Modelling spatial and temporal variations of annual suspended sediment yields from small agricultural catchments.

Estimates of sediment yield are important for ecological and geomorphological assessment of fluvial systems and for assessment of soil erosion within a catchment. Many regulatory frameworks, such as the Convention for the Protection of the Marine Environment of the North-East Atlantic, derived from the Oslo and Paris Commissions (OSPAR) require reporting of annual sediment fluxes. While they may be measured in large rivers, sediment flux is rarely measured in smaller rivers. Measurements of sediment transport at a national scale can be also challenging and therefore, sediment yield models are often utilised by water resource managers for the predictions of sediment yields in the ungauged catchments. Regression based models, calibrated to field measurements, can offer an advantage over complex and computational models due to their simplicity, easy access to input data and due to the additional insights into factors controlling sediment export in the study sites. While traditionally calibrated to long-term average values of sediment yields such predictions cannot represent temporal variations. This study addresses this issue in a novel way by taking account of the variation from year to year in hydrological variables in the developed models (using annual mean runoff, annual mean flow, flows exceeded in five percentage of the time (Q5) and seasonal rainfall estimated separately for each year of observations). Other parameters included in the models represent spatial differences influenced by factors such as soil properties (% poorly drained soils and % peaty soils), land-use (% pasture or % arable lands), channel slope (S1085) and drainage network properties (drainage density). Catchment descriptors together with year-specific hydrological variables can explain both spatial differences and inter-annual variability of suspended sediment yields. The methodology is demonstrated by deriving equations from Irish data-sets (compiled in this study) with the best model efficiency of 0.84 and best model fit of adjusted R2 of 0.82. Presented approach shows the potential for regression based models to model contemporary suspended sediment yields in small river systems.

Measurement differences between turbidity instruments, and their implications for suspended sediment concentration and load calculations: A sensor inter-comparison study.

The use of turbidity for indicating environmentally detrimental levels of suspended and colloidal matter in freshwater systems, and for defining acceptable water quality standards in national and European drinking water regulations, is well established. Turbidity is therefore frequently adopted as a surrogate for suspended sediment concentrations (SSC), or as a relative and objective measure of water clarity in monitoring programmes. Through systematic, controlled experimentation, we tested the response of 12 commercially available turbidity sensors, of various designs, to gauge their measurement consistency when benchmarked against pre-prepared sediment suspensions of known SSC. Results showed that despite calibration to a Formazin standard, sensor responses to identical SSC solutions (in the range of 20-1000 mg L-1) varied considerably. For a given SSC, up to five-fold differences in recorded turbidity were recorded across the tested instruments. Furthermore, inconsistent measurements were identified across instruments, regardless of whether they operated using backscatter or side-scatter optical principles. While the findings may have implications for compliance with turbidity-based water quality standards, they are less likely to be an issue when turbidity is being used as a surrogate for SSC, provided that instrument use remains constant and that instrument drift is not an issue. In this study, a field comparison of a subset of four study sensors showed that despite very different absolute turbidity readings for a given SSC, well correlated and reliable turbidity - SSC ratings were established (as evidenced by r2 coefficients from 0.92 to 0.98). This led to reasonably consistent suspended sediment load estimates of between 64.7 and 70.8 tonnes for a rainfall event analysed. This study highlights the potential for issues to arise when interpreting water turbidity datasets that are often assumed to be comparable, in that measurement inconsistency of the type reported here may remain unknown to water resource decision-makers and practitioners.

Evaluating the relationship between biotic and sediment metrics using mesocosms and field studies.

