Barbronia weberi (Clitellata,Hirudinida, Salifidae) has ovary cords of the Erpobdella type

The organization of the ovaries in representative of the Salifidae (Hirudinida, Erpobdelliformes) was studied at the ultrastructural level for the first time. Like in other leeches, the ovaries of Barbronia weberi are composed of an outer envelope (i.e., an ovisac made up of two coelomic epithelia, muscle cells, and connective tissue) and several internal units, which are broadly similar to the ovary cords found in representatives of the Erpobdellidae. There are usually 6–8 ovary cords that are twisted or cambered with a narrow apical part and a broader, irregularly shaped distal end in each ovisac of B. weberi. Each ovary cord is built from somatic and germ‐line cells and the latter tend to form multicellular cysts that are equipped with a central cytoplasmic core (cytophore). There are two morphologically different subpopulations of germ‐line cells: oocytes and more numerous nurse cells. Growing oocytes form protuberances on the ovary cord surface and eventually detach from the cord and float freely in the ovisac lumen, whereas the other components of germ‐line cysts (i.e., nurse cells and cytophore) degenerate. It should be pointed out that there is a prominent gradient of germ‐cell development along the long axis of the cord. The somatic cells form the ovary cord envelope (the so‐called spongiosa cells) and also penetrate the spaces between germ‐line cells. Both kinds of the somatic cells, that is, those forming the cord envelope and the somatic cells that are associated with oocytes (follicular cells) have a well‐developed system of intercellular channels. Additionally, one prominent somatic cell, the apical cell, was found at the apical tip of each ovary cord. Because the aforementioned features of ovary cords found in B. weberi are very similar (with a few minor exceptions) to the ovary cords that have been described in Erpobdella octoculata and E. johanssoni, we propose the term “ovary cords of the Erpobdella type” for them. Our results support a close phylogenetic relationship between Salifidae and Erpobdellidae. J. Morphol. 275:479–488, 2014. © 2013 Wiley Periodicals, Inc.     

ProBDNF inhibits collective migration and chemotaxis of rat Schwann cells

Schwann cell migration, including collective migration and chemotaxis, is essential for the formation of coordinate interactions between Schwann cells and axons during peripheral nerve development and regeneration. Moreover, limited migration of Schwann cells imposed a serious obstacle on Schwann cell-astrocytes intermingling and spinal cord repair after Schwann cell transplantation into injured spinal cords. Recent studies have shown that mature brain-derived neurotrophic factor, a member of the neurotrophin family, inhibits Schwann cell migration. The precursor form of brain-derived neurotrophic factor, proBDNF, was expressed in the developing or degenerating peripheral nerves and the injured spinal cords. Since “the yin and yang of neurotrophin action” has been established as a common sense, proBDNF would be expected to promote Schwann cell migration. However, we found, in the present study, that exogenous proBDNF also inhibited in vitro collective migration and chemotaxis of RSC 96 cells, a spontaneously immortalized rat Schwann cell line. Moreover, proBDNF suppressed adhesion and spreading of those cells. At molecular level, proBDNF inhibits F-actin polymerization and focal adhesion dynamics in cultured RSC 96 cells. Therefore, our results suggested a special case against the classical opinion of “the yin and yang of neurotrophin action” and implied that proBDNF might modulate peripheral nerve development or regeneration and spinal cord repair through perturbing native or transplanted Schwann cell migration.     

Ultrastructure des cellules de Sertoli humaines aux stades embryonnaires précoces de la différenciation gonadique

