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Causal analysis of molecular patterning at neural plate and early neural tube stages has shown that the central nervous system (CNS) of vertebrates is essentially organized into transverse neural segments or neuromeres and longitudinal zones which follow the curved axis of the brain. The intersection of the longitudinal and transverse patterning processes in the embryonic brain leads to the formation of a checkerboard pattern of distinct progenitor domains called "fundamental morphological units" (FMUs). The topologically invariant pattern formed by the ventricular surfaces of the FMUs of a given taxon represents the "Bauplan" or "blueprint" of the brain of that taxon. The FMUs initially represent thin epithelial fields; during further development they are transformed into three-dimensional radial units, extending from the ventricular surface to the meningeal surface. It is of note that the boundaries of the neuromeres, longitudinal zones, and radial units all strictly adhere to a non-Cartesian coordinate system inherent to the CNS of all vertebrates. The major neural histogenetic processes, including cellular proliferation, radial migration, and differentiation, as well as the formation of grisea (cell masses, nuclei, and cortices), occur principally within the confines of the FMUs, although tangential migration may also take cells to distant sites. Hence, recognition and delimitation of these units is essential for the identification and interpretation of grisea. An outline of the procedure to be followed in these processes of identification and interpretation is presented, and a list of the pertinent homology criteria is provided. [ABSTRACT FROM AUTHOR]

Bergquist and Källén as well as Puelles and collaborators have presented models of the developing vertebrate brain, the basic units of which are formed by intersection of transversely oriented neuromeres and longitudinally arranged zones. These units represent initially discrete, developmentally independent compartments, but during later development some (many?) are invaded by sizable numbers of neuroblasts generated in adjacent units. No consensus exists with regard to the number and arrangement of the units involved in the formation of the telencephalon and hypothalamus. [ABSTRACT FROM AUTHOR]

A method for measuring the susceptibility of a patient to develop decubitus ulcers is described and initially evaluated. It is based on an indirect, noninvasive measurement of the transient regional blood flow response after a test pressure load which simulates the external stimulus for pressure-sore formation. This method was developed to determine the individual risk of a patient and to study the subfactors which contribute to the susceptibility. This would also offer the possibility of evaluating the effect of preventive treatment aimed at reducing the susceptibility. The method was found to discriminate between preselected elderly patients at risk on the one hand, and non-risk patients and healthy young adults on the other hand. No differences in blood flow responses were found between the non-risk elderly patients and the healthy young adults. This suggests that age per se is not a factor in the formation of pressure sores. In the risk group the recovery time after pressure relief was found to be three times as long as the duration of the pressure exercise. This indicates that the recovery time after pressure exercise may be as important as the period of pressure exercise in deducing the risk of developing decubitus ulcers. [ABSTRACT FROM AUTHOR]

A quantitative electron microscopic analysis was undertaken of the development of the pyramidal tract, at the level of the third cervical spinal segment, in rats ranging in age from the day of birth to three months old. The axon number was calculated as the product of axon density, determined in a systematic random sample of electron micrographs, and tract area. During the first postnatal week the tract contains thin unmyelinated axons and growth cones. Growth cones are abundant in neonatal rats, but can still be observed occasionally at the end of the first postnatal week, indicating a continuous addition of pyramidal tract axons during the first postnatal week. Myelination starts around P10. By the end of the first postnatal month approximately 50% of the axons have already been myelinated. Myelination proceeds during further maturation, but in the three month old rat 28% of the axons are still unmyelinated. The total number of axons increases rapidly after birth up to 153 000 at the fourth postnatal day. Subsequently, the number of axons is reduced by nearly 50% to 79 000 in the adult rat. The axon loss is most prominent during the second postnatal week, when 32 000 axons are climinated, but continues for several weeks at a slower rate. [ABSTRACT FROM AUTHOR]

