Repair of the external granular layer of the hamster cerebellum after prenatal and postnatal administration of methylazoxymethanol.
01 May 1970-Teratology (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 3, Iss: 2, pp 119-133
TL;DR: In animals treated during intrauterine life and examined on the day of birth a large number of cells in the external granular layer were destroyed, but some seemingly healthy ones always remained, and by the 20th postnatal day no morphological differences could be detected between the treated and control animals.
Abstract: The purpose of this experiment was to examine the influence of methylazoxymethanol acetate (Mam ac) on cell proliferation and regeneration of the external granular layer in the cerebellum of the hamster. Pregnant hamsters were treated with 10 mg/kg/day Mam ac on days 13–15 of gestation and youngsters on the second, third, and fourth or fourth, fifth and sixth postnatal days. In animals treated during intrauterine life and examined on the day of birth a large number of cells in the external granular layer were destroyed, but some seemingly healthy ones always remained. In those permitted to live, surviving cells formed a new external granular layer and by the 20th postnatal day no morphological differences could be detected between the treated and control animals. In animals treated on the second to fourth postnatal days practically all the cells of the external granular layer were destroyed. By the tenth day the Purkinje cells were located throughout the molecular zone. Many of them showed a cytoplasmic cone extending centrally instead of toward the periphery. The internal granular layer contained only a few cells, apparently owing to failure of the normal inflow of neurons from the external granular layer. In animals treated on the fourth to sixth postnatal days most cells in the external granular layer were destroyed. During the following days surviving cells presumably gave rise to a new external granular layer. The cells of this layer failed to migrate centrally. Instead they remained located in the molecular layer where they formed an extra layer of cells, which had the appearance of granule cells. The animals were ataxic, although retinal abnormalities may have been partially responsible for the symptoms.
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TL;DR: Development of a culture system for mammalian olfactory epithelium has permitted the process of neurogenesis to be examined in vitro, and data are presented which suggest that the precursor follows a simple lineage program, dividing to give rise to two N-CAM+ daughter neurons.
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TL;DR: The small cell size and failure to form branchlet spines suggest that the Purkinje cell abnormality may be closer to the primary effect of the mutant gene than the more flagrant hypoplasia and degeneration of granule cell neurons.
Abstract: Postnatal development of the cerebellar cortex has been compared in staggerer mutant and unaffected littermate mice. From postnatal day 3 to about day 21 the external granular layer in staggerer mice is decreased in thickness and area, and the number of postmitotic granule cell neurons is reduced. Those granule cells that are generated seem to differentiate normally, with the remarkable exception that they from only primitive junctions with Purkinje cell dendritic shafts. These specialized junctions are not superseded by the normal parallel fiber: Purkinje spine synapses and disappear by the third week. Purkinje cell somata and dendrites are smaller than normal at all stages examined. The dendrites are not confined to the sagittal plane as in the normal and, unique among mutant or other animals described to date, they exhibit virtually no branchlet spines. All other cortical synaptic relations of granule and Purkinje cells, including climbing fiber: Purkinje spine synapses, appear qualitatively normal. However, by 28 days virtually all staggerer granule cells have degenerated. While the primary genetic defect remains unknown, we postulate that the morphological abnormalities may be attributable to a block in the normal developmental relationship between granule cells and Purkinje cells. The small cell size and failure to form branchlet spines suggest that the Purkinje cell abnormality may be closer to the primary effect of the mutant gene than the more flagrant hypoplasia and degeneration of granule cell neurons.
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TL;DR: This work was undertaken to determine the sites of cell proliferation in the cerebral cortex of the hamster during prenatal life and shortly after birth, and to examine the differentiation of the neuroblasts during migration and after arrival at their final location.
Abstract: This work was undertaken: (1) to determine the sites of cell proliferation in the cerebral cortex of the hamster during prenatal life and shortly after birth; (2) to study the migration pattern of neuroblasts before and shortly after birth; and (3) to examine the differentiation of the neuroblasts during migration and after arrival at their final location.