The morphofunctional development of Sertoli cells defines the testicular differentiation. These somatic cells are mostly of mesonephric origin and can be first recognized in 7 week-old embryos altogether with the formation of testicular cords. The latter organize as primordial germ cells surrounded by pre-Sertoli cells. Due to the great synthetic activity of pre-Sertoli cells the rough endoplasmic reticulum develops. The basal lamina of the cords becomes distinguishable at 7 to 8 weeks of development. Either prespermatogonia and pre-Sertoli cells actively proliferate but the latter greatly outnumber prespermatogonia. Many interdigitations and cytoplasmic processes are observed between neighboring pre-Sertoli cells. Due to the proliferative activity a sort of compartmentalization is established inside the cords in which pre-Sertoli cells tend to localize closer to the basal membrane embracing the prespermatogonia with long and thin cytoplasmic processes. One of the main features typical of differentiating pre-Sertoli cells is the irregular nucleus and the prominent nucleolus. When the embryo is 14 to 20 weeks-old the most significative change is the maximum development of the Leydig cells. Testicular cords do not show lumen at all, so they cannot be termed “tubules”     

Role of neurotropins in rat embryonic testis morphogenesis (cord formation)

The process of seminiferous cord formation is the first morphological event that differentiates a testis from an ovary and indicates male sex determination. Cord formation occurs by embryonic Day 14 (Day 0 = plug date; E14) in the rat. A series of experiments were conducted to determine if neurotropins and their receptors are important for the process of rat embryonic cord formation. The expression of low affinity neurotropin receptor (p75/LNGFR) was determined by immunohistochemistry on sections of both testis and ovary from E13 through birth (Day 0, P0) with an antibody to p75/LNGFR. The staining for p75/LNGFR was present in the mesonephros of E13 gonads and in a sex-specific manner appeared around developing cords at E14 in the embryonic testis. At birth, staining for p75/LNGFR was localized to a single layer of cells (i.e., peritubular cells) that surrounded the seminiferous cords. The genes for both neurotropin 3 (NT3) and for corresponding high affinity neurotropin trkC receptor were found to be expressed in the E14 rat testis, as well as other neurotropins and receptors. Immunocytochemical analysis of E14 rat testis demonstrated that NT3 was localized to the Sertoli cells and trkC was present in individual cells of the interstitium at E16 and in selected preperitubular cells at E18. Previously, the peritubular cells adjacent to the cords were demonstrated to be derived from migrating mesonephros cells around the time of cord formation. To determine if neurotropins were involved in cord formation, the actions of neurotropins were inhibited. A high affinity neurotropin receptor (trk)-specific kinase inhibitor, K252a, was used to treat organ cultures of testes from E13 rats prior to cord formation. Treatment of E13 testis organ cultures with K252a completely inhibited cord formation. K252a-treated organ cultures of E14 testis that contained cords did not alter cord morphology. A second experiment to inhibit neurotropin actions utilized a specific antagonist trk-IgG chimeric fusion protein and E13 testis organ cultures. The trk-IgG molecules dimerize with endogenous trk receptors and inhibit receptor signaling and activation of ligand function. Forty percent of E13 testis organ cultures treated with trkC-IgG had significantly reduced cord formation. TrkA-IgG had no effect on initiation of cords; however, in fifty percent of the treated organs, a "swollen" appearance of the cord structures was observed. Experiments using trkB-IgG chimeric protein on E13 organ cultures had no effect on cord formation or cord morphology. The testes from trkC and NT3 knockout mice were examined to determine if there were any morphological differences in the testis. NT3 knockouts appeared to have normal cord morphology in E15 and E17 testis. TrkC knockout mice also had normal cord morphology in E14 and P0 testis. Both NT3 and trkC knockout-mice testis had less interstitial area than wild-type controls. In addition, the trkC knockout mice have an increased number of cells expressing p75LNGFR within the cords when compared to controls or NT3 knockout mice. Combined observations suggest compensation between the different neurotropin ligands, receptors, and/or possibly different growth factors for this critical biological process. In summary, results suggest a novel nonneuronal role for neurotropins in the process of cord formation during embryonic rat testis development. The hypothesis developed is that neurotropins are involved in the progression of male sex differentiation and are critical for the induction of embryonic testis cord formation.     

