Ultrastructural changes in the cerebral cortex of an 100 1/2-year-old man

Age changes in fields 39 and 40 (after Broadman) have been studied in a 100 years and 6 months old man died from peritonitis resulted from the surgical intervention, performed in connection with strangulation of the hernia. In the medical history there were no ++neuro-physical signs. The material was taken in 1 h 15 min after clinical death had been stated. The results obtained have been compared with those studied in the brain of persons, who had not yet reached the age of 100 years and had not any signs of ++neuro-physical disturbances and died after urgent surgical interventions in the abdominal cavity. In this group of persons the material for investigation was taken in 15-30 min after clinical death had been stated. The technique for treatment the material, its preparation for electron-microscopical examination is identical. Immersion fixation has been applied. The material obtained from an old animal fixed by means of vital perfusion of 2.5% glutaraldehyde solution is also used. In the person of 100 years and 6 months old the changes do not practically differ from those obtained from persons of younger age, however, the time from the statement of clinical death up to obtaining the material essentially influences preservation of the synaptic apparatus components.     

Development of the human cerebral cortex: a histochemical study

In recent years, improvement in diagnostic techniques has led to better recognition of "disorders of cortical development". These disorders constitute a significant cause of epilepsy, mental retardation, developmental delay and neurological deficits in childhood, and may also contribute to the pathogenesis of psychological and neurodegenerative diseases in adults. Hitherto, however, few systematic studies of the human fetal cortex have been performed, and little is known about the ontogenetic processes of the neocortex in man. The aim of the study is to establish an understanding of the developmental events that occur in the second and third trimesters of gestation, by investigating the biochemical patterns of development of the human neocortex during this period. The temporal and spatial patterns of expression of the neuronal markers gamma-aminobutyric acid (GABA), choline acetyltransferase (ChAT), dopamine beta hydroxylase (DBH), dopamine receptor DR1 and synaptophysin, as well as the glial cell markers glial fibrillary acidic protein (GFAP), S100B and excitatory amino acid transporter protein GLT-1 are delineated in the fetal cortex using immunohistochemistry. Results of this study showed that different neuronal and glial cell proteins follow different developmental patterns and many show inter- or intra-regional variations in expression. Details of these patterns are described and discussed. The early expression of these proteins suggests that they play important roles in the developmental processes of cell proliferation, migration and differentiation. Both neurotransmitters and glial cell proteins probably function outside the confines of synapses in the fetal brain, as paracrine/autocrine factors. Early developmental events seem to be dictated by an innate programme, whereas late events may be more susceptible to extrinsic influences. It is hoped that knowledge of the normal developmental process can lead to better understanding of the causes and mechanisms of "disorders of cortical development", and to better treatments.     

Development of the human cerebral cortex: Boulder Committee revisited

In 1970 the Boulder Committee described the basic principles of the development of the CNS, derived from observations on the human embryonic cerebrum. Since then, numerous studies have significantly advanced our knowledge of the timing, sequence and complexity of developmental events, and revealed important inter-species differences. We review current data on the development of the human cerebral cortex and update the classical model of how the structure that makes us human is formed.     

Patterns of postradiation recovery of the spermatogenic epithelium in rodents and man

On the basis of the data reported in the literature a model is proposed describing the kinetics of the post-irradiation recovery of the main spermatogenous epithelium populations. In studying the spermatogenous epithelium structure of rodents and comparing the experimental and theoretical curves the parameters necessary for the kinetics estimations have been quantitated and their specific variations analysed. From these the parameters have been obtained and the kinetic curves shaped with a reference to human spermatogenous epithelium.     

The associative parietal cortex and spatial processing in rodents

It is widely acknowledged that the hippocampal formation has a central function in rodents' spatial memory and navigation. However, recent work has shown that other structures participate in specific spatial processing. That is so for the associative parietal cortex (APC). Although this neocortical region is far less developed in rodents than in humans and non-human primates, APC damage in rodents induces deficits which affect both egocentrically and allocentrically organized spatial behaviours. On the basis of behavioural (following parietal lesions) and neuroanatomical data, we propose that the APC could be at the interface between the level of perception of the physical world (egocentrically organized) and that of representations or maps (allocentrically organized) of this world. Reciprocally, the APC could also be involved in the transformation, in the opposite direction, of computations made on the basis of representations into motor actions necessary for the efficient execution of oriented behaviours within the physical world.     

