A quantitative study of synaptic patterns in turtle visual cortex

The distribution of different synaptic types has been analyzed quantitatively in the molecular and subcellular layers of turtle ?vislual”? cortex. The density of vesicle-containing-profiles (VCPs) is 122.2/400 square μm in the molecular layer and 61.0/400 square μm in the subcellular layer. In both layers, approximately 85% of VCPs conatin round vesicles (RVCPs), 12%, flat vesicles (FVCPs) and 1%, dense core vesicles (DVCPs). Vacuolar invaginations (VIs) are not uncommon in the molecular layer (3.4%) but are rare in the subcellular layer (0.6%). Synaptic conatacts are formed in the plane of section by three out of ten RVCPs and FVCPs, while only one out of the 146 DVCPs sampled in this study was associated with a membrane differentiation. In the molecualr layer, the percentage distribution of the different subgroups of synaptic types is as follows: round-asymmetrical contacts, 82.5% (77.5% on dendritic spines and 5.0% on dendritic shafts); round-symmetrical contacts, 3.8% (2.3% on spines and 1.5% on shafts);flat-symmetrical contacts, 13.1% (8.8% on shafts and 4.3% on spines; flatasymmetrical contacts 0.6% (0.4% on spines and 0.2% on shafts)). In the subcellular layer, the distribution is quite different: round-asymmetrical contacts. 72.4% (38.6% on shafts and 33.8% on spines); round-symmertical contacts, 12.8% (8.2% on shafts and 4.6% on spines); flat-symmetrical contacts, 13.9% (9.3% on shafts and 4.6% on spines); flat-asymmetrical contacts, 0.9% all on dendritic shafts. The density distribution of VCPs in the molecular layer changes with depth. RVCPs are fewer on the distal third of the apical dendrites, and most numerous in the middle third with a small dercease in number in th proximal third. FVCPs are more homogeneously distributed, perhaps increasing slightly in number towards the proximal parts of the dendritets. RVCPs are most numerous on dendritic spines. These spines are of two types whose relative number varies with depth. Large organelle-filled spines predominate in the upper third while small ?empty”? spines are most numerous in the lower third of the molecular layer.     

Excitatory transmitter amino acid-containing neurons in the rat visual cortex: a light and electron microscopic immunocytochemical study

The distribution and morphology of neurons labelled with antisera to glutamate or aspartate were examined, at the light and electron microscope levels, in the rat visual cortex. Using widely accepted light microscopic features as well as well-established nuclear, cytoplasmic, and synaptic criteria, we noted that glutamate-immunoreactive neurons were pyramidal cells distributed in layers II-VI, with an increased concentration in layers II and III. Aspartate immunoreactivity was localized chiefly to pyramidal neurons in layers II-VI. However, approximately 10% of immunolabeled cells were nonpyramidal neurons scattered throughout the cortex. Cell-body measurements revealed that, for both groups of neurons, layer V contained the largest labelled neurons, whereas layers IV and VI contained the smallest. Furthermore, in every layer, aspartate-stained neurons were larger than glutamate-positive cells. Finally, glutamate- and aspartate-labelled axon terminals formed asymmetrical synapses, which are presumably excitatory in nature, primarily with dendritic spines. These findings, together with recent detailed studies of the projections of glutamate- and aspartate-labelled cortical neurons, may provide essential background information for studies aimed to elucidate the function(s) of excitatory amino acids in the cortex and their role in pathological conditions.     

