The Virtual Navigation Toolbox: Providing tools for virtual navigation experiments

Spatial navigation research in humans increasingly relies on experiments using virtual reality (VR) tools, which allow for the creation of highly flexible, and immersive study environments, that can react to participant interaction in real time. Despite the popularity of VR, tools simplifying the creation and data management of such experiments are rare and often restricted to a specific scope-limiting usability and comparability. To overcome those limitations, we introduce the Virtual Navigation Toolbox (VNT), a collection of interchangeable and independent tools for the development of spatial navigation VR experiments using the popular Unity game engine. The VNT's features are packaged in loosely coupled and reusable modules, facilitating convenient implementation of diverse experimental designs. Here, we depict how the VNT fulfils feature requirements of different VR environments and experiments, guiding through the implementation and execution of a showcase study using the toolbox. The presented showcase study reveals that homing performance in a classic triangle completion task is invariant to translation velocity of the participant's avatar, but highly sensitive to the number of landmarks. The VNT is freely available under a creative commons license, and we invite researchers to contribute, extending and improving tools using the provided repository.

Combined sodium glucose co-transporter-2 inhibitor and angiotensin-converting enzyme inhibition upregulates the renin-angiotensin system in chronic kidney disease with type 2 diabetes: Results of a randomized, double-blind, placebo-controlled exploratory trial

AIM

Sodium glucose co-transporter-2 inhibitors (SGLT-2i) improve cardiorenal outcomes in patients with chronic kidney disease (CKD), with and without type 2 diabetes. The molecular mechanisms underlying these pleiotropic effects remain unclear, yet it is speculated that SGLT-2i elicit a neurohormonal modulation resulting in renin-angiotensin system (RAS) activation. We hypothesized that combined SGLT-2 and angiotensin-converting enzyme inhibition (ACEi) favours RAS regulation towards the beneficial angiotensin-(1-7)-driven axis.

MATERIALS AND METHODS

This randomized controlled prospective study investigated the effect of 12 weeks treatment with the SGLT-2i empagliflozin on top of ACEi on the molecular RAS dynamics in 24 diabetic and 24 non-diabetic patients with CKD. Systemic RAS peptides were quantified by mass spectrometry.

RESULTS

In patients with type 2 diabetes, combined SGLT-2i and ACEi significantly upregulated plasma renin activity [pre-treatment median and interquartile range 298.0 (43.0-672.0) pmol/L versus post-treatment 577.0 (95.0-1543.0) pmol/L; p = .037] and angiotensin I levels [pre-treatment 289.0 (42.0-668.0) pmol/L versus post-treatment 573.0 (93.0-1522.0) pmol/L; p = .037], together with a significant increase of angiotensin-(1-7) levels [pre-treatment 14.0 (2.1-19.0) pmol/L versus post-treatment 32.0 (5.7-99.0) pmol/L; p = .012]. Empagliflozin treatment resulted in a 1.5 to 2-fold increase in main RAS peptides in patients with diabetes compared with placebo. No significant effect of empagliflozin on top of ACEi on RAS peptides was found in patients with CKD without diabetes.

CONCLUSION

A distinct RAS modulation by SGLT-2i occurs in diabetic kidney disease reflected by enhancement of the beneficial angiotensin-(1-7) providing a molecular background for this renoprotective therapeutic approach.

Citizen science and online data: Opportunities and challenges for snake ecology and action against snakebite

The secretive behavior and life history of snakes makes studying their biology, distribution, and the epidemiology of venomous snakebite challenging. One of the most useful, most versatile, and easiest to collect types of biological data are photographs, particularly those that are connected with geographic location and date-time metadata. Photos verify occurrence records, provide data on phenotypes and ecology, and are often used to illustrate new species descriptions, field guides and identification keys, as well as in training humans and computer vision algorithms to identify snakes. We scoured eleven online and two offline sources of snake photos in an attempt to collect as many photos of as many snake species as possible, and attempt to explain some of the inter-species variation in photograph quantity among global regions and taxonomic groups, and with regard to medical importance, human population density, and range size. We collected a total of 725,565 photos-between 1 and 48,696 photos of 3098 of the world's 3879 snake species (79.9%), leaving 781 "most wanted" species with no photos (20.1% of all currently-described species as of the December 2020 release of The Reptile Database). We provide a list of most wanted species sortable by family, continent, authority, and medical importance, and encourage snake photographers worldwide to submit photos and associated metadata, particularly of "missing" species, to the most permanent and useful online archives: The Reptile Database, iNaturalist, and HerpMapper.

Spatial Attentional Selection Modulates Early Visual Stimulus Processing Independently of Visual Alpha Modulations

The capacity-limited human brain is constantly confronted with a huge amount of sensory information. Selective attention is needed for biasing neural processing towards relevant information and consequently allows meaningful interaction with the environment. Activity in the alpha-band has been proposed to be related to top-down modulation of neural inhibition and could thus represent a viable candidate to control the priority of stimulus processing. It is, however, unknown whether modulations in the alpha-band directly relate to changes in the sensory gain control of the early visual cortex. Here, we used a spatial cueing paradigm while simultaneously measuring ongoing alpha-band oscillations and steady-state visual evoked potentials (SSVEPs) as a marker of continuous early sensory processing in the human visual cortex. Thereby, the effects of spatial attention for both of these signals and their potential interactions were assessed. As expected, spatial attention modulated both alpha-band and SSVEP responses. However, their modulations were independent of each other and the corresponding activity profiles differed across task demands. Thus, our results challenge the view that modulations of alpha-band activity represent a mechanism that directly alters or controls sensory gain. The potential role of alpha-band oscillations beyond sensory processing will be discussed in light of the present results.

Crowdbreaks: Tracking Health Trends Using Public Social Media Data and Crowdsourcing

In the past decade, tracking health trends using social media data has shown great promise, due to a powerful combination of massive adoption of social media around the world, and increasingly potent hardware and software that enables us to work with these new big data streams. At the same time, many challenging problems have been identified. First, there is often a mismatch between how rapidly online data can change, and how rapidly algorithms are updated, which means that there is limited reusability for algorithms trained on past data as their performance decreases over time. Second, much of the work is focusing on specific issues during a specific past period in time, even though public health institutions would need flexible tools to assess multiple evolving situations in real time. Third, most tools providing such capabilities are proprietary systems with little algorithmic or data transparency, and thus little buy-in from the global public health and research community. Here, we introduce Crowdbreaks, an open platform which allows tracking of health trends by making use of continuous crowdsourced labeling of public social media content. The system is built in a way which automatizes the typical workflow from data collection, filtering, labeling and training of machine learning classifiers and therefore can greatly accelerate the research process in the public health domain. This work describes the technical aspects of the platform, thereby covering the functionalities at its current state and exploring its future use cases and extensions.

Wet Markets and Food Safety: TripAdvisor for Improved Global Digital Surveillance

Background

Wet markets are markets selling fresh meat and produce. Wet markets are critical for food security and sustainable development in their respective regions. Due to their cultural significance, they attract numerous visitors and consequently generate tourist-geared information on the Web (ie, on social networks such as TripAdvisor). These data can be used to create a novel, international wet market inventory to support epidemiological surveillance and control in such settings, which are often associated with negative health outcomes.

Objective

Using social network data, we aimed to assess the level of wet markets’ touristic importance on the Web, produce the first distribution map of wet markets of touristic interest, and identify common diseases facing visitors in these settings.

