Semblant Land Plants from the Middle Ordovician of the Prague Basin Reinterpreted as Animals

Two plant-like fossil are described from the middle Ordovician of the Prague Basin, Czech Republic. Both fossils bear a strong superficial resemblance to early land plants, but anatomical data indicate an affinity with animals. New evidence on internal structure demonstrates that the putative plant Boiophyton pragense Obrhel is a dendroid graptolite. The relationships of other heavily coalified, branched axes found in associated strata are more obscure. Scanning electron microscopy of surface features suggests that these plant-like remains are fossils of the collagenous stipes of gorgonacean octocorals.     

The formation of a neo-intima in textile prostheses implanted in the aorta of rats and dogs

Summary The formation of a neo-intima in textile prostheses implanted in the rat and dog aorta was studied by means of light- and scanning electron microscopy. Two independent cellular layers (the superficial and deep ingrowth layers) developed on the free surface and under the fibrin layer initially deposited on the inner surface of the prostheses. The superficial ingrowth layer invades the prosthesis from both the proximal and distal aortic stumps and extends over the primary fibrin layer, or replaces it. This layer consists mainly of smooth muscle cells of the triangular aortic type covered by endothelial-like cells. The deep ingrowth layer originates from cellular elements of the prosthetic bed. Fibroblasts, myofibroblasts and spindle-shaped smooth muscle cells invade the fibrin layer through the interstices of the fabric structure of the prosthesis. Precursors of endothelial cells, however, are absent from this population. The superficial and the deep ingrowth layers may become joined by progressive replacement of the fibrin layer, but remain distinguishable because of their different cellular components.When a continuous cellular layer is established on the inner surface of the prosthesis, and this is then covered by endothelial-like cells, the neo-intima formed remains stable during long-term studies.     

Changes in cells's secretory organelles and extracellular matrix during endochondral ossification in the mandibular condyle of the growing rat

The mandibular condyle from 20-day-old rats was examined in the electron microscope with particular attention to intracellular secretory granules and extracellular matrix. Moreover, type II collagen was localized by an immunoperoxidase method. The condyle has been divided into five layers: (1) the most superficial, articular layer, (2) polymorphic cell layer, (3) flattened cell layer, (4) upper hypertrophic, and (5) lower hypertrophic cell layers. In the articular layer, the cells seldom divide, but in the polymorphic layer and upper part of the flattened cell layer, mitosis gives rise to new cells. In these layers, cells produce two types of secretory granules, usually in distinct stacks of the Golgi apparatus; type a, cylindrical granules, in which 300-nm-long threads are packed in bundles which appear "lucent" after formaldehyde fixation; and type b, spherical granules loaded with short, dotted filaments. The matrix is composed of thick banded "lucent" fibrils in a loose feltwork of short, dotted filaments. The cells arising from mitosis undergo endochondral differentiation, which begins in the lower part of the flattened cell layer and is completed in the upper hypertrophic cell layer; it is followed by gradual cell degeneration in the lower hypertrophic cell layer. The cells produce two main types of secretory granules: type b as above; and type c, ovoid granules containing 300-nm-long threads associated with short, dotted filaments. A possibly different secretory granule, type d, dense and cigar-shaped, is also produced. The matrix is composed of thin banded fibrils in a dense feltwork. In the matrix of the superficial layers, the "lucency" of the fibrils indicated that they were composed of collagen I, whereas the "lucency" of the cylindrical secretory granules suggested that they transported collagen I precursors to the matrix. Moreover, the use of ruthenium red indicated that the feltwork was composed of proteoglycan; the dotted filaments packed in spherical granules were similar to, and presumably the source of, the matrix feltwork. The superficial layers did not contain collagen II and were collectively referred to as perichondrium. In the deep layers, the ovoid secretory granules displayed collagen II antigenicity and were likely to transport precursors of this collagen to the matrix, where it appeared in the thin banded fibrils. That these granules also carried proteoglycan to the matrix was suggested by their content of short dotted filaments. Thus the deep layers contained collagen II and proteoglycan as in cartilage; they were collectively referred to as the hyaline cartilage region.     

The relationship of the superficial and deep facial fascias: relevance to rhytidectomy and aging.

