Attachment Zone Research Articles

The structure of mixed synapses in Mauthner neurons during exposure to substances altering gap junction conductivity

The aim of the present work was to study the effects of dopamine, ecdysone, and chlorpromazine, substances which alter the conductivity of gap junctions (GJ), on the ultrastructure of mixed synapses in goldfish Mauthner neurons. These studies showed that dopamine, which increased the electrical conductivity of mixed synapses, appeared to target desmosome-like contacts (DLC). Hypertrophy of DLC, along with increases in the numbers of bridges within their clefts, showed that the mechanism by which dopamine increased electrical conductivity involved neuronal actin. This was indicated by the transformation of isolated monomeric muscle actin into polymerized actin in the presence of dopamine. Conversely, GJ were degraded by dopamine. Ecdysone, which also increased GJ conductivity, altered GJ structure, increasing the numbers of GJ at the attachment zone and decreasing the sectional length. but had virtually no effect on DLC structure. Ecdysone also showed no interaction with DLC in in vitro conditions. The mechanism of action of ecdysone is thus associated primarily with GJ function. Chlorpromazine, which decreased GJ conductivity, partially or completely degraded the fibrillar juxtamembrane material of DLC, preventing actin polymerization, with corresponding in vitro effects, but produced no changes in GJ. The mechanism of its action therefore appears to be based on changes in the state of neuronal actin.

An evolutionarily conserved coiled-coil protein implicated in polycystic kidney disease is involved in basal body duplication and flagellar biogenesis in Trypanosoma brucei.

Trypanosoma brucei is a flagellated protozoan with a highly polarized cellular structure. TbLRTP is a trypanosomal protein containing multiple SDS22-class leucine-rich repeats and a coiled-coil domain with high similarity to a mammalian testis-specific protein of unknown function. Homologues are present in a wide range of higher eukaryotes including zebra fish, where the gene product has been implicated in polycystic kidney disease. Western blot analysis and immunofluorescence with antibodies against recombinant TbLRTP indicate that the protein is expressed throughout the trypanosome life cycle and localizes to distal zones of the basal bodies. Overexpression and RNA interference demonstrate that TbLRTP is important for faithful basal body duplication and flagellum biogenesis. Expression of excess TbLRTP suppresses new flagellum assembly, while reduction of TbLRTP protein levels often results in the biogenesis of additional flagellar axonemes and paraflagellar rods that, most remarkably, are intracellular and fully contained within the cytoplasm. The mutant flagella are devoid of membrane and are often associated with four microtubules in an arrangement similar to that observed in the normal flagellar attachment zone. Aberrant basal body and flagellar biogenesis in TbLRTP mutants also influences cell size and cytokinesis. These findings demonstrate that TbLRTP suppresses basal body replication and subsequent flagellar biogenesis and indicate a critical role for the LRTP family of proteins in the control of the cell cycle. These data further underscore the role of aberrant flagellar biogenesis as a disease mechanism.

Pattern Formation withinEscherichia coli: Diffusion, Membrane Attachment, and Self-Interaction of MinD Molecules

In E. coli, accurate cell division depends upon the oscillation of Min proteins from pole to pole. We provide a model for the polar localization of MinD based only on diffusion, a delay for nucleotide exchange, and different rates of attachment to the bare membrane and the occupied membrane. We derive analytically the probability density, and correspondingly the length scale, for MinD attachment zones. Our simple analytical model illustrates the processes giving rise to the observed localization of cellular MinD zones.

Spermiogenesis and sperm ultrastructure of Diphterostomum brusinae (Digenea, Zoogonidae), a parasite of Diplodus annularis (Pisces, Teleostei).

