Cellular interactions in lymph node development

The organized accumulation of lymphocytes is a biological phenomenon used to optimize both homeostatic immune surveillance, as well as chronic responses to pathogenic stimuli. During embryonic development, circulating hemopoietic cells gather at predestined sites throughout the body, where they are subsequently arranged in T and B cell-specific areas characteristic of secondary lymphoid organs. In contrast, the body seems to harbor a limited second set of selected sites that support formation of organized lymphoid aggregates. However, these are only revealed at times of local, chronic inflammation, when so-called tertiary lymphoid structures appear. Once thought of as two distinct phenomena, recent insights suggest that highly similar networks of paracrine interactions regulate the formation of both secondary and tertiary lymphoid structures. This review will focus on these cellular interactions between organizing and inducing cell populations leading to the formation of lymph nodes or organized inflammatory infiltrates.     

Analysis of environmental and species effects on the magnitude of biomass investment in the reproductive effort of annual pasture plants

Summary In annual pastures utilized for grazing, the amount and quality of the standing dry matter in the dry season is of importance for the performance of the animals. Often both characteristics decline at the end of the green season. It is shown, that dispersal of the reproductive structures of the vegetation may be the main reason for this phenomenon. Determination of the reproductive effort of the annuals indicates that the proportion of their total production invested in reproductive tissue may be as high as that of cultivated species. It is shown that the harvest index (or seed ratio) of annual species is closely related to nutrient (mainly nitrogen) transfer from vegetative organs to the reproductive organs in the period between flowering and maturity, when in most cases, additional uptake of nitrogen from the soil is negligible. The effect of environmental and genetic effects on these processes is discussed.Present address: Laboratory of Soils and Fertilizers, Agricultural University, P.O. Box 14, Wageningen, The Netherlands     

Comparative immunohistochemistry of the cephalic sensory organs in Opisthobranchia (Mollusca,Gastropoda)

The structure and function of the central nervous systems of opisthobranch gastropods have been studied extensively. However, the organisation and function of the peripheral nervous system are poorly understood. The cephalic sensory organs (CSOs) are known to be chemosensory structures in the head region of opisthobranchs. In the present study, we used immunohistochemical methods and confocal laserscanning microscopy to comparatively examine the CSOs of different opisthobranchs, namely Acteon tornatilis, Aplysia punctata, Archidoris pseudoargus and Haminoea hydatis. We wanted to characterise sensory epithelia in order to infer the function of sensory structures and the organs they constitute. Immunoreactivity against the three antigens tyrosine hydroxylase, FMRFamide and serotonin was very similar in the CSOs of all investigated species. Tyrosine hydroxylase-like immunoreactivity was detected primarily in subepidermal sensory cell bodies, which were much more abundant in the anteriorly situated CSOs. This observation indicates that these cells and the respective organs may be involved in contact chemoreception and mechanoreception. The dominant features of FMRFamide-like immunoreactivity, especially in the posterior CSOs, were tightly knotted fibres which reveal glomerulus-like structures. This suggests an olfactory role for these organs. Serotonin-like immunoreactivity was detected in an extensive network of efferent fibres, but was not found within any peripheral cell bodies. Serotonin-like immunoreactivity was found in the same glomerulus-like structures as FMRFamide-like immunoreactivity, indicating a function of serotonin in the efferent control of olfactory inputs. Besides this functional implication, this study could also add some knowledge on the doubtful homology of the CSOs in opisthobranch gastropods.     

Ultrastructural investigations on the differentiation of genital hard structures in free-living platyhelminths and their phylogenetic significance

Ultrastructure and differentiation of penis stylets and stylet needles have been investigated in representatives of various groups of free-living platyhelminths, viz. the Acoela, Macrostomida, Typhloplanoida, Kalyptorhynchia, and Dalyellioida. In all these groups, the differentiation of such hard parts occurs intracellularly but in different ways in the different groups. The ultrastructure of the bursal mouth piece in an acoel platyhelminth is not comparable to the hard structures in male copulatory organs. The presence of penial copulatory organs having intracellular hard structures appears to be an autapomorphy of the Euplatyhelminthes. Several characters in the ultrastructure and development of these structures can be used as autapomorphies for various platyhelminth groups.     