The presence of free D-aspartic acid in rodents and man

Free D-aspartic acid is present in appreciable quantities in the brain and other tissues of rodents and in human blood. In the newborn rat, the highest concentration of D-aspartic acid was found in cerebral hemispheres, where, at 164 nmol/g (8.4% of the total aspartic acid), the level of D-aspartic acid exceeds that of many essential L-amino acids. The highest ratio of D- to total aspartic acid (38%) occurred in neonatal blood cells. In the adult rat, the highest concentration was present in the pituitary gland (127 nmol/g, 3.8%). Within the central nervous system marked regional differences are present and characteristic changes with development take place. In general, the levels of D-aspartic acid fall rapidly with increasing age. In cerebral hemispheres adult values (13 nmol/g, 0.43%) are approached within one week. D-aspartic acid concentrations may also be higher in young humans since fetal blood, taken from placental cord, contains 2.6 nmol/g (4.9%) of D-aspartic acid, a value five times that of adult human blood. These distributional patterns and developmental changes may be the result of differences in the ability of various tissues to dispose of an extraneous metabolite, or, reflect alterations in a specific functional requirement for D-aspartic acid.     

A light and electron microscopic study of GAT-1-positive cells in the cerebral cortex of man and monkey

Summary Specimens of human cerebral cortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the GABA transporter GAT-1. Cortical material from macaque monkeys was prepared similarly. Large numbers of GAT-1-positive non-pyramidal neurons were observed in layers I, II, V, and VI of the cortex. Electron microscopy also showed that the GAT-1-positive axon terminals formed symmetrical and not asymmetrical synapses, suggesting that they were the terminals of non-pyramidal neurons. Processes of cells in the walls of blood vessels were also labelled. We conclude that GAT-1 is present in cell bodies and axon terminals of non-pyramidal neurons, and a population of mural cells in blood vessels, in the primate cerebral cortex.     

Development of the various glial cell types in the cerebral cortex of postnatal rats

The present quantitative study in the postnatal rats showed the rapid growth of the various glial cell types in the cerebral cortex. Among them, the increase of microglia was most dramatic. The increase was about 15 times, covering a period of 15 days extending from 5 days of age to 20 days. The majority of the microglia observed were in the outer third of the cortex. During the same period, the number of oligodendrocytes and astrocytes also showed a steady but moderate increase. The increase of oligodendrocytes was most significant between 5 and 10 days. Their density was greater in the inner third of the cortex. Astrocytes were distributed uniformly throughout. Examination of the cerebral cortex in 1- to 3-day-old rats by electron microscopy showed sporadic ameboid microglia cells and glioblasts. The possibility that they served as the precursor cells of microglia and macroglia (astrocytes and oligodendrocytes), respectively, was considered.     

Development and plasticity of the cerebral cortex: from molecules to maps.

The role played by environmental influences in the development of the nervous system has been subject to intense study for the last three decades. Many laboratories are currently engaged in characterizing the exact contributions of activity-dependent or -independent processes to the development of the mammalian neocortex. Here we introduce a special issue devoted to the topic and briefly review recent progress in this exciting field. At the systems level, many investigators are now distinguishing between an "establishment" phase of cortical connections, where activity-dependent and independent mechanisms could operate, and a later "maintenance" phase, which appears to be controlled by neuronal activity. A particularly interesting recent example of the role of top-down vs. bottom-up influences in the development of cortical connections is the emergence of orientation selectivity in visual cortex: we propose a synthetic view highlighting the role of the thalamo-cortical reciprocal projection in this process. Finally, at the cellular level, NMDA receptors, neurotrophins and many other molecules contribute to activity-dependent rearrangement of cortical connections during appropriate critical periods of development.