This paper constitutes the first ultrastructural study of spermiogenesis and the spermatozoon of a Digenea belonging to the family Zoogonidae, Diphterostomum brusinae. Spermiogenesis follows the general pattern found in the digeneans. It begins with the formation of a differentiation zone in the spermatid. The two centrioles give rise to flagella. These two flagella undergo a rotation of 90 degrees and fuse with the median cytoplasmic process. The proximo-distal fusion occurs at the level of attachment zones. The mature spermatozoon of D. brusinae presents all the features found in the digeneans gametes: two axonemes, mitochondrion, nucleus and two bundles of parallel cortical microtubules. Nevertheless, several characteristics distinguish the spermatozoon of D. brusinae from other digeneans, in particular the external ornamentations of the plasma membrane and the anterior and posterior extremities. The description of the ultrastructural features of reproduction in this species would contribute to the understanding of the phylogenetic relationships in the Zoogonidae family.

The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure

BackgroundThe evidence of hairs grouped into well-defined follicular units has given a new vision of hair anatomy and pathology. The sebaceous glands and the arrector pili muscle, as part of the pilosebaceous unit, should be viewed as important parts of this organized follicular unit structure. ObjectiveThis study was performed to define the morphology and the relationships between the sebaceous glands, muscles, and follicles within the context of the follicular unit structure. MethodsThis study analyzes horizontal, microscopic serial sections of large areas of normal human scalp skin stained with hematoxylin and eosin, Masson's trichrome, and desmin. The course of the arrector pili muscles from their superficial origins to their follicular attachments was followed in each section, which enabled us to match each muscle with its corresponding follicular unit. ResultsSerial, horizontal sections show that, at the upper isthmus, the arrector pili muscle is arranged as a muscular unit structure at the periphery of each follicular unit. Then, at a lower level, the muscle divides and encircles the sebaceous gland, and penetrates between the sebaceous lobules towards the follicular attachment zone. ConclusionMicrophotographic evaluation of large areas of scalp is important for assessing the anatomical relationships between the sebaceous glands, arrector pili muscles, and hair follicles as components of the follicular unit. We introduce the anatomical concept of a follicular unit served by a muscular unit, which can be identified in horizontal sections made at the upper level of the isthmus. This muscular unit results from the merging of the arrector pili muscles that originate from the hair follicles contained in that particular follicular unit. This anatomical disposition suggests that the arrector pili muscles could play an important role in the integrity of the follicular unit as well as in the secretion of the sebum contents.

Inability of unpacked gooseneck liners to stop the sample liquid after injection with band formation (fast autosampler) into hot GC injectors.

With the introduction of the fast autosampler, the rules on how to perform splitless injection should have been revisited: the fast autosampler releases the sample liquid as a band that is no longer nebulized by solvent vapors as in previous injection techniques. In empty gooseneck liners, the sample liquid is shot to the bottom of the injector and jumps around in a largely uncontrolled manner. Visual experiments showed that the liquid is partially rejected. Another portion passes by the column inlet into the column attachment region, while the last part may directly enter the column. The impact on chromatography was investigated by using a mixture of n-alkanes: the higher boiling components passing by the column entrance into the zone of the column attachment were largely lost, i.e., were discriminated against the volatile components. It was concluded that empty gooseneck liners are not suitable for injection by fast autosamplers.

Strain gradients in transpressional to transtensional attachment zones

Abstract Attachment zones couple the rheological layers of lithosphere. In wrench settings, attachment zones accommodate the transition from relatively continuous wrenching at depth to discrete strike-slip faulting of rigid blocks in the upper crust. Strain is controlled by a component of wrench shearing as well as a component of horizontal shearing associated with the differential displacement of finite-width rigid blocks. Strain modelling of wrench attachments predicts high lateral and vertical strain gradients and specific foliation patterns showing antiforms and funnel-shaped synforms. Lineations are shallowly plunging and oriented close to the direction of wrenching. Shear sense reverses across the vertical axial surfaces of synforms and antiforms. In transpression and transtension attachments developed during low-angle oblique convergence or divergence, the pattern of foliation and lineation is similar to that produced in wrench attachments. Transpression attachments display gradients in the shape of the finite strain ellipsoid, from flattening at the base to strongly constrictional beneath the rigid blocks, owing to the increased effect of the horizontal shear component. Conversely, transtension attachments show constriction at the base changing to flattening beneath the rigid blocks. The location of this fabric change within attachment zones is insensitive to finite displacement and angle of convergence or divergence, and therefore should be one of the most robust criteria to identify transpression and transtension attachments. In general, the component of coaxial flow that characterizes transpressional and transtensional systems decreases upward through attachment zones, due to the increased role of the horizontal simple shear in the finite vorticity. These strain and kinematic gradients are a robust result of attachment modelling and can be used as indicators of attachments developed in wrench, transpression, or transtension.