An ongoing research challenge is the detection of biological responses to elevated sediment and the identification of sediment-specific bioassessment metrics to evaluate these biological responses. Laboratory mesocosms and field observations in rivers in Ireland were used to evaluate the relationship between a range of biological and sediment metrics and to assess which biological metrics were best at discerning the effects of excess sediment on macroinvertebrates. Results from the mesocosm study indicated a marked decrease in the abundance of sensitive taxa with increasing sediment surface cover. % EPT (Ephemeroptera, Plecoptera, Trichoptera) and % E abundances exhibited the strongest negative correlation with sediment surface cover in the mesocosm study. The field study revealed that % EPT abundance was most closely correlated with % sediment surface cover, explaining 13% of the variance in the biological metric. Both studies revealed weaker relationships with a number of other taxonomy-based metrics including total taxon abundance, total taxon richness and moderate relationships with the Proportion of Sediment-sensitive Invertebrates metric (PSI). All trait-based metrics were poorly correlated with sediment surface cover in the field study. In terms of sediment metrics, % surface cover was more closely related to biological metrics than either re-suspendable sediment or turbidity. These results indicate that % sediment surface cover and % EPT abundance may be useful metrics for assessing the effect of excessive sediment on macroinvertebrates. However, EPT metrics may not be specific to sediment impact and therefore when applied to rivers with multiple pressures should be combined with observations on sediment cover.

The impact of cattle access on ecological water quality in streams: Examples from agricultural catchments within Ireland.

Unrestricted cattle access to rivers and streams represent a potentially significant localised pressure on freshwater systems. However there is no consensus in the literature on the occurrence and extent of impact and limited research has examined the effects on aquatic biota in the humid temperate environment examined in the present study. Furthermore, this is one of the first times that research consider the potential for cattle access impacts in streams of varying water quality in Northern Europe. We investigated the effects of cattle access on macroinvertebrate communities and deposited fine sediment levels, in four rivers of high/good and four rivers of moderate water quality status which drain, low gradient, calcareous grassland catchments in Ireland. We assessed the temporal variability in macroinvertebrates communities across two seasons, spring and autumn. Site specific impacts were evident which appeared to be influenced by water quality status and season. All four high/good water status rivers revealed significant downstream changes in community structure and at least two univariate metrics (total richness and EPT richness together with taxon, E and EPT abundance). Two of the four moderate water status rivers showed significant changes in community structure, abundance and richness metrics and functional feeding groups driven in the main by downstream increases in collectors/gatherers, shredders and burrowing taxa. These two moderate water status rivers had high or prolonged livestock activity. In view of these findings, the potential for some of these sites to achieve at least high/good water quality status, as set out in the EU Water Framework Directive, may be compromised. The results presented highlight the need for additional research to further define the site specific factors and livestock management practices, under different discharge conditions, that increase the risk of impact on aquatic ecology due to these cattle-river interactions.

Constant pressure fluid infusion into rat neocortex from implantable microfluidic devices.

Implantable electrode arrays capable of recording and stimulating neural activity with high spatial and temporal resolution will provide a foundation for future brain computer interface technology. Currently, their clinical impact has been curtailed by a general lack of functional stability, which can be attributed to the acute and chronic reactive tissue responses to devices implanted in the brain. Control of the tissue environment surrounding implanted devices through local drug delivery could significantly alter both the acute and chronic reactive responses, and thus enhance device stability. Here, we characterize pressure-mediated release of test compounds into rat cortex using an implantable microfluidic platform. A fixed volume of fluorescent cell marker cocktail was delivered using constant pressure infusion at reservoir backpressures of 0, 5 and 10 psi. Affected tissue volumes were imaged and analyzed using epifluorescence and confocal microscropies and quantitative image analysis techniques. The addressable tissue volume for the 5 and 10 psi infusions, defined by fluorescent staining with Hoescht 33342 dye, was significantly larger than the tissue volume addressed by simple diffusion (0 psi) and the tissue volume exhibiting insertion-related cell damage (stained by propidium iodide). The results demonstrate the potential for using constant pressure infusion to address relevant tissue volumes with appropriate pharmacologies to alleviate reactive biological responses around inserted neuroprosthetic devices.

Fluvial-controlled metal and As mobilisation, dispersal and storage in the Río Guadiamar, SW Spain and its implications for long-term contaminant fluxes to the Doñana wetlands.

