic vesicles (30–40 nm in diameter) are present, and none of these is clustering, although some are docking on the presynaptic membrane. In the perikaryal rind of the ventral ganglion, several glial somata are shown surrounding a single neuronal soma. Finger-like processes of the glial somata extend into extracellular spaces and contact the surface of the neuron. The functional significance of these findings is discussed.     

Ultrastructural organization of the anterior sensory neuropile in the metathoracic ganglion of the locust Locusta migratoria]

The study of serial sections of the metathoracic ganglion of Locusta migratoria showed that the fibres of the tympanal nerve terminate in the dorsal half of the anterior sensory neuropile (ASN). Three types of synaptic endings were found in the ASN. Endings type I contain dense-core vesicles 600-850 A in diameter, more or less uniformly distributed in the axoplasm. They do not form specialized contacts with postsynaptic fibres and are localized only in the most ventral part of the ASN. Endings type II contain clear round vesicles 400-450 A in diameter (rare 250-300 A) and form typical synapses with dense pre-and postsynaptic membranes and synaptic cleft 150-200 A. Four types of contacts formed by these endings with postsynaptic fibres were found: 1 : 1 synapses; convergent, divergent and serial. All of them are well presented in the auditory neuropile. Endings type III contain both dense-core and clear vesicles in different relation. Only clear vesicles of these endings are connected with the active sites of the membrane.     

大鼠脊髓胶状质内GABA能神经元突触联系的超微结构研究

本文用免疫电镜方法对脊髓胶状质内ＧＡＢＡ能神经元的突触联系进行了超微结构研究。结果表明;脊髓胶状质内有许多ＧＡＢＡ能神经元胞体和末梢分布;标记的ＧＡＢＡ能神经末梢可作为突触前成分与未标记的ＧＡＢＡ形成输一树突触。未标记的末梢可与标记的ＧＡＢＡ末梢形成输一轴突触。此外,标记的ＧＡＢＡ能神经末梢还可作为突触前成分与标记的ＧＡＢＡ能轴突、树突或胞体形成输－轴、轴－树或轴－体突触,即自调节突触。上述结果揭示：ＧＡＢＡ能末梢可对脊髓胶状质内其它神经元产生抑制或脱抑制作用。值得注意的是胶状质内含ＧＡｎＡ的神经结构可形成各种形式的自调节突触,并借此实现其对脊髓功能的复杂调节。     

Ultrastructure of nerve plexus in flatworms

Summary Synaptic components from the peripheral nervous system of the polyclad flatworm, Notoplana acticola, are described from electron microscopic observations. Quasineuropile, defined as clusters of neurites containing synaptic vesicles, occurs as scattered islands along the peripheral nerve cords of the plexus. Some neurite clusters only contain one type of synaptic vesicle but others are mixed. The most usual synaptic configuration consists of a single presynaptic element and a pair of postsynaptic neurites sharing a common synaptic cleft. These synapses are polarized and contain clear, 420 Å vesicles. GABA-type synapses are also found. At least two kinds of solid-core vesicles also occur.     

Ultrastructural features of presumptive vasopressinergic synapses in the hypothalamic magnocellular secretory nuclei of the rat

Despite convincing physiological evidences for vasopressin (VP) autoregulation in the supraoptic (SON) and paraventricular (PVN) nuclei, the morphological demonstration of VP synapses has lagged behind. The present work investigates the possible existence of such synapses in the SON and PVN of the rat. Electron microscopy of sections immunostained with VP antibody (1:5,000) and conjugated with avidin-biotin demonstrated presynaptic terminals containing neurosecretory granule (NSG)-like bodies, 80-100 nm in diameter. The terminals formed axodendritic, axosomatic and axoaxonic synapses, though the postsynaptic elements remained largely unidentified. Other ultrastructural features of synaptic specialization were evident. The NSG-like bodies exhibited a varying and dynamic relationship to the presynaptic membrane, suggesting their involvement in synaptic mechanisms.     