Vertical coupling and decoupling in the lithosphere

Recent advancements in the understanding of mountain belts have focused on vertical coupling of the lithospheric layers. This volume describes the extent to which observed or inferred sub-horizontal coupling or attachment zones provide vertical kinematic linkage between rheologically distinct layers in the continental lithosphere. A common theme is whether the deformation, which partitioned differently in each layer, is linked kinematically across attachment zones and driven by flow in the deeper crust and mantle lithosphere. The papers are divided into six sections. The first analyses the extent to which mantle flow controls deformation of the overlying layers. The Vertical axis block rotations section uses geological and palaeomagnetic data to constrain the role and magnitude of basal shear across mid-crustal attachment zones. The Lower crustal flow and topography section addresses the time-dependent development of orogenic plateaux and their role in the orogenic cycle. Multiple examples of the spatial and temporal development of lithospheric coupling are given in both the Orogenic examples and Subduction examples sections. Finally, rheological constraints of vertical coupling in the lithosphere are investigated.

Attachment formation during partitioning of oblique convergence in the Ketilidian orogen, south Greenland

Abstract Subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts. A mid-crustal attachment zone is exposed in the Palaeoproterozoic Ketilidian orogen, south Greenland, which formed as a result of north-directed oblique convergence at a cordilleran-type margin. Rifting ( c. 2.1 Ga) and compressional deformation and magmatism (> 1850 Ma) on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 Ma now separated into three episodes or peaks of activity. The first episode was focused on the back-arc region and was followed by the main arc construction phase during which transpression was partitioned into strike-slip and contraction components. Despite the longevity of this active margin system, individual tectonic events took place rapidly, e.g. development of fore-arc D 1 -D 3 and accompanying high-temperature, low-pressure metamorphism took place over c. 12 Ma. We explain the fore-arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks. This migration may be attributed to an increase in the geothermal gradient accompanied by, or followed by, exhumation of the mid-crust. The partially molten, hence weak, attachment zone solidified and strengthened during cooling before emplacement of the post-orogenic rapakivi suite during the third distinct phase of mild sinistral transpression.

About this title

Recent advancements in the understanding of mountain belts have focused on vertical coupling of the lithospheric layers. This volume describes the extent to which observed or inferred sub-horizontal coupling or attachment zones provide vertical kinematic linkage between rheologically distinct layers in the continental lithosphere. A common theme is whether the deformation, which partitioned differently in each layer, is linked kinematically across attachment zones and driven by flow in the deeper crust and mantle lithosphere. The papers are divided into six sections. The first analyses the extent to which mantle flow controls deformation of the overlying layers. The Vertical axis block rotations section uses geological and palaeomagnetic data to constrain the role and magnitude of basal shear across mid-crustal attachment zones. The Lower crustal flow and topography section addresses the time-dependent development of orogenic plateaux and their role in the orogenic cycle. Multiple examples of the spatial and temporal development of lithospheric coupling are given in both the Orogenic examples and Subduction examples sections. Finally, rheological constraints of vertical coupling in the lithosphere are investigated.

Distributed strike-slip faulting, block rotation and possible intracrustal vertical decoupling in the convergent zone of SW Japan

