Growth models (including terminal and segmental branching) for topological binary trees.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
R W Verwer
Publications and source records attributed to R W Verwer.
Activation of vasopressin neurons in the human supraoptic and paraventricular nucleus in senescence and senile dementia.
A recent study has shown that vasopressin (AVP) cells in the human supraoptic (SON) and paraventricular (PVN) nuclei increase in size after 60 years of age, suggesting that AVP production is increased in senescence. In the present study, the same brain material was used for the determination of nucleolar size in immunocytochemically identified AVP and oxytocin (OXT) neurons as an additional parameter for peptide production. A strong correlation was found between nucleolar size and cell size, both in AVP and OXT neurons. Nucleolar size of AVP but not of OXT neurons increased significantly in senescence. Observations in brains from patients with senile dementia of the Alzheimer type (SDAT) were commensurate with their ages. These results strongly support the hypothesis that AVP neurons in the SON and PVN are activated in old age.
Adolescent↗
A simple statistical test for the vertex ratio using Monte Carlo simulation.
The vertex ratio is the crucial quantity in vertex analysis, which is a method to characterize the mode of growth of neuronal tree structures (i.e. dendrites and axons). In this report we propose the use of the Monte Carlo test to calculate a level of significance for the vertex ratio. As a result the vertex ratio can be used to analyse neuronal trees with respect to a range of growth hypotheses, including terminal and segmental growth.
Animals↗
Synaptic characteristics of identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. A quantitative Golgi-electron microscope study.
The visual cortex of 20 day old rats and rabbits has been considered as mature on the basis of the observations that the dendritic arborization and the overall synaptic population have almost reached their adult stage in these animals. In the present study we have investigated the visual cortex of 20 day and 7 month old (adult) rabbits in order to determine whether this apparent adult appearance also holds for the synaptic organization of individual neurons. Neurons mainly located in layers III and IV of the primary visual cortex (area 17) were Golgi-impregnated, gold toned and deimpregnated and were then, after embedding in plastic, sectioned serially. The number and length of synaptic profiles, and the length of the neuronal boundaries were analysed in every tenth section. From these counts and measurements the size distribution of the synaptic discs, the number of synapses per 100 micron2 neuronal surface and the receptive surface expressed as the percentage of the total neuronal surface covered with synaptic contacts were estimated using stereological methods. At both ages studied, the density of synapses was significantly higher for the non-pyramidal neurons than for the pyramidal neurons. Differences in the amount of receptive surface were parallel to the differences observed for the number of synapses per 100 micron2. At day 20 the receptive surface of the non-pyramidal neurons was significantly larger than that of the pyramidal neurons. The receptive surface of the non-pyramidal neurons in the adult stage was not only larger than that of the pyramidal neurons in the adults, but also larger than that of the day 20 non-pyramidal neurons. From our results the following conclusions can be drawn: (1) The synaptic input received by the pyramidal neurons is mainly established at day 20 of postnatal life, i.e. prior to the establishment of adult visual behaviour. (2) The non-pyramidal neurons complete their maturation in a later stage than the pyramidal neurons. (3) Medium to large sized synaptic contacts are newly formed after day 20 and are mainly added to the synaptic population on dendrites of non-pyramidal neurons. (4) The specific increase in the number of synapses on non-pyramidal neurons is discussed in relation to intracortical inhibition which is thought to be important for the fine regulation of visual function during development.
Animals↗
New classification methods of branching patterns.
Binary branching patterns are described in this paper by their topological structure. The statistical properties of these structures appear to be highly dependent on their growth patterns. As such, observed trees may be used for testing growth models. This paper describes three options in the construction of frequency distributions of topological parameters and their corresponding probability distributions, arising from the terminal and segmental growth models. The construction of these distributions makes the analysis of observed tree structures possible in those experimental conditions where small numbers of observations or differing sizes of trees would form serious obstacles to alternative analytical procedures.
Classification↗
The exact probabilities of branching patterns under terminal and segmental growth hypotheses.
Explore the source record for details and available documents.
Animals↗
A new method for the topological analysis of neuronal tree structures.
Statistical analysis of the frequencies of observed branching patterns of neuronal arborescences is an important means of studying neuronal growth and of characterizing axonal or dendritic populations. We recently derived simple formulae for the exact probabilities of occurrence of types of neuronal trees for both segmental and terminal growth. Additionally, the existence of a natural ordering of the neuronal tree types enables the application of the Kolmogorov goodness-of-fit test. In the present report it is illustrated how these facilities can be incorporated in the analysis of neuronal arborizations. Interesting features are that very large neuronal arborizations can be analyzed completely and that only small sample sizes are required for the estimation of the critical level corresponding to the growth hypothesis. Further, it is indicated how populations of neuronal tree structures may be compared with each other without reference to a particular growth theory.
Animals↗
The effect of shape assumptions on the estimation of the numerical density of synapses from thin sections.
Explore the source record for details and available documents.
Animals↗
Incorporation of diaminopimelic acid into the old poles of Escherichia coli.