Controversy persists regarding the relationship of the superficial facial fascia (SMAS) to the mimetic muscles, deep facial fascia, and underlying facial nerve branches. Using fresh cadaver dissection, and supplemented by several hundred intraoperative dissections, we studied facial soft-tissue anatomy. The facial soft-tissue architecture can be described as being arranged in a series of concentric layers: skin, subcutaneous fat, superficial fascia, mimetic muscle, deep facial fascia (parotidomasseteric fascia), and the plane containing the facial nerve, parotid duct, and buccal fat pad. The anatomic relationships existing within the facial soft-tissue layers are (1) the superficial facial fascia invests the superficially situated mimetic muscles (platysma, orbicularis oculi, and zygomaticus major and minor); (2) the deep facial fascia represents a continuation of the deep cervical fascia cephalad into the face, the importance of which lies in the fact that the facial nerve branches within the cheek lie deep to this deep fascial layer; and (3) two types of relationships exist between the superficial and deep facial fascias: In some regions of the face, these fascial planes are separated by an areolar plane, and in other regions of the face, the superficial and deep fascia are intimately adherent to one another through a series of dense fibrous attachments. The layers of the facial soft tissue are supported in normal anatomic position by a series of retaining ligaments that run from deep, fixed facial structures to the overlying dermis. Two types of retaining ligaments are noted as defined by their origin, either from bone or from other fixed structures within the face.(ABSTRACT TRUNCATED AT 250 WORDS)     

The histology and affinities of sinacanthid fishes: primitive gnathostomes from the Silurian of China

On the basis of well preserved specimens from the Lower Silurian of the Tarim Basin, Xinjiang Uygur Autonomous Region and Shiqian County, Guizhou Province, People's Republic of China we describe in detail the histological structure of sinacanthid spines, the only known remains of a group of fishes common in Silurian strata from China. The sinacanthids have previously been assigned either to the acanthodians or to the chondrichthyans. The spine structure is composed of an outer layer of atubular dentine and an inner layer of globular calcified cartilage, and the nature and distribution of these tissues indicates that the spines were formed as a result of interaction between the endoskeleton and dermoskeleton. The tissue distribution and style of growth described herein places the sinacanthids crownwards of the placoderms, and possibly within the total group Chondrichthyes. However, before they can be firmly placed within a phylogenetic scheme, further evidence is required both on the general anatomy of sinacanthids and on the nature of chondrichthyan apomorphies.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 379–386.     

The fine structure and deposition of the larval cuticle of the sheep blowfly (Lucilia Cuprina)

The cuticle of Lucilia is composed of an untanned endocuticle and a complex epicuticle of four layers, superficial layer, outer epicuticle, cuticulin and dense layer. The outer epicuticle and attached epicuticular filaments are resistant to acid hydrolysis. During deposition of the cuticle of each larval instar, the cuticulin and dense layers are formed first, followed by the outer epicuticle, which appears to be laid down by secretions from the epidermis passing through the cuticulin via epicuticular filaments. The outer epicuticle is found in the position normally occupied by the wax layer of other insect species.     

Dynamic remodeling of dendritic arbors in GABAergic interneurons of adult visual cortex

Despite decades of evidence for functional plasticity in the adult brain, the role of structural plasticity in its manifestation remains unclear. To examine the extent of neuronal remodeling that occurs in the brain on a day-to-day basis, we used a multiphoton-based microscopy system for chronic in vivo imaging and reconstruction of entire neurons in the superficial layers of the rodent cerebral cortex. Here we show the first unambiguous evidence (to our knowledge) of dendrite growth and remodeling in adult neurons. Over a period of months, neurons could be seen extending and retracting existing branches, and in rare cases adding new branch tips. Neurons exhibiting dynamic arbor rearrangements were GABA-positive non-pyramidal interneurons, while pyramidal cells remained stable. These results are consistent with the idea that dendritic structural remodeling is a substrate for adult plasticity and they suggest that circuit rearrangement in the adult cortex is restricted by cell type–specific rules.     