Methods

A Google search was performed on 31 food market–related keywords, with the first 150 results for each keyword evaluated based on their relevance to tourism. Of all these queries, wet market had the highest number of tourism-related Google Search results; among these, TripAdvisor was the most frequently-occurring travel information aggregator, prompting its selection as the data source for this study. A Web scraping tool (ParseHub) was used to extract wet market names, locations, and reviews from TripAdvisor. The latter were searched for disease-related content, which enabled assignment of GeoSentinel diagnosis codes to each. This syndromic categorization was overlaid onto a mapping of wet market locations. Regional prevalence of the most commonly occurring symptom group - food poisoning - was then determined (ie, by dividing the number of wet markets per continent with more than or equal to 1 review containing this syndrome by the total number of wet markets on that continent with syndromic information).

Results

Of the 1090 hits on TripAdvisor for wet market, 36.06% (393/1090) conformed to the query’s definition; wet markets were heterogeneously distributed: Asia concentrated 62.6% (246/393) of them, Europe 19.3% (76/393), North America 7.9% (31/393), Oceania 5.1% (20/393), Africa 3.1% (12/393), and South America 2.0% (8/393). Syndromic information was available for 14.5% (57/393) of wet markets. The most frequently occurring syndrome among visitors to these wet markets was food poisoning, accounting for 54% (51/95) of diagnoses. Cases of this syndrome were identified in 56% (22/39) of wet markets with syndromic information in Asia, 71% (5/7) in Europe, and 71% (5/7) in North America. All wet markets in South America and Oceania reported food poisoning cases, but the number of reviews with syndromic information was very limited in these regions (n=2).

Conclusions

The map produced illustrates the potential role of touristically relevant social network data to support global epidemiological surveillance. This includes the possibility to approximate the global distribution of wet markets and to identify diseases (ie, food poisoning) that are most prevalent in such settings.

The problem of home choice in skyline-based homing

Navigation in cluttered environments is an important challenge for animals and robots alike and has been the subject of many studies trying to explain and mimic animal navigational abilities. However, the question of selecting an appropriate home location has, so far, received only little attention. This is surprising, since the choice of a home location might greatly influence an animal’s navigation performance. To address the question of home choice in cluttered environments, a systematic analysis of homing trajectories was performed by computer simulations using a skyline-based local homing method. Our analysis reveals that homing performance strongly depends on the location of the home in the environment. Furthermore, it appears that by assessing homing success in the immediate vicinity of the home, an animal might be able to predict its overall success in returning to it from within a much larger area.

[Cost analysis of patient blood management]

BACKGROUND

Patient blood management (PBM) is a multidisciplinary approach focusing on the diagnosis and treatment of preoperative anaemia, the minimisation of blood loss, and the optimisation of the patient-specific anaemia reserve to improve clinical outcomes. Economic aspects of PBM have not yet been sufficiently analysed.

OBJECTIVES

The aim of this study is to analyse the costs associated with the clinical principles of PBM and the project costs associated with the implementation of a PBM program from an institutional perspective.

MATERIALS AND METHODS

Patient-related costs of materials and services were analysed at the University Hospital Frankfurt for 2013. Personnel costs of all major processes were quantified based on the time required to perform each step. Furthermore, general project costs of the implementation phase were determined.

RESULTS

Direct costs of transfusing a single unit of red blood cells can be calculated to a minimum of €147.43. PBM-associated costs varied depending on individual patient requirements. The following costs per patient were calculated: diagnosis of preoperative anaemia €48.69-123.88; treatment of preoperative anaemia (including iron-deficiency anaemia and megaloblastic anaemia) €12.61-127.99; minimising perioperative blood loss (including point-of-care diagnostics, coagulation management and cell salvage) €3.39-1,901.81; and costs associated with the optimisation of the tolerance to anaemia (including patient monitoring and volume therapy) €28.62. General project costs associated with the implementation of PBM were €24,998.24.

CONCLUSIONS

PBM combines various alternatives to the transfusion of red blood cells and improves clinical outcome. Costs of PBM vary from institution to institution and depend on the extent to which different aspects of PBM have been implemented. The quantification of costs associated with PBM is essential in order to assess the economic impact of PBM, and thereby, to efficiently re-allocate health care resources. Costs were determined at a single university hospital. Thus, further analyses of both the costs of transfusion and the costs of PBM-principles will be necessary to evaluate the cost-effectiveness of PBM.

Moraxella catarrhalis induces CEACAM3-Syk-CARD9-dependent activation of human granulocytes

The human restricted pathogen Moraxella catarrhalis is an important causal agent for exacerbations in chronic obstructive lung disease in adults. In such patients, increased numbers of granulocytes are present in the airways, which correlate with bacteria-induced exacerbations and severity of the disease. Our study investigated whether the interaction of M. catarrhalis with the human granulocyte-specific carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-3 is linked to NF-κB activation, resulting in chemokine production. Granulocytes from healthy donors and NB4 cells were infected with M. catarrhalis in the presence of different inhibitors, blocking antibodies and siRNA. The supernatants were analysed by enzyme-linked immunosorbent assay for chemokines. NF-κB activation was determined using a luciferase reporter gene assay and chromatin-immunoprecipitation. We found evidence that the specific engagement of CEACAM3 by M. catarrhalis ubiquitous surface protein A1 (UspA1) results in the activation of pro-inflammatory events, such as degranulation of neutrophils, ROS production and chemokine secretion. The interaction of UspA1 with CEACAM3 induced the activation of the NF-κB pathway via Syk and the CARD9 pathway and was dependent on the phosphorylation of the CEACAM3 ITAM-like motif. These findings suggest that the CEACAM3 signalling in neutrophils is able to specifically modulate airway inflammation caused by infection with M. catarrhalis.

17β-estradiol protects 7-day old rats from acute brain injury and reduces the number of apoptotic cells

OBJECTIVE

To test a possible neuroprotective activity of 17β-estradiol in the neonatal rat brain exposed to hypoxic-ischemia (controlled hypoxia after unilateral carotid artery ligation).

METHODS

Seven-day-old Wistar rats underwent ligation of the left common carotid artery followed by 80 minutes hypoxia in 8% oxygen inducing an ipsilateral brain damage. Seven days later (d14), brains were analyzed quantitatively using a macroscopic and microscopic score for structural damage, hemisphere volumes were calculated, and immunohistochemistry for cleaved-caspase-3 (marker for apoptotic cells) was performed. Animals from the study group (n = 19) received 17β-estradiol (0.05 µg/g body weight intraperitoneally) before (-64, -40, and -16 hours) and after (+3 hours) the hypoxia (hour 0: start of the hypoxia) and the control group (n = 21) received mock treatment.

RESULTS

Of the 21 pups, 13 in the NaCl group had macroscopically a severe brain damage and 7 of 19 animals in the study group encountered only discrete to mild lesions. Microscopic brain damage in the study group was significantly lower (score 1.5 ± 0.7 vs 2.8 ± 0.8, P < .05). The determined volumes of the affected hemisphere were significantly lower in the NaCl group than in the treatment group. The numbers of apoptotic cells in both hemispheres was equal in the estradiol group, but in the control group, there were significantly more apoptotic cells in the affected hemisphere (control group: ipsilateral: 1435 ± 653 vs contralateral: 143 ± 57 cells, P < .05).

