The evolution of large human brain size has had important implications for the biology of our species. Humans achieve their large brain sizes through a growth pattern that is distinct from that of other primates. In humans, very rapid brain growth that is typical of the fetal period is extended through the first year of postnatal life. The rapid growth in brain size contributes to very high daily energy requirements during infancy and early childhood. Recent studies of human brain growth and energy needs show that over half of a newborn's resting energy budget is allocated to the brain. Energy demands of the brain peak at about age five years (65% of basal energy expenditure), and decline to 20–25 percent of basal metabolism in adulthood. To accommodate these high metabolic demands, human infants are born with high levels of body fat and continue to gain fat during the first year of life. In addition, breast milk is a rich source of energy and fatty acids that are essential for brain development. Regulation of body growth during childhood also helps to compensate for the high energy demands of the brain.
Macrophages of humans could be extracted in large numbers from the connective tissue using a newly developed, not particularly difficult method. These macrophages were compared with the peritoneal macrophages of mice using light-, scanning and transmission electron-microscopic methods. The sterility of the cell suspension and the high yield of macrophages has allowed the first in vitro study of histiocytes to take place, in contrast to the classic 'microexudate-coated surface method'. The activity of the human in comparison with peritoneal murine macrophages has been evaluated using numerous histochemical and immunological techniques. These methods prove a modulation of the macrophage activity of healthy humans and mice under exemplary conditions of extremely strenuous physical exercising, in accordance with earlier experimental findings on animals alone. The degenerative changes which occur under these experimental conditions in the skeletal muscular system show an invasion of cells of the immune system, which are integrated into an explanation of the increased activity of macrophages. These results find their place in a new theoretical concept supporting the general validity of the co-operation of macrophages and other cells of the immune system in pathological degeneration and regeneration processes in the skeletal muscular system. It has been shown that the increased activity of human and murine macrophages brought about by extreme strenuous physical exercising, insofar as one is able to order them into a progressive scheme of stress happenings, fit very well into the concepts of the 'alarm reaction' phase. The activity of macrophages proves to be sensitive to the mediators of tumours of mesenchymal origin, with respect to the initial stage of phagocytosis, to the further biochemical deterioration, to the cytotoxicity and to the amount of cells; this, however, is not able to halt the rapid growth of sarcoma in a long term experiment. The proof of a weakened migration of macrophages in sarcoma-bearing animals raises the interest in those substances which are able to positively modulate the migration activity. On the one hand the migratory performance of macrophages in sarcoma-bearing animals in a short-term experiment was increased by the introduction of an anabolic steroid hormone. On the other hand, however, a different degree of success was registered for the further parameters of macrophage activity during short- and long-term experimental investigations.(ABSTRACT TRUNCATED AT 400 WORDS)
Detailed investigation on cleavage lines over the entire area of the body was undertaken in 3 each of male and female cadavers. The directions of cleavage lines showed sex and individual differences. Minute comparison of the diagrams obtained in this study with earlier diagrams revealed the presence of delicate differences in the directions of cleavage lines. Microscopical evaluation of cleavage lines showed that in the regions where cleavage lines were linearly arranged, collagen fibers were regularly arranged in a uniform direction, conforming to the direction of cleavage lines from the shallow reticular layer immediately below the papillary layers to the inner reticular layer where sebaceous and sweat glands existed and that in the regions where cleavage lines were ramified, collagen fibers in these layers lacked directional regularity. The morphology of cleavage lines were considered most influenced by collagen fibers in the epidermal reticular layers from their shallow layers immediately below the papillary layers to the layer where sebaceous and sweat glands existed.