Veratridine-stimulated central synapses in culture: A quantitative ultrastructural analysis

Synapses in explant cultures of fetal rat neocortex at day 18 in vitro were stimulated by veratridine (10^?4M) for 20 min. The cultures were subsequently processed for electron microscopy and the synapses were analyzed by quantitative techniques, incorporating set mathematical treatment. The mean values of area, perimeter, and form factor of the presynaptic elements significantly increased following veratridine stimulation, compared to the values of control synapses. The length of the postsynaptic thickening also increased, while synaptic curvature did not change significantly in the veratridine group. A fivefold reduction was observed in the mean number of synaptic vesicles per presynaptic element and in the vesicle-terminal area ratio, following veratridine stimulation. The cytoplasm-terminal area ratio and the occurrence of vacuoles/cisternae significantly increased after veratridine application. Planar measurement of membranes (boundary length) of different presynaptic organelles revealed that the total membrane did not change significantly in the veratridine group. The data indicated an increase in volume and swelling of the pre- and postsynaptic elements, considerable depletion of synaptic vesicles, and preservation of the total presynaptic membrane following veratridine stimulation in nerve tissue culture.     

Ultrastructural studies on the afferent synaptic input to oxytocin-containing neurons in the paraventricular nucleus of the hypothalamus

A diverse afferent synaptic input to immunostained oxytocin magnocellular neurons of the paraventricular nucleus of the rat hypothalamus is described. By electron microscopy, immunoreactive material is present within cell bodies and neuronal processes and it is associated primarily with neurosecretory granules and granular endoplasmic reticulum. Afferent axon terminals synapse on perikarya, dendritic processes, and possibly axonal processes of oxytocin-containing neurons. The presynaptic elements of the synaptic complexes contain clear spherical vesicles, a mixture of clear spherical and ellipsoidal vesicles, or a mixture of clear and dense-centered vesicles. The postsynaptic membranes of oxytocinergic cells frequently show a prominent coating of dense material on the cytoplasmic face which gives the synaptic complex a marked asymmetry.     

Innervation des cellules du pancréas endocrine du Poisson Téléostéen Xiphophorus helleri H.

Summary The pancreatic islet tissue of the bony fish Xiphophorus helleri H. is innervated by amyelinic fibers. Neuroglandular junctions on the islet cells show a structure similar to that of the synapses of the central nervous system. Presynaptic projections, intrasynaptic lines, and postsynaptic bands are to be observed. In the nerve endings two kinds of vesicles occur: large granular vesicles (diameter:850–1150 Å) and small clear vesicles (diameter: 500–650 Å). Synaptic vesicles are gathered around the presynaptic dense projections. This precise organization suggests the existence of a direct nervous control involved in the metabolism of the pancreatic hormones.

Avec la collaboration technique de M. D. Streicher.     

Neural Organization of the Median Ocellus of the Dragonfly : II. Synaptic structure

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.     

Regions of putative acetylcholine receptors at synaptic contacts between neurons maintained in culture and subsequently fixed in solutions containing tannic acid

Summary Spinal cord neurons from 9-day chick embryos were maintained in culture for up to 35 days and then fixed in 4% cacodylate-buffered glutaraldehyde containing 2% tannic acid. After about 15 days in culture a small percentage of the synaptic specializations present were characterized by striking electron-dense striations averaging 15 nm in width, oriented perpendicular to the postsynaptic membrane. These structures increased in frequency with time in culture (to a maximum of about 10% of all synapses in the oldest cultures); they were asymmetrical, protruding approximately 8 nm into the synaptic cleft, and more deeply (approximately 15–18 nm), into the postsynaptic cytoplasm. On the basis of earlier work by Sealock (1980) they are interpreted as concentrations of acetylcholine receptors.Similar membrane differentiations were also seen associated with active-zone areas of a few presynaptic membranes, and the possibility that these represent presynaptic acetylcholine receptors is discussed. Additional observations reported are (1) the presence of striations resembling those seen at the postsynaptic membrane in the membranes of some postsynaptic vesicles, and (2) filamentous links between the striations and cytoskeletal elements of the postsynaptic cell.     

Axons containing neuropeptide Y innervate arginine vasopressin-containing neurons in the rat paraventricular nucleus. Dual electron microscopic immunolabeling

Synaptic connections between neurons immunoreactive for arginine vasopressin (AVP) and axon terminals immunoreactive for neuropeptide Y (NPY) were found in the magnocellular part of the paraventricular nucleus (PVN) in the rat hypothalamus. In pre-embedding double immunolabeling, NPY axon terminals labeled with diaminobenzidine (DAB) reaction product established synaptic junctions on the perikarya and neuronal processes of AVP neurons labeled with silver-gold particles. Ultrastructural morphology of the neurons was more suitably preserved by a combination of pre- and post-embedding procedures. The presynaptic NPY terminals contained many small clear vesicles and a few cored vesicles, and DAB chromogen (immunoreaction product) was located on the surface of the vesicular profiles and on the core. The postsynaptic AVP neurons possessed many large secretory granules labeled with gold particles. At the synaptic junctions, small clear vesicles were accumulated at the presynaptic membrane, and the postsynaptic membrane was coated with a dense accumulation of fine electron dense particles. The perikarya also received synapses made by immuno-negative axon terminals containing many small clear vesicles and a few cored vesicles. These terminals were found more frequently than those containing NPY.     