Flood-related contaminant (As, Cd, Cu, Pb, Zn) remobilisation, dispersal and storage in the Río Guadiamar was investigated following the 1998 Aznalcóllar tailings dam failure, along with records of floodplain contaminant loading in the decades preceding the tailings release. A series of post-spill floods resulted in the transfer of vast quantities of sediment-borne heavy metals and As towards the lower reaches of the Guadiamar and the borders of the Doñana National Park, but over-bank flood deposits collected between May 1999 and March 2002 show a systematic fall in contaminant concentrations following successive flood events. Geochemical improvements can largely be attributed to sediment mixing of contaminated and 'clean' material derived from calcareous catchment soils. Longer-term contaminant patterns in floodplain sediment cores show higher heavy metal and As loading rates operating before the opening of the Aznalcóllar pit in 1979 and in some instances pre-dating 1954. The remobilization and dispersal of historically contaminated alluvium in the upper Guadiamar means that the post-clean-up contaminant signature in flood-transported sediments largely reflects chronic, long-term metal mining in the Guadiamar catchment, rather than the acute effects of the Aznalcóllar spill. Generally results present a cautiously optimistic prognosis for the sensitive wetlands of Doñana, but high dissolved (aqueous) heavy metal (especially Cu and Zn) concentrations in the upper Guadiamar emphasise the need for addressing contaminant 'hotspots' in the region and for maintaining flow requirements for aquatic ecosystems. This study illustrates the importance of establishing antecedent geomorphological-geochemical conditions in a spill-impacted river system, both for assessing the impacts of a single catastrophic pollution event and for developing appropriate strategies for remediation.

Effects of insertion conditions on tissue strain and vascular damage during neuroprosthetic device insertion.

Long-term integration of neuroprosthetic devices is challenged by reactive responses that compromise the brain-device interface. The contribution of physical insertion parameters to immediate damage is not well described. We have developed an ex vivo preparation to capture real-time images of tissue deformation during device insertion using thick tissue slices from rat brains prepared with fluorescently labeled vasculature. Qualitative and quantitative assessments of damage were made for insertions using devices with different tip shapes inserted at different speeds. Direct damage to the vasculature included severing, rupturing and dragging, and was often observed several hundred micrometers from the insertion site. Slower insertions generally resulted in more vascular damage. Cortical surface features greatly affected insertion success; insertions attempted through pial blood vessels resulted in severe tissue compression. Automated image analysis techniques were developed to quantify tissue deformation and calculate mean effective strain. Quantitative measures demonstrated that, within the range of experimental conditions studied, faster insertion of sharp devices resulted in lower mean effective strain. Variability within each insertion condition indicates that multiple biological factors may influence insertion success. Multiple biological factors may contribute to tissue distortion, thus a wide variability was observed among insertions made under the same conditions.

Dexamethasone treatment reduces astroglia responses to inserted neuroprosthetic devices in rat neocortex.

Microfabricated neural prosthetic devices hold great potential for increasing knowledge of brain function and treating patients with lost CNS function. Time-dependent loss of brain-device communication limits long-term use of these devices. Lost CNS function is associated with reactive responses that produce an encapsulating cellular sheath. Since early reactive responses may be associated with injuries produced at the time of device insertion, for example, vascular damage and disruption of the blood-brain barrier, we tested the effectiveness of the synthetic glucocorticoid, dexamethasone, in controlling insertion- and device-associated reactive responses. Dexamethasone (200 microg/kg) was administered as subcutaneous injections for 1 or 6 days beginning on the day of device insertion. Single shank microfabricated silicon devices were inserted into pre-motor cortex of adult rats. Reactive responses were assessed by immunohistochemistry for glial fibrillary acidic protein (astrocytes), CD11b (microglia), and laminin that labeled extracellular protein deposited around the insertion site and in association with vascular elements. Data were collected by confocal microscopy imaging of 100-microm-thick tissue slices. Reactive responses in vehicle control animals were similar to non-injected control animals. Dexamethasone treatment profoundly effected early and sustained reactive responses observed 1 and 6 weeks following device insertion, respectively. Dexamethasone treatment greatly attenuated astroglia responses, while microglia and vascular responses appeared to be increased. The 6-day treatment was more effective than the single injection regime. These results suggest that anti-inflammatory agents can be used to control reactive responses around inserted neural prosthetic devices and may provide a means to insure their long-term function.