Abstract Between the Median Tectonic Line (MTL) and the Japan Sea, the western Chugoku region of SW Japan is cut by a series of N45°E first-order faults and oblique (N60°–N170°E) second-order faults. This fault network, probably formed during Late Cretaceous-Palaeocene times (70–60 Ma), defines a regional block structure. Pre-Plio-Quaternary kinematical indicators suggest left-lateral motion along the first-order faults and right-lateral motion along some of the second-order faults. Geomorphological evidence and earthquake focal mechanisms indicate that Plio-Quaternary slip senses are opposite to Pre-Plio-Quaternary ones. The overall fault pattern is geometrically and kinematically similar to patterns obtained by experimental modelling of simple shear deformation distributed at the base of a brittle layer analogue over its entire width. This similarity suggests the possibility of a mid-crustal, flat-lying partial attachment zone which could have controlled the formation of the western Chugoku fault network in Cretaceous to Palaeocene times. The zone, presently inactive, could correspond to the ‘proto-MTL’, a low-angle fault recently imaged by seismic reflection studies and whose trace approximately coincides with the present-day MTL. Reactivation of the system occurred twice after its formation: firstly in Miocene times, during the opening of the Japan Sea and concomitant clockwise rotation of the entire SW Japan arc; and secondly in Late Pliocene to Quaternary times, after a shift of the relative direction of convergence between the Philippine and Eurasia plates. Unlike the first reactivation, the second reactivation led to an inversion of the sense of slip along the faults.

The evolution of an exposed mid-lower crustal attachment zone in Fiordland, New Zealand

Abstract Studies of convergent margins suggest that large subhorizontal shear zones in the lower crust help regulate how displacements are transferred horizontally and vertically through the lithosphere. We present structural data from the Fiordland belt of SW New Zealand that illustrate the progressive evolution of a 25 km thick section of exhumed, Early Cretaceous middle and lower crust. The data show that the mechanisms by which displacements were relayed through the crust during a 25 Ma cycle of arc-related magmatism, high-grade metamorphism and contraction changed repeatedly. During the period 126–120 Ma, a ≥10 km thick batholith composed of gabbroic-dioritic magma was emplaced into the lower crust. Melt-enhanced shear zones evolved at the upper and lower contacts of the batholith where magma and steep temperature gradients created strength contrasts. By ∼ 120 Ma, partial melting of mafic-intermediate lower crust resulted in the formation of high-pressure (14–16 kbar) migmatite and steep, regionally extensive vein networks up to 10 km below the batholith. Melt segregation and transfer through and out of the lower crust were aided by melt-induced fracture arrays and ductile deformation in shear zones. During the period 116–105 Ma, differential shortening of the crust produced a network of subhorizontal and subvertical shear zones at different crustal depths. Near-vertical shear zones up to 15 km wide formed at the deepest part of the section. These shear zones cut upwards across the entire lower crust to merge with a gently dipping upper amphibolite facies fold-and-thrust zone that formed in the middle crust. A 1 km thick, subhorizontal shear zone underlies this mid-crustal fold-and-thrust zone and physically connected shear zones that formed at different crustal depths. Our data suggest that deformation above and below this mid-lower crustal attachment zone was coupled kinematically and accommodated subhorizontal arc-normal displacements in the middle crust and oblique sinistral displacements on steep shear zones in the lower crust. The steep lower crustal shear zones also record components of subhorizontal arc-normal shortening and vertical thickening. These results strongly suggest that large, kinematically coupled networks of flat and steep shear zones separated the Fiordland crust into distinctive structural domains and relayed displacements vertically and horizontally through the lithosphere during Early Cretaceous oblique convergence.

Transtensional deformation at the junction between the Okinawa trough back-arc basin and the SW Japan island arc

Abstract The Okinawa trough is a back-arc basin currently forming above the subducting Philippine Sea plate by crustal stretching of the Eurasia lithosphere. Existing geophysical investigations have revealed that the northern part of the Okinawa trough consists of a series of en echelon left-stepping grabens or half-grabens, some of which were formed in Miocene times and are presently inactive. In the Kyushu island, three major zones of extensional deformation are recognized. They are characterized by 20–40 km long sediment-filled basins lying on the hanging-wall side of N60°- to N80°-trending, north- or NW-dipping normal faults. These basins display an en echelon left-stepping arrangement. The ages of faulted rocks, the ages of graben-filling sediments and radiometric ages newly obtained on pseudotachylites associated with normal faulting indicate that extension started at 13 Ma at the southern end of Kyushu and migrated northwards in the middle part of Kyushu (Beppu Bay), where it is still active today. The continentward-dipping, listric geometry inferred in depth for the fault systems is consistent with that of faults imaged by existing seismic profiles obtained off-shore in the Okinawa trough and across the Beppu Bay. The spatial association between Miocene or younger normal faults and pre-Miocene regional low-angle thrust faults suggests the possibility of a reactivation of some of the thrust faults as low-angle detachment faults merging in depth into a mid-crustal partial attachment zone.