The Ultrastructure of the Nervous System of Gyratrix hermaphroditus (Turbellaria, Rhabdocoela)

The peripheral nervous system and the synapses of G. hermaphroditus are studied with the electron microscope. There is a submuscular as well as a subepithelial plexus. The subepithelial plexus is found among the muscles and between the muscles and the basement membrane. It consists of fibres containing large lucent and lysosome-like vesicles and fibres with only small lucent (synaptic) vesicles. In the deeper lying submuscular plexus also dense and dense-cored vesicles occur in the fibres. Cell bodies are not observed in the plexuses. The separate nerve supplies of the pharynx and the gonads contain nerve cells of the neurosecretory type. Fibres of the same kinds as in the brain are also seen here. The synapses in the neuropile are of two kinds. 1. Symmetrical synapses with an additional presynaptic network are most common. 2. Synapses without thickenings of membranes are observed between lateral membranes of neurites. In the peripheral nervous system are two other kinds of synapses also observed. 1. Asymmertical synapses with a denser and wider postsynaptic thickening and 2. neuromuscular junctions. Neurites containing accumulations of small vesicles against the basement membrane are also described. The organization of the peripheral nervous system is described and discussed in relation to the systematic position of G. hermaphroditus.     

Ganglioside composition of subcellular fractions,including pre- and postsynaptic membranes,fromTorpedo electric organ

Gangliosides were isolated from four subcellular fractions of the electric organ ofTorpedo marmorata: synaptosomes, presynaptic membranes, postsynaptic membranes, and synaptic vesicle membranes. This exploited a principal advantage offered by this tissue: facile separation of pre-and postyynaptic elements. Total ganglioside concentration in presynaptic membranes was approximately twice that of synaptosomes and 15 times that of postsynaptic membranes (47.7, 24.4, and 3.21 g of lipid sialic acid per mg protein, respectively). Synaptic vesicle membranes had the highest overall concentration (78.9) relative to protein, but a concentration approximately comparable to that of presynaptic membranes when expressed relative to phospholipid. The thin-layer patterns of these two fractions were similar, both in terms of total pattern and the specific pattern of gangliotetraose structures as revealed by overlay with cholera toxin B subunit; these were notable for the paucity of monosialo structures and the virtual absence of GM1. Postsynaptic membranes, on the other hand, had a significantly higher content of monosialogangliosides including the presence of GM1. The synaptosomal pattern resembled that of the presynaptic membranes and synaptic vesicles. Thus, a clear difference in ganglioside pattern could be discerned between the pre- and postsynaptic elements of the electric organ.Abbreviations SVs synaptic vesicles - TLC thin-layer chromatography - cholera B-HRP B subunit of cholera toxin linked to horseradish peroxidase     

Histochemical and cytochemical studies of alkaline phosphatase activity in the synapses of rat brain.

Although a number of studies have been carried out on alkaline phosphatase (A1-P), this enzyme has not definitely been detected in synapses at the electron-microscopic level. Recently, we have successfully demonstrated, by perfusing specimens with 1% glutaraldehyde for fixation for as short a time as 8-10 min, that A1-P activity is localized on the presynaptic and postsynaptic membranes of the rat central nervous system (CNS). There were four types of presynaptic membrane: (1) those with the activity only on the membrane, (2) those with the activity only on the synaptic vesicle membrane, (3) those with the activity on both the presynaptic membrane and the synaptic vesicle membrane, and (4) those entirely free of the activity. The postsynaptic membranes were classified into two varieties: (1) those with the activity in the postsynaptic membrane and the postsynaptic thickening, and (2) those entirely without the activity. Thus, the occurrence of the enzyme activity assumed various combinations of presynaptic and postsynaptic involvement. The incidence of synapses either with presynaptic or postsynaptic activity varied distinctly from site to site.