Scales in young Polypterus senegalus are elasmoid: new phylogenetic implications

A component of the basal plate which has a plywood-like organization similar to that of the elasmoid scales of teleosts is described in the scales of Polypterus senegalus for the first time. The origin and development of this structure is studied in young (50-117 mm, standard length) and adult (225 and 240 mm) specimens using light and electron microscopy. In 50 mm fish, the scales are imbricated and composed mainly of a succession of orthogonal collagen layers forming a plywood-like structure, the isopedin. The outer surface of the scale is ornamented locally by irregular patches of collagenous material. The layers are not mineralized, whereas the superficial patches are well calcified. The isopedin thickens until it has 12-15 layers and then stops growing (88 mm fish). It mineralizes irregularly from its upper part, and two vascular regions, surrounded by woven-fibered osseous material, form on the outer and deeper surfaces of the isopedin. These regions thicken while the vascular canals close by centripetal deposition of parallel-fibered osseous tissue. The outer region is the superficial part of the mature scale (called here osteodentin), which is covered by the ganoine deposited by the epidermal cells. The deeper part constitutes the definitive basal plate, composed of parallel-fibered osseous tissue. The results show 1) that the young ganoid scales of Polypterus senegalus have a structure similar to that of typical elasmoid scales; and 2) that the isopedin structure does not change during ontogeny and so represents a permanent record of the first ontogenetic stages. The phylogenetic implication of these results is that the elasmoid scales of teleosts arose by a process of paedomorphosis.     

Cortico-cortical connections in the parietal area of the cerebral cortex

Layer-by-layer arrangement of the commissural and associative fibers has been studied in the cat parietal cortex. The commissural fibers are distributed in all the layers of the parietal cortex in the contralateral hemisphere, except the superficial part of the I layer. These fibers mainly terminate in the III, IV layers of the contralateral parietal cortex, though their termination in other layers is not excluded. The associative fibers of the parietal cortex are distributed in all the layers of the sensomotor area, except the superficial part of the I layer. They mainly terminate in the III, IV, V layers of the primary somatosensory and in the III, V layers of the motor cortex.     

Structure of the dermal scales in gymnophiona (Amphibia)

Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization. Dermal scales are small flat disks set in pockets in the transverse ridges of the skin. Each pocket contains several scales of various sizes. A ring of “hypomineralization” of varying diameter may occur on scales of a particular dermal pocket but bears no relation to the diameter of these scales. Three different layers form the scales and are seen on sections perpendicular to the surface. The cells of the basal layer lie deepest. Each of the two or three more superficial fibrous layers is composed of bundles of fibres that are oriented in parallel. The orientation varies among layers. The striation of the fiber scales has a periodicity comparable to that of the surrounding dermal fibers. Squamulae form a discontinuous layer on the scale surface and are the only mineralized part of the scale. The minerals are deposited both on the collagen fibers passing from the fibrous layers into the squamulae, and in the interfibrillar spaces. Spherical concretions, either isolated or coalescent, reaching up to 1 μm, are found on the surface of the squamulae. The dermal scales of Gymnophiona present some analogies with those of evolved bony fishes. Their characteristics could make them an original model for the study of mineralization.     

Microstructure of the linguliformean brachiopod Linnarssonia from the Lower Cambrian of Sichuan, China

Acrotretoids, one of the oldest brachiopod groups, are abundant in the Lower Cambrian Jiulaodong Formation. The shell of Linnarssonia sp. is composed of two layers: a primary layer and a columnar secondary layer. The primary layer is mostly exfoliated, resulting in exposure of the openings to the central canal of the columns. Filae are seen on the surface of the columnar layer, indicating that the columnar secondary layer has influenced changes in ornament on the shell surface. The larval shell has only very weak ripples; the post-larval shell has obvious concentric ribs. Small pits of variable shape cover almost the entire shell surface. The secondary layer is composed of several columnar laminations, each of which comprises both the upper and lower laminae and the cylindrical columns between them. On the inner side of shell the thin columnar laminations increase. The new microstructural data show that two shell layers are developed in Early Cambrian acrotretoid brachiopods; the columnar lamination may be a primitive feature of the microstructural development of the Brachiopoda and may help establish the affinity between different stem-group brachiopods.     