The Anfeg post-collisional Pan-African high-K calc-alkaline batholith (Central Hoggar, Algeria), result of the LATEA microcontinent metacratonization

The Anfeg batholith (or composite laccolith) occupies a large surface (2000 km 2) at the northern tip of the Laouni terrane, just south of Tamanrasset in Hoggar. It is granodioritic to granitic in composition and comprises abundant enclaves that are either mafic microgranular enclaves (MME) or gneissic xenoliths. It intruded an Eburnian (≈2 Ga) high-grade basement belonging to the LATEA metacraton at approximately 608 Ma (recalculated from the U–Pb dating of [Tectonics 5 (1986) 955]) and cooled at approximately 4 kbar, with a temperature of about 750 °C. This emplacement occurred mainly along subhorizontal thrust planes related to Pan-African subvertical mega-shear zones close to the attachment zone of a strike-slip partitioned transpression system. Although affected by some LILE mobility, the Anfeg batholith can be ascribed to a high-K calc-alkaline suite but characterized by low heavy REE contents and high LREE/HREE ratios. The MME belong to the Anfeg magmatic trend while some xenoliths belong to Neoproterozoic island arc rocks. The Anfeg batholith defines a Nd–Sr isotopic initial ratios trend ( ε Nd/( 87Sr/ 86Sr) i from −2.8/0.7068 to −11.8/0.7111) pointing to a mixing between a depleted mantle and an old Rb-depleted granulitic lower crust. Both sources have been identified within LATEA and elsewhere in the Tuareg shield ( ε Nd/ 87Sr/ 86Sr) i of +6.2/0.7028 for the depleted mantle, −22/0.708 for the old lower crust. The model proposed relates the above geochemical features to a lithospheric delamination along the subvertical mega-shear zones that dissected the rigid LATEA former passive margin without major crustal thickening (metacratonization) during the general northward tectonic escape of the Tuareg terranes, a consequence of the collision with the West African craton. This delamination allowed the uprise of the asthenosphere. In turn, this induced the melting of the asthenosphere by adiabatic pressure release and of the old felsic and mafic lower crust due to the high heat flow. A gradient in the mantle/crust ratio within the source of the Pan-African magmatism is observed in LATEA from the northeast (Egéré-Aleksod terrane) where rare plutons are rooted within the Archaean/Eburnian basement to the southwest (Laouni terrane) where abundant batholiths, including Anfeg, have a mixed signature. Some mantle melts with only slight crustal contamination (Laouni troctolitic layered intrusions) are even present. This suggests that the southern boundary of LATEA microcontinent is not far south of the Tuareg shield.

Occurrence of Botrytis cinerea and Subsequent Disease Expression at Different Positions on Leaves and Bunches of Grape.

The occurrence of Botrytis cinerea and subsequent disease expression at different positions on leaves and bunches of grape was determined from 1996 to 2000. Different techniques were used to detect viable inoculum on material obtained from table (cvs. Barlinka and Dauphine) and wine grape (cv. Merlot) vineyards. Isolations were made from berry skins on Kerssies' B. cinerea selective medium or on water agar medium supplemented with paraquat. Leaves and parts of bunches bearing three to seven berries on a short rachis section were used untreated or treated with paraquat, or were frozen for 1 h at -12°C. Paraquat and freezing were used to terminate host resistance and to promote the development of the pathogen from the tissues. The material was used untreated to detect the pathogen on the surface, or were surface-sterilized to detect mycelia (latent infection) in the tissue. B. cinerea occurred in a consistent pattern in leaves and bunches in all vineyards. Based on the combined data for tissues exposed and unexposed to paraquat, B. cinerea occurred predominantly in bunches and was mostly associated with the bases of the berry and the pedicel. Overall, approximately 30% of the berries yielded B. cinerea at these positions. The next prominent positions occupied were leaf blades, rachises, and laterals, of which approximately 20% yielded B. cinerea. The pathogen occupied the petioles less often (10%), and the berry cheek infrequently (5%). The stylar end of the berries, on the other hand, was virtually free (0.02%) of the pathogen. Disease expression in bunches displayed the pattern showed by the inoculum ecology, and symptoms consistently developed first at the berry-pedicel attachment zone. The isolation studies showed that the pathogen seldom occurred on the surface or in the skin tissue near the base, cheek, or stylar end of berries. Latent infections in the berry base were also few at véraison and harvest. Collectively, the findings indicate that conidia dispersed in early season in bunches, and residing superficially at the berry-pedicel attachment zone, are a major factor in B. cinerea bunch rot.

