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A Schüz

Publications and source records attributed to A Schüz.

14 recordsLinked to original sources
PubMed1996

Basic connectivity of the cerebral cortex and some considerations on the corpus callosum.

Studies on the connectivity of the cerebral cortex have lent strong support to the idea that the cortex is an associative network in which information is stored by ways of Hebbian cell assemblies. One of the main arguments for this is the elaborated system of cortico-cortical long-range connections which allows distant regions of the cortex to interact. Part of this system is the corpus callosum, which is responsible for the co-operation of the two cortical hemispheres. The following points are interesting with regard to interhemispheric co-operation: (1) the callosal system includes fewer neurons than the system of intrahemispheric long-range connections; (2) the mirror image activity induced by the callosal system may be advantageous for the ignition of cell assemblies; (3) the fibres of the corpus callosum differ considerably in thickness, which may be considered as anatomical evidence for more direct co-operation of the two hemispheres in some tasks rather than in others; and (4) a complex relationship between brain size and fibre thickness becomes evident in the corpus callosum, in which only some fibres seem to compensate for the longer conduction times in larger brains.

Animals↗
PubMed1995

Constancy and variability in cortical structure. A study on synapses and dendritic spines in hedgehog and monkey.

Synapses and dendritic spines were investigated in the parietal cortex of the hedgehog (Erinaceus europaeus) and the monkey (Macaca mulatta). There was no significant difference in the density of synapses between the two species (14 synapses/100 microns2 in the hedgehog, 15/100 microns2 in the monkey), neither in the size of the synaptic junctions, in the proportion of Type I and Type II synapses (8-10% were of Type II in the hedgehog, 10-14% in the monkey) nor in the proportion of perforated synapses (8% in the hedgehog, 5% in the monkey). The only striking difference at the electron microscopic level concerned the frequency of synapses in which the postsynaptic profile was deeply indented into the presynaptic terminal. Such synapses were 10 times more frequent in the monkey. Dendritic spines were investigated in Golgi-preparations. The density of spines along dendrites was similar in both species. The results are discussed with regard to connectivity in the cortex of small and large brains.

Animals↗
PubMed1994

Synapses on axon collaterals of pyramidal cells are spaced at random intervals: a Golgi study in the mouse cerebral cortex.

In this study we investigated the arrangement of synapses on local axon collaterals of Golgi-stained pyramidal neurons in the mouse cerebral cortex. As synaptic markers we considered axonal swellings visible at high magnification under the light microscope. Such axonal swellings coincide with synaptic boutons, as has been demonstrated in a number of combined light and electron microscopic studies. These studies also indicated that, in most cases, one bouton corresponds precisely to one synapse. Golgi-impregnated axonal trees of 20 neocortical pyramidal neurons were drawn with a camera lucida. Axonal swellings were marked on the drawings. Most swellings were 'en passant'; occasionally, they were situated at the tip of short, spine-like processes. On axon collaterals, the average interval between swellings was 4.5 microns. On the axonal main stem, the swellings were always less densely packed than on the collaterals. Statistical analysis of the spatial distribution of the swellings did not reveal any special patterns. Instead, the arrangement of swellings on individual collaterals follows a Poisson distribution. Moreover, the same holds to a large extent for the entire collection of pyramidal cell collaterals. This suggests that a single Poisson process, characterized by only one rate parameter (number of synapses per unit length), describes most of the spatial distribution of synapses along pyramidal cell collaterals. These findings do not speak in favour of a pronounced target specificity of pyramidal neurons at the synaptic level. Instead, our results support a probabilistic model of cortical connectivity.

Animals↗
PubMed1992

Maturation of neurons in neocortical slice cultures: A light and electron microscopic study on in situ and in vitro material.

Using light and electron microscopic methods, we investigated the development and morphology of neurons in neocortical slice cultures. Slices taken from the visual cortex of 6-day-old rats and cultivated for 14 or 20 days were compared with in situ material of corresponding age (P 20 and P 26). Maturation and differentiation of pyramidal and non-pyramidal cells kept in vitro were found to have progressed considerably. In the light microscope the neurons exhibited a morphological appearance strikingly similar to that of the neurons of the neocortex in situ at the same age. The fine structure of the tissue in vitro also had a mature appearance, corresponding in most respects to the material in situ. Synapses and dendritic spines were well-developed. Sometimes a spine apparatus was contained in the sections and occasionally a myelinated fiber could be seen. GABA-immunoreactive cells making symmetric synaptic contacts were also present. Despite these similarities, some quantitative differences could be observed. In slice cultures, only 52% of the synapses were located on spines (78% in situ). In vitro, a larger proportion of synapses (30%) showed a postsynaptically concave curvature than was the case in situ (12%). The areal density of synapses in vitro reached only about 70% of that in situ. This was probably a side-effect of the larger size of dendritic and axonal profiles on electron micrographs of in vitro-material. The most striking difference was that large synapses and synapses containing a large amount of synaptic vesicles were considerably more frequent in vitro than in situ.