The skeletal influence on muscle development was investigated taking an experimental and comparative approach. Chick hindlimbs of HH stage 23 were operated in order to induce the development of an enlarged, elongated fibula - similar to the condition in bird ancestors. The skeletal change resulted in a series of secondary alterations in the later-forming zeugopod muscles. By comparing the results to the zeugopod musculature in other birds and in reptiles it could be shown that changes did not occur at random but resembled the patterns of interspecific variation and ancestral arrangement. It is concluded that skeletal elements influence muscle morphogenesis during a certain period of development. A classification of four phases in muscle development is presented: formation of the premuscular masses; individuation of separate muscles; final shaping and insertion; development maintenance and growth. The factors acting on each level are discussed and it is suggested that skeletal influence becomes effective in phase 3. The results also emphasize the role of development in evolution. The experimental reestablishment of an ancestral epigenetic condition within a developing organ system resulted in ancestral features of subsequently forming characters. This suggests that modification of epigenetic control of gene expression may be an important mechanism in evolutionary change.
In 6- to 34-month-old Chbb:THOM (Wistar) rats, Purkinje, stellate/basket, granule and large Golgi cells exhibited neither sex-specific differences nor an age-related decrease in their total number. Cell density of granule cells decreased with advancing age and is regarded as an unreliable parameter for the estimation of total cell number unless individual shrinkage factors, protracted growth of the granular layer, and regional differences are taken into account as well. Regional differences were found in the number of granule, stellate/basket and large Golgi cells in relation to Purkinje cells. Differences in the physiology of local cerebellar circuits are expected from these numerical differences.
The fissuration and myelination in cerebella of trisomy 19 mice and of chromosomally balanced control animals on postnatal days (PD) 2, 5, 10, 12, and 15 were analyzed morphologically and morphometrically. In trisomy 19 mice, an increasing fissuration lag with a fissuration pattern and sequence identical to those of the control animals was found. The nuclear volume density of the trisomic glia cell in the neocerebellar commissure also developed like that of control mice, with an increase shortly before and parallel to the beginning of myelination and with a decrease in its further course. The trisomic axons and myelin sheaths were normally structured but axonal growth and myelination in the neocerebellar commissure were retarded. The quantitative relations of the assumed axon/glia interactions were similar to those of the control animals. The fissuration and myelination in the cerebellum of trisomy 19 mice did not seem to be pathologically changed but seemed to be differently retarded. On PD 15, a myelination lag of less than 5 days but a fissuration lag of nearly 10 days was found. This observation and the assumption of a differently retarded growth of the cerebellar cortex compared with cerebellar subcortical regions lead to the suggestion that the trisomy might result in a progressively asynchronous and disproportional development of different CNS structures.
Fresh volumes of the human telencephalon, cerebral cortex, diencephalon, and of the rhombencephalon including cerebellum were determined in a series of 10 normal specimens ranging in age from 63 to 176 days after conception. The volumetric growth of these parts shows a nonlinear dependence on age with a smaller increase during the 3d ontogenetic month and a stronger increase from the 4th month on. These data were analyzed together with previous measurements of 28 brains taken from the Yakovlev Collection in Washington, D.C., and the Vogt Collection in Düsseldorf. These brains range in age from 137 to 22,900 days after conception. These samples were reproduced in a model using sigmoid logistic functions. The entire brain and all analyzed parts show a monotonous growth. The individual regions develop heterochronously. The diencephalon is the first part to reach its ideal volume, with a main growth spurt between 100 and 420 days after conception. The rhombencephalon including the cerebellum is the last, with its main growth spurt between 240 and 650 days after conception. The growth of the entire brain is determined to a great extent by that of the telencephalon, having a main growth spurt between 175 and 580 days after conception. The prenatal growth is described separately with the asymmetric sigmoid function according to Gompertz. This yields a better approximation of the data collected from the early prenatal period.