DISCUSSION

17β-Estradiol protects newborn rat brains from hypoxic-ischemic injury, in terms of both microscopic cell injury and apoptosis.

First Observations of Mycosphaerella pini on Scots Pine in Finland

Red band needle blight of pines caused by Mycosphaerella pini (anamorph Dothistroma septosporum) has recently been recorded on Scots pine (Pinus sylvestris) at 14 rural districts in southern and central Finland. Scots pine is the most common and commercially most important tree species in Finland. Red bands with aggregations of conidial stromata on otherwise brown attached needles were frequently encountered on saplings and young trees in dense stands and sporadically on lower twigs of mature trees within 2 m of the ground. These symptoms and signs, typical for M. pini (1), were also observed on needles of P. contorta and P. cembra, which occur in Finland in low frequency. Symptoms of red band needle blight and abundant conidial stromata were found in March and April of 2008 after a mild and rainy winter. After this time, the frequency at which fresh acervuli were observed decreased. Conidia were isolated after squeezing conidial stromata into a drop of sterile water and rinsing out the drop onto water agar from where single conidia were picked up from under the microscope with a modified Pasteur pipette. The conidia were hyaline, smooth, thin walled, filiform, 2.0 to 2.7 (2.4) μm wide, and 15 to 37 (29.4) μm long. Germination of the conidia on water agar was 100%. The cultures grew slowly and reached a diameter of 4 to 10 mm within 3 weeks on modified orange serum agar (2) at 20°C and abundantly produced conidia. Complete sequences of the internal transcribed spacer (ITS) region including the 5.8S rRNA gene were obtained for three isolates from different rural districts: Hartola (61°34'N, 26°01'E), Kangasniemi (61°59'N, 26°39'E), and Suonenjoki (62°37'N, 27°07'E). These sequences are deposited in GenBank with Accession Nos. EU834294, EU834295, and EU834296 and are identical to each other and to more than 50 M. pini sequences in GenBank, including those of several Estonian and Austrian isolates. These isolates are deposited in the culture collection of the Finnish Forest Research Institute with identifiers Dot1, Dot2, and Dot8. Symptoms were reproduced after inoculation of 1-year-old Scots pine seedlings growing in seedling trays with 115 cm³ cavities. A conidial suspension (5 to 6·× 10³ conidia ml^-1) was prepared from two single-conidial cultures (Dot10 and Dot15), combined, and sprayed during July 2008 onto 192 seedlings until needles looked completely wet. Sixty-four seedlings were sprayed with distilled water as a control treatment. Seedlings were incubated outdoors in Suonenjoki and covered with a transparent plastic hood for the first 5 days after inoculation. The first symptoms (brown segments and red bands on needles) appeared on inoculated seedlings 1 month later, and conidial stromata appeared after another 2 to 4 weeks. M. pini was reisolated from the acervuli of 10 sample needles. Three months after inoculation, all inoculated seedlings showed symptoms while all noninoculated seedlings were healthy. It is possible that M. pini has spread recently from the south since it was identified for the first time in Estonia 2 years earlier (3). Although the Gulf of Finland separates Finnish pine forests from Estonian pine forests by approximately 50 to 100 km, spores may have been aerially disseminated over this distance. Alternatively, introduction of M. pini to Finland may have occurred on imported seedlings. References: (1) Anonymous. OEPP/EPPO Bull. 35, 303, 2005. (2) M. Hanso and R. Drenkhan. Plant Pathol. 57:170, 2008. (3) M. M. Müller et al. Mycol. Res. 98:593, 1994.

Sources of synchronized induced Gamma-Band responses during a simple object recognition task: a replication study in human MEG

Natural stimuli are compiled of numerous features, which are cortically represented in dispersed structures. Synchronized oscillations in the Gamma-Band (>30 Hz; induced Gamma-Band Responses, iGBRs), are regarded as a plausible mechanism to re-integrate these regions into a meaningful cortical object representation. Using electroencephalography (EEG) it was demonstrated that the generators of iGBRs can be localized to temporal, parietal, posterior, and frontal areas. The present magnetoencephalogram (MEG) study intended to replicate these findings in order contribute to the ongoing debate regarding the possible functional difference of high-frequency signals as measured by both techniques. During a standard object recognition task we found an augmentation of the iGBR after the presentation of meaningful as opposed to meaningless stimuli at approximately 160-440 ms after stimulus onset. This peak was localized to inferior temporal gyri, superior parietal lobules and the right middle frontal gyrus. Importantly, most of these brain structures were significantly phase-locked to each other. The implications of these results are twofold: (1) they present further evidence for the view that iGBRs signify neuronal activity in a broadly distributed network during object recognition. (2) MEG is well suited to detect induced high-frequency oscillations with a very similar morphology as revealed by EEG recordings, thereby eliminating known problems with electroencephalographical methods (e.g. reference confounds). In contrast to the iGBR, the localization of event-related fields (ERFs) and evoked Gamma-Band Response (eGBRs) revealed generators in focal visual areas, and thus, seem to mirror early sensory processing.

Aggregation and vesiculation of membrane proteins by curvature-mediated interactions

Membrane remodelling plays an important role in cellular tasks such as endocytosis, vesiculation and protein sorting, and in the biogenesis of organelles such as the endoplasmic reticulum or the Golgi apparatus. It is well established that the remodelling process is aided by specialized proteins that can sense as well as create membrane curvature, and trigger tubulation when added to synthetic liposomes. Because the energy needed for such large-scale changes in membrane geometry significantly exceeds the binding energy between individual proteins and between protein and membrane, cooperative action is essential. It has recently been suggested that curvature-mediated attractive interactions could aid cooperation and complement the effects of specific binding events on membrane remodelling. But it is difficult to experimentally isolate curvature-mediated interactions from direct attractions between proteins. Moreover, approximate theories predict repulsion between isotropically curving proteins. Here we use coarse-grained membrane simulations to show that curvature-inducing model proteins adsorbed on lipid bilayer membranes can experience attractive interactions that arise purely as a result of membrane curvature. We find that once a minimal local bending is realized, the effect robustly drives protein cluster formation and subsequent transformation into vesicles with radii that correlate with the local curvature imprint. Owing to its universal nature, curvature-mediated attraction can operate even between proteins lacking any specific interactions, such as newly synthesized and still immature membrane proteins in the endoplasmic reticulum.

Sustained spatial attention to vibration is mediated in primary somatosensory cortex

Focusing attention to a specific body location has been shown to improve processing of events presented at this body location. One important debate concerns the stage in the somatosensory pathway at which the neural response is modulated when one attends to a tactile stimulus. Previous studies focused on components of the somatosensory evoked potential to transient stimuli, and demonstrated an early cortical attentional modulation. The neural basis of sustained spatial stimulus processing with continuous stimulation remains, however, largely unexplored. A way to approach this topic is to present vibrating stimuli with different frequencies for several seconds simultaneously to different body locations while subjects have to attend to the one or the other location. The amplitude of the somatosensory steady-state evoked potential (SSSEP) elicited by these vibrating stimuli increases with attention. On the basis of 128 electrode recordings, we investigated the topographical distribution and the underlying cortical sources by means of a VARETA approach of this attentional amplitude modulation of the SSSEP. Sustained spatial attention was found to be mediated in primary somatosensory cortex with no differences in SSSEP amplitude topographies between attended and unattended body locations. These result patterns were seen as evidence for a low-level sensory gain control mechanism in tactile spatial attention.