Two new fluorescent dyes applicable for visualization of fungal cell walls.

Two fluorophores, Solophenyl Flavine 7GFE 500 and Pontamine Fast Scarlet 4B, not heretofore reported upon are described as useful dyes of fungal cell walls, septa and bud scars examined microscopically. The dyes, depending on the filter sets used, yield fluorescently stained material generally in the blue to green and yellow to red wavelengths for Solophenyl Flavine 7GFE 500 and Pontamine Fast Scarlet 4B, respectively. They provide an excellent alternative to the more commonly used fluorophore, Calcofluor White M2R. The two fluorophores, in addition to being used at various spectral wavelengths from mercury arc sources, can be used with laser sources providing 488 nm and 543 nm line wavelengths, common to most scanning confocal microscopes. Unlike Calcofluor, Solophenyl Flavine 7GFE 500 and Pontamine Fast Scarlet 4B do not fade quickly when exposed to selected light wavelengths; however, like Calcofluors they are compatible with living fungal cells.

Topographically modified surfaces affect orientation and growth of hippocampal neurons.

Extracellular matrix molecules provide biochemical and topographical cues that influence cell growth in vivo and in vitro. Effects of topographical cues on hippocampal neuron growth were examined after 14 days in vitro. Neurons from hippocampi of rat embryos were grown on poly-L-lysine-coated silicon surfaces containing fields of pillars with varying geometries. Photolithography was used to fabricate 1 microm high pillar arrays with different widths and spacings. Beta(III)-tubulin and MAP-2 immunocytochemistry and scanning electron microscopy were used to describe neuronal processes. Automated two-dimensional tracing software quantified process orientation and length. Process growth on smooth surfaces was random, while growth on pillared surfaces exhibited the most faithful alignment to pillar geometries with smallest gap sizes. Neurite lengths were significantly longer on pillars with the smallest inter-pillar spacings (gaps) and 2 microm pillar widths. These data indicate that physical cues affect neuron growth, suggesting that extracellular matrix topography may contribute to cell growth and differentiation. These results demonstrate new strategies for directing and promoting neuronal growth that will facilitate studies of synapse formation and function and provide methods to establish defined neural networks.

Brain responses to micro-machined silicon devices.

Micro-machined neural prosthetic devices can be designed and fabricated to permit recording and stimulation of specific sites in the nervous system. Unfortunately, the long-term use of these devices is compromised by cellular encapsulation. The goals of this study were to determine if device size, surface characteristics, or insertion method affected this response. Devices with two general designs were used. One group had chisel-shaped tips, sharp angular corners, and surface irregularities on the micrometer size scale. The second group had rounded corners, and smooth surfaces. Devices of the first group were inserted using a microprocessor-controlled inserter. Devices of the second group were inserted by hand. Comparisons were made of responses to the larger devices in the first group with devices from the second group. Responses were assessed 1 day and 1, 2, 4, 6, and 12 weeks after insertions. Tissues were immunochemically labeled for glial fibrillary acidic protein (GFAP) or vimentin to identify astrocytes, or for ED1 to identify microglia. For the second comparison devices from the first group with different cross-sectional areas were analyzed. Similar reactive responses were observed following insertion of all devices; however, the volume of tissue involved at early times, <1 week, was proportional to the cross-sectional area of the devices. Responses observed after 4 weeks were similar for all devices. Thus, the continued presence of devices promotes formation of a sheath composed partly of reactive astrocytes and microglia. Both GFAP-positive and -negative cells were adherent to all devices. These data indicate that device insertion promotes two responses-an early response that is proportional to device size and a sustained response that is independent of device size, geometry, and surface roughness. The early response may be associated with the amount of damage generated during insertion. The sustained response is more likely due to tissue-device interactions.

Algorithms for accurate 3D registration of neuronal images acquired by confocal scanning laser microscopy.