An electron microscopic study of neurons during postnatal development of the rat cerebral cortex

The differentiation and maturation of the neurons of rat cerebral cortex during the first three weeks of postnatal life has been studied with the light and electron microscopes. At birth, the supeficial cortex is largely made up of undifferentiated cells, tightly packed together in vertical columns between which the developing process and blood vessels, and relatively extensive extracellular spaces are found. During the first two weeks, these cells diferentiate into either neuroblasts and neurons, or into spongioblasts and neuroglia. In the case of neurons but not neuroglia, this maturation occurs in a gradient from the depths toward the surface. The round undifferendtiated cells are characterized by an absence of processes, a thin rim of perinuclear cytoplasm containing few organelles, and a peripheral clumping of condensed nuclear chromatin. The differentiating neuroblasts display increasing numbers of cytoplasmic organelles, especially endoplasmic reticulum, evenly dispersed nuclear chromatin, and presumptive apical dendrites. The rough endoplasmic reticulum of neuroblasts become swollen during the transition into neurons during the second week. The endoplasmic reticulum forms subsurface cisterns that transiently evaginate the cell membrane, forming conspicuous diverticuli in the neuropil at the same time that the cells display an increase of cytoplasmic matrix density and increasing numbers of ribosomes. During the three weeks following birth, organelles increase in number and complexity, synapses develop, the extracellular spaces disappear, and the maturing neurons become separated from one another by the growth of neuropil and nonnervous elements. At the end of this three week period the cortical tissue and its neurons are apparently mature and the adult pattern of cortical fine structure is established.     

Synaptic connections of callosal projection neurons in the vibrissal region of mouse primary motor cortex: an electron microscopic/horseradish peroxidase study

Reciprocal axonal projections between homotypic areas of the vibrissal region of mouse primary motor cortex (MsI) (Porter and White: Neurosci. Lett. 47:37-40, '84) suggested the existence of reciprocal synaptic connections between callosal projection neurons and callosal afferents. In the present study, the retrograde transport of horseradish peroxidase (HRP) was combined with lesion-induced degeneration to identify synapses between callosal afferents and callosal neurons in the corresponding region of the contralateral cortex. The procedure was as follows: MsI was injected with HRP and aspirated on the following day. After 4 days, the animals were perfused and motor cortex was processed for HRP according to a variation of the Adams (Brain Res. 176:33-47,'77) technique, and postfixed in OsO4. The methods used consistently filled fine dendritic branches and spines with dense reaction product, thus allowing examination of synaptic contacts with these processes. All callosal projection neurons were identified as pyramidal neurons, having somata in cortical layers II/III and V. Labeled cells from each of the two levels were prepared for electron microscopy, and that part of each cell's apical dendrite that traversed the superficial cortical layers, where most callosal axons terminate, was cut in an unbroken series of thin sections. Micrographs were taken of all labeled profiles in each thin section, and tracings of the profiles were assembled to reconstruct the apical dendrites. Data on the distribution, type, and amount of callosal and other synapses with the shaft and spines of the apical dendrites were obtained by examining the reconstructions. In addition, profiles of basal dendrites of layer II/III cells were examined in thin sections to ascertain the numbers of callosal and other synapses formed with their shafts and spines. The proportion of synapses that each dendrite formed with callosal axon terminals was compared to the concentration of callosal afferents in the neuropil. Dendrites of both layer II/III and layer V pyramidal cells synapsed with callosal axon terminals. The apical and basal dendrites of layer II/III neurons formed a similar proportion of their synapses with callosal afferents, and this was similar to the concentration of callosal synapses in the surrounding neuropil. Segments of apical dendrites belonging to layer V and layer II/III neurons course through neuropil containing nearly the same concentration of degenerating callosal terminals, but the layer V cells form fewer callosal synapses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lateralization of opioid receptors in turtle visual cortex