Feature-selective attention enhances color signals in early visual areas of the human brain

We used an electrophysiological measure of selective stimulus processing (the steady-state visual evoked potential, SSVEP) to investigate feature-specific attention to color cues. Subjects viewed a display consisting of spatially intermingled red and blue dots that continually shifted their positions at random. The red and blue dots flickered at different frequencies and thereby elicited distinguishable SSVEP signals in the visual cortex. Paying attention selectively to either the red or blue dot population produced an enhanced amplitude of its frequency-tagged SSVEP, which was localized by source modeling to early levels of the visual cortex. A control experiment showed that this selection was based on color rather than flicker frequency cues. This signal amplification of attended color items provides an empirical basis for the rapid identification of feature conjunctions during visual search, as proposed by "guided search" models.

Responses of N-Terminal Pro-Brain Natriuretic Peptide (NT-proBNP) and Cardiac Troponin I (cTnI) to Competitive Endurance Exercise in Recreational Athletes

The present study was designed to investigate whether the stress of a half-marathon race can induce myocardial cell injury or left ventricular dysfunction in moderately trained runners of both gender, as assessed by post-race plasma concentrations of biochemical cardiac-specific markers and by quantitative echocardiographic measurements. We examined 12 male (mean+/-SD); age: 42.8+/-7.3 yr; height: 177.6+/-7.4 cm; body mass: 75.6+/-9.4 kg; BMI: 24.1+/-1.8 and 13 female (mean+/-SD); age: 39.0+/-6.5 yr; height: 164.6+/-6.2 cm; body mass: 58.4+/-9.8 kg; BMI: 21.5+/-3.4 recreational runners, who completed a half-marathon race. Blood samples were collected from each subject before the half-marathon race as well as 20 min and 2 h post-race and cardiac troponin I (cTnI) and N-terminal pro-brain natriuretic peptide (NT-proBNP) were measured. Quantitative echocardiographic analyses of wall dimensions and ejection fraction were also obtained from 14 of 25 subjects within 1 wk after the race. Both blood markers showed significant changes (p<0.05-0.001) over the time course of the three blood draws. A significant percentage of laboratory analytes analyzed in this study were outside the reference ranges and fulfilled conventional criteria for cardiac muscle damage. However, echocardiography within one week following the competition did not show any evidence that running a half-marathon competition damages the myocardium. Strenuous endurance exercise in middle-aged recreational runners induces a significant elevation of biochemical cardiac-specific markers, which may reflect transient subclinical myocardial damage, but can also reflect a physiological reparative or adaptive process.

Decreased tissue reaction to bioprosthetic heart valve material afterL-glutamic acid treatment. A morphological study

Degenerative alterations of two different glutaraldehyde (GA)-fixed bioprosthetic heart valve materials were investigated in subcutaneous rat implants: Bovine pericardium, prepared according to clinically used bioprosthetic heart valve material (BHV) was compared to alternatively preserved pericardium (APHV), which was fixed in GA and treated with L-glutamic acid. Following 63 days of subcutaneous implantation, calcification of APHV implants was significantly lower as compared to BHV implants (13 +/- 6 versus 158 +/- 18 micrograms Ca/mg dry weight tissue; p less than 0.05). In BHV implants ultrastructural investigations showed nucleation of plate-shaped hydroxyapatite crystals at the surface of collagen fibrils and in remnants of connective tissue cells; no signs of calcification could be detected in APHV implants. The time-course of the inflammatory reaction was determined by quantification of immunohistochemical stained mononuclear host-cells invading the implants. In both preparation groups inflammatory reaction reached maximum 42 days after implantation. However, infiltration rate of inflammatory cells was markedly decreased in APHVs as compared to BHVs (p less than 0.05).

Intracellular acidification by inhibition of the Na+/H+-exchanger leads to caspase-independent death of cerebellar granule neurons resembling paraptosis

Potassium withdrawal is commonly used to induce caspase-mediated apoptosis in cerebellar granule neurons in vitro. However, the underlying and cell death-initiating mechanisms are unknown. We firstly investigated potassium efflux through the outward delayed rectifier K+ current (Ik) as a potential mediator. However, tetraethylammoniumchloride, an inhibitor of Ik, was ineffective to block apoptosis after potassium withdrawal. Since potassium withdrawal reduced intracellular pH (pHi) from 7.4 to 7.2, we secondly investigated the effects of intracellular acidosis. To study intracellular acidosis in cerebellar granule neurons, we inhibited the Na+/H+ exchanger (NHE) with 4-isopropyl-3-methylsulfonylbenzoyl-guanidine methanesulfonate (HOE 642) and 5-(N-ethyl-N-isopropyl)-amiloride. Both inhibitors concentration-dependently induced cell death and potentiated cell death after potassium withdrawal. Although inhibition of the NHE induced cell death with morphological criteria of apoptosis in light and electron microscopy including chromatin condensation, positive TUNEL staining and cell shrinkage, no internucleosomal DNA cleavage or activation of caspases was detected. In contrast to potassium withdrawal-induced apoptosis, cell death induced by intracellular acidification was not prevented by insulin-like growth factor-1, cyclo-adenosine-monophosphate, caspase inhibitors and transfection with an adenovirus expressing Bcl-XL. However, cycloheximide protected cerebellar granule neurons from death induced by potassium withdrawal as well as from death after treatment with HOE 642. Therefore, the molecular mechanisms leading to cell death after acidification appear to be different from the mechanisms after potassium withdrawal and resemble the biochemical but not the morphological characteristics of paraptosis.

[Muscle cell proteins are selectively released into the blood stream by marathon running]

In 19 marathon runners of both sexes, plasma concentrations of total creatine kinase (CK) activity, CKMB mass, myoglobin and troponin I were determined before and immediately after the race. Total CK activity and myoglobin increased significantly in all runners and showed neither a correlation with the individual age of the runners nor with the time they needed to reach the goal. In 12 of the runners, CKMB mass increased during the race to a level suggesting myocardial necrosis. However, the runners did not show any detectable deterioration of cardiac function after the race. The appearance of considerable amounts of muscle proteins in plasma precipitated by the muscle strain during the race seems explained by damage of skeletal muscle detected by histological studies. These phenomena may also be a consequence of profoundly disturbed cellular permeability, perhaps due to a kind of local stunning of muscle tissue by prolonged muscular strain.

Sustained division of the attentional spotlight

By voluntarily directing attention to a specific region of a visual scene, we can improve our perception of stimuli at that location. This ability to focus attention upon specific zones of the visual field has been described metaphorically as a moveable spotlight or zoom lens that facilitates the processing of stimuli within its 'beam'. A long-standing controversy has centred on the question of whether the spotlight of spatial attention has a unitary beam or whether it can be divided flexibly to disparate locations. Evidence supporting the unitary spotlight view has come from numerous behavioural and electrophysiological studies. Recent experiments, however, indicate that the spotlight of spatial attention may be divided between non-contiguous zones of the visual field for very brief stimulus exposures (&<100 ms). Here we use an electrophysiological measure of attentional allocation (the steady-state visual evoked potential) to show that the spotlight may be divided between spatially separated locations (excluding interposed locations) over more extended time periods. This spotlight division appears to be accomplished at an early stage of visual-cortical processing.