An anterograde tracer study has been made of the developing corticospinal tract (CST) in the rat using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Analysis of normal Rager stained material revealed that corticospinal axons reach upper cervical spinal cord levels at the day of birth (PO). Postnatal rats ranging in age from one (P1) to fourteen (P14) days received multiple WGA-HRP injections into the cortex of their left hemisphere and were allowed to survive for 24 h. The first labeled CST fibers caudally extend into the third thoracic spinal cord segment at P1; into the eighth thoracic segment at P3; into the first or second lumbar segment at P7 and into the second to third sacral segment at Pg. Thus the outgrowth of the leading 'pioneer' fibers of the CST is completed at P9 but later developing axons are continuously added even beyond P9. Quantitative analysis of the amount of label along the length of the outgrowing CST revealed a characteristic pattern of labeling varying with age. The most striking features of that pattern are: (1) the formation of two standing peaks at the level of the cervical and lumbar enlargements respectively and (2) the transient presence of a smaller running peak which moves caudally with the front of the outgrowing bundle. The standing peaks are ascribed to the branching of the axon terminals at both intumescences, whereas the running peak probably arises by the accumulation of tracer within the growth cones at the tips of the outgrowing CST axons. Factors such as the number of axons, the varying axon diameters, the branching collaterals, the presence of varicosities, the transport rate of the tracer, the uptake of the tracer at the injection site, which possibly may affect the amount of label present in both the entire bundle and in the individual axons are discussed. Current research is focused upon an analysis of the relation between the site of injection within the cortex and the pattern of labeling of the CST. A delay of two days was found between the arrival of the CST axons at a particular spinal cord level and their outgrowth into the adjacent spinal gray. However, combined HRP and electronmicroscopic experiments are necessary to determine the factors behind the maturation of the CST as well as the maturation of the spinal gray. [ABSTRACT FROM AUTHOR]

An electron microscopic study has been made of the tip of the growing pyramidal tract in the rat. This part of the developing bundle, designated as the growthzone, has been examined at the levels of the medulla oblongata and the third spinal segment at embryonic day 20 and on the day of birth, respectively. The tip of the pyramidal tract contains, apart from axons, numerous larger profiles. An analysis of serial sections revealed that these represent either growth cones or preterminal periodic varicosities. In the growth cones of the corticospinal axons three zones can be distinguished: a proximal 'tubular', an intermediate 'vesicular-reticular' and a distal 'fine-granular' zone. As distinct from the classical descriptions the corticospinal growth cones end in a single or, less frequently, in two more or less parallel filopodia. None of the growth cones analyzed in this study showed multiple filopodia radiating from the terminal expansion as observed at the end of growing axons in tissue cultures and in developing spinal fibre tracts of nonmammalian vertebrates. As regards the varicosities, most of these structures are characterized by a light cytoplasmic density. Others, however, contain a denser cytoplasm, closely resembling that of the vesiculo-reticular part of growth cones. [ABSTRACT FROM AUTHOR]

In this paper the serotonin-containing neurons in the diencephalon and mesencephalon of the trout have been studied by immunocytochemistry. Serotonin-immunoreactive perikarya, fibres and terminals were visualized by using well-characterized antibodies to serotonin. Six areas could be demonstrated to contain serotonin-immunoreactive cellbodies. 1. A group of cells, situated ventral to the commissura posterior; 2. A region within the confines of the nucleus recessi lateralis and a few scattered cells dorsally to this nucleus; 3. Neurons, situated ventral to the recessus lateralis hypothalami, within the nucleus tuberis inferior; 4. Cells which are situated within the borders of the nucleus recessi posterioris; 5. A number of cells, situated within the nucleus raphes superior and finally: 6. Perikarya, located dorsolateral to the nucleus raphes superior. The following three regions showed a very high density of serotonin-immunoreactive fibres and terminals: A. the most dorsal portion of the nucleus diffusus tori lateralis; B. the area dorsal to the recessus lateralis and C. the area surrounding the recessus posterior. [ABSTRACT FROM AUTHOR]

in order to determine the time and site of origin and the final location of various cell groups in the spinal cord, tadpoles of Xenopus laevis, ranging from stage 48 to stage 56 were treated with tritiated thymidine and sacrified at various stages from 49 to 66 (stages according to Nieuwkoop and Faber (1967). From the poorly developed matrix at stage 48-49 not only ventral horn cells, but also neuroblasts of the intermediate zone and the dorsal horn arise. Both the matrix and the ventricle expand in a dorsal direction. From the well-developed matrix at stage 54, in which the mitotic activity is almost exclusively confined to its dorsal part, mainly cells of the dorsal horn develop. However, this later-stage matrix also gives rise to a considerable number of neuroblasts, which become located in the central parts of the intermediate zone and the ventral horn. Generally the later-born cells come to lie dorsomedially to the older ones. The neuroblasts of the lateral motor column, however, migrate through and settle ventrolaterally to their predecessors. Our observations do not support the basal plate-alar plate concept of His (1893). [ABSTRACT FROM AUTHOR]