The opioid μ-agonist morphine, the δ-agonist [ -Ala², -Leu⁵]enkephalin (DADL) and the κ-agonist bremazocine locally applied to the surface of turtle visual cortex inhibited the orthodromic evoked potential (EP; fast negative component N₁). After application of the σ-agonist SKF 10.047 the inhibition was followed by facilitation of EP. The lack of cross-desensitization to the inhibitory action of opioids upon EP indicates that the drugs exert their effects via different opioid receptors. Bremazocine and morphine predominantly inhibited the left cortical EP, whereas DADL was a potent inhibitor of the right cortical EP. Thus, the opioid receptors which modulate evoked electrical activity of the left visual cortex (LVC) apparently belong mostly to the κ- and μ-type, while σ-receptors were predominantly responsible for the modulation of electrical activity in the right visual cortex (RVC). Besides, we have studied in vivo binding of the κ-agonist [³H]ethylketocyclazocine ([³H]EKC) and the σ-agonist [³H]DADL to LVC and RVC. The binding was specific and could be accounted for by the interaction with membrane opioid receptors and/or specific uptake of these drugs by cortex cells. [³H]EKC and [³H]DADL exhibited a more effective binding to LVC and RVC membranes, respectively. The results obtained in vitro apparently indicate that LVC and RVC differ in the number of κ- and σ-binding sites. Thus, turtle brain may have a side-specific mechanism for selective neurochemical regulation of neuron activity in LVC and RVC realized predominantly via κ- and σ-receptor, respectively.     

Synaptic immunolocalization of glyoxylate-complex molecules in the striate areas of the rat cerebral cortex: Light and electron microscopic studies

The location of glyoxylate-complex molecules has been investigated in several areas of the rat cerebral cortex using the immunohistochemical peroxidase-antiperoxidase (PAP) method. Antibodies against glyoxylate-complex molecules have been developed in the rabbit after immunization with a glyoxylate-bovine serum albumin conjugate. Observations carried out with the light microscope demonstrated positive immunostaining at the membrane level of scattered neurons located in all cortical areas, mainly in cortical layer IV. The striate areas (17, 18, 18a) had both the greatest number of immunopositive neurons and the most intense ones. At the electron microscopic level, it was observed that in the striate areas an immunopositive reaction was located mainly in the periphery of synaptic vesicles of some nerve endings, and in both pre- and postsynaptic membranes of these synaptic structures. The presence of glyoxylic acid and glyoxylate-complex molecules in such areas leads us to suggest that these substances could play an important role in selected synaptic contacts in which some pyramidal and non-pyramidal neurons are involved. J. Neurosci. Res. 51:268–274, 1998. © 1998 Wiley-Liss, Inc.     

Synaptic patterns in the visual cortex of the cat and monkey. Electron microscopy of Golgi preparations

Primary visual cortex (area 17) from macaque monkeys, cats and kittens was stained by a rapid Golgi method modified to give optimal preservation of fine structure. Single impregnated neurons were identified in the light microscope, and then cut in serial thin sections for electron microscopy. As in conventional E.M. material, synapses in the Golgi preparations could be classified into types 1 and 2: type 1 synapses possessed round vesicles in the axon and a pronounced postsynaptic opacity; type 2 synapses had smaller, flattened vesicles in the axon and a slight postsynaptic opacity. Synapses onto impregnated cells were identified by the presynaptic opacities (dense projections), and classified as type 1 or 2 according to the shape and size of the vesicles. Pyramidal cells and spiny stellate cells (found in layer 4) had a similar synaptic environment: type 1 synapses occurred only on the spines, while type 2 synapses were found on dendritic shafts, cell bodies, and axon initial segments. Spinefree stellate cells possessed both type 1 and type 2 synapses on the cell body and on the dendritic shafts, the type 2 synapses being most frequent near to, the type 1 synapses far from, the cell body. Synapses formed by the axon terminals of nine cells were located, and were classified as type 1 or 2 on the basis of the thickness of the postsynaptic opacity. The axons of pyramidal and spiny stellate cells formed type 1 synapses; those of spinefree and sparsely spinous cells formed type 2 synapses. In the 12-day old to 5-week old kittens, cells corresponding to the spinefree cells of the adult cat did possess spines. These transient spines were commonest on and near the cell body, and were the sites of type 1 synapses. On these and other grounds, the spiny stellate cells of layer 4 were concluded to be closely related to pyramidal cells, and quite distinct from the class of spinefree and sparsely spinous cells. The interpretation of conventional E.M. preparations of cerebral cortex is discussed.     