The morphology of photophores in the garrick,cyclothone braueri (Family: Gonostomatidae): an ultrastructure study

A contribution to the knowledge of the photophore structure of the mesopelagic fish Cyclothone braueri (Gonostomatidae) from the central Mediterranean Sea (Strait of Messina) is given by means of a structural and ultrastructural study, to better identify and classify the real anatomical structures costituing these luminous organs. The photocytes exhibit numerous secretory granules, of different electron density, embedded in an extremely developed rough endoplasmic reticulum. The lens appear to be composed of tightly contiguous polyhedral cells. The reflector is made up of cells rich in guanine crystals, embedded in an amorphous matrix and is surrounded by a layer of connective tissue containing melanocytes. Unlike the present knowledge, it is shown that the bioluminescence emitted from C. braueri light organs has glandular nature, with photophores similar to type α from Bassot classification. The phenomenon of adaptive convergence, documenting how the morphology and physiology of the light organs of teleosts is similar in different species despite their taxonomic distance, is confirmed also for C. braueri.     

Ultrastructural investigations on the nuchal organ of the protandric polychaete,Ophryotrocha puerilis (Polychaeta,Dorvilleidae)

Summary The nuchal organs of the protandric hermaphrodite Ophryotrocha puerilis were studied by electron microscopy. Ophryotrocha puerilis is the first species hitherto described which possesses four instead of two nuchal organs. These sensory structures are located as ciliary pits at the posterior margin of the prostomium. Histologically, the nuchal organs are composed of supporting cells with long motile cilia and bipolar sensory cells, the perikarya of which form four distinct nuchal ganglia adjoining the brain. These structural components are concentrically arranged around the central sensory area. This area is covered by a modified cuticle, whereas the cuticle above the peripheral region of the sense organ exhibits the appearance typical for polychaetes. Two types of vesicular material are produced in the basal supporting cells, a dense-cored one within the central supporting cells only and a clear irregular-shaped one in all of these cells. The first type is considered to be responsible for the formation of the modified cuticle. The significance of these most probably long-distance chemoreceptory organs and their possible role in reproductive behaviour is discussed.     

Long-Term In Vivo Imaging of Multiple Organs at the Single Cell Level

Two-photon microscopy has enabled the study of individual cell behavior in live animals. Many organs and tissues cannot be studied, especially longitudinally, because they are located too deep, behind bony structures or too close to the lung and heart. Here we report a novel mouse model that allows long-term single cell imaging of many organs. A wide variety of live tissues were successfully engrafted in the pinna of the mouse ear. Many of these engrafted tissues maintained the normal tissue histology. Using the heart and thymus as models, we further demonstrated that the engrafted tissues functioned as would be expected. Combining two-photon microscopy with fluorescent tracers, we successfully visualized the engrafted tissues at the single cell level in live mice over several months. Four dimensional (three-dimensional (3D) plus time) information of individual cells was obtained from this imaging. This model makes long-term high resolution 4D imaging of multiple organs possible.     

Antennal sensory organs of a troglobitic coleoptera,Speonomus hydrophilus jeannel (Catopidae): An ultrastructural study by chemical fixation and cryofixation

The ultrastructure of 12 antennal sensory organs of the cavernicolous beetle Speonomus hydrophilus (Coleoptera : Catopidae) after chemical fixation or cryofixation is described. This work helps us to compare the results of the 2 types of fixation; cryofixation is more difficult and hazardous, but when it succeeds, the cell preservation is better than with conventional chemical fixation; the cell shapes are more regular and rounded, and some details, such as microtubule subunits, can be visible only after cryofixation. On the basis of these ultrastructural features, the sensory organs are functionally classified. The structures of these organs are compared in epigean and troglobitic Coleoptera.     

The role of ventral and preventral organs as attachment sites for segmental limb muscles in Onychophora

Background

The so-called ventral organs are amongst the most enigmatic structures in Onychophora (velvet worms). They were described as segmental, ectodermal thickenings in the onychophoran embryo, but the same term has also been applied to mid-ventral, cuticular structures in adults, although the relationship between the embryonic and adult ventral organs is controversial. In the embryo, these structures have been regarded as anlagen of segmental ganglia, but recent studies suggest that they are not associated with neural development. Hence, their function remains obscure. Moreover, their relationship to the anteriorly located preventral organs, described from several onychophoran species, is also unclear. To clarify these issues, we studied the anatomy and development of the ventral and preventral organs in several species of Onychophora.