Determination of fifteen nucleotides in cultured human mononuclear blood and umbilical vein endothelial cells by solvent generated ion-pair chromatography

The paper describes the development of a method for the determination of 15 nucleotides in cultured mononuclear blood and umbilical vein endothelial cell lysates by solvent generated ion-pair chromatography. The phase system is generated via a mobile phase of 100 mM phosphoric acid adjusted to pH 6.2 with triethylamine. Nucleotides are eluted by applying a linear magnesium ion gradient. The method is robust, highly reproducible and easily adaptable to other cell lysates and allows the separation and quantitation of the nucleotides with detection limits in the range from 17 (ADP) to 126 (CDP) pmol in 20-microl aliquots.

Endothelial cell compatibility of azithromycin and erythromycin

Phlebitis is a severe local adverse event related to the use of parenteral macrolides. In order to evaluate the effect of azithromycin and erythromycin on human venous endothelial cells, we set up an in vitro model. The intracellular levels of purine nucleotides, as adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP) and guanosine 5'-triphosphate (GTP), were measured by means of high-performance liquid chromatography. Incubation of cells with 2 mg/mL azithromycin and erythromycin resulted in a rapid decline of intracellular ATP from 12.5 +/- 0.9 nmol/million cells to 4.1 +/- 0.3 and 2.6 +/- 0.4 nmol/million cells, respectively, after 60 min. In addition, ADP was extensively depleted from 2.1 +/- 0.17 nmol/million cells to 0.8 +/- 0.09 and 0.8 +/- 0.13 nmol/million cells after 60 min. After exposure of 0.5 mg/mL azithromycin and erythromycin, no significant decline of intracellular high-energy phosphate levels occurred after 20 and 60 min. Based on these results, solutions of azithromycin and erythromycin may not be well tolerated and may cause local adverse reactions even if diluted according to the manufacturer's recommendation.

Comparison of data transformation procedures to enhance topographical accuracy in time-series analysis of the human EEG

We describe a methodology to apply current source density (CSD) and minimum norm (MN) estimation as pre-processing tools for time-series analysis of single trial EEG data. The performance of these methods is compared for the case of wavelet time-frequency analysis of simulated gamma-band activity. A reasonable comparison of CSD and MN on the single trial level requires regularization such that the corresponding transformed data sets have similar signal-to-noise ratios (SNRs). For region-of-interest approaches, it should be possible to optimize the SNR for single estimates rather than for the whole distributed solution. An effective implementation of the MN method is described. Simulated data sets were created by modulating the strengths of a radial and a tangential test dipole with wavelets in the frequency range of the gamma band, superimposed with simulated spatially uncorrelated noise. The MN and CSD transformed data sets as well as the average reference (AR) representation were subjected to wavelet frequency-domain analysis, and power spectra were mapped for relevant frequency bands. For both CSD and MN, the influence of noise can be sufficiently suppressed by regularization to yield meaningful information, but only MN represents both radial and tangential dipole sources appropriately as single peaks. Therefore, when relating wavelet power spectrum topographies to their neuronal generators, MN should be preferred.

Modulation of induced gamma band responses and phase synchrony in a paired associate learning task in the human EEG

It has been proposed that associative learning is accomplished by the formation of cell assemblies and synchronous activity among the neurons of such an assembly. Induced gamma band responses (GBRs) and phase synchrony between electrode sites are discussed as a signature of activity within a cell assembly. To examine the activation of this network due to memory recall, a paired associate learning paradigm was used. EEG was analyzed in the frequency domain. Results showed a significant increase of induced GBRs at posterior and anterior electrode sites in the recall sequence of the learning condition. Furthermore, phase synchrony revealed a broad distribution pattern of phase synchrony between posterior and frontal electrode sites.

Human large-scale oscillatory brain activity during an operant shaping procedure

The present study aimed at examining the oscillatory brain-electric correlates of human operant learning using high-density electroencephalography (EEG). Induced gamma-band activity (GBA) was studied using a fixed-interval reinforcement schedule with a variable limited hold period, which was decreased depending on response accuracy. Thus, participants' behavior was shaped during the course of the learning session. After each response, numbers indicating the money value of that response served as reinforcing stimuli. Random reinforcement and self-paced button pressing without reinforcement were added as control conditions. GBA around 40 Hz was enhanced at posterior electrodes in response to visual feedback stimuli during shaping and random reward compared to the self-paced pressing condition where no visual feedback was provided. Furthermore, shaping was associated with a pronounced left frontal lower gamma (20-30 Hz) increase in response to feedback stimuli, whereas this pattern was not observed in the random reinforcement and self-paced pressing conditions. The present findings are in line with the notion that macroscopic high-frequency dynamics of neuronal cell assemblies may be regarded as a mechanism involved in learning and memory formation.

Genotoxicity of N-nitrosodicyclohexylamine in V79 cells in the sister chromatid exchange test and the single cell gel assay

Dicyclohexylaminexnitrite is used in chemical formulations as an anti-corrosion agent. N-Nitrosodicyclohexylamine (N-NO-DCHA) can be formed by nitrosation from dicyclohexylamine during the application of these formulations. As most of the nitrosamines are genotoxic carcinogens, the genotoxic potential of N-NO-DCHA was investigated in V79 Chinese hamster cells in the single cell gel assay and the sister chromatid exchange (SCE) test. In addition, N-NO-DCHA cytotoxicity was determined in the neutral red assay. Neutral red uptake was suppressed up to 50% after 24 h incubation at a concentration of approximately 135 microM. In the single cell gel assay, a significantly elevated and dose-dependent induction of DNA lesions was detected in a concentration range from 5 microM to 100 microM (P<0.001). The use of proteinase K (1 mg/ml) in the lysing solution did not influence these results. In the SCE analysis, a significant induction of SCE was found at a minimum concentration of 5 microM N-NO-DCHA as well. A dose-dependent SCE induction could be detected up to the maximum concentration tested in the assay (100 microM). In conclusion, N-NO-DCHA is genotoxic in V79 cells in the single cell gel assay and the SCE test. With respect to human health hazard prevention, a substitution of dicyclohexylaminexnitrite in chemical formulations used to prevent corrosion is recommended.

Effects of emotional arousal in the cerebral hemispheres: a study of oscillatory brain activity and event-related potentials

OBJECTIVE

The present study aimed at examining the time course and topography of oscillatory brain activity and event-related potentials (ERPs) in response to laterally presented affective pictures.

METHODS

Electroencephalography was recorded from 129 electrodes in 10 healthy university students during presentation of pictures from the international affective picture system. Frequency measures and ERPs were obtained for pleasant, neutral, and unpleasant pictures.

RESULTS

In accordance with previous reports, a modulation of the late positive ERP wave at parietal recording sites was found as a function of emotional arousal. Early mid gamma band activity (GBA; 30-45 Hz) at 80 ms post-stimulus was enhanced in response to aversive stimuli only, whereas the higher GBA (46-65 Hz) at 500 ms showed an enhancement of arousing, compared to neutral pictures. ERP and late gamma effects showed a pronounced right-hemisphere preponderance, but differed in terms of topographical distribution.

CONCLUSIONS

Late gamma activity may represent a correlate of widespread cortical networks processing different aspects of emotionally arousing visual objects. In contrast, differences between affective categories in early gamma activity might reflect fast detection of aversive stimulus features.