Role of social and individual experience in interaction of the meadow ant Formica pratensis (Hymenoptera: Formicidae) with ladybird imagines and hoverfly larvae

The ability to recognize aphidophages is one of the key points in the protection ants provide aphids against their natural enemies. Behavior of honeydew collectors from nature (“field,” control) and laboratory reared “naive” ants of Formica pratensis Retzius, which had never met either “mature” workers or aphids and aphidophages, was observed during their pairwise interactions with ladybird imagines and hoverfly larvae. The majority of the “naive” ants perceived ladybirds as an enemy at their first encounter attacking them immediately without any prior antennation. Ants seem to have a certain innate “enemy image” that lets them react very quickly to protect aphids. Hoverfly larvae were rarely attacked by both “field” and “naive” ants (>15%). During tests with ladybirds ants from nature attacked them and also demonstrated the most aggressive reactions (series of bites and “death grip”) less frequently than the “naive” ants. The percentage of ants avoiding aphidophages after a contact with their chemical defense (reflex bleeding and glue‐like saliva) was significantly higher in the control group. Whereas the “naive” ants did not learn to avoid danger, foragers from nature usually tried to avoid negative experience and used tactics of “short bites.” Overall, experience has been proved to be unimportant for displaying key behavioral reactions underlying ant–ladybird interaction. However, accumulation of experience has been assumed to play an important role in the formation of behavioral strategy that allows honeydew collectors to drive aphidophages away with lower energy costs and avoid or minimize negative consequences of aphidophages’ chemical defense.     

Modeling and development of a low frequency contactless dielectrophoresis (cDEP) platform to sort cancer cells from dilute whole blood samples

Contactless dielectrophoresis (cDEP) devices are a new adaptation of dielectrophoresis in which fluid electrodes, isolated from the main microfluidic channel by a thin membrane, provide the electric field gradients necessary to manipulate cells. This work presents a continuous sorting device which is the first cDEP design capable of exploiting the Clausius-Mossotti factor at frequencies where it is both positive and negative for mammalian cells. Experimental devices are fabricated using a cost effective technique which can achieve 50 μm feature sizes and does not require the use of a cleanroom or specialized equipment. An analytical model is developed to evaluate cDEP devices as a network of parallel resistor-capacitor pairs. Two theoretical devices are presented and evaluated using finite element methods to demonstrate the effect of geometry on the development of electric field gradients across a wide frequency spectrum. Finally, we present an experimental device capable of continuously sorting human leukemia cells from dilute blood samples. This is the first cDEP device designed to operate below 100 kHz resulting in successful manipulation of human leukemia cells, while in the background red blood cells are unaffected.     

Neural and Glial Secretion in the Spinal Cord of the Lamprey (Lampetra planeri)

In the spinal cord of Lampetra planeri neurosecretion and glial secretion could be demonstrated with histochemical methods and the aid of the electron microscope. Neurosecretion is present in either all or some “dorsal cells” which are scattered along the whole spinal cord. These cells have the characteristic fine structure of highly active secretory neurons. The cells produce three types of secretory material. One not bound to vesicles in form of a finely granulated substance, a second one in spherical, uniformely electron-dense elementary vesicles with a diameter of 100–140 nm, and a third one in vesicles of the monoamine type. In the most caudal part of the spinal cord glial secretion is present. Groups of glial cells produce a fine, granulated material and release it into the adjacent intercellular space. From there the material extends into other intercellular spaces of the spinal cord. We are of the opinion that the “dorsal cells” are forerunners of the cells of Dahlgren in higher vertebrates and that the neurosecretion and glial secretion in the spinal cord of lampreys demonstrate very primitive conditions.     