Histological studies of the dorsal nasal,Angularis Oculi,and facial veins of sheep (Ovis aries)

Selective brain cooling (SBC) requires vasoactivity in the superficial veins of the face of the animal. This vasoactivity is possible because of an adequate amount of smooth muscle in the tunica media of each of these superficial vessels, enabling it to act as a “muscle sphincter.” In this study, the angularis oculi, dorsal nasal, distal, and proximal parts of the facial veins in sheep were examined histologically to describe an anatomical basis for SBC. Measurements of the tunica media thickness, the lumen diameter, and the ratio of these measurements showed that the relative tunica media thicknesses in the angularis oculi vein and the dorsal nasal vein are statistically smaller (P < 0.001) than in the distal or the proximal parts of the facial vein. In the angularis oculi, dorsal nasal, and distal part of the facial vein, the tunicae mediae were composed of five to seven circularly arranged smooth muscle layers, suggesting their ability to vasoconstrict. The proximal part of the facial vein possesses both circularly and longitudinally arranged smooth muscle layers. The circular smooth muscle layers suggest a vasoconstrictory function, whereas the longitudinal smooth muscle layers imply a vasodilatory function in this part of the facial vein. Both the dorsal nasal and the proximal part of the facial vein, but not the angularis oculi or the distal part of the facial vein, possess endothelial valves near their confluences with other veins. It was concluded from this study that the angularis oculi and the distal part of the facial vein vasoconstrict, whereas the proximal part of the facial vein vasodilates, enabling the necessary changes in blood flow in SBC. J. Morphol. 237:275–281, 1998. © 1998 Wiley-Liss, Inc.     

Superficial architecture of the jaw-closing muscles of the cat (Felis catus): the temporo-masseteric complex

The muscle fiber fascicles of the temporo-masseter complex of the cat were minutely dissected. Some heads were embedded in paraffin while others were put into methyl-methacrylate resin and sections were made. The results of this anatomical study demonstrate that this complex consists of the masseter muscle, the temporal muscle and two well individualized transitional fascicles: the maxillomandibularis and zygomato-comandibularis muscles. The masseter and temporal muscles are composed of individualized compartments in which the orientation and aponeuroses of the fibers of which they are composed differ with regard to the centric occlusion plane. The masseter muscle consists of a superficial fascicle made up of two layers, an intermediate fascicle, and a deep fascicle composed of two layers. The temporal muscle consists of one anterior orbital part and one posterior temporal part. This structure is in accordance with the mammalian archetype described by Gaspard and Saban. These findings should lead towards a homology-based nomenclature founded on comparative anatomy studies of mammalian species. Such a classification would permit the comparison of results obtained from physiological and histochemical studies of these complex muscle fibers when they are published by different researchers.     

An injection-corrosion study on the angioarchitecture of rat skin]

The angioarchitecture of the skin in the SD strain rat was investigated by scanning electron microscopy using resin cast. The neck part of rat skin was composed of 3 layers of vascular networks: the first layer (superficial layer), the second layer (middle layer), and the third layer (deep layer). Two types of capillary architectures were present around the hair follicle: small architectures composed of random network and large architectures composed of 3 parts distinguished by the construction of network. The large architecture, the capillary of hair papilla and the capillary network of sebaceous gland was thought to compose one circulation unit. The afferent vessels into such units branched from Kandelaberarterie-Petersen occurring from the 3rd layer, ascended to the 2nd layer, then descended to the bottom of the network and composed the capillary architecture. There were 2 types of efferent vessels from such circulation unit. They occurred from superficial and deep part, respectively, of the vascular architecture around the hair follicle and descended straight to the 3rd layer. The presence of straight vessels between the 2 nd and 3 rd layer, and the simple arrangement of vascular layers were thought to be characteristic of the angioarchitecture of the rat skin.     