Tritiated thymidine was injected in pregnant hamsters at various days of gestation and in newborn animals. When one hour after treatment the parietal cortex of the embryos was examined for DNA synthesis, labeled cells were found in the neuroepithelial layer but not in the cortical layers. In the newborn radioactive cells were found both in the neuroepithelial layer and in the subependymal layer, a layer consisting of polymorph cells and developing at the end of prenatal life. Hence during embryonic life cell proliferation in the parietal cortex is restricted to the neuroepithelial layer, but in the newborn the subependymal layer is also ctive in cell production.
When the generation time of the neuroepithelium was determined, the DNA synthetic phase was found to be six hours, the pre-duplication and prophase about one and one-half hours and the post-duplication stage about four and one-half hours. Hence the duration of the generation time of the neuroepithelial cells during embryonic life is about 12 hours.
To examine the migration pattern of the neurons formed during embryonic and postnatal life, pregnant hamsters were injected at successive days of gestation and the embryos sacrificed at the twentieth postnatal day. A similar procedure was followed for newborn animals. It was thus found that neuroblasts formed during the early stages of development occupy the deep layers of the cortex, while those formed during the later stages of intrauterine life and during the first postnatal days occupy the more superficial layers. Hence, neuroblasts produced during the final stages of development migrate through the cell layers formed at previous days to reach the surface of the cortex. The time required for this migration varied in the newborn hamster from three to five days.
When newborn hamsters were injected with tritiated thymidine and the labeled cells traced during the following ten days, it was noted that the cells released by the neuroepithelial layer arrived in the deeper layer of the cortex about 48 hours after labeling. The cells were characterized by a spindle-shaped nucleus while the cytoplasm was seen to extend in peripheral direction. Shortly after arrival at the surface of the cortex the cells lost their spindle shape and the nucleus became oval-shaped with a pale nucleoplasm. Subsequently the cells were characterized by a small round pale nucleus with two or three nucleoli close to the nuclear membrane. Approximately nine days after treatment the labeled cells were clearly recognizable as advanced neuroblasts with a large, pale nucleus and one or two nucleoli.
171 citations
References
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TL;DR: It is postulated that undifferentiated cells migrate postnatally from the forebrain ventricles to the hippocampus where they become differentiated, implicating that they may function as receptors of gonadal hormones.
Abstract: In the autoradiograms of young rats injected with thymidine-H3 many of the granule cells of the dentate gyrus were found labeled. The number of labeled cells declined rapidly with increased age at the time of injection. Histological studies showed the presence in young rats of a large germinal matrix of mitotic cells in the ependymal and subependymal layers of the third and lateral ventricles. The areal extent and cell population of this germinal pool declined rapidly from birth on, with a transient rise with a peak at about 15 days. During this latter period the number of “undifferentiated” cells near the granular layer of the dentate gyrus showed a rapid rise with a subsequent decline. The decline in the number of “undifferentiated” cells was accompanied by a rise in the number of differentiated granule cells. Cell counts in homologous parts of the dentate gyrus indicated a six-fold increase in the number of differentiated granule cells from birth to three months. We postulated that undifferentiated cells migrate postnatally from the forebrain ventricles to the hippocampus where they become differentiated. The possible functional significance of delayed hippocampal neurogenesis is discussed with reference to our finding of incorporation of testosterone-H3 by cells of the hippocampus, implicating that they may function as receptors of gonadal hormones.
3,476 citations
TL;DR: The 1958 coating technique of Messier and Leblond for radioautography was investigated in the hope of eliminating artefacts and discovering the optimum conditions for reliable quantitativeRadioautography, and it is concluded that NTB2 bulk emulsion is the most suitable.