Differential gene expression in the EphA4 knockout spinal cord and analysis of the inflammatory response following spinal cord injury

Mice lacking the axon guidance molecule EphA4 have been shown to exhibit extensive axonal regeneration and functional recovery following spinal cord injury. To assess mechanisms by which EphA4 may modify the response to neural injury a microarray was performed on spinal cord tissue from mice with spinal cord injury and sham injured controls. RNA was purified from spinal cords of adult EphA4 knockout and wild-type mice four days following lumbar spinal cord hemisection or laminectomy only and was hybridised to Affymetrix All-Exon Array 1.0 GeneChips?. While subsequent analyses indicated that several pathways were altered in EphA4 knockout mice, of particular interest was the attenuated expression of a number of inflammatory genes, including Arginase 1, expression of which was lower in injured EphA4 knockout compared to wild-type mice. Immunohistological analyses of different cellular components of the immune response were then performed in injured EphA4 knockout and wildtype spinal cords. While numbers of infiltrating CD3+ T cells were low in the hemisection model, a robust CD11b+ macrophage/microglial response was observed post-injury. There was no difference in the overall number or spread of macrophages/activated microglia in injured EphA4 knockout compared to wild-type spinal cords at 2, 4 or 14 days post-injury, however a lower proportion of Arginase-1 immunoreactive macrophages/activated microglia was observed in EphA4 knockout spinal cords at 4 days post-injury. Subtle alterations in the neuroinflammatory response in injured EphA4 knockout spinal cords may contribute to the regeneration and recovery observed in these mice following injury.     

Ovary cord structure and oogenesis in Hirudo medicinalis and Haemopis sanguisuga (Clitellata, Annelida): remarks on different ovaries organization in Hirudinea

In Hirudo medicinalis and Haemopis sanguisuga, two convoluted ovary cords are found within each ovary. Each ovary cord is a polarized structure composed of germ cells (oogonia, developing oocytes, nurse cells) and somatic cells (apical cell, follicular cells). One end of the ovary cord is club-shaped and comprises one huge apical cell, numerous oogonia, and small cysts (clusters) of interconnected germ cells. The main part of the cord contains fully developed cysts composed of numerous nurse cells connected via intercellular bridges with the cytophore, which in turn is connected by a cytoplasmic bridge with the growing oocyte. The opposite end of the cord degenerates. Cord integrity is ensured by flattened follicular cells enveloping the cord; moreover, inside the cord, some follicular cells (internal follicular cells) are distributed among germ cells. As oogenesis progresses, the growing oocytes gradually protrude into the ovary lumen; as a result, fully developed oocytes arrested in meiotic metaphase I float freely in the ovary lumen. This paper describes the successive stages of oogenesis of H. medicinalis in detail. Ovary organization in Hirudinea was classified within four different types: non-polarized ovary cords were found in glossiphoniids, egg follicles were described in piscicolids, ovarian bodies were found characteristic for erpobdellids, and polarized ovary cords in hirudiniforms. Ovaries with polarized structures equipped with apical cell (i.e. polarized ovary cords and ovarian bodies) (as found in arhynchobdellids) are considered as primary for Hirudinea while non-polarized ovary cords and the occurrence of egg follicles (rhynchobdellids) represent derived condition.     

Ovary cords organization in Hirudo troctina Johnson, 1816 and Limnatis nilotica (Savigny, 1822) (Clitellata,Hirudinea)

In both examined species of Hirudinea there are paired spheroid ovisacs, and within each ovisac two convoluted ovary cords occur. The morphology of the cords is characteristic: their apical end is club-shaped, the central part is narrow and may contain developing oocytes, whereas the basal end of the cord is irregularly shaped and composed of degenerating cells. The ovary cords are built of somatic and germ-line cells; the latter are united into syncytial cysts. Each germ cell in such a cyst has only one stable cytoplasmic bridge connecting it to the central anuclear cytoplasmic mass, the cytophore. Initially all germ-line cells in a given cyst are morphologically identical, then the fates of cells diversify. Most of them become nurse cells and eventually degenerate; the rest continue meiosis, gather macromolecules, cell organelles and nutritive material and become oocytes. The oogenesis found in the species studied should be regarded as meroistic. Previtellogenic oocytes protrude from the cord into the ovisac lumen, whereas the vitellogenic ones float freely in the ovisac lumen. The somatic cells found in the ovary cords are: follicular cells which form the envelope of the cord and are also found among germ cells inside the cord, and one, huge apical cell that always is located at the top of the club-shaped end of the ovary cord. The apical cell has several characteristic features, e.g., it forms long cytoplasmic projections filled with intermediate filaments and it is connected to the neighbouring cells (both somatic and germ-line) via hemidesmosomes. We suggest that the apical cell forms the niche for maintaining germ and somatic stem cells. Generally, the organization of the ovary cords found in both studied species is broadly similar to those described in other hirudiniform leeches studied to date.     

