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[New findings on pathogenic mechanisms of collagen fiber damage during development of periodontal diseases].

This paper reviews new knowledge on collagen destruction of the periodontium during development of periodontal diseases. Numerous clinical and experimental studies reveal important data in regard to recognition of these pathogenetic mechanisms. Two of them are described: intracellular-not depending on collagenase and extracellular-depending on collagenase. Which of these mechanisms is more important or what their concrete relationship is like, is still unknown.

Collagen↗
PubMed1986

The organization and development of the hippocampal mossy fiber system.

The anatomical organization and development of the hippocampal mossy fiber system has been reviewed with special reference to its organization in the common laboratory rat. The mossy fibers originate from the granule cells of the dentate granular layer and the few granule cells found scattered in the dentate molecular layer and hilus. Via a complex system of collaterals the mossy fibers terminate on several types of neurons in the hilus, e.g. the basket cells and the mossy cells. Upon leaving the hilus to pass into Ammon's horn, the mossy fibers converge to form a distinct band of fibers that terminates on the proximal part of the apical and basal dendrites of the pyramidal and basket cells of the regio inferior. In some mammalian species the mossy fibers may continue into the adjacent part of the regio superior. Despite differences in the number of granule cells and pyramidal cells at different septotemporal levels this organization is relatively uniform along the septotemporal extent of the hippocampus. During development the mossy fibers grow out in a sequential manner that matches the pattern of neurogenesis and the aggregation of the cells of origin. From the level at which they originate, the fibers diverge along the septotemporal axis in such a way that the oldest granule cells have the most extensive projections. The adult topographic organization, which is already apparent at the earliest developmental stages, is thus formed in a stepwise fashion. It is concluded that the organization of the hippocampal mossy fibers indicates that neuronal specificity should not be explained by cellular recognition alone, but rather as the cumulated product of the preceding sequence of developmental events that include neurogenesis, migration, aggregation and directed axonal outgrowth.

Animals↗
PubMed1986

Development of cell and fiber lamination in the mouse superior colliculus.

The emergence of laminar organization in the superior colliculus was investigated in the mouse with several anatomical methods, including tritiated-thymidine autoradiography, Golgi impregnation, and general stains for cell bodies and for fibers. The sequence of neurogenesis, cell migration, and early morphological differentiation of neurons was shown to exhibit a discontinuity between the lower and upper divisions (i.e., between the deep and intermediate "gray" and "white" layers and the superficial "gray" and "white" layers). These events proceed in an inside-out order within the lower division, but the same events within the upper division commence in advance of the completion of this progression. Thus, peak generation times for layers of the lower division proceed from (embryonic day) E11 to E13 and for the upper division from E12 to E13. Cell migration, as monitored with tritiated-thymidine labelling, reflects closely the pattern of cytogenesis. This is most clearly evident on E15 when a population of E11-labelled cells is divided into superficial and deep layers (the strata superficiale and profundum--SS and SP) by the interposition of E13-labelled cells at an intermediate level (stratum intermedium--SI). A contingent of the latter cells continue their migration and join their predecessors within the SS on E17, a time point when cell migrations are largely complete. Paralleling this sequence of arrival of neurons and the formation of three primary layers, both the time course of accumulation of fiber fascicles and the early morphological differentiation of neurons in the interval from E13 to E17 tends to proceed from SP to SS and from SS to SI. Thus, the transverse fiber system and large multipolar neurons of SP develop in advance of the longitudinal fiber system and vertically oriented neurons of SS, which in turn develop precociously with respect to the longitudinal fibers and medium-sized multipolar neurons of SI. In contrast, later events of differentiation that underly a major radial growth and an architectonic sublamination of the primary strata proceed in a simpler inside-out sequence from E17 to (postnatal day) P6. The major morphogenetic events underlying the establishment of statification in the colliculus appear to involve the operation of relatively independent programs of assembly for the two basic subdivisions. It is probable that selective cell-cell interactions contribute to the delivery of concurrently generated neurons to different laminae as well as to the deployment of axons in a manner that respects laminar boundaries.