Abstract: The 1958 coating technique of Messier and Leblond for radioautography—the most recent modification of the liquid emulsion method—was investigated in the hope of eliminating artefacts and discovering the optimum conditions for reliable quantitative radioautography.From a review of the properties of the various bulk emulsions available, it is concluded that NTB2 bulk emulsion is the most suitable. The proper handling of the emulsion (transportation, storage and testing operations) is described, as well as the details of an improved coating techniqe. Comparison is made of this method with the other most widely used, the strippingfilm technique.The main features of the improved coating technique are as follows:1. Various fixatives may be used for radioautography. Zenker and presumably other mercury-containing fixatives are unreliable, but can be used after complete removal of mercury salts.2. Dipping the sections into celloidin prevents the infiltration of the tissue by emulsion, but is otherwise unnecessary ...
967 citations
TL;DR: An hypothesis is presented which accounts for the extensive cell migrations during histogenesis as a means for attaining particular synaptic contacts.
961 citations
TL;DR: In one experiment rats were injected with single does of thymidine‐H3 at 6 hours, 2, 6 and 13 days of age, or with multiple doses during two periods of early life, and were killed when 2, 4 and 6 months old.
Abstract: In one experiment rats were injected with single does of thymidine-H3 at 6 hours, 2, 6 and 13 days of age, or with multiple doses during two periods of early life, and were killed when 2, 4 and 6 months old. In the autoradiographic analysis attention was focused on the time of origin and differentiation of basket, stellate and granule cells in different regions of the cerebellar cortex. In another, non-radioactive study, in rats ranging in age from newborn to adult, the development of the cerebellum was studied with quantitative and qualitative histological techniques.
In the sagittal plane the area of the cerebellum increases over 20-fold from birth to 21 days. This increase is primarily due to the growth of the cerebellar cortex, much of the increment in the area of the subcortical regions occurring after 21 days. During the first week the growth of the different layers, excepting the proliferative external granular layer, is sluggish. During this period, the cells of the external granular layer do not differentiate but provide stem cells to this growing proliferative matrix. These proliferating and migrating cells of the external granular layer are the precursors of the basket, stellate and granule cells of the cortex; glia cells probably arise from cells multiplying locally. The first cells to differentiate are situated in the lower half of the molecular layer and include basket cells. Stellate cells differentiate later, with a peak at the end of the second week. The bulk of granule cells differentiate during the second and third weeks, with 25–80% of them, depending on the region, being formed between 11–21 days. These differences, together with several histological criteria (thickness of external granular and molecular layers, appearance of Purkinje cells) were used for constructing regional developmental maps of the cerebellar cortex. Granule cells differentiate in the depth of vermian fissures before they do over the exposed surfaces of the lobes; the ventral lobes (lingula and nodulus) mature before the anterior lobes; and the last maturing vermian lobes are the tuber, declive and culmen. The hemispheres, with some exceptions, mature later than the vermis, with the paraflocculus being among the last maturing structures.
702 citations
TL;DR: The results support the concept that some germinal layers of the central nervous system are programmed to produce a succession of cell types, larger cells before smaller ones, as in the olfactory formation.
Abstract: Time of origin (final cell division) of neurons and neuroglia of the mouse olfactory and accessory olfactory formations was determined by autoradiography. Animals were injected with thymidine-H3 at various developmental stages and killed at or near maturity. In the olfactory formation mitral cells (the largest neurons) arise first, mainly over the three day period from the eleventh day of gestation (E11) to E13, tufted cells chiefly from E13 to E18, and granule cells (the smallest neurons) mainly from E18 to postnatal day 20. Most of the smaller and more superficial peripheral tufted cells arise later than the deeper and larger middle and internal tufted cells. All three types of granule cells have a time of origin extending well into postnatal life, with internal granule cells arising over a longer and later period than periglomerular cells or granule cells of the mitral cell layer. Neuroglial precursors undergo final cell division chiefly between E17 and P10. In the phylogenetically less evolved accessory olfactory formation, mitral cells originate earlier than their homologues in the olfactory formation; mitral cells principally from E10 to E12 and granule cells chiefly from E12 to E18. The results support the concept that some germinal layers of the central nervous system are programmed to produce a succession of cell types, larger cells before smaller ones.
525 citations