DC arc photography and modelling

Direct-current arc furnaces operate with a graphite cathode positioned above a molten slag and metal bath contained inside a furnace vessel. The plasma arc, consisting of ionised particles at extremely high temperatures, forms a conducting path between the graphite cathode and the molten bath. The power provided by the arc can be controlled by adjusting the arc length and the current. The high-intensity plasma arc emanates from a relatively small attachment area on the graphite electrode, and extends down to the surface of the molten bath. Photographs of the arc are presented and compared to models of the shape of the arc. These models provide a description of how the arc voltage varies as a function of arc length and current, for a given set of conditions in the furnace. The arc attachment zone, where the arc impinges on the molten slag surface, is highly turbulent and operates at a very high temperature. This promotes very rapid melting, fast reaction kinetics, and effective mixing. The impingement of the arc causes a crater-like depression in the surface of the slag. This has a significant effect on the distribution of current in the molten slag, and the voltage drop across the slag. The shape and size of this depression has been photographed, and the resulting information used in a model of the depression.

The arrector pili muscle and the follicular unit of the scalp: a microscopic anatomy study.

The arrector pili muscle is a smooth muscle bundle that attaches to the bulge region of the follicle and extends to its superior attachment in the upper dermis. Hair follicles in the scalp are grouped, forming well-defined anatomic structures known as follicular units, which are composed of terminal and vellus hairs, the associated sebaceous glands, and the arrector pili muscles. To describe the microscopic anatomy of the arrector pili muscles in relation to the follicular units, using horizontal sections of scalp skin. Normal scalp skin was obtained from 20 adult cadavers. Tissue specimens were horizontally sectioned at all levels of depth, including the infundibulum, isthmus, and inferior segment. Sections were stained with hematoxylin and eosin, and Masson's trichrome. The distribution of hair follicles in follicular units was only present above the insertions of the arrector pili muscles, at the infundibulum and isthmus. Masson's trichrome proved to be a very useful stain to delineate the follicular units. At the isthmus level, bulky cords of arrector pili muscle were located specifically at one pole of the follicular unit. These bulky cords appeared to be located at the same pole in different follicular units. At the isthmus level, above their follicular attachments, the arrector pili muscles that originate from their respective follicles join together, forming a single muscular structure that extends upward to its superior attachment zone. An anatomic model is proposed in which a single arrector pili muscular structure is shared by all the follicles contained within the follicular unit.

The mucosal attachment to titanium implants with different surface characteristics: an experimental study in dogs.