Results

Our anatomical data, based on histology, and light, confocal and scanning electron microscopy in five species of Peripatidae and three species of Peripatopsidae, revealed that the ventral and preventral organs are present in all species studied. These structures are covered externally with cuticle that forms an internal, longitudinal, apodeme-like ridge. Moreover, phalloidin-rhodamine labelling for f-actin revealed that the anterior and posterior limb depressor muscles in each trunk and the slime papilla segment attach to the preventral and ventral organs, respectively. During embryonic development, the ventral and preventral organs arise as large segmental, paired ectodermal thickenings that decrease in size and are subdivided into the smaller, anterior anlagen of the preventral organs and the larger, posterior anlagen of the ventral organs, both of which persist as paired, medially-fused structures in adults. Our expression data of the genes Delta and Notch from embryos of Euperipatoides rowelli revealed that these genes are expressed in two, paired domains in each body segment, corresponding in number, position and size with the anlagen of the ventral and preventral organs.

Conclusions

Our findings suggest that the ventral and preventral organs are a common feature of onychophorans that serve as attachment sites for segmental limb depressor muscles. The origin of these structures can be traced back in the embryo as latero-ventral segmental, ectodermal thickenings, previously suggested to be associated with the development of the nervous system.

     

A new physiological phenomenon of mammalian body for organ and tissue neo-regeneration in vivo: adult stem cell technology in the perspective of literature

A new phenomenon by which adult developed mammalian and human body, can neo-regenerate its own tissue/organ in vivo, is recognized as "Desired Metaplasia". Reserve stem cells present in the tissues of adult developed body, are responsible for repair and replacement of lost tissues and cells during life, is plasia. Chronic tissue damage, due to long-standing causative factor, is taken care of and protected by forming resistant tissues, is metaplasia. Both these changes take place at the anatomical abode of the tissues. When stem cells of one tissue are colonized with another tissue/organ system, away from its anatomical abode, the neo-organo-histogenesis takes place by a phenomenon of desired metaplasia. This being new is critically, analytically and scientifically studied and discussed with reference to the available literature. An attempt has been made to establish the scientific account of the phenomenon. The laws of nature and embryology, as well as the basic philosophy responsible for neo-regeneration of tissues and organs in vivo, are discussed. In conclusion, the mammalian and human bodies can neo-regenerate their tissues and organs in vivo by desired metaplasia, provided certain criteria of embryological organogenesis are strictly observed.     

Composite scaffolds for the engineering of hollow organs and tissues

Several types of synthetic and naturally derived biomaterials have been used for augmenting hollow organs and tissues. However, each has desirable traits which were exclusive of the other. We fabricated a composite scaffold and tested its potential for the engineering of hollow organs in a bladder tissue model. The composite scaffolds were configured to accommodate a large number of cells on one side and were designed to serve as a barrier on the opposite side. The scaffolds were fabricated by bonding a collagen matrix to PGA polymers with threaded collagen fiber stitches. Urothelial and bladder smooth muscle cells were seeded on the composite scaffolds, and implanted in mice for up to 4 weeks and analyzed. Both cell types readily attached and proliferated on the scaffolds and formed bladder tissue-like structures in vivo. These structures consisted of a luminal urothelial layer, a collagen rich compartment and a peripheral smooth muscle layer. Biomechanical studies demonstrated that the tissues were readily elastic while maintaining their pre-configured structures. This study demonstrates that a composite scaffold can be fabricated with two completely different polymer systems for the engineering of hollow organs. The composite scaffolds are biocompatible, possess adequate physical and structural characteristics for bladder tissue engineering, and are able to form tissues in vivo. This scaffold system may be useful in patients requiring hollow organ replacement.     

On the ecological and evolutionary significance of storage in clonal plants

Environmental heterogeneity has received wide attention in clonal plant research over the last decade. Most studies have focussed on the effects of spatial variation in environmental conditions on the performance of ramets and genets, while the effects of temporal heterogeneity have only occasionally been studied. As a consequence, our current knowledge about functional responses of clonal plants to habitat patchiness is biased towards spatial aspects of environmental heterogeneity. Nevertheless, temporal changes in biotic and abiotic conditions do occur in most natural habitats, and they are very likely to affect plant growth and performance, and to create positive selection pressures on traits that can buffer plants against unfavorable consequences of this variability. Storage of resources is a widespread phenomenon in clonal plant species. Typical clonal structures such as stolons, rhizomes and hibernacles serve as storage organs. However, the ecologic significance of storage in clonal plant structures remains partly unclear. We suggest that the lack of understanding with respect to resource storage in clonal plants be related to our poor knowledge of ecologic implications of temporal habitat heterogeneity in natural environments. Resource storage can be understood as a safety measure against temporal changes in the growing conditions of plants. This paper summarizes existing information about the ecologic relevance of storage in clonal plants and it tries to develop a framework for further investigation of resource storage as a strategy to enhance the performance of clonal plants in temporally variable environments.     