In vitro effects of mycophenolic acid on the nucleotide pool and on the expression of adhesion molecules of human umbilical vein endothelial cells

The immunosuppressive drug mycophenolate mofetil (MMF) and its active metabolite mycophenolic acid (MPA) selectively inhibit inosine 5'-monophosphate dehydrogenase (IMPDH), and therefore interfere with cellular guanine nucleotide biosynthesis. IMPDH is additionally involved in the synthesis of membrane glycoproteins, some of which are adhesion receptors known to play an active part in the regulation of cell-cell contacts, which are crucial in the process of recruitment and transendothelial infiltration of activated leucocytes in the transplanted organ. As a consequence, MPA leads to a reduction of cellular infiltrates in the course of transplant rejection. In the present study, the effects of MPA on human umbilical vein endothelial cells (HUVEC) are investigated at both molecular and cellular levels. In our experiments, HUVECs are treated with tumor necrosis factor-alpha (TNF-alpha; 10 ng/ml) in order to mimic activation occurring at a rejection crisis. The dose-dependent influence of concomitant incubation with MPA (5-20 micromol/l; 48 h, 37 degrees C, 5% CO2) on their intracellular nucleotide profile is observed by determining the concentrations of purine and pyrimidine nucleotides, using a HPLC method based on solvent generated ion-exchange. The possibility of synergistic effects is investigated by incubating endothelial cells with mixtures of three different immunosuppressants (mycophenolic acid; cyclosporin A, 100 ng/ml; prednisolone, 1 micromol/l)--a combination commonly used after transplantation--varying the amount of MPA (5-20 micromol/l). Stimulation with TNFalpha does not significantly modulate the intracellular levels of nucleotides quantitated. In the presence of MPA concentrations of at least 5 micromol/l, GTP levels (68+/-12%) are significantly decreased compared to controls (100%). At a concentration of 20 micromol/l MPA, the GTP amount is reduced to 58+/-7%. In contrast to these observations, the levels of UDP and UTP are increasing significantly under coincubation with MPA concentrations greater than 5 micromol/l. At 20 micromol/l MPA, UDP and UTP are increased to 147+/-19% and 114+/-11%, respectively. All other nucleotides (CTP, ADP, ATP) reveal no significant alterations in their intracellular concentrations under the conditions applied. Incubation of TNFalpha-treated HUVEC monolayers, with a mixture of three immunosuppressive drugs varying the amount of MPA, show no significant differences compared with the data observed after incubation with MPA alone. In addition, the influence of MPA (10 micromol/l) on a cellular level is observed by measuring the cell surface expression of adhesion molecules on cytokine-stimulated HUVECs, using TNFalpha (10 ng/ml), interferon-gamma (100 ng/ml), interleukin-1beta (10 ng/ml) and interleukin-8 (20 ng/ml). Expression of the intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), endothelial leucocyte adhesion molecule-1 (ELAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1) was assessed by flow cytometry. Activation of endothelial cell monolayers with TNFalpha significantly increases the mean fluorescence intensity of VCAM-1 (361+/-14%) and ICAM-1 (429+/-47%) surface expression, compared to controls, and additionally induces E-selectin expression (2919+/-134%). The same tendencies, but in a lesser degree, are observed under stimulation of cells with either IFNgamma or IL-1beta. Incubation with a combination of TNFalpha and MPA leads to a significant reduction in VCAM-1 (329+/-13%) and E-selectin (2613+/-167%) expression, compared to the values obtained for HUVEC incubated with the cytokine alone. Treatment of the cells with IL-1beta/MPA also reduces the expression of VCAM-1 to a level significantly lower than the level observed after stimulation with IL-1beta. Incubation with MPA alone reveals no significant modulation in the expression of all surface molecules tested compared to the values of unstimulated HUVECs. The experiments show that the immunosuppressive action of MPA not only inhibits lymphocyte proliferation but also decreases the expression of adhesion molecules on endothelial cells, which are the first target of the cellular rejection process.

Determination of the effects of mycophenolic acid on the nucleotide pool of human peripheral blood mononuclear cells in vitro by high-performance liquid chromatography

Immunosuppressive drugs are needed to prevent the rejection of transplanted organs by the immune system. Immunosuppressive antimetabolites act by interrupting cell metabolism. Their mechanism of action can be studied in vitro by measuring the inhibition of biochemical activities which is reflected by changes in the nucleotide content. In our experiments, human peripheral blood mononuclear cells (PBMC) isolated from healthy volunteers were used. After PBMC stimulation with phytohaemagglutinin (PHA) to mimic activation occurring at a rejection crisis, cells were exposed to varying concentrations of different immunosuppressants (i.e., mycophenolic acid, cyclosporin A and prednisolone) for 68 h at 37 degrees C. Changes in nucleotide content were observed by determining the concentrations of 15 nucleotides using a newly developed HPLC method. The results obtained for mycophenolic acid (MPA; final concentrations in a range between 0.1 and 5 micromol/l), cyclosporin A (CsA; final concentrations between 100 ng/ml and 1 microg/ml) and prednisolone (final concentrations between 0.5 and 10 micromol/l) are given as percentage changes in nucleotide content versus controls and are expressed as mean +/- confidence interval. The possibility of synergistic effects was investigated by incubating the cells with mixtures of all three immunosuppressive drugs varying the amount of mycophenolic acid. In addition, we have shown the effects of MPA/guanosine co-incubation on the intracellular nucleotide levels. Stimulation of peripheral blood mononuclear cells with phytohaemagglutinin led to a significant increase of pyrimidine and purine nucleotides versus control values (100%). Pyrimidine (CTP, UDP, UTP) and purine nucleotides (GDP, GTP, ADP, ATP) were elevated up to 153+/-14% and 142+/-17%, respectively. Under co-incubation of cells with MPA, the GTP level decreased in a dose-related manner to 56+/-3% of control at a MPA final concentration of 5 micromol/l. Concomitantly, an increase of UTP values to 203+/-18% versus control was observed under co-incubation with 1 micromol/l MPA. Co-incubation of mononuclear cells with guanosine (50 micromol/l) compensated for the effects of MPA on intracellular GTP levels. Combination of MPA, CsA and prednisolone did not alter intracellular nucleotide profiles of PBMC compared to those under MPA incubation alone. The depletion of the guanine nucleotide pool and concomitant increase of uridine nucleotides under the influence of the immunosuppressive drug mycophenolic acid is caused by its inhibitory effects on the key enzyme of de novo purine biosynthesis, inosine 5'-monophosphate dehydrogenase (IMPDH).

Functional correlates of macroscopic high-frequency brain activity in the human visual system

The present article reviews empirical findings of large-scale gamma oscillations in the human brain, in the context of their functional correlates. Evidence supporting the fact that high-frequency neuronal oscillations are involved in several aspects of visual processing is presented, with a focus on bottom-up and top-down visual feature processing, selective attention, and emotional evaluation. This evidence suggests that visual processing involves the integrated activity of wide spread neuronal assemblies that can be studied with respect to time course and topography, employing frequency-domain analyses. Possible mechanisms underlying these phenomena are considered. Furthermore, the effects of attention and motivation, as well as characteristics of experimental paradigms are discussed as determinants of reliability and validity of measures of high-frequency oscillations.