An electron microscopic study of meningiomas

Summary Seventeen surgically removed meningiomas of the endotheliomatous and five of the fibromatous type were investigated with an electron microscope. Differences of the development of cytoplasmic processes and the relations between plasma membranes of blastomatous cells were observed in endotheliomatous meningiomas. In four of the fibromatous tumors the cell groups were surrounded by spaces of connective tissue. Although most of the tumor cells were light cells and are not essentially different from the tumor cells of the endotheliomatous meningiomas, the histological structure of fibromatous meningiomas is clearly distinguished from the endotheliomatous type, because of the greater amount of connective tissue. The dark cells may be divided into two types: the first was found in those four tumors, where the connective tissue is well developed, while the second one only occurred in one of the tumors. The analysis of the inner cell structure as well as the presence of interstages between dark and light cells makes it probable that dark and light cells are different types of one original cell. The cause of this different appearance of the menigioma cells is discussed. The fine structure of the tumor cells showed a great similarity with that of normal arachnoidal cells. Conclusions on the blastodermic origin of normal and blastomatous meningial cells on the basis of ultrastructural characteristics, however, seem to be premature.

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Zusammenfassung 17 chirurgisch entfernte Meningiome vom endotheliomatösen und 5 vom fibromatösen Typ wurden elektronenmikroskopisch untersucht. Unterschiede im Entwicklungsgrad der cytoplasmatischen Fortsätze und der Beziehungen zwischen den Plasmamembranen der Tumorzellen wurden in den endotheliomatösen Meningeomen beobachtet. In 4 fibromatösen Tumoren sind die zelligen Areale von bindegewebigen Räumen umgeben. Auch wenn die meisten Tumorzellen helle Zellen sind und sich nicht wesentlich von den Tumorzellen der endotheliomatösen Meningiome unterscheiden, ist die histologische Anordnung der fibromatösen klar von derjenigen der endotheliomatösen Meningeome zu trennen. Ausschlaggebend dafür ist die starke Entwicklung des Bindegewebes. Die Dunkelzellen lassen sich in zwei Typen gliedern: Typ I wird in vier Tumoren mit stark ausgebildetem Bindegewebe angetroffen. Die Analyse der inneren Zellstruktur sowie das Vorliegen von Übergängen zwischen hellen und dunklen Zellen machen es wahrscheinlich, daß diese nur verschiedene Typen einer einzigen Ursprungszelle darstellen. Die Bedeutung dieser verschiedenen Erscheinungsformen der Meningiomzellen wird diskutiert. Die Ultrastruktur der Tumorzellen ähnelt derjenigen der normalen arachnoidalen Zellen. Rückschlüsse auf die blastodermale Herkunft der normalen und tumoralen meninigalen Zellen auf Grund ihrer ultrastrukturellen Merkmale erscheinen verfrüht.

     

Synaptic organization in the dorsal cochlear nucleus of the cat: a light and electron microscopic study

This report describes some observations of the synaptic organization of one region of the cat dorsal cochlear nucleus (DCN). The large “fusiform cell” and its innervation from the cochlea are emphasized. The morphology of the mature fusiform cell and its postnatal development are described in rapid Golgi impregnations of perfusion-fixed littermate cats. The mature features are correlated with profiles of fusiform cell bodies, apical dendrites, and basal dendritic trunks in electron micrographs from adult cat brains. Small neurons and granule cells are also identified in electron micrographs. In Golgi impregnations, axons of small cells and granule cells may terminate upon fusiform cells. Six classes of axons can be distinguished in rapid Golgi impregnations of the DCN. Two classes are of cochlear origin. One axonal class arises from small cells. The sources of the remaining axonal classes have not been identified in this study. Primary afferents can terminate as large, mossy endings in the DCN neuropil. They can also participate in axonal nests along with axons and dendrites of small cells. In electron micrographs, four synaptic endings can be distinguished. Primary cochlear fibers end in large terminals with asymmetrical synaptic complexes and round, clear vesicles. Primary axons can end in glomeruli, resembling those of the cerebellum, or in synaptic nests which are conglomerates of neuronal processes including other types of endings. The origins of the other synaptic types are not yet known. According to this study, primary afferent input could influence fusiform cells directly or indirectly, via small cells and granule cells.     