Findings from in vitro studies have indicated that the orientation and proliferation of cells on titanium surfaces may be influenced by the topography of the surface on which they are grown. It may be argued, therefore, that differences may occur in the mucosal attachment to titanium implants with different surface roughness. The present experiment was performed to study the composition of the soft tissue barrier that formed to implants prepared with well-defined smooth or rough surfaces. Five beagle dogs were used. Four implants made of c.p. titanium were placed in the right edentulous mandibular premolar region. After 3 months, two different types of abutments were connected: one experimental (OA) with a dual, thermal acid-etched surface ('Osseotite'), and one regular (RA) abutment with a 'turned' surface. At the end of a 6-month period during which proper plaque control had been maintained, biopsies including the implant and the surrounding soft and hard tissues were obtained, decalcified and processed for light and electron microscopy. A confocal He-Ne laser profilometer was used to study the surface topography of the abutments. The attachment between the peri-implant mucosa and titanium abutments with either a turned (RA; 'smooth') or acid-etched (OA; 'rough') surface was similar from both a quantitative and a qualitative aspect. The attachment comprised a barrier epithelium and a zone of connective tissue attachment of similar dimension at RA and OA. It was further observed that the 'inner' zone of the connective tissue attachment at both types of abutment was composed of about 30-33% fibroblasts and 63-66% collagen. It was demonstrated that the soft tissue attachment that formed to implants made of c.p. titanium was not influenced by the roughness of the titanium surface.

Mid-crustal partitioning and attachment during oblique convergence in an arc system, Palaeoproterozoic Ketilidian orogen, southern Greenland

Abstract: The Ketilidian orogen in SE Greenland contains a continental magmatic arc (Julianehåb batholith) and forearc which formed in the overriding plate of a Palaeoproterozoic oblique subduction boundary between c. 1854 and 1795 Ma. During uplift and deformation of the forearc between c. 1795 and 1780 Ma, its sedimentary sequences were invaded by arc-type magmas and metamorphosed at HT–LP upper amphibolite facies conditions which led to widespread anatexis and generation of abundant S-type granites. Transpression during early deformation (D 1 ) was partitioned into arc-parallel, sinistral strike-slip in the magmatic arc rocks of the batholith and arc-normal contraction in the sedimentary and volcaniclastic sequences of the proximal forearc (Psammite Zone). Subsequently, D 1 fabrics in the Psammite Zone were overprinted and transposed in an intense, flat-lying, D 2 ductile shear zone with arc-parallel stretching lineations and top-NE kinematic indicators. The kinematic significance of the D 2 shear zone is that it accommodated vertical differences in strain and displacement and permitted deformation to be partitioned differently at different levels in the crust. As such, it is an attachment or coupling zone that provided kinematic linkage between deformation at different crustal levels during NE transport of a forearc sliver. Overprinting of the upper crustal domain of D 1 strike-slip partitioned transpression in the forearc during D 2 is attributed to migration of the attachment zone to a higher crustal level. This migration was a consequence of an enhanced geothermal gradient in the proximal part of the forearc due to the emplacement of batholith-related plutonic suites during D 2 .

Soft tissue reactions to plaque formation at implant abutments with different surface topography. An experimental study in dogs.

The mucosal attachment that forms to titanium implants, uncontaminated by bacterial plaque comprises, independent of the surface characteristics of the abutment, one barrier epithelium and one zone of connective tissue attachment. It was suggested that abutments with a rough surface may accumulate more plaque than abutments with a smooth surface and that such an enhanced rate of plaque build-up may favor the development of inflammatory lesions in the periimplant mucosa. The aim of the present experiment was to study some reactions of the periimplant mucosa to plaque accumulation on implant abutments designed with either a rough or a smooth external surface. In five beagle dogs, four fixtures were placed and submerged in the premolar region. In a second stage procedure performed after 3 months, abutments with two different types of surface topography, one rough, acid-etched (OA) and one smooth, turned abutment (TA), were installed in a random order. After 6 months of undisturbed plaque formation, the animals were sacrificed and biopsies obtained. Tissue samples were prepared for light microscopy and exposed to histometric and morphometric measurements. Six months of plaque accumulation resulted in the establishment of an inflammatory lesion (pl-ICT) in the connective tissue of the periimplant mucosa, the location, size and composition of which did not differ between OA and TA sites. In addition, most OA and TA sites harbored a second inflammatory cell infiltrate in the tissue lateral to the abutment/fixture junction (ab-ICT). While pl-ICT was dominated by plasma cells and lymphocytes, ab-ICT contained a comparatively large number of polymorphonuclear leukocytes. The different surface characteristics of abutment made of c.p. titanium failed to influence plaque formation and the establishment of inflammatory cell lesions in the periimplant mucosa.