Tissue engineering with electric fields: immobilization of mammalian cells in multilayer aggregates using dielectrophoresis

Positive dielectrophoresis can be used to create aggregates of animal cells with 3D architectures. It is shown that the cells, when pulled together into an aggregate by positive dielectrophoresis in a low-conductivity iso-osmotic solution, adhere to each other. The adherence of the cells to each other is non-specific and increases in time, and after 10-15 min becomes strong enough to immobilize the cells in the aggregate, enabling the ac electric field to be released, and the iso-osmotic buffer to be replaced by growth or other media. Cell viability is maintained. The new method of immobilization significantly simplifies the construction of aggregates of animal cells by dielectrophoresis, and increases the utility of dielectrophoresis in tissue engineering and related areas.     

Inhibition of platelet-derived growth factor actions in the embryonic testis influences normal cord development and morphology

Platelet-derived growth factors (PDGFs) are paracrine factors with roles in mesenchymal-epithelial interactions during normal and pathologic processes. Previously, PDGF and its receptor (PDGFR) have been shown to be present in perinatal, peripubertal, and adult rat testes. The role of PDGF in embryonic testicular cord formation is not known. The hypothesis tested is that PDGFs and PDGFRs are expressed during cord formation and that inhibition of their action influences normal cord formation during embryonic testis development. Embryonic Day (E) 13 gonadal organ cultures were used. Organs were cultured for 3 days and treated daily with vehicle or a PDGFR-specific tyrosine phosphorylation inhibitor (i.e., the tyrphostin AG1295 or AG1296). Vehicle-treated testes formed normal cords, whereas tyrphostin-treated testes formed "swollen cords," a phenomenon characterized by a significant decrease in the number of cords per testis area and increased cord diameter due to fusion of cords. Expression of PDGF and PDGFR in E13, E14, E16, Postnatal Day (P) 0, and P20 testes was examined. Messenger RNAs for PDGF-A and -B and PDGF alpha- and beta-receptors were expressed in isolated testes during all developmental periods examined. Immunoreactivity for PDGF was present throughout the testicular compartment at E14, restricted primarily to testicular cords at E16, and present in cells of the testicular cords with a stronger immunoreactivity in certain interstitial cell types of P0 testis. PDGFR beta-receptor immunoreactivity was primarily localized to the mesonephros of E14 organs and the testicular interstitium of E16 and P0 testes. Tyrphostins did not affect apoptotic cell number in the testis. PDGF had no effect on cell growth in P0 testis cultures. The results show that PDGFs and PDGFRs are expressed in embryonic testis during cord formation in a tissue-specific manner. Inhibition of PDGF actions does not inhibit cord formation but does alter normal cord development and morphology. The observations provide insight into the factors involved in male sex differentiation and embryonic testis development.     

Prenatal development of the palatine gland of rats

The present study aimed to elucidate the prenatal development of the rat palatine gland. Parasagittal 5 microm thick serial sections made from Wistar rats at embryonic days (E) 17 to 22 were stained with haematoxylin-eosin (HE), Alcian blue-Kernechtrot or immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU) as a marker of proliferating cells. Additionally, three-dimensional images of developing glandular parenchyma were reconstructed from serial HE sections with a personal computer. At E 17, several thickenings of the palatal epithelium had appeared which thereafter became the epithelial cords. Branching and lumenization commenced at E 20, and immature acini were observed at E 21. Three-dimensional reconstruction showed that the proximal part of the epithelial cord differentiated into the duct, and the distal part of the epithelial cord differentiated into the acinus. In immunohistochemical staining, there were many BrdU-positive cells in the epithelial cords including thickenings of the palatal epithelium, ducts, and acini. The BrdU labeling index of the cells of the epithelial cord was the highest (statistically significant) of the three in the primitive palatine gland. In conclusion, during the development of the rat palatine gland, epithelial cords with very high proliferative activity arise from the palatal epithelium, and then the proximal part of the epithelial cord differentiates into the duct, and the distal part of the epithelial cord differentiates into the acinus. Proliferation of these glandular parenchyma contributes to the growth of the developing palatine gland.     