Diversity of endophytic fungi of single Norway spruce needles and their role as pioneer decomposers

The diversity of endophytic fungi within single symptomless Norway spruce needles is described and their possible role as pioneer decomposers after needle detachment is investigated. The majority (90%) of all 182 isolates from green intact needles were identified as Lophodermium piceae. Up to 34 isolates were obtained from single needles. Generally, all isolates within single needles had distinct randomly amplified microsatellite (RAMS) patterns. Single trees may thus contain a higher number of L. piceae individuals than the number of their needles. To investigate the ability of needle endophytes to act as pioneer decomposers, surface-sterilized needles were incubated on sterile sand inoculated with autoclaved or live spruce forest humus layer. The dry weight loss of 13-17% found in needles after a 20-week incubation did not significantly differ between the sterilized and live treatments. Hence, fungi surviving the surface sterilization of needles can act as pioneer decomposers. A considerable portion of the needles remained green during the incubation. Brown and black needles, in which the weight loss had presumably taken place, were invaded throughout by single haplotypes different from L. piceae. Instead, Tiarasporella parca, a less common needle endophyte, occurred among these invaders of brown needles. Needle endophytes of Norway spruce seem thus to have different abilities to decompose host tissues after needle cast. L. piceae is obviously not an important pioneer decomposer of Norway spruce needles. The diversity of fungal individuals drops sharply when needles start to decompose. Thus, in single needles the decomposing mycota is considerably less diverse than the endophytic mycota.

Genotoxic effects of N-nitrosodicyclohexylamine in isolated human lymphocytes

Dicyclohexylamine x nitrite is classified as an "experimental equivocal tumorigenic agent" by the National Toxicology Program. Since no genotoxic effects of the substance itself are known, the reported tumorigenic potential of dicyclohexylamine x nitrite could be due to generation of N-nitrosodicyclohexylamine (N-NO-DCHA), which occurs under conditions of use and can be detected in foils that contain dicyclohexylamine x nitrite. Therefore, we investigated possible mutagenic properties of N-NO-DCHA in the Ames test and the cytokinesis-block micronucleus assay with human lymphocytes. Since N-NO-DCHA is not commercially available, the substance was synthesized and purified by thin-layer chromatography. Identity was confirmed by gas chromatography/mass spectroscopy (GC/MS) and 1H- and 13C-NMR. More than 97% purity was achieved. Stability and availability in the solvent were checked by GC/MS. N-NO-DCHA induced micronuclei in isolated human lymphocytes at a dose range of 15-100 micrograms/ml (= 71.4-476.2 microM), exceeding the base rate significantly at one or two nontoxic concentrations in four out of six experiments. For the Ames test, arochlor-1254-, beta-naphthoflavone/phenobarbital- and pyrazole-induced S9-fractions were used with Salmonella typhimurium TA100, TA1535, TA98 and TA104. No effects were seen in the Ames test, with the exception of microcolony induction at doses higher than 250 micrograms (= 1.2 mmol) N-NO-DCHA/plate using TA104 and 20% arochlor-1254 induced S9 at pH 6.5. In conclusion, N-NO-DCHA was negative in the Ames test using TA98, TA100 and TA1535, inconclusive using TA104, and weakly genotoxic in the in vitro micronucleus test with isolated human lymphocytes. With regard to the tumorigenicity of the majority of nitrosamines, our data underline the necessity of further studies on possible genotoxic effects of N-NO-DCHA.

[High freuquency oscillatory activity in the human brain]

Synchronized neural activity in animal visual cortex in the frequency range above 20 Hz, the gamma band, has been proposed as a signature of temporal feature binding. More and more research in humans by means of noninvasive electrophysiological recordings was stimulated by these studies. Here, research on evoked and induced gamma band activity in human EEG and MEG mainly in the auditory and visual modality is reviewed and their role in perceptual processes, feature integration and language processing is discussed. In addition, research on the attentional modulation of gamma band activity is reviewed. In contrast to evoked gamma band activity, which occurs right after stimulus onset, induced gamma band activity can be recorded with a latency of 200 to 400 ms and a frequency range of 30 to 95 Hz. Cumulative consistent experimental evidence allows us to conclude that gamma band activity in the human cortex is related to neuronal information processing and cognitive functions, e.g. memory processes. The findings are discussed in the light of different functional theories of induced gamma band activity.

Serum crosslaps in comparison to serum osteocalcin and urinary bone resorption markers

In this study we evaluated the routine practice and clinical application of serum crosslaps to urinary-crosslaps, -N-telopeptide-related fraction of type 1 collagen, -deoxpyridinoline, -totalpyridinoline and serum osteocalcin. The utility of both the serum and urine immunoassays for bone formation and resorption marker were tested in a cohort of 593 female and male patients from our outpatient clinic for osteology and rheumatology and compared to important osteoporosis risk factors like age, gender, E2 deficiency, bone density and chronic renal failure. The biochemical maker of bone formation, serum osteocalcin exhibit significant correlations to all five tested serum and urinary markers of bone resorption (p < 0.0001) crosswise to all different groups of patients. The group of chronic renal failure patients showed no significant correlation between the tested bone turnover parameters and the serum creatinine level except a significant increase and correlation for serum crosslaps and for the ratio of serum and urinary crosslaps. Associations between the age of the patients and the markers of bone turnover were rather poor. We found a significant, negative association between serum and urinary bone turnover markers and bone density and were interested, whether in patients with bone density < 2.5 SD an enhanced bone turnover could be detected in the same way as for E2 deficiency. Applying a discriminant analysis it was possible to discriminate between the patient with BD < 2.5 SD and those with BD > 1.0 SD with a sensitivity of 70% and a specificity of 65% using serum crosslaps. In case of urinary crosslaps the discriminatory power was slightly lower (sensitivity: 65.6%, specificity: 67.5%) and for serum osteocalcin the discriminatory power was negligible higher (sensitivity: 79%, specificity: 56%). The highly significant correlation between the urinary and serum crosslinked peptides by ELISA and serum osteocalcin supports the concept that these respective indices of bone formation and resorption both in urine and serum reflect a coupled process in vivo with sensitivity and specificity to pathological bone density, estrogen deficiency and chronic renal failure.

Suppression of the auditory middle-latency response and evoked gamma-band response in a paired-click paradigm

When two clicks are presented within 500 ms and the clicks are separated by several seconds, a typical finding is a suppression of the amplitude of the P50 component of the middle-latency auditory-evoked response. In the present study, we investigated whether only the P50 or also the earlier components Po, Na, Pa and Nb, and the exogenous components N100 and P200 exhibit an amplitude suppression to the second click. In addition, we studied the suppression behaviour of the auditory-evoked 40-Hz gamma-band response in the time and frequency domain. We found a significant amplitude suppression to the second click for all components of the auditory-evoked potential following Po, which was most pronounced at electrode Cz. When testing the successive peaks and troughs of the evoked 40-Hz gamma-band response in the time domain, we found a significant amplitude suppression for peaks and troughs with the same latency and polarity as the middle-latency components following Po, which was most pronounced at electrodes Fz and Cz. Consequently, the amplitude of the 40-Hz evoked gamma-band response in the frequency domain paralleled the findings of the time domain, with a significant amplitude suppression to the second tone, which was most pronounced at electrodes Fz and Cz. Results are discussed with reference to the early sensory-gating hypothesis.

