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Notes: Summary The early development and the structural organization of the human cerebral cortex, prior to the appearanc of the cortical plate (Carnegie stage 22, ca. 54 days), was studied in two embryos: 43 (stage 18) and 50 day old (stage 20), respectively. It has been shown that the human cerebral cortex begins its ontogenetic development around the sixth rather than around the eighth week of gestation as it has been previously assumed. The human cerebral cortex starts to develop soon after the cerebral vesicles have been formed (stage 15) and a primitive internal capsule has been established (stage 17, ca. 41 days). By stage 18 of human development fibres from this primitive internal capsule have reached and probably have penetrated into the developing cerebral vesicle, through its more superficial zone. Fibres from this primitive internal capsule have been traced backward through the ventral thalamus to the mesencephalic tegmentum. The possible existence of primitive ascending fibres from the mid-brain which terminate in the superficial zone of the developing cerebral cortex (tegmento-thalamostriato-cortical tract) is suggested. The arrival of these primitive corticipetal fibres establishes in the outer zone of the cerebral cortex a primordial plexiform lamina or an external white matter. Horizontal-bipolar cells (embryonic Cajal-Retzius neurons) begin to differentiate by stage 18 of human development (43 days in our case). By stage 20 (50 days in our case), the primordial plexiform lamina is well established, extends throughout the entire surface of the developing cerebral cortex, and is considered to be functionally active. It is, by this age, a superficial, 40 μm thick, complex fibrillar neuronal organization composed of numerous horizontal corticipetal fibres (demonstrable with silver methods), horizontal-bipolar Cajal-Retzius neurons and a few other, less defined, cellular elements. This primordial plexiform lamina is considered to represent a primitive “premammalian” cortical organization. The next event in cortical ontogenesis is the appearance of the cortical plate or the mammalian neocortical grey at stage 22 (ca. 54 days). Migrating neuroblasts attracted toward the preexisting primordial plexiform lamina and guided by glial fibres start to accumulate within it. The appearance of the mammalian neocortical grey divides the primordial plexiform lamina into a superficial plexiform or layer I (external white matter) and a deep plexiform or layer VII (subplate zone). Layer I is considered to play a significant role in the overall structural organization of the cerebral cortex by controlling the migration of all its pyramidal neurons. In cortical ontogenesis the mammalian neocortical grey (cortical plate) will only give rise to layers VI, V, IV, III and II of the adult cerebral cortex. These observations further corroborate the concept of the dual origin, composition and nature of the mammalian cerebral cortex including that of man. They also demonstrate that the human cerebral cortex starts to develop much earlier than was previously thought.

Notes: Summary The composition and structural organization of layer I of the human motor cortex were studied throughout the course of prenatal cortical neurogenesis with the rapid Golgi method. The components of layer I are six. The specific afferents of layer I (primitive corticipetal fibers) and the Cajal-Retzius neurons are its essential intrinsic components, while the apical dendritic bouquets of all pyramidal neurons and the axonic terminations of all Martinotti neurons are its essential extrinsic elements. These four components are recognized throughout the entire course of prenatal cortical neurogenesis. The small neurons and terminals from afferent systems of lower cortical strata, which are incorporated into layer I late in cortical neurogenesis, represent its non-essential components. The specific afferents of layer I are the first corticipetal fibers to arrive at the developing telencephalic vesicle marking the beginning of cortical neurogenesis. These primitive fibers extend throughout the surface of the cerebral vesicle establishing an external white matter. They are considered to be the stimulus for the development and maturation of the Cajal-Retzius neurons. Together they form a primitive cortical organization, the primordial plexiform layer, which precedes the appearance of the cortical plate and is considered to be common to and shared by amphibians, reptiles and mammals including man. Layer I evolves from this primordial cortical lamination. The Cajal-Retzius neurons are all characterized by a single descending axonic process which becomes a long horizontal (tangential) fiber in the lower half of layer I. Although the body and main dendrites of these neurons are only found at strategic and old cortical regions (e.g. the motor, acoustic and visual areas) their long horizontal axons extend, anteroposteriorly, throughout the entire surface of the cerebral cortex and establish synaptic connections with the apical dendrites of all pyramidal neurons regardless of location, cortical depth or functional role. In the course of cortical development, all developing pyramidal neurons ascend through the cortical plate in order to establish primary synaptic contacts with layer I. Only then, do they become ready to be displaced downward by the arrival of the next set of migrating neuroblasts. All pyramidal neurons of the cerebral cortex are actually suspended from layer I anchored to it by their apical dendritic bouquets. The need for all pyramidal neurons to reach and establish original synaptic connections with layer I could explain the remarkable ‘inside-out’ formation of the cortical plate. This fact could also explain the characteristic shape of these neurons, as well as their abundance, structural uniformity and universal radial orientation to layer I. The functional role of layer I seems to be the spreading of the same kind of primitive information to all pyramidal neurons of the cerebral cortex whether they be motor, sensory, acoustic, visual or associational in nature, or whether they be large or small. The observations presented in this study further corroborate the concept of the dual origin of the mammalian cerebral cortex. The study emphasizes the important role played by layer I in the overall organization of the cerebral cortex. It proposes that in the course of cortical neurogenesis all future pyramidal neurons are attracted to layer I where they establish original synaptic connections and all receive from it the same kind of primitive information needed for their maturation. There seems to be no obvious reason to believe that the original synaptic contacts established between all pyramidal neurons and layer I disappear in the course of cortical neurogenesis. On the contrary, the progressive growth of the apical dendritic bouquets within layer I seems to indicate that they actually expand.