The continuous positive and negative dielectrophoresis of microorganisms

The continuous dielectrophoresis of living cells is described. The technique uses stream-centered transport of suspended microorganisms through an especially shaped non-uniform electric field. The cells can be given a positive or negative displacement, i.e., can be pushed into or out of the region of higher field intensity, depending upon the frequency of the applied ac field, and upon the relative permittivities of the cells and the suspending medium. Yeast (Saccharomyces cerevisiae) and algal cells (Chlorella vulgaris) were found to provide spectra of dielectrophoretic responses varying with the applied frequency (10 to 600 kHz) and conductivity.     

The field-dependence of the solid-state photo-CIDNP effect in two states of heliobacterial reaction centers

The solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect is studied in photosynthetic reaction centers of Heliobacillus mobilis at different magnetic fields by ¹³C MAS (magic-angle spinning) NMR spectroscopy. Two active states of heliobacterial reaction centers are probed: an anaerobic preparation of heliochromatophores (“Braunstoff”, German for “brown substance”) as well as a preparation of cells after exposure to oxygen (“Grünstoff”, “green substance”). Braunstoff shows significant increase of enhanced absorptive (positive) signals toward lower magnetic fields, which is interpreted in terms of an enhanced differential relaxation (DR) mechanism. In Grünstoff, the signals remain emissive (negative) at two fields, confirming that the influence of the DR mechanism is comparably low.     

Development of the ovary and ontongeny of mRNA and protein for P450 aromatase (arom) and estrogen receptors (ER) α and β during early fetal life in cattle

Estradiol-17β is the predominant steroid produced during early stages of ovarian development in ruminants and steroid hormones have been hypothesized to regulate ovigerous cord formation, germ cell meiosis and ovarian vascular development. Therefore, the objective was to determine the presence and localization of mRNA and protein encoding cytochrome P450 aromatase (P450arom), and estrogen receptors α (ERα) and β (ERβ) during ovarian development in fetuses of cattle on days 35, 45, 60, 75, 90 and 105 after breeding (n = 4/age) using in situ hybridization and immunohistochemistry. No ovarian tissue was found in the day 35 fetuses, but was found in all later ages studied. There appeared to be little organization of specific structures in ovaries on days 45 and 60, although germ cells could be identified. Evidence of the beginning of ovigerous cord formation was found on day 60. By day 75 of gestation, the ovigerous cords were more extensive and mesonephric-derived cell streams were detectable. By day 90 (and still present at day 105), both ovigerous cords and cell streams/rete tubules were definitive structures of the developing ovaries. Ovaries appeared to develop in “lobular” segments around the periphery of the ovary. Some lobes appeared to be at slightly different developmental stages, as assessed by the extent or definition of ovigerous cord formation.The localization of mRNAs for P450arom, ERα and ERβ were closely associated with protein content. At days 45 and 60, mRNA and protein of P450arom and ERβ were located throughout ovaries with signal in medulla being denser than in the cortex. P450arom mRNA or protein was punctate, but not evident in germ cells. From day 75, P450arom was increasingly becoming localized to cell streams or clusters of cells (rete tubules) in the medulla, and by days 90 and 105 of gestation, was more definitively localized to cell streams and/or rete tubules. Similar to P450arom, ERβ mRNA and protein were observed in cells in the medulla, and also in germ cells, pre-granulosa cells and some surface epithelial cells. ERα mRNA and protein were predominately in the surface epithelium in ovaries of all ages with fainter signal for ERα protein also being observed in pre-granulosa and stromal cells including the cell streams/rete tubules. ERα protein was also detected in a few germ cells at days 90 and 105 of gestation. Thus, in cattle, estradiol-17β has the potential to regulate, in an autocrine/paracrine manner, a number of different cell types during ovarian development.     

