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R W Verwer

Publications and source records attributed to R W Verwer.

15 recordsLinked to original sources
PubMed1992

Tree asymmetry--a sensitive and practical measure for binary topological trees.

The topological structure of a binary tree is characterized by a measure called tree asymmetry, defined as the mean value of the asymmetry of its partitions. The statistical properties of this tree-asymmetry measure have been studied using a growth model for binary trees. The tree-asymmetry measure appears to be sensitive for topological differences and the tree-asymmetry expectation for the growth model that we used appears to be almost independent of the size of the trees. These properties and the simple definition make the measure suitable for practical use, for instance for characterizing, comparing and interpreting sets of branching patterns. Examples are given of the analysis of three sets of neuronal branching patterns. It is shown that the variance in tree-asymmetry values for these observed branching patterns corresponds perfectly with the variance predicted by the used growth model.

Animals↗
PubMed1990

Analysis of binary trees when occasional multifurcations can be considered as aggregates of bifurcations.

The geometrical properties of neurons are important for the way they function within neural circuits. The arborescent processes of neurons that are necessary for the transmission of the information are formed by branching and elongation of segments. In studies that model the outgrowth the tree structures have generally been considered as binary. However, multifurcations do occur. It will be shown that if the multifurcations can be considered as aggregates of bifurcations they may be included in the topological analysis of neuronal branching patterns.

Animals↗
PubMed1989

Organization of projections from the mediodorsal nucleus of the thalamus to the basolateral complex of the amygdala in the rat.

Mediodorsal thalamic (MD) projections to the basolateral amygdaloid complex of the rat were investigated with the anterograde neuronal tracer, Phaseolus vulgaris-leucoagglutinin. Iontophoretic injections were made in distinct subdivisions of the rostral and caudal part of the MD. Both the medial and lateral division of the MD showed a projection to the basolateral complex and there appears to be a topographical organization of the innervation in the rostrocaudal direction: the rostral and caudal part of the MD project to respectively the mid-rostrocaudal and rostral part of the basolateral complex.

Amygdala↗
PubMed1986

Application of growth models to the topology of neuronal branching patterns.

The variation in topological structure of branching patterns may contain essential information with respect to the way these branching patterns have grown. For the understanding of how growth modes finally result in a particular variety in topological patterns, model studies may provide indispensible tools. These studies imply the mathematical formulation of growth models and the development of statistical procedures to compare model predictions with observed data. Recent literature shows two main approached in these model studies, viz. subtree partition analysis (SPA) and vertex analysis. This paper will briefly review the current status with respect to SPA and will apply the model approach to sets of dendritic trees taken from pyramidal, multipolar non-pyramidal and from Purkinje cells. The results show that the topological properties of many dendrites are not in agreement with the hypothesis of random terminal growth and that substantial branching of intermediate segments and/or branching dependent of the position of segments in the tree (topological distance from the cell body) must be assumed. Only two parameters are required to incorporate these assumptions in the model. In all cases up to now it is possible to find parameter values such that the model predictions of topological properties are in agreement with the observations.

Animals↗
PubMed1986

Descriptive and comparative analysis of geometrical properties of neuronal tree structures.

The morphology of neurons is an important factor for the identification and the study of the changes that occur in the nervous system during development or as a result of disease or an experimental treatment. A number of methods to describe the topological aspects of neuronal morphology is discussed. Furthermore it is illustrated how different groups of neurons can be compared. Although both topological and metrical aspects are considered in the comparative sections emphasis is put on counting instead of measuring. Our intention is to present quick and easy methods that are applicable to camera lucida drawings.

Animals↗
PubMed1986

Alzheimer's disease: maintenance of neuronal and synaptic densities in frontal cortical layers II and III.

Neuronal loss and alterations of the cortical neuropil were previously described on necropsic material from patients with senile dementia of the Alzheimer type, and the results compared to age-matched case controls. In frontal cortex biopsic material from our patients with Alzheimer's disease, the numerical densities of neurons and synapses were not significantly different from controls, indicating that changes in the highest cognitive functions might not depend on a generalized loss of neurons and synapses and that quantitative morphological differences may exist between Alzheimer's disease and senile dementia of the Alzheimer type.

Alzheimer Disease↗
PubMed1985

The vasopressin and oxytocin neurons in the human supraoptic and paraventricular nucleus; changes with aging and in senile dementia.

The neuropeptides vasopressin (AVP) and oxytocin (OXT) are supposed to be involved not only in peripheral functions (e.g. diuresis, labour and lactation) but also in central processes that are frequently disturbed during aging and senile dementia (e.g. fluid and electrolyte homeostasis and cognitive functions). A concomitant decrease in activity of the hypothalamo-neurohypophyseal system (HNS) with aging has been postulated in the literature, but has not yet been established. In order to investigate possible age-related changes in the human HNS, immunocytochemically identified AVP and OXT neurons in the paraventricular and supraoptic nucleus (PVN and SON) were analysed morphometrically in subjects from 10 to 93 years of age, including patients with senile dementia of the Alzheimer type (SDAT). Cell size was used as a parameter for peptide production. Mean profile area of OXT cells did not show any significant changes with increasing age. Mean profile area of AVP cells, however, showed an initial decrease up to the sixth decade of life, after which a gradual increase was observed. Size of AVP and OXT cell nuclei did not change significantly with aging. Observations in brains from patients with SDAT were within the range for their age group. The present results do not support degeneration or diminished function of the HNS in senescence or SDAT, as generally presumed in the literature, but suggest an activation of AVP cells after 80 years of age. The activation of AVP cells in senescence is in accordance with previous findings in the aged Wistar rat.

Adolescent↗
PubMed1985

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↗
PubMed1985

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↗
PubMed1978

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↗
PubMedDate not supplied

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↗