Modulation of induced gamma band activity in the human EEG by attention and visual information processing

Here we present a series of four studies aimed to investigate the link between induced gamma band activity in the human EEG and visual information processing. We demonstrated and validated the modulation of spectral gamma band power by spatial selective visual attention. When subjects attended to a certain stimulus, spectral power was increased as compared to when the same stimulus was ignored. In addition, we showed a shift in spectral gamma band power increase to the contralateral hemisphere when subjects shifted their attention to one visual hemifield. The following study investigated induced gamma band activity and the perception of a Gestalt. Ambiguous rotating figures were used to operationalize the law of good figure (gute Gestalt). We found increased gamma band power at posterior electrode sites when subjects perceived an object. In the last experiment we demonstrated a differential hemispheric gamma band activation when subjects were confronted with emotional pictures. Results of the present experiments in combination with other studies presented in this volume are supportive for the notion that induced gamma band activity in the human EEG is closely related to visual information processing and attentional perceptual mechanisms.

Mutagenicity of N-nitrosodiethylamine in the Ames test with S. typhimurium TA1535 is due to volatile metabolites and is not dependent on cytochrome P4502E1 induction

N-Nitrosodiethylamine (NDEA) is carcinogenic in all investigated animal species at relatively low dosages. No threshold has been detected for these carcinogenic effects. The substance has been extensively investigated in various in vitro systems, revealing only weak mutagenicity at relatively high dosages. We reinvestigated NDEA in the Ames test with Salmonella typhimurium TA1535 to establish appropriate modifications of the standard Ames test protocol, to achieve a dose-dependent mutagenic response at a reasonably low dose range. Two main modifications were evaluated. Since the metabolism of dialkylnitrosamines is postulated to be mainly dependent on cytochrome P4502E1, a pyrazole-induced rat liver S9 was applied. The second modification involved a gastight preincubation, since metabolites of NDEA might evaporate from the incubation mixture. Cytochrome P4502E1 induction in Wistar rats was achieved by pyrazole treatment. For comparison, a rat liver S9-fraction produced by beta-naphtoflavone/phenobarbital induction was used. N-Nitrosopyrrolidine served as positive control for pyrazole-induced S9-mix with TA1535. NDEA showed no mutagenic response under all test conditions in the presence of pyrazole-induced S9-mix. A strong mutagenic response, exceeding the base rate up to 15-fold at a dose range of 25-1000 microg/plate, was observed using beta-naphtoflavone/phenobarbital-induced S9-mix, gastight preincubation and TA1535. In conclusion the Ames test with gastight preincubation can be useful for the testing of volatile compounds or substances leading to gaseous metabolites. The weak response of NDEA in the Ames test observed previously seems mainly to be due to the volatile character of its mutagenic metabolites. Our results do not support the hypothesis that cytochrome P4502E1 is a major toxifying enzyme for the formation of Ames-test-positive metabolites from NDEA.

MEG gamma band activity in schizophrenia patients and healthy subjects in a mental arithmetic task and at rest

OBJECTIVES

High frequency oscillations have been suggested as a correlate of cognitive processes and have recently also been implicated in aberrant forms of information processing. The present study investigated whether magnetoencephalographic (MEG) gamma band activity (20-71 Hz) can serve as an index of cognitive processes in the absence of external stimulation and to what extent gamma activity differs between healthy people and schizophrenia patients.

METHODS

The amount and topography of MEG power in the gamma band range was examined in 15 schizophrenia patients and 15 healthy comparison subjects while performing a complex mental arithmetic task and at rest.

RESULTS

In healthy subjects a left frontal and left fronto-temporal increase in gamma power was observed during mental arithmetic. Schizophrenia patients either failed to display such a task effect (30-45 Hz) or had reversed lateralization with enhanced activity over right frontal and right fronto-temporal regions under cognitive demands (45-71 Hz). In the frequency band from 60 to 71 Hz patients showed less gamma at fronto-temporal, posterio-temporal and occipital sites irrespective of the task.

CONCLUSIONS

These results indicate, first, that gamma topography can index cognitive activation in a very complex and purely internal task. Second, groups differed in the pattern of activation during the task, a result which may be consistent with working memory dysfunction in schizophrenia. Third, the general topographic difference between healthy subjects and patients is in line with the notion of abnormalities in the thalamocortical circuit in schizophrenia.

In vitro effects of mycophenolic acid on cell cycle and activation of human lymphocytes

The immunosuppressant mycophenolic acid (MPA) selectively inhibits proliferation of T- and B-lymphocytes by blocking inosine 5'-monophosphate-dehydrogenase (IMPDH), the key enzyme for de-novo-synthesis of guanine nucleotides. In an in vitro study the effects of MPA on human peripheral blood lymphocyte activation markers and on cell cycle characteristics were investigated. Mononuclear cells from healthy volunteers were incubated with phytohaemagglutinin (PHA) and increasing doses of MPA. After 72 h incubation an aliquot of the cells was stained with propidium iodide and measured by FACS analyses to assess the DNA shape. In addition, the expression of the activation markers HLA-DR and CD25 on T- and B-lymphocytes was determined by flow cytometry analysis.PHA stimulation led to a significant increase of the S-phase of cell cycle. PHA stimulation clearly increased mean fluorescence intensity (MFI) of HLA-DR expression on B-lymphocytes. PHA stimulation also elevated the number of CD25 positive B-lymphocytes. Expression of HLA-DR on T-lymphocytes was not influenced by PHA, whereas CD25 expression and MFI significantly increased. All the observed PHA induced effects were reduced by co-incubation with increasing doses of MPA. The data presented show that in vitro the immunosuppressive effect of MPA can be demonstrated using FACS technology on a cellular level. MPA leads to an inhibition of cell cycle proliferation in peripheral blood lymphocytes.

Serum osteocalcin and urinary crosslaps are suitable markers of bone turnover in response to short-term hormone replacement therapy

In this study we evaluated the effect of short-term hormone replacement therapy (HRT) on bone formation (serum osteocalcin) and resorption markers (urinary type I collagen peptides (crosslaps), urinary total free pyridinoline (TPYRI) and urinary free deoxypyridinoline (DPYRI)) as well as female sex hormones (serum estradiol, follicle stimulating hormone (FSH) and luteinizing hormone (LH)) in a group of early postmenopausal women with severe estrogen deficiency. The 46 healthy postmenopausal women with serum estradiol levels < 10 ng/l were subsequently divided into two groups, according to their compliance with HRT. In the group taking HRT significant changes from baseline values could be observed in estradiol, FSH, urinary crosslaps and serum osteocalcin levels after 6 months, whereas no changes could be observed in LH, TPYRI and DPYRI from baseline values. In the group which refused HRT all values were increased relative to baseline values, indicating increased bone turnover. Serum osteocalcin and urinary crosslaps were significantly decreased in women taking HRT in comparison to the group refusing HRT. After 6 months the treated patients showed a decrease in urinary crosslaps of 42% (SD 12%) and in serum osteocalcin of 24% (SD 6%) in comparison with baseline values. In patients who refused HRT, urinary crosslaps were increased by 43% (SD 20%) and serum osteocalcin levels decreased by 2% (SD 9%) compared to baseline values. In postmenopausal women suffering from severe estrogen deficiency (estradiol < 10 ng/l) serum osteocalcin and urinary crosslaps are significantly increased, indicating a clear correlation between estrogen deficiency and an increase in bone resorption as well as bone formation. The recommended HRT dose was sufficient to reduce the rate of bone turnover to premenopausal values. Serum osteocalcin and urinary crosslaps are suitable candidates not only for the assessment of a high postmenopausal bone turnover, but also for monitoring the response to and for verifying the actual intake of HRT or other antiresorptive treatment.