Menkes disease: a Golgi and electron microscopic study of the cerebellar cortex

A neuropathological study of a case of Menkes disease is reported, illustrating the involvement of different types of neuronal cells. The cerebellum showed the most striking abnormalities: severe lack of internal granule cells. Purkinje cells with weeping willow pattern, numerous segmental enlargements of dendritic trunks and secondary branches, and presence of numerous eosinphilic spherical bodies in the molecular layer were the most conspicuous features. Using electron microscopy, the dendritic enlargements were observed to be made of both proliferated and enlarged mitochondria, and of saccules of smooth endoplasmic reticulum. The spheroid bodies in the molecular layer were mainly made of concentric lamellar structures which seemed to be proliferated smooth endoplasmic reticulum. The relationship between these morphological abnormalities and the metabolic disorder of Menkes disease is discussed.     

An electron microscopic study on atypical presenile dementia with numerous Lewy bodies in the cerebral cortex

A report was made of an autopsied case of presenile dementia presenting the clinically characteristic symptoms of Alzheimer's disease and Pick's disease. The neuropathological findings were senile changes, namely, numerous senile plaques, neurofibrillary tangles, granulovacuolar degeneration and Pick bodies, etc., and numerous Lewy bodies in the brain stem and in the cerebral cortex. We studied mainly the ultrastructure of Lewy bodies in the cerebral cortex in this paper. The features of ultrastructural components of Lewy bodies presented types which might correspond to the various profiles of Lewy bodies observed by a light microscope. In addition, we studied the senile changes in the cerebral cortex ultrastructurally and considered that some relationship possibly existed between Lewy bodies and senile changes.     

An electron microscopic study of scrapie in the mouse

Summary Electron microscopic examination of mouse scrapie brain has shown small vesicles in nerve cells to be formed by dilatation of endoplasmic reticulum sacs. Vacuoles seen in paraffin sections are due to great dilatation of nerve fibres, or swelling and possible confluence of astrocyte processes. Myelin degenerative changes were widespread. Dense bodies and pleomorphic inclusions were common in nerve cells. It is suggested that astroglial hypertrophy may interfere with nerve cell nutrition so that nervous disturbance results from neuroglial dysfunction.

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Zusammenfassung Die elektronenmikroskopische Untersuchung von Gehirnen Scrapie-kranker Mäuse zeigte, daß durch die Erweiterung der Räume des endoplasmatischen Reticulums in den Nervenzellen kleine Bläschen entstehen. Die in den Paraffinschnitten zu sehenden Vacuolen entsprechen einer starken Verdickung von Nervenfasern oder einer Schwellung und möglichen Konfluenz von Astrocytenfortsätzen. Verbreitet bestehen degenerative Markscheidenveränderungen. Dichte Gebilde (dense bodies) oder pleomorphe Einschlüsse sind häufig in Nervenzellen anzutreffen. Es wird vermutet, daß die Astrogliahypertrophie mit der Ernährung der Nervenzellen interferiert, so daß infolge der Dysfunktion der Neuroglia eine neuronale Störung entsteht.

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With 8 Figures in the Text     

Effect of maternal protein malnutrition on the developing cerebral cortex of mouse embryo: An electron microscopic study

This study was undertaken to elucidate the effects of maternal protein malnutrition on the matrix cell and the differentiation of neurons in the embryonic mouse cerebrum. Mothers fed a low protein diet from the 8th to the 16th day of gestation, carried 16-day-old embryos whose cerebral cortex width was reduced significantly; some of the matrix cells and migrating young neurons showed degeneration including necrosis in their ultrastructural morphology. However, when these pregnant mice were subsequently fed a normal diet from the 16th day of gestation to term, no significant changes from the controls in the width of the cortex and in ultrastructural morphology were found at birth. In contrast, mothers fed a low protein diet from the 13th day of gestation, delivered their embryos 1 day prior to term, i.e., on the 19th day of gestation. Thus, they were compared with the control fetuses of the 19th day of gestation. Their mean body weight was about 51% of that of age-matched controls and the width of their cerebral cortex was significantly smaller. Electron microscopic observation of the cytoplasm of neurons in layer II of their cerebral cortex contained more ribosomes than did the control specimens and neuronal processes in the intercellular space were decreased.     