25 male brains meeting the criteria for normativity and available in serial sections suitable for morphometric studies were selected from the Yakovlev Collection. Growth parameters were calculated based on the generalized logistic function. The ideal weight is 1,313 g (SD = 41), with a half value time of 387 (SD = 26) ontogenetic days and a growth factor of 4.0 (SD = 0.5). Comparison of growth parameters derived from a sample of 161 normative male brains collected at the Department of Neuroanatomy of the Medical School in Hannover revealed an ideal weight of 1,353 g (SD = 14), a half value time of 401 (SD = 10) ontogenetic days and a growth factor of 4.0 (SD = 0.2). The minor discrepancies in the corresponding parameters reflect the small sample size and a considerable lack of developmental data of the three first postnatal decades in the material derived from the Yakovlev Collection. It was, therefore, deemed necessary to analyze these data in combination with data derived from other sources of human material. A comparison of human with animal growth parameters derived from mice, cats and tree shrews reveals differences in brain development. Histological shrinkage of the 25 male brains of the Yakovlev Collection related to fixation, embedding, and staining was assessed. Fetal brains shrank by about 75%, and adult brains by about 50%. The degree of shrinkage was inversely proportional to the age of the brain and was also characterized by individual variations of up to 20%. Therefore, shrinkage had to be corrected on an individual basis in order to determine the true growth of brain regions as reflected by morphometric analysis of histological serial sections.
The fresh volumes of the cortical area of the hippocampal formation were determined in 29 male, normative human brains ranging in age from 137 to 36,221 ontogenetic days inclusive of mid-gestation to the 99th postnatal year. The data were fitted by the 3-, 4-, and 5-parametric logistic functions. The ideal value P1 of the left hippocampal formation is 3 ml (SD = 0.1), the half-value time is 306 (SD = 32) ontogenetic days and the growth factor is 2.5 (SD = 0.4). The maximal daily growth rate of 8 mm3 occurs at approximately the half value time. According to the theory of Dobbing and Sands [1979], this period of rapid growth of the hippocampal formation with other brain regions suggests the existence of heterochronous development.
Proceeding from the hypothesis that cellular differentiation processes are correlated with structural changes of the cell membrane, the expression of antigen and lectin receptors, as well as lectin-like molecules during migration and differentiation of pre- and perinatal neurons in the cerebral cortex, was analysed. It could be shown that a number of cell surface structures exist throughout the whole pre- and perinatal period, e.g. receptors for Robinia pseudoacacia lectin (RPL), pokeweed lectin (PWL) and concanavalin A (ConA) and the Ia and H-2-D/K antigens of the major histocompatibility complex (MHC). The expression of other cell surface structures, for example receptors for peanut and Limulus polyphemus lectin (LPL) and of Thy-1, is determined by the developmental stage; i.e. in the perinatal period higher amounts are found than in early prenatal stages. Binding sites for Phaseolus vulgaris lectin, PWL and anti-Thy-1.2 are not only demonstrated on perikaryal membranes, but additionally on diverse tangential or radial fibre structures. While on cells of the ventricular layer - the proliferating cell compartment - peanut lectin (PNL) receptors are observed in low density, LPL receptors in high density, in the migration zone, i.e. the intermediate layer, receptors are found predominantly for PNL and only few cells carry a significant number of LPL-binding sites. After the preneurons have migrated through the intermediate layer and the neighbouring cortical plate, remaining at the pia-near border of the latter, LPL receptors are again expressed on the cell surface of the now bipolar preneurons, while PNL receptors cannot be demonstrated any more. Experimental evidence is put forward indicating the possibility that this modulation of exposed carbohydrate residues on the cell surface might be mediated by a membrane-associated enzyme system on the same single molecule. For the investigation of neuronal cell interaction the ability of disintegrated suspended preneurons was used to reaggregate spontaneously in vitro and to build histiotypic cell formations within these reaggregates. It was found that this reaggregation of suspended neuronal single cells is dependent on the presence of ionized calcium, on the temperature, and on the conditions that influence the frequency of cell contacts. Furthermore, the structures expressed on the cell surface of preneurons during the pre- and perinatal period were investigated in regard to their influence on the reaggregation of these cells by means of a blockade by monoclonal antibodies or saccharides, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