The surface stress theory of the ontogeny of the bacterial rod depends critically on whether the old poles continue to incorporate new material into the stress-bearing murein. If insertion of peptidoglycan continues, then seemingly the shape must become gradually rounder due to the surface stress resulting from the internal hydrostatic pressure. We have reanalysed our earlier experimental data by classifying grains with respect to distance from the nearest pole, and not from the cell centre as was done previously, and conclude that old poles do incorporate new diaminopimelic acid residues. This eliminates the model we have proposed for Gram-positive rods, which assumed diffuse growth on the cylindrical sides and that poles once formed would be rigid. The new results are consistent with another model (presented elsewhere) in which insertion of new murein occurs all over the surface, although not equally. This new model leads to elongation and division if the energetics of wall expansion is altered by the cell in a control region at a particular point of the cycle by the cell.
Amino Acids, Diamino↗
Sex differences in effects of environmental stimulation on brain weight of previously undernourished rats.
Neonatally undernourished male and female rats were housed under differential (enriched vs standard) environmental conditions during refeeding from 30 days post-partum (dpp). Animals were killed at 170 dpp and whole brain, forebrain and cerebellar weights compared with those of normally-fed, differentially housed control animals. A sex difference was observed in the response to environmental enrichment. Enriched females showed significantly increased brain weights, irrespective of previous nutritional history. Enriched males failed to show any significant alteration in brain weight. Autopsy results indicated that the enriched condition was stressful to males but not to females. The results cast doubt on the notion that infantile undernutrition may limit later effects of differential experience on the brain.
Animals↗
Oriented fragmentation of Escherichia coli sacculi by sonication.
Isolated murein sacculi of Escherichia coli PA3092 were physically ruptured by sonication. Electron microscopical analysis showed that the rupturing occurred preferentially prependicular to the long axis of the cell. The fragmentation of the sacculi increased with longer sonication times. It was found that the extent of cross-linkage was more affected by the sonication than was the average glycan chain length. These data confirm earlier observations and indicate that the glycan chains run predominantly perpendicular to the long axis of the cell. By contrast, the peptide cross-links are more dispersely oriented.
Bacterial Proteins↗
Pattern of meso-dl-2,6-diaminopimelic acid incorporation during the division cycle of Escherichia coli.
The topography of meso-DL-2,6-diaminopimelic acid incorportion into the cell envelope of Escherichia coli W7 (doubling time, tau, = 70 min) has been studied by autoradiography. To follow the incorporation pattern during the division cycle, cells have been classified according to length and the silver grain distributions have been determined in the two cell halves. In particular, the question of equivalence (with respect to the grain distributions) of the two cell halves has been investigated statistically. The grain localizations have been determined separately for the left cell halves (highest number of grains) and right cell halves. The highest probability of finding grains was in the central area for cells of all length classes. In the longest cells (dividing or nondividing) incorporation occurred in the future septal regions of the prospective daughter cells. Autoradiography of tritiated thymidine-labeled cells indicated the presence of an atypical deoxyribonucleic acid replication cycle (at tau = 70 min). Initiation of deoxyribonucleic acid replication occurred during the latter part of the division cycle, and its termination occurred in the next cycle.
Amino Acids, Diamino↗
Arrangement of glycan chains in the sacculus of Escherichia coli.
A novel of Escherichia coli endopeptidase was used for a selective partial hydrolysis of the peptide bridges which interlink the glycan chains in E. coli sacculi. The loosening of the murein network revealed, in the electron microscope, a preferential orientation of the glycan chains, more or less perpendicular to the length axis of the cell. Control incubations with E. coli transglycosylase or egg-white lysozyme did not leave ordered structures behind.
Escherichia coli↗
Electron microscopy of isolated cell walls of Bacillus subtilis var. niger.
Isolated cell walls of Bacillus subtilis have astriated appearance in the electron microscope. The structure persists when teichoic acids are removed. It is inferred that the structure bears on the arrangement of the peptidoglycan chains.
Bacillus subtilis↗
Synapses of the cerebellar cortex molecular layer after chronic alcohol consumption.
The cerebellar molecular layer of chronic alcohol treated rats showed degenerated parallel fiber boutons and vacated Purkinje cell spines after 6 months of alcohol feeding; degenerated Purkinje cell dendrites were concomitantly observed. The number of synapses between parallel fibers and Purkinje cell spines decreased after 6 months whereas their mean synaptic diameter increased throughout the experiment. Conversely, synapses between parallel fibers and dendrites of interneurons increased in 18-month alcohol-fed group. Quantifications were done using a discrete unfolding procedure. It was also observed that some parallel fiber terminals simultaneously established synapses with multiple Purkinje cell spines and with dendrites of interneurons. These results were obtained from groups of 6 rats alcohol-fed for 1, 3, 6, 12 and 18 months and compared with age-matched pair-fed controls. Previous reports of alcohol-induced degenerative changes in the adult rat central nervous system were, thus, fully corroborated. Furthermore, there was evidence of remodeling processes pointing to compensatory plastic mechanisms in the cerebellar circuitry albeit not sufficient to overcome its alcohol-induced deterioration.
Alcoholism↗