Postnatal development of neurons and synapses in the visual and motor cortex of rabbits: a quantitative light and electron microscopic study

Introductory to a morphological investigation on the effects of early visual deprivation and on the critical periods in early postnatal life we have studied quantitatively the normal postnatal growth of neurons and synapses in the visual and motor cortex of rabbits. The major results of this analytical study are: (1) rapid decrease in neuron density and a rapid increase in neuronal volume are observed. They are almost completed at postnatal Day 10, i.e., before natural eye opening. The drop in neuron density is caused to a very large extent by an increase in cortical volume and not by a considerable disappearance of neurons; (2) the formation of synaptic contact zones starts at Day 6 to 7 and is most pronounced between Day 10 and Day 21, i.e., after natural eye opening. At Day 27 synaptic density has reached adult levels in the visual cortex and is in excess of the adult level in the motor cortex. In visual area I and in the motor cortex a significant difference in synaptic increase is observed between the left and right hemisphere, resulting in a lower synaptic density in the left counterparts at Day 27 and in adult animals [56,57]. In the visual cortex a small but highly correlated increase in synaptic vesicle density is observed. In the motor cortex no correlated relation between age and vesicle density is observed. In both cortical areas synaptic vesicle density has reached about 70 percent of the adult level at Day 27; and (3) in newborn and young rabbits the motor cortex seems to be more mature than the visual cortex.     

A quantitative electron microscopic study of the ageing human cerebral cortex

Summary A recent quantitative electron microscopic study of biopsy samples of the cerebral cortex of neurologically normal individuals, aged between 15 and 54 years, has shown that atypical inclusions are present in neuronal and glial processes in small but appreciable numbers (Rees). It would be of interest to know whether these inclusions accumulate with age. This study therefore applied the same quantitative methods used in the previous study, to autopsy samples of frontal and temporal cortex from 3 non-demented ageing human brains (70–76 years).The results showed that in the areas of cortex examined, the number of inclusions in neuronal processes did not increase with age. However, the number of dense deposits in the cell bodies and processes of oligodendrocytes did increase significantly with age. In agreement with previous studies corpora amylacea were found in astrocytic processes. Senile plaques were not observed.     

Synaptic plasticity of feedback connections in rat visual cortex

The issue we want to address in the present paper is to establish whether electrical stimulation of latero medial (LM) area, a secondary visual area in the rat, is able to induce Long Term Potentiation (LTP) and Long Term Depression (LTD) in primary visual cortex (V1). To this aim rat slices containing area V1 and LM were prepared at P23 and P40 and field potentials in layers 2/3 of area V1 were recorded stimulating LM. We showed that it was never possible to induce LTP in area V1, unless bicuculline, a gamma-aminobutyric acid (GABA) receptors blocker, was applied to the slice. In contrast, LTD was normally inducible. Thus, cortical gabaergic circuitry in area V1 controls LTP but not LTD elicited by stimulation of feedback connections from LM.     

An electron microscopic study of childhood dermatomyositis

Summary Muscle biopsies from 12 patients with a typical clinical picture of dermatomyositis have been examined by electron microscopy. Endothelial cells of intramuscular blood vessels, their basal lamina, pericytes, muscle fibers, and satellite cells show degenerative or regenerative alterations. In nine patients, tubular arrays were noted in the cisterns of endoplasmic reticulum of endothelial cells, pericytes, lymphocytes, macrophages and satellite cells. Other types of inclusions were also observed. The pathogenesis of the disease is discussed.