This paper presents automated and accurate algorithms based on high-order transformation models for registering three-dimensional (3D) confocal images of dye-injected neurons. The algorithms improve upon prior methods in several ways, and meet the more stringent image registration needs of applications such as two-view attenuation correction recently developed by us. First, they achieve high accuracy ( approximately 1.2 voxels, equivalent to 0.4 micro m) by using landmarks, rather than intensity correlations, and by using a high-dimensional affine and quadratic transformation model that accounts for 3D translation, rotation, non-isotropic scaling, modest curvature of field, distortions and mechanical inconsistencies introduced by the imaging system. Second, they use a hierarchy of models and iterative algorithms to eliminate potential instabilities. Third, they incorporate robust statistical methods to achieve accurate registration in the face of inaccurate and missing landmarks. Fourth, they are fully automated, even estimating the initial registration from the extracted landmarks. Finally, they are computationally efficient, taking less than a minute on a 900-MHz Pentium III computer for registering two images roughly 70 MB in size. The registration errors represent a combination of modelling, estimation, discretization and neuron tracing errors. Accurate 3D montaging is described; the algorithms have broader applicability to images of vasculature, and other structures with distinctive point, line and surface landmarks.

Attenuation correction in confocal laser microscopes: a novel two-view approach.

Confocal microscopy is a three-dimensional (3D) imaging modality, but the specimen thickness that can be imaged is limited by depth-dependent signal attenuation. Both software and hardware methods have been used to correct the attenuation in reconstructed images, but previous methods do not increase the image signal-to-noise ratio (SNR) using conventional specimen preparation and imaging. We present a practical two-view method that increases the overall imaging depth, corrects signal attenuation and improves the SNR. This is achieved by a combination of slightly modified but conventional specimen preparation, image registration, montage synthesis and signal reconstruction methods. The specimen is mounted in a symmetrical manner between a pair of cover slips, rather than between a slide and a cover slip. It is imaged sequentially from both sides to generate two 3D image stacks from perspectives separated by approximately 180 degrees with respect to the optical axis. An automated image registration algorithm performs a precise 3D alignment, and a model-based minimum mean squared algorithm synthesizes a montage, combining the content of both the 3D views. Experiments with images of individual neurones contrasted with a space-filling fluorescent dye in thick brain tissue slices produced precise 3D montages that are corrected for depth-dependent signal attenuation. The SNR of the reconstructed image is maximized by the method, and it is significantly higher than in the single views after applying our attenuation model. We also compare our method with simpler two-view reconstruction methods and quantify the SNR improvement. The reconstructed images are a more faithful qualitative visualization of the specimen's structure and are quantitatively more accurate, providing a more rigorous basis for automated image analysis.

Selective adhesion of astrocytes to surfaces modified with immobilized peptides.

Under serum-free conditions, rat skin fibroblasts, but not cortical astrocytes, selectively adhered to glass surfaces modified with the integrin-ligand peptide RGDS. In contrast, astrocytes, but not fibroblasts, exhibited enhanced adhesion onto substrates modified with KHIFSDDSSE, a peptide that mimics a homophilic binding domain of neural cell adhesion molecule (NCAM). Astrocyte and fibroblast adhesion onto substrates modified with the integrin ligands IKVAV and YIGSR as well as the control peptides RDGS and SEDSDKFISH were similar to that observed on aminophase glass (reference substrate). This study is the first to demonstrate the use of immobilized KHIFSDDSSE in selectively modulating astrocyte and fibroblast adhesion on material surfaces, potentially leading to materials that promote specific functions of cells involved in the response(s) of central nervous system tissues to injury. This information could be incorporated into novel biomaterials designed to improve the long-term performance of the next generation of neural prostheses.

Axonal outgrowth of hippocampal neurons on micro-scale networks of polylysine-conjugated laminin.