The morphogenesis and histogenesis of the spinal cord of Xenopus were examined. The study encompasses the developmental period between stage 41 and stage 66 (stages according to Nieuwkoop and Faber 1967). This period can roughly be divided into three phases. From stage 50 up to stage 53 strong proliferation and rapid growth are the most striking features. This developmental phase is preceded and followed by less dynamic periods. From stage 41 up to stage 50 the rate of proliferation is relatively low. The numbers of cells in the matrix and in the mantle layer are very small. In the mantle layer two classes of early differentiated transient neurons can be distinguished: primitive giant sensory or Rohon-Beard cells and primitive motor neurons. From stage 46 onward the originally tube-shaped spinal cord swells at the thoracic level into a thoracic enlargement. After stage 50 the proliferation strongly increases until a maximum at stage 53. Concomitantly a considerable acceleration of growth takes place. The major part of the mitoses are always concentrated in the dorsal part of the matrix. From stage 51 onward the cervical and lumbar regions show much more mitoses than the thoracic part. Distinct cervical and lumbar enlargements develop and are going to mask the thoracic swelling of the cord. From stage 54 on proliferation continues on an increasingly low level. The period between stage 54 and stage 66 is characterized by differentiation of the spinal neuronal elements. [ABSTRACT FROM AUTHOR]

The macroscopic anatomy of the brain of the single surviving crossopterygian species Latimeria chalumnae is described and depicted. The brain of this fish is slender and elongated. The rhombencephalon is well developed; its ventricular aspect shows four longitudinally arranged ridges which roughly correspond to the functional zones of Herrick and Johnston. The cerebellum comprises two extremely large auriculae and an unpaired, evaginated corpus cerebelli. The mesencephalon is small and does not show any marked differentiation of its surface. In the diencephalon, ventricular sulci mark the boundaries between the epithalamus, dorsal thalamus, ventral thalamus and hypothalamus. The dorsal thalamus protrudes into the ventricular cavity. The telencephalon can be clearly divided into a dorsal pallium and a ventral subpallium. The pallium is represented by a thickened, solid body. It is partly covered by a membranous roof, which in the median plane constitutes an ependymal septum. The subpallium is thin-walled and clearly evaginated. This structure and the ventral part of the pallium enclose a distinct lateral ventricle. The olfactory bulbs are connected with the telencephalon proper by extremely long olfactory peduncles. Interestingly, the brain of Latimeria appears to have gross structural features in common with all major groups of fish, i.e. the Chondrichthyes or cartilaginous fishes, the Dipnoi or lung fishes and the Actinopterygii or ray-finned fishes. Thus, with respect to the shape of the rhombencephalon and of the vestibulolateral lobe of the cerebellum, Latimeria approaches the chondrichthyan condition; the mesencephalon, the diencephalon and the subpallial parts of the telencephalon share a number of features with their dipnoan homologues, whereas the corpus cerebelli, the pallium and the membranous parts of the telencephalon clearly resemble the corresponding structures in the actinopterygians. No special structural affinities to the amphibians were noticed. [ABSTRACT FROM AUTHOR]

The corpus cerebelli of mormyrid fishes is strongly developed and differentiated into four lobes: C1−C4. Although all of these lobes contain the characteristic cerebellar layers: granular, ganglionic and molecular, they show distinct architectonic differences. A previous study revealed that the ganglionic layer of C1, in addition to Purkinje elements contains conspicuous giant cells. In the present paper the results of a further analysis of C1 are reported. This analysis is based on serially sectioned brains of Gnathonemus petersii, stained according to Nissl, Bodian and Häggquist. Semi-thin sections were stained with p-phenylenediamine. Routine EM techniques were used to visualize synaptic relations. Mossy fibres and granule, Golgi, Purkinje and stellate cells are located characteristically throughout C1. It appeared that the giant cells of a previous study represent the largest elements of a population which has been termed now the eurydendroid cells. The average size of the latter is somewhat larger than that of the Purkinje cells, but both groups of cells show a considerable overlap in the size of their somata. Purkinje cells and eurydendroid cells are present throughout the ganglionic layer and both have a flattened, sagittally oriented, dendritic tree that extends into the molecular layer. Yet, the eurydendroid cells (EC) display the following characteristics which distinguish them from Purkinje cells (PC): (1) In EC the Nissl substance is dispersed diffusely throughout the soma, whereas in PC it tends to be concentrated around the nucleus, (2) The soma/nucleus ratio for EC is distinctly larger than for PC, (3) The dendritic trees of EC extend over a larger stretch of the molecular layer than those of PC, hence the term EC, (4) The dendrites of EC are more widely spaced and oriented less strictly parallel to each other than those of PC, (5) The dendrites of EC are somewhat irregular in outline and not covered with spines, in contrast to those of PC, (6) The axons of EC are oriented radially and join bundles of coarse fibres which leave the cerebellum whereas the axons of PC extend and ramify within the ganglionic layer, (7) The somata of EC, contrary to those of PC, are enveloped by a dense axonal plexus which forms numerous synaptic terminals on them. The numerical ratio of EC: PC was 1:5.5. The circuitry in C1 and the possible functional roles of its constituent neurons are discussed. It is pointed out that in this lobe the axons of PC impinge on EC and that the latter constitute its output system. [ABSTRACT FROM AUTHOR]