Notes: Summary The neocortex of the cat undergoes a series of fundamental transformations of its fibrillar-neuronal organization during the course of early prenatal cortical ontogenesis. Some of these transformations assume structural chracteristics and neuronal features which resemble those of phylogenetically older cortical organizations. Following the arrival of corticipetal fibers at the marginal zone of the cerebral vesicle a very primitive neocortical organization, the primordial plexiform layer develops. It is characterized by the external location of the white matter with both corticipetal and a few corticofugal fibers and a few immature neurons sandwiched between the fibers. The primitive plexiform layer is present in the cat from the 20th to the 25th day of gestation. The external (superficial) location of the white matter of the primordial plexiform layer of the cat neocortex is reminiscent of the amphibian cortical organization. It also resembles other primitive structures (spinal cord) of the central nervous system. In view of its short duration and because of the immaturity of its fibrillar-neuronal elements, the primordial plexiform layer is considered to be a transient neocortical organization possibly without functional activity in the cat. The appearance of the cortical plate (25th day of gestation) causes the subdivision of the primordial plexiform layer into an outer and an inner zone. The outer zone becomes layer I and the inner zone layer VI of the neocortex. Both of these layers remain as such throughout cortical development. From the 25th to the 45th day of gestation the fibrillarneuronal structure of layers I and VI develop while the cortical plate grows, passively, by the progressive addition of new cells. The progressive fibrillar-neuronal organization of layers I and VI and the development of structural and functional interactions between them constitutes the primordial neocortical organization of the cerebral cortex of the cat. It is characterized by a superficial (layer I) and a deep (layer VI) plexiform layer composed predominantly of collaterals from the corticipetal fibers arriving at the developing cortex and by three basic types of neurons. The horizontal neurons of layer I with descending axons terminating in layer VI, and the Martinotti neurons of layer VI with ascending axons terminating in layer I, are associative neurons. The large stellate neurons of layer VI are projective neurons. The axons of these cells before entering the white matter send ascending recurrent collaterals to layer I. The fibrillar-neuronal organization of the neocortex during this gestational period (primordial neocortical organization) resembles the organization of the reptilian neocortex. It is postulated that the primordial neocortical organization of the cat is functionally active during this gestational period. The arrival of new types of afferent fibers at the lower region of the cortical plate (45th day of gestation) causes the maturation of the pyramidal neurons of this region of the neocortex. These neurons are recognized at this age as the pyramidal neurons of layer V of the neocortex of the cat. The appearance of these afferent fibers and the maturation of the pyramidal neurons of layer V marks the transformation of the neocortex from its primitive reptilian structure into a distinctly mammalian organization. It is postulated that the cortical plate (pyramidal plate) is a recent addition in neocortical phylogeny representing a mammalian transformation. An analogy seems to exists among the pyramid-like neurons of the amphibian cortex, the pyramid-like neurons of the reptilian neocortex and the pyramid-like neurons (stellate) of layer VI of the mammalian neocortex. This analogy differs from the classical one postulated by Cajal which includes the pyramidal neurons of the mammalian neocortex, which are here considered as recent additions to neocortical phylogeny and hence as distinct mammalian neurons.

Notes: Summary A detailed analysis of the structural organization, staining properties and distribution of the nests formed around the soma of the pyramidal neurons of the primary motor and visual areas of the human cerebral cortex is presented. The presence of pericellular nests in the human primary visual cortex (area 17), first postulated by Cajal seven decades ago, is confirmed. A simple method is introduced which consists of the reconstruction of transparent montages by superimposing various consecutive camera lucida drawings of any given structure. It has been possible, with this method, to reconstruct and to illustrate the complex structure of the pericellular nests of the human cerebral cortex. In addition, it has been possible to demonstrate, for the first time, the central, apparently empty and transparent cavity of the pericellular nest which is occupied by the unstained body of the pyramidal neuron. Transparent montages so constructed impart to the structure they represent a distinct and clear sense of depth which could be used in the study and in the reconstruction of other complex structures of the nervous system. It is hoped that the recognition of the pericellular nests of the human cerebral cortex as real anatomical entities and as a complex type of axosomatic synapses will encourage neurophysiological investigations of their possible functional role.