A Transcultural Model of the Centrality of “Thinking a Lot” in Psychopathologies Across the Globe and the Process of Localization: A Cambodian Refugee Example

We present a general model of why “thinking a lot” is a key presentation of distress in many cultures and examine how “thinking a lot” plays out in the Cambodian cultural context. We argue that the complaint of “thinking a lot” indicates the presence of a certain causal network of psychopathology that is found across cultures, but that this causal network is localized in profound ways. We show, using a Cambodian example, that examining “thinking a lot” in a cultural context is a key way of investigating the local bio-cultural ontology of psychopathology. Among Cambodian refugees, a typical episode of “thinking a lot” begins with ruminative-type negative cognitions, in particular worry and depressive thoughts. Next these negative cognitions may induce mental symptoms (e.g., poor concentration, forgetfulness, and “zoning out”) and somatic symptoms (e.g., migraine headache, migraine-like blurry vision such as scintillating scotomas, dizziness, palpitations). Subsequently the very fact of “thinking a lot” and the induced symptoms may give rise to multiple catastrophic cognitions. Soon, as distress escalates, in a kind of looping, other negative cognitions such as trauma memories may be triggered. All these processes are highly shaped by the Cambodian socio-cultural context. The article shows that Cambodian trauma survivors have a locally specific illness reality that centers on dynamic episodes of “thinking a lot,” or on what might be called the “thinking a lot” causal network.     

An insulator-based (electrodeless) dielectrophoretic concentrator for microbes in water

Dielectrophoresis (DEP), the motion of a particle caused by an applied electric field gradient, can concentrate microorganisms non-destructively. In insulator-based dielectrophoresis (iDEP) insulating microstructures produce non-uniform electric fields to drive DEP in microsystems. This article describes the performance of an iDEP device in removing and concentrating bacterial cells, spores and viruses while operated with a DC applied electric field and pressure gradient. Such a device can selectively trap particles when dielectrophoresis overcomes electrokinesis or advection. The dielectrophoretic trapping behavior of labeled microorganisms in a glass-etched iDEP device was observed over a wide range of DC applied electric fields. When fields higher than a particle-specific threshold are applied, particles are reversibly trapped in the device. Experiments with Bacillus subtilis spores and the Tobacco Mosaic Virus (TMV) exhibited higher trapping thresholds than those of bacterial cells. The iDEP device was characterized in terms of concentration factor and removal efficiency. Under the experimental conditions used in this study with an initial dilution of 1 x 105 cells/ml, concentration factors of the order of 3000x and removal efficiencies approaching 100% were observed with Escherichia coli cells. These results are the first characterization of an iDEP device for the concentration and removal of microbes in water.     

Probing the influence of myelin and glia on the tensile properties of the spinal cord

Although glia have been historically classified as the structurally supporting cells of the central nervous system, their role in tissue mechanics is still largely unstudied. The influence of myelin and glia on the mechanical properties of spinal cord tissue was examined by testing embryonic day 18 chick embryo spinal cords in uniaxial tension following disruption of the glial matrix using either ethidium bromide (EB) or an antibody against galactocerebroside (αGalC) in the presence of complement. Demyelination was confirmed by myelin basic protein immunoreactivity and quantified using osmium tetroxide staining. A substantial loss of astrocytes and oligodendrocytes concurrent with demyelination was observed following EB injection but not αGalC injection. No morphological changes were observed following injection of saline or IgG with complement as controls for EB and αGalC. Demyelinated spinal cords demonstrated significantly lower stiffness and ultimate tensile stress than myelinated spinal cords. No significant differences were observed in the tensile response between the two demyelinating protocols. The results demonstrate that the glial matrix provides significant mechanical support to the spinal cord, and suggests that myelin and cellular coupling of axons via the glial matrix in large part dictates the tensile response of the tissue.