The mobile receptor hypothesis and “cooperativity” of hormone binding. Application to insulin

The mobile receptor hypothesis has been proposed to describe the process by which hormone receptor binding initiates a biological response; it states that receptors, which can diffuse independently in the plane of the membrane, reversibly associate with effectors to regulate their activity. The affinity for effector is greater when the receptor is occupied by hormone.A mathematical expression of the mobile receptor hypothesis is used to show that: (1) The predicted kinetics of hormone receptor binding may be indistinguishable from “negative cooperativity”. (2) Receptor occupancy and biological response may be coupled in a non-linear fashion.By choosing specific parameters, most of the existing data on insulin binding and biological responses can be explained in terms of the mobile receptor hypothesis. Thus, the following are easily explained: (1) A single homogeneous receptor may appear kinetically to be composed of two classes (of high and low affinity) of receptors. (2) Occupancy of the apparent class of high affinity receptors is related linearly to the biological response. (3) The same receptor in different tissues may appear to have different affinity. (4) The binding of different biologically active insulin analogues may exhibit different degrees of “cooperatively.” These considerations may also be pertinent to intepretations of other hormone-receptor systems and of various ligand-macromolecule interactions.     

The mobile receptor hypothesis and "cooperativity" of hormone binding. Application to insulin.

The mobile receptor hypothesis has been proposed to describe the process by which hormone receptor binding initiates a biological response; it states that receptors, which can diffuse independently in the plane of the membrane, reversibly associate with effectors to regulate their activity. The affinity for effector is greater when the receptor is occupied by hormone. A mathematical expression of the mobile receptor hypothesis is used to show that: (1) The predicted kinetics of hormone receptor binding may be indistinguishable from "negative cooperativity." (2) Receptor occupancy and biological response may be coupled in a non-linear fashion. By choosing specific parameters, most of the existing data on insulin binding and biological responses can be explained in terms of the mobile receptor hypothesis. Thus, the following are easily explained: (1) A single homogeneous receptor may appear kinetically to be composed of two classes (of high and low affinity) of receptors. (2) Occupancy of the apparent class of high affinity receptors is related linearly to the biological response. (3) The same receptor in different tissues may appear to have different affinity. (4) The binding of different biologically active insulin analogues may exhibit different degrees of "cooperativity." These considerations may also be pertinent to interpretations of other hormone-receptor systems and of various ligand-macromolecule interactions.     

Surgical anatomy of the mimic muscle system and the facial nerve: importance for reconstructive and aesthetic surgery

Mimic muscles are arranged in four layers regarding their origins, and these four layers should be considered when muscle tissue is added or lifted. All mimic muscles are built up by parallel fibers. Mean values of length, width, and thickness of the three lip elevators have been determined. These data might be of importance when dealing with this muscle system, which appears rather different from all other muscles in the human. The individual muscles receive their innervating facial nerve branches from their deeper surface when they belong to the superficial (first, second, or third) layer and from outside when they lie in the deepest (fourth) layer. Nerve branches communicate at least four times before innervating their respective muscles.     

Laminar and Dorsoventral Molecular Organization of the Medial Entorhinal Cortex Revealed by Large-scale Anatomical Analysis of Gene Expression

Neural circuits in the medial entorhinal cortex (MEC) encode an animal’s position and orientation in space. Within the MEC spatial representations, including grid and directional firing fields, have a laminar and dorsoventral organization that corresponds to a similar topography of neuronal connectivity and cellular properties. Yet, in part due to the challenges of integrating anatomical data at the resolution of cortical layers and borders, we know little about the molecular components underlying this organization. To address this we develop a new computational pipeline for high-throughput analysis and comparison of in situ hybridization (ISH) images at laminar resolution. We apply this pipeline to ISH data for over 16,000 genes in the Allen Brain Atlas and validate our analysis with RNA sequencing of MEC tissue from adult mice. We find that differential gene expression delineates the borders of the MEC with neighboring brain structures and reveals its laminar and dorsoventral organization. We propose a new molecular basis for distinguishing the deep layers of the MEC and show that their similarity to corresponding layers of neocortex is greater than that of superficial layers. Our analysis identifies ion channel-, cell adhesion- and synapse-related genes as candidates for functional differentiation of MEC layers and for encoding of spatial information at different scales along the dorsoventral axis of the MEC. We also reveal laminar organization of genes related to disease pathology and suggest that a high metabolic demand predisposes layer II to neurodegenerative pathology. In principle, our computational pipeline can be applied to high-throughput analysis of many forms of neuroanatomical data. Our results support the hypothesis that differences in gene expression contribute to functional specialization of superficial layers of the MEC and dorsoventral organization of the scale of spatial representations.