Notes: Summary A Golgi study of the structural organization of the early developmental stages of the cerebral cortex of the cat has been presented. It has been demonstrated that the structural organization of the mammalian neocortex undergoes a series of fundamental transformations in the course of its early embryonic development. A clear understanding of these early structural changes is essential to comprehend the multi-layered nature of the mammalian cerebral cortex. In order of appearance the following basic transformations have been recognized in mammalian cortical ontogenesis. A. The first recognizable change in the undifferentiated neuroepithelial structure of the cerebral vesicle is the arrival and penetration of corticipetal fibers through its superficial region. The penetration of these afferent fibers into the cerebral vesicle forms a clear plexiform region under the pial surface just above the matrix zone. This clear plexiform region corresponds to the classical marginal zone and is composed, at first, of corticipetal fibers and their collaterals. B. The arrival of these corticipetal fibers induces maturation of some neurons. Primitive-looking and still-developing neurons begin to appear scattered among the afferent fibers without forming any distinct lamination. This combination of an external white matter of afferent fibers with scattered neurons among the fibers has been named the primordial plexiform layer of the mammalian cerebral cortex. Its structure represents a primitive type of nervous organization which is reminiscent of the amphibian brain. In mammalian cortical ontogenesis this primitive plexiform layer has a short duration and it is established as a distinct structure prior to the appearance of the cortical plate. C. The appearance and the formation of the cortical plate within the primordial plexiform layer results in the separation of its neurons and fibers into a superficial and a deep plexiform lamination. Structural and functional interrelationships soon start to develop between the neuronal elements of the superficial and the deep plexiform laminations establishing the primordial neocortical organization, which is characterized by specific types of neurons and fibers. Its structural organization resembles somewhat that of the cerebral cortex of some reptiles. It is important to emphasize that the neurons and fibers of this primordial neocortical organization persist and become components of the adult cerebral cortex. The superficial plexiform becomes layer I and the deep lamination becomes layer VII of the adult mammalian cerebral cortex. Therefore, the cortical plate represents the primordium of only layers VI, V, IV, III, and II of the adult cerebral cortex. The cortical plate is considered to be a distinct mammalian structure of a more recent phylogenetic origin. D. The last significant transformation consists of the sequential growth and maturation of the cortical plate which follows an “inside-out” progression. The maturation of the neurons of the cortical plate and hence the formation of its laminations seems to be due to the sequential and progressive arrival of corticipetal fibers which takes place during the late embryonic stages of development. According to these observations the mammalian cerebral cortex has a double origin and a possible dual nature. A new interpretation of the basic structural organization of the mammalian neocortex based primarily on this dual nature is introduced and analyzed in this communication. It proposes new ideas concerning the origin, the embryonic development, and the phylogenetic evolution of the mammalian cerebral cortex which differ somewhat from the classical conceptions of cortical development.