Animals↗
PubMed1989

Density of neurons and synapses in the cerebral cortex of the mouse.

Quantitative anatomical investigations provide the basis for functional models. In this study the density of neurons and synapses was measured in three different areas (8, 6, and 17) of the neocortex of the mouse. Both kinds of measurements were made on the same material, embedded in Epon/Araldit. In order to determine the synaptic density per mm3, the proportion of synaptic neuropil was also measured; it was found to be 84%. The cortical volume occupied by cell bodies of neurons and glia cells amounted to 12%, that by blood vessels to 4%. The total average was 9.2 x 10(4) neurons/mm3 and 7.2 x 10(8) synapses/mm3. About 11% of the synapses were of type II. The density of neurons increased with decreasing cortical thickness; thus the number of neurons under a given surface area was about constant. The synaptic density, on the other hand, was almost constant in the three areas, the number of synapses under a given cortical surface area tended, therefore, to increase with cortical thickness. The average number of synapses per neuron was 8,200, with a tendency to increase with increasing cortical thickness. Shrinkage of the tissue was also measured for various staining techniques. No shrinkage occurred during perfusion with 3.7% formaldehyde or with a solution of buffered paraformaldehyde and glutaraldehyde and during fixation in situ. Electron microscopical material showed almost no shrinkage, whereas Nissl-preparations on paraffin-embedded material had only 43% of their original volume. After Nissl stain on frozen sections the volume had shrunken to 68% and after Golgi impregnation and embedding in celloidin to 70%. The total volume of the neocortex was 112 mm3 (both hemispheres together). The total number of neurons was thus 1.0 x 10(7) and the total number of synapses 8.1 x 10(10).

Animals↗
PubMed1987

Synaptic density on non-spiny dendrites in the cerebral cortex of the house mouse. A phosphotungstic acid study.

A modification of the phosphotungstic acid method was used to investigate long segments of non-spiny dendrites in the electron microscope. The number of synapses on these dendrites was counted. The density was 1.9 synapses per micron of dendritic length. Taking into account the synapses not contained in the sections, (which are thinner than the dendrites) one gets a real density of 3.3 synapses per micron. This is more than the average density of synapses along spiny dendrites. It demonstrates that spines are not necessary for large numbers of synaptic contacts.

Animals↗
PubMed1986

Comparison between the dimensions of dendritic spines in the cerebral cortex of newborn and adult guinea pigs.

Dendritic spines in the cerebral cortex of newborn and adult guinea pigs were compared quantitatively. An increase in the average diameter of the head by 21% and in the diameter of the stalk by 29% was found. No difference could be measured in the average length of the spines of both age groups. When plotting the individual measurements against each other, a slight correlation could be found only between the size of the spine head and the thickness of the stalk.

Age Factors↗
PubMed1986

Spatiotemporal receptive fields: a dynamical model derived from cortical architectonics.

We assume that the mammalian neocortex is built up out of some six layers which differ in their morphology and their external connections. Intrinsic connectivity is largely excitatory, leading to a considerable amount of positive feedback. The majority of cortical neurons can be divided into two main classes: the pyramidal cells, which are said to be excitatory, and local cells (most notably the non-spiny stellate cells), which are said to be inhibitory. The form of the dendritic and axonal arborizations of both groups is discussed in detail. This results in a simplified model of the cortex as a stack of six layers with mutual connections determined by the principles of fibre anatomy. This stack can be treated as a multi-input-multi-output system by means of the linear systems theory of homogeneous layers. The detailed equations for the simulation are derived in the Appendix. The results of the simulations show that the temporal and spatial behaviour of an excitation distribution cannot be treated separately. Further, they indicate specific processing in the different layers and some independence from details of wiring. Finally, the simulation results are applied to the theory of visual receptive fields. This yields some insight into the mechanisms possibly underlying hypercomplexity, putative nonlinearities, lateral inhibition, oscillating cell responses, and velocity-dependent tuning curves.

Afferent Pathways↗
PubMed1985

Comparison of the septal areas in New Guinean and European brains.

In 1966, septal nuclei of unusual size in brains of kuru-diseased Fore people from the Eastern Highlands of New Guinea were reported (Beck and Gajdusek, 1966). Microscopic investigation which did not reveal any pathological changes in these nuclei led to the question of whether their large size could be a characteristic feature of the Fore (and perhaps also of other ethnic groups of New Guinea), rather than a consequence of the disease. We had at our disposal brains from patients of coastal areas of New Guinea who did not suffer from kuru. The septal areas of eight cases were investigated by serial sections and compared to those of nine European brains. No difference in size comparable to that reported in the earlier study could be detected. We conclude that a possible pecularity in the size of the septal nuclei of Fore people cannot be generalized to the entire population of New Guinea.

Adolescent↗
PubMed1985

Synaptic density on the axonal tree of a pyramidal cell in the cortex of the mouse.