Microcontact printing was used to define an interconnected lattice network of polylysine-conjugated laminin, a protein-polypeptide ligate that is an effective promoter of neuron outgrowth on material surfaces. In the presence of serum proteins, rat hippocampal neurons selectively adhered to features of polylysine-conjugated laminin as narrow as 2.6 microm in width. Adhering neurons extended long axonal processes, which precisely followed and did not deviate from the prescribed patterns, demonstrating that neurons respond to this protein with high selectivity and that these techniques effectively provide long-range guidance of axonal outgrowth. Further examination of neuron response under serum-free cell culture conditions demonstrated that the outgrowth-promoting activity of polylysine-conjugated laminin was attributed to biologically active laminin. Together, these results demonstrate that polylysine-conjugated laminin provides for high-precision guidance of neuron attachment and axon outgrowth on material surfaces in a serum-independent manner. This ability to guide hippocampal neuron response in low-density, serum-free culture with high precision is valuable for the development of advanced, neuron-based devices.

Optimal scheduling of tracing computations for real-time vascular landmark extraction from retinal fundus images.

Recently, this group published fast algorithms for automatic tracing (vectorization) of the vasculature in live retinal angiograms, and for the extraction of visual landmarks formed by vascular bifurcations and crossings. These landmarks are used for feature-based image matching for controlling a computer-assisted laser retinal surgery instrument currently under development. This paper describes methods to schedule the vascular tracing computations to maximize the rate of growth of quality of the partial tracing results within a frame cycle. There are two main advantages. First, progressive image matching from partially extracted landmark sets can be faster, and provide an earlier indication of matching failure. Second, the likelihood of successful image matching is greatly improved since the extracted landmarks are of the highest quality for the given computational budget. The scheduling method is based on quantitative measures for the computational work and the quality of landmarks. A coarse grid-based analysis of the image is used to generate seed points for the tracing computations, along with estimates of local edge strengths, orientations, and vessel thickness. These estimates are used to define criteria for real-time preemptive scheduling of the tracing computations. It is shown that the optimal schedule can only be achieved in perfect hindsight, and is thus unrealizable. This leads to scheduling heuristics that approximate the behavior of the optimal algorithm. One such approximation produced approximately 400% improvement in the quality of the partial results at a defined milestone, as compared to random scheduling. The resulting algorithm can be readily implemented on conventional and multiple-processor systems, and is being applied to computer-assisted laser retinal surgery.

Attachment of astroglial cells to microfabricated pillar arrays of different geometries.

We studied the attachment of astroglial cells on smooth silicon and arrays of silicon pillars and wells with various widths and separations. Standard semiconductor industry photolithographic techniques were used to fabricate pillar arrays and wells in single-crystal silicon. The resulting pillars varied in width from 0. 5 to 2.0 micrometer, had interpillar gaps of 1.0-5.0 micrometer, and were 1.0 micrometer in height. Arrays also contained 1.0-micromter-deep wells that were 0.5 micrometer in diameter and separated by 0.5-2.0 micrometer. Fluorescence, reflectance, and confocal light microscopies as well as scanning electron microscopy were used to quantify cell attachment, describe cell morphologies, and study the distribution of cytoskeletal proteins actin and vinculin on surfaces with pillars, wells, and smooth silicon. Seventy percent of LRM55 astroglial cells displayed a preference for pillars over smooth silicon, whereas only 40% preferred the wells to the smooth surfaces. Analysis of variance statistics performed on the data sets yielded values of p > approximately.5 for the comparison between pillar data sets and < approximately.0003 in the comparison between pillar and well data sets. Actin and vinculin distributions were highly polarized in cells found on pillar arrays. Scanning electron microscopy clearly demonstrated that cells made contact with the tops of the pillars and did not reach down into the spaces between pillars even when the interpillar gap was 5.0 microm. These experiments support the use of surface topography to direct the attachment, growth, and morphology of cells. These surfaces can be used to study fundamental cell properties such as cell attachment, proliferation, and gene expression. Such topography might also be used to modify implantable medical devices such as neural implants and lead to future developments in tissue engineering.

Correlation of astroglial cell function on micro-patterned surfaces with specific geometric parameters.