A scanning electron microscope study of the mesothoracic and metathoracic scolopophorous organs of Lethocerus (Belostomatidae-heteroptera)

The presence of scolopophorous organs in aquatic Heteroptera has been reported in a number of species. This study presents a morphological investigation of these sensory structures of Lethocerus (Belostomatidae) as observed with the scanning electron microscope (SEM). Paired mesothoracic and metathoracic organs are present. Externally, each sensory structure consists of a raised sensory membrane. The distal-most portion consists of thickenings of this sensory membrane (sclerite). The receptor neurons of the mesothoracic organ are of two types—one discolopidial sensillum and 12 monoscolopidial sensilla. The former is attached to the internal wall and distal thickening of the sensory membrane, while the latter are dispersed throughout the interior and attached to the internal wall of the sensory membrane. The structure of the organs suggest that an effective stimulus could be a compression of the membrane. A discussion of possible functions (pressure reception and hearing) is included.     

Feeling the vibes: chordotonal mechanisms in insect hearing.

To hear, insects use diverse external structures, which transform acoustic signals to mechanical ones, coupled to astonishingly uniform mechanosensory transducers, the chordotonal organs. New evidence showing that chordotonal organs and vertebrate auditory hair cells are developmentally related and that chordotonal organs and insect bristle organs are mechanistically related suggests that all these ciliated mechanoreceptors may be derived from the same ancestral molecular mechanotransduction complex. Identification of these elusive molecules will settle this issue.     

Differential distribution of pyrokinin-isoforms in cerebral and abdominal neurohemal organs of the American cockroach

Different pyrokinin isoforms were identified from major neurohemal organs of the American cockroach. During their isolation they were recognized by bioassay using a hyperneural muscle preparation that is sensitive to pyrokinins. All structures were elucidated by sequence analysis and mass spectrometry. The primary structures of the novel peptides isolated from the retrocerebral complex are LVPFRPRL-NH2 (designated Pea-PK-3) and DHLPHDVYSPRL-NH2 (designated Pea-PK-4). A pyrokinin, labeled Pea-PK-5, was isolated from abdominal perisympathetic organs. Structural analysis of this peptide yielded the sequence GGGGSGETSGMWFGPRL-NH2. The threshold concentrations of the identified pyrokinins for an eliciting effect on contractions of the hyperneural muscle preparations differed dramatically. This indicates that the different distribution of pyrokinin-isoform observed in neurohemal organs may be associated with different functions. This is the first report of a differential distribution of peptide-isoforms in the neurohemal organs of insects.     

Cross infection of guinea pigs with different pneumococcal serotypes in the presence of the carrier state

The possibility of the pneumococcal cross infection of guinea pigs in experimental conditions, the time course of the distribution of pneumococci in their organs, and the duration, within the time limits of the experiment, of persistence of the given infective agent were studied. Normal animals placed in the same room with infected ones were shown to become the carriers of definite pneumococcal serotypes. As a result, these studies revealed that nasopharyngeal carriership and infection of different organs were not directly interrelated and the method of infection of guinea pigs did not influence the time course of distribution of pneumococci in their organs. The data on the duration of persistence of the infective agent, as well as on the importance of this phenomenon for determination of the relationship between pneumococcal carriership and disease, are presented.     

Selective suppression of lipid peroxidation in the brain under stress

The time course of lipid peroxidation (LP) products was studied in the heart, liver, and brain of rats exposed to 1, 6 and 12 h stress and compared with the extent of LP induction in these organs in vitro. It was shown that the LP activation in the internal organs with maximum in 1 h stress was accompanied by 2 fold decrease in LP products in the brain. More prolonged stress eliminated differences between tissues in all organs approaching the LP level to the control. The LP induction in vitro also revealed reciprocal relations between the LP intensity in brain and internal organs which remained in control group as well. Possible role of the LP suppression in brain induced by acute stress and significance of the phenomenon are under discussion.