Animals↗
PubMed1985

The development of the Bergmann fiber palisades in the cerebellum of the normal rat and in the weaver mouse.

The development of the Bergmann fiber palisades in the rat cerebellum was investigated by PAP immunocytochemistry using an anti-GFAP antibody. The Bergmann fibers are organized in parallel palisades as early as the second postnatal day and probably even earlier. This observation suggests that the organization and orientation of the palisades precedes the orientation of the parallel fibers in the same direction. Some Bergmann fiber palisades were also found in the adult homozygous weaver mouse, although it was more difficult to find palisades in these mutants than in the heterozygous or normal animals. The results are consistent with the hypothesis that during the early stages of cerebellar development the Bergmann fiber palisades organize the orientation of the parallel fibers in the longitudinal plane of the folium.

Animals↗
PubMed1996

Myosin regulatory light chain modulates the Ca2+ dependence of the kinetics of tension development in skeletal muscle fibers.

To determine the role of myosin regulatory light chain (RLC) in modulating contraction in skeletal muscle, we examined the rate of tension development in bundles of skinned skeletal muscle fibers as a function of the level of Ca(2+) activation after UV flash-induced release of Ca(2+) from the photosensitive Ca(2+) chelator DM-nitrophen. In control fiber bundles, the rate of tension development was highly dependent on the concentration of activator Ca(2+) after the flash. There was a greater than twofold increase in the rate of tension development when the post-flash [Ca(2+)] was increased from the lowest level tested (which produced a steady tension that was 42% of maximum tension) to the highest level (producing 97% of maximum tension). However, when 40-70% of endogenous myosin RLC was extracted from the fiber bundles, tension developed at the maximum rate, regardless of the post-flash concentration of Ca(2+). Thus, the Ca(2+) dependence of the rate of tension development was eliminated by partial extraction of myosin RLC, an effect that was partially reversed by recombination of RLC back into the fiber bundles. The elimination of the Ca(2+) dependence of the kinetics of tension development was specific to the extraction of RLC rather than an artifact of the co-extraction of both RLC and Troponin C, because the rate of tension development was still Ca(2+) dependent, even when nearly 50% of endogenous Troponin C was extracted from fiber bundles fully replete with RLC. Thus, myosin RLC appears to be a key component in modulating Ca(2+) sensitive cross-bridge transitions that limit the rate of force development after photorelease of Ca(2+) in skeletal muscle fibers.

Animals↗
PubMed1989

Axonal guidance and the development of muscle fiber-specific innervation in Drosophila embryos.

The outgrowth of peripheral nerves and the development of muscle fiber-specific neuromuscular junctions were examined in Drosophila embryos using immunocytochemistry and computer-enhanced digital optical microscopy. We find that the pioneering of the peripheral nerves and the formation of the neuromuscular junctions occur through a precisely orchestrated sequence of stereotyped axonal trajectories, mediated by the selective growth cone choices of pioneer motoneurons. We have also examined the establishment of the embryonic muscle fibers and, using intracellular dye fills, have identified cells that are putative muscle pioneers. The muscle fibers of the bodywall have completed their morphogenesis prior to the initiation of synaptic contacts, and owing to the timing of neurite outgrowth from the CNS, synaptogenesis is synchronous at muscle fibers throughout the bodywall. At each muscle fiber the innervating axons make their initial contacts on a characteristic surface domain of the target cell's membrane. Through stereotyped growth cone-mediated trajectories the motoneurons actively establish the basic anatomical features of the mature neuromuscular junction, including the stereotyped, muscle fiber-specific branch anatomy. These events occur without significant process pruning or apparent synapse elimination. Our results suggest that the basic elements of the mature neuromuscular innervation, including the details of the ending trajectory on the target cell's surface, are formed by the precise navigation and presumed recognition by the motoneuron growth cones of muscle membrane surface features.

Animals↗