Microcontact printing techniques were used to modify silicon substrates with arrays of hexagonal features of N1[3-(trimethoxysilyl) propyl]diethylenetriamine (DETA) surrounded by octadecyltrichlorosilane (OTS), which are hydrophilic, cell-adhesive and hydrophobic, non-adhesive organosilanes, respectively. In the presence of serum proteins, LRM55 cell adhesion and morphology on these modified surfaces were best correlated to the width of the cell-adhesive features. On surfaces modified with small (5 microm in width) cell-adhesive features, LRM55 cells elaborated only thin processes. As feature width was increased, cells on these surfaces exhibited increased cell spreading and elaborated wide processes. On surfaces modified with large (>35 microm in width) features, single cells adhered to and spread upon individual DETA features. In a similar fashion, LRM55 cell adhesion density increased with increasing feature width; this correlation could be represented by a simple, second-order relation, and was independent of all other measures of pattern geometry. The results of this study provide evidence that micro-patterning may be effective in controlling astrocyte interaction with implant materials.

In vivo activation and in situ BDNF-stimulated nuclear translocation of mitogen-activated/extracellular signal-regulated protein kinase is inhibited by ethanol in the developing rat hippocampus.

In order to test the hypothesis that ethanol (EtOH)-induced changes in growth factor signal transduction contribute to the teratogenic effects of EtOH in the developing brain, neonatal rat pups were administered a single dose of EtOH during the brain growth spurt (5 days of age, PN5). Hippocampal mitogen-activated/extracellular signal-regulated protein kinase (MAPK/ERK) activation was analyzed one to 6 h after exposure by electrophoretic-mobility shift assay combined with western blot. Brain-Derived Neurotrophic Factor (BDNF) was used to stimulate ERK in hippocampal slices prepared from PN5 pups and activation and cellular localization was determined with immunofluorescence combined with confocal microscopy. EtOH decreased ERK activation in vivo and decreased nuclear translocation of BDNF-stimulated ERK in situ. These data suggest EtOH-induced inhibition of growth factor signaling may contribute to the development of fetal alcohol syndrome and alcohol-related birth defects.

Cerebral astrocyte response to micromachined silicon implants.

The treatment of neurologic disorders and the restoration of lost function due to trauma by neuroprosthetic devices has been pursued for over 20 years. The methodology for fabricating miniature devices with sophisticated electronic functions to interface with nervous system tissue is available, having been well established by the integrated circuit industry. Unfortunately, the effectiveness of these devices is severely limited by the tissue reaction to the insertion and continuous presence of the implant, a foreign object. This study was designed to document the response of reactive astrocytes in the hope that this information will be useful in specifying new fabrication technologies and devices capable of prolonged functioning in the brain. Model probes fabricated from single crystal silicon wafers were implanted into the cerebral cortices of rats. The probes had a 1 x 1-mm tab, for handling, and a 2-mm-long shaft with a trapezoidal cross-section (200-microm base, 60microm width at the top, and 130 microm height). The tissue response was studied by light and scanning electron microscopy at postinsertion times ranging from 2 to 12 weeks. A continuous sheath of cells was found to surround the insertion site in all tissue studied and was well developed but loosely organized at 2 weeks. By 6 and 12 weeks, the sheath was highly compacted and continuous, isolating the probe from the brain. At 2 and 4 weeks, the sheath was disrupted when the probe was removed from the fixed tissue, indicating that cells attached more strongly to the surface of the probe than to the nearby tissue. The later times showed much less disruption. Scanning electron microscopy of the probes showed adherent cells or cell fragments at all time points. Thus, as the sheath became compact, the cells on the probe and the cells in the sheath had decreased adhesion to each other. Immunocytochemistry demonstrated that the sheath was labeled with antibodies to glial fibrillary acidic protein (GFAP), an indicator for reactive gliosis. The tissue surrounding the insertion site showed an increased number of GFAP-positive cells which tended to return to control levels as a function of time after probe insertion. It was concluded that reactive gliosis is an important part of the process forming the cellular sheath. Further, the continuous presence of the probe appears to result in a sustained response that produces and maintains a compact sheath, at least partially composed of reactive glia, which isolates the probe from the brain.