The aim of this study was to investigate the density and distribution of synapses on the axonal tree of a pyramidal cell in the mouse cortex. The method used was a new variation of Golgi-electron microscopy involving the modification of Colonnier, the photochemical method of Blackstad and the use of phosphotungstic acid. A segment of axon collateral of 87 microns carried 17 synapses, the proximal 27 microns being free of synapses. The main axon was postsynaptic down to a length of 30 microns. On the following 163 microns there were six presynaptic elements. On the proximal parts of four other collaterals, five synapses were found; a few synapses might, however, have been missed on these ramifications. Most of the synapses were located on thickenings already visible in the light microscope. The synaptic size varied by a factor of 2.7. The results are compared to estimates derived from former statistical investigations with other light and electron microscopical methods.

Animals↗
PubMed1981

[Prenatal development and postnatal changes in the guinea pig cortex: microscopic evaluation of a natural deprivation experiment. II. Postnatal changes].

In order to approach the question of how the brain is moulded by environmental stimuli, the neocortex of guinea-pigs just before birth was compared to that of adult animals. In part I of this work we have already seen that the majority of synapses and dendritic spines is already developed before birth in this animal. The investigation was made in precallosal and postcallosal cortex. The samples for electronmicroscopy were taken from the second layer. After birth the following changes have been observed in these areas of the guinea-pig cortex: 1. A slight increase in the thickness of dendrites and dendritic spines (fig. 4). (A changes in the distribution of spines along the dendrite could not be observed; fig. 5). 2. An increase in the number of myelinated fibers, especially in the first layer (fig. 16). 3. An increase in the diameter of the individual synaptic contact area by an average of 10% (fig. 6) which is, however, only significant in the precallosal area. The frequency distribution of synaptic size was similar in prenatal and adult guinea-pigs (fig. 7). 4. A significant increase in the relative number of synapses with postsynaptic perforations (fig. 1c) from 6% to 10% of all synapses. An increase in the thickness of the postsynaptic thickening of asymmetric synapses (fig. 15).

Aging↗
PubMed1981

[Prenatal development and postnatal changes in the guinea pig cortex: microscopic evaluation of a natural deprivation experiment. I. Prenatal development].

The present paper is based on the question, to what extent the cortical structure is determined by genetic factors and how far it is dependent on environmental stimuli. Some deprivation experiment in the literature have supported the assumption tha excitation coming from the sense organs contributes to the formation of synaptic connections in the cortex. This made it possible to invoke the formation of synapses (or dendritic spines) as a substrate of learning processes. Results of experiments on the influence of artificial environments on the formation of synapses have been, however, somewhat contradictory. On this background it was interesting to investigate the cortical development of the guinea-pig, an animal which is highly developed at birth. This percocity separates in time the process of genetically determined development from the changes due to environmental stimuli, which are amply overlapping in altricial animals such as mouse, rat, and cat. A comparison between the cortices of prenatal and adult guinea-pigs showed that the density of dendritic spines has reached adult values already before birth (12/10 micrometers dendritic length before birth, 11,5/10 micrometers in adult animals, fig. 5-8, and 17). The counts have been made on basal dendrites of Golgi-impregnated pyramidal cells in the upper third of the cortex. Also, the difference in the density of synapses on electronmicrographs in animals just before birth (8,9 x 10(8)/mm(3)) and in adult animals (9,4 x 10(8)/mm(3)) was not significant (figs. 13, 14, and 16). The samples have been taken from the second cortical layer. The two areas investigated showed small but significant differences in the time course of spine formation. In both areas the density of spines reached a maximum first and then decreased slightly toward the adult values. However, in the postcallosal area the maximum was reached earlier than in the precallosal area (fig. 9). The decrease in spine density after the maximum, about 18% in both areas, may be partly explained by the growth of dendrites. From the increase in brain volume between birth and adult age and from the density of synapses at different stages, one can conclude that the total number of synapses at birth is about two thirds of that in adult animals. Similarly, the proportion of spines present at birth was at least the same or even higher (fig. 12). Thus, most of the connections in the cortex of the guniea pig are formed without the influence of environmental stimuli. This puts strong doubts on the idea of the formation of synapses or dendritic spines as memory traces. Synapses and spines seem to be the prerequisites of learning rather than the result of it. In part II the question will be examined, if postnatal changes in the cortex of the guinea-pig, especially on spines and synapses, are possible candidates for memory traces.

Animals↗
PubMedDate not supplied

Pyramidal cells with different densities of dendritic spines in the cortex of the mouse.

Neighbouring pyramidal cells in the mouse cortex sometimes have different densities of dentritic spines. This was shown by a quantitative analysis of 10 neurons. For this, a method was worked out which corrects for the spines hidden behind (and in front of) the dendrite. The main result is that there is a positive correlation between the spine densities on different parts of the dendritic tree of one neuron. The possible functional meaning of these findings is briefly discussed.

Animals↗