Notes: Summary The individual prenatal ontogenetic history of the horizontal neurons (the Cajal-Retzius cells) of layer I, the Martinotti neurons of layer VI, the pyramid-like neurons (the polymorphous or spindle cells) of layer VI, and the pyramidal neurons of layer V of the cat neocortex have been investigated. These neurons undergo, in the course of prenatal ontogenesis, a series of significant changes in their dendritic and axonic arborizations resulting in their complete structural transformation. Some of these changes have led to the appearance of new types of neurons quite different from the original in their morphological features as wells as in the territory of distribution of their axons. The horizontal neurons of layer I (superficial plexiform layer) come to assume the morphological characteristics of Cajal-Retzius cells late in prenatal ontogenesis. Also, the pyramid-like neurons of layer VI (deep plexiform layer) acquire the features of polymorphous (spindle) neurons of layer VI late in prenatal neocortical ontogenesis. Certainly, the resulting functional transformations that these neuronal changes cause are important and of great significance in the understanding of the organization of the mammalian neocortex. In the course of prenatal ontogenesis the following occur: the horizontal neurons of layer I lose their axonic connections with layer VI and acquire an increasing relevance in the structural organization of layer I; the pyramid-like neurons of layer VI lose their axonic and dendritic connections with layer I and undergo pronounced regressive changes in their dendritic and axonic arborizations; and the Martinotti neurons lose their axonic connections with layer I and also undergo regressive changes in their dendritic arborizations. In addition, the structural-functional interrelationships among these three neurons, which are quite prominent during early neocortical ontogenesis, fade away in the course of late prenatal ontogenesis and possibly disappear altogether by the time of birth in the cat. These three neurons are the basic neuronal elements of the early, precallosal organization (the primordial neocortical organization) of the mammalian neocortex. Phylogenetically, these three types of neurons are very old ones and have been described in the cerebral cortices of amphibians and reptiles. Therefore, it is not surprising that the early, precallosal organization of the mammalian neocortex should resemble the structural organization of the reptilian (general cortex) neocortex. It is postulated in this communication that these neuronal transformations are the result of a restructuring in the organization of the mammalian neocortex which follows the arrival of the callosal fibers and of a new type of corticipetal fibers at the pyramidal plate. this restructuring represents a transformation of the fibrillary-neuronal structure of the mammalian neocortex from its early, precallosal (reptilian) organization into a more distinctly mammalian one. The mammalian neocortical organization is characterized by the sequential maturation of several strata of true pyramidal neuronal systems. In the course of prenatal ontogenesis the fibrillar and neuronal elements of the early, precallosal neocortical organization lose progressively their relevance in the structural organization of the mammalian neocortex while the new pyramidal neuronal systems acquire an increasing relevance in it.

Notes: Previous primary and secondary co-transfections of genomic DNA from a metastatic human small cell lung cancer cell line into NIH/3T3 cells resulted in a murine fibrosarcoma cell line (Tx93B) that produced frequent spontaneous lung metastases in subcutaneously injected tumor-bearing nude mice. In order to transfer the acquired metastatic behavior to additional cell lines that could then be tested in syngeneic immunocompetent animals, DNA from Tx93B cells was transfected without additional neo gene into Balb/c embryo fibroblasts, which led to the isolation of a tertiary transfectant cell line (D3) of low spontaneous metastatic potential in normal Balb/c mice. Subsequent cell lines established serially from lung metastases in mice injected with D3, and metastatic descendants of D3 (all selected for the original neo marker in G-418), resulted in three generations of metastatically variant cell lines capable of causing pulmonary metastases in 11.1%, 54.6%, and 89.5%, respectively, of subcutaneously injected animals, and in 100% of normal mice injected intraperitoneally. There was no apparent ras-family oncogene participation in the metastatic behavior of either of the two DNA donor cell lines or in the metastatically variant tertiary transfectants. Gelatin zymography indicated that the secretion of gelatinolytic enzymes in vitro by the variant cell lines was inversely proportional to their metastatic capability. Human Alu repeat gene sequences detected in the metastatic variants suggested that co-transfected metastasis-associated genes present in the original human DNA donor cell may have contributed to acquisition of the metastatic phenotype by the tertiary transfectant cell lines. The increase in metastatic potential observed in successive generations of the D3-derived tumor cell lines, further suggested that selection for cells having increased metastatic capability had occurred during passage in vivo accounting for the phenotypic change. Because of their common origin and progressively metastatic nature these cell lines may prove useful in the identification of metastasis-associated genes accessible through the use of differential expression cloning strategies.

Notes: [Auszug] Fig. 1 Gene targeting strategy to introduce AML1-ETO into the mouse Cbfa2 locus, a, Human AMU locus around the t(8;21) breakpoint, b, Targeting vector. Black box, exon 5; gray box, sequences derived from the human AML1–ETO fusion gene; white box, phosphoglycerate kinase (PGK)-neo cassette; ...

Notes: Summary A study of the embryoids (embryo-like structures) encountered in one ovarian and one testicular teratoma is presented. Both teratomas are mixed types and composed of all types of tissues which are encountered in teratomas. The embryoids are classified according to their morphologic characteristic and their embryonic age. Three main categories of embryoids are recognized: the complete, the imperfect and the amorphous forms. Each category is composed of several types of embryoids. The advanced forms of the trophoblastic stage of embryoid development are presented and described for the first time. The embryoids are considered to be derived from parthenogenesis of primordial, premeiotic germ cells. The embryonic evolution of these embryoids constitutes the architecture of the teratomas. The benign or malignant behavior of a teratoma depends on the tendency toward histologic maturity or immaturity of its embryoids respectively.

Notes: Summary A unique patient with subdiaphragmatic total anomalous pulmonary venous connection (TAPVC) in whom individual pulmonary veins drain into a myocardium-encircled saccular confluence, which may represent a persistent and atretic common pulmonary vein (CPV), is presented.