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D Ebert

Publications and source records attributed to D Ebert.

At least 19 recordsLinked to original sources
PubMed2006

Quantitative PCR to detect, discriminate and quantify intracellular parasites in their host: an example from three microsporidians in Daphnia.

Reliable detection, discrimination and quantification of parasites are important for host-parasite studies and diagnostics. Microsporidial infections are problematic in this respect. Their discrimination and quantification using light microscopy is difficult because spores are the only light microscopically visible form of the parasite and they offer few distinct characters. We developed a quantitative PCR (qPCR) assay based on SYBR Green chemistry to quantify the microsporidia Glugoides intestinalis, Octosporea bayeri and Ordospora colligata in their host, the freshwater crustacean Daphnia magna. The assay allows the quantification of infection intensities in whole animals and is more than an order of magnitude more sensitive than light microscopy. Sampling and DNA extraction account for more than 90% of the residual variance in infection intensity data and this variance considerably impairs the resolution of qPCR. Where higher resolution is required, we propose using the ratio of parasite to host DNA as the measure of infection intensity. We show that this measure is robust and greatly improves resolution of qPCR. Additionally, this method can be applied to compare samples of unequal volume.

Animals↗
PubMed2006

Founder events as determinants of within-island and among-island genetic structure of Daphnia metapopulations.

The genetic structure of metapopulations offers insights into the genetic consequences of local extinction and recolonization. We studied allozyme variation in rock pool metapopulations of two species of waterfleas (Daphnia) with the aim to understand how these dynamics influence genetic differentiation. We screened 138 populations of D. magna and 65 populations of D. longispina from an area in the archipelago of southern Finland. The pools from which they were sampled are separated by distances between 1.5 and 4710 m and located on a total of 38 islands. The genetic population structure of the two species was strikingly similar, consistent with their similar metapopulation ecology. The mean F(PT) value (differentiation among pools with respect to the total metapopulation) was 0.55 and a hierarchical analysis showed that genetic differentiation was strong (>0.25) among pools within islands as well as among whole islands. Within islands, pairwise genetic differentiation increased with geographic distance, indicating isolation by distance due to spatially limited dispersal. Previous studies have shown strong founder events occurring during colonization in our metapopulation. We suggest that the genetic population structure in the studied metapopulations is largely explained by three consequences of these founder events: (i) strong drift during colonization, (ii) local inbreeding, which results in hybrid vigour and increased effective migration rates after subsequent immigration, and (iii) effects of selection through hitchhiking of neutral genes with linked loci under selection.

Animals↗
PubMed2005

Galantamine: a cholinergic patch in the treatment of alcoholism: a randomized, placebo-controlled trial.

OBJECTIVES: The involvement of the central cholinergic system in alcohol abuse behavior is well known. It is possible that the reinforcing effects of ethanol are partially mediated by nicotinic receptors, which modulate neurotransmitter release. It was demonstrated that the application of a cholinesterase inhibitor reduces alcohol consumption in alcohol-preferring rats. This suggests that galantamine (GAL), a cholinesterase inhibitor, could be effective when seeking to prolong abstinence in recently detoxified alcoholics. This study represents the first reported clinical trial of a cholinergic drug in alcohol-relapse prevention. PATIENTS AND METHODS: We investigated the efficacy and safety of GAL by conducting a 24-week randomized, placebo-controlled, multicentric clinical trial on 149 recently detoxified alcoholics. Survival analyses (Kaplan-Meier) were performed to reveal evidence of prolonged abstinence periods in patients who received GAL. RESULTS: Our findings did not support our hypothesis. GAL did not extend the time to first severe relapse. However, additional post hoc analyses suggest that relapsed patients treated with GAL consume less ethanol per drinking day than patients treated with placebo. CONCLUSIONS: GAL seems to be ineffective when used in relapse prevention of detoxified alcoholics. It is possible that alcohol needs to be "on board" for GAL to be beneficial. This could explain why our post hoc analysis showed that GAL possibly reduces the alcohol consumption of relapsers. If confirmed, GAL could play a role in the reduction of harmful alcohol use and at-risk consumption.

Administration, Cutaneous↗
PubMed2005

Different mechanisms of transmission of the microsporidium Octosporea bayeri: a cocktail of solutions for the problem of parasite permanence.

Periods of low host density impose a constraint on parasites with direct transmission, challenging their permanence in the system. The microsporidium Octosporea bayeri faces such constraint in a metapopulation of its host, the cladoceran Daphnia magna, where ponds frequently lose their host population due to ponds drying out in summer and freezing in winter. We conducted experiments aimed to investigate the mechanisms of transmission of O. bayeri, and discuss how these mechanisms could contribute to the parasite's permanence in the system. Spores accumulate in the fat cells and the ovaries of the host, and vary in morphology, possibly corresponding to 3 different spore types. Horizontal transmission occurred through the release of spores from dead hosts, with the proportion of infected hosts depending on the spore dose. Further, spores are able to persist outside the host both in dry and wet conditions. Vertical transmission occurred to both parthenogenetic and sexual offspring. The former were invariably infected, while the sexually produced resting eggs (= ephippia) had a less efficient transmission. The parasite may be carried by the ephippia, and thus disperse to new ponds together with the host. Together, these mechanisms may allow the parasite to endure periods of harsh environmental conditions both outside and inside the host.

Animals↗
PubMed2005

Phenotypic plasticity of host-parasite interactions in response to the route of infection.

The microsporidium Octosporea bayeri can infect its host, the planktonic crustacean Daphnia magna, vertically and horizontally. The two routes differ greatly in the way the parasite leaves the harbouring host (transmission) and in the way it enters a new, susceptible host (infection). Infections resulting from each route may thus vary in the way they affect host and parasite life-histories and, subsequently, host and parasite fitness. We conducted a life-table experiment to compare D. magna infected with O. bayeri either horizontally or vertically, using three different parasite isolates. Both the infection route and the parasite isolate had significant effects on host life-history. Hosts matured at different ages depending on the parasite isolate, and at a size that varied with infection route. The frequency of host sterility and the host's life-time reproductive success were affected by both the infection route and the parasite isolate. The infection route also affected parasite life-history. The production of parasite spores was much higher in vertically than in horizontally infected hosts. We found a trade-off between the production of spores (the parasite's horizontal fitness component) and the production of infected host offspring (the parasite's vertical fitness component). This study shows that hosts and parasites can react plastically to different routes of infection, suggesting that ecological factors that may influence the relative importance of horizontal and vertical transmission can shape the evolution of host and parasite life histories, and, consequently, the evolution of virulence.

Age Factors↗
PubMed2004

Within-host dynamics of a microsporidium with horizontal and vertical transmission: Octosporea bayeri in Daphnia magna.

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence parasite virulence, transmission to new hosts, and, consequently, epidemiology and evolution. Here we describe the within-host dynamics of 3 spore-types of O. bayeri from infections that were acquired either horizontally or vertically. In all treatments the number of spores increased exponentially until spore density reached a plateau, suggesting density-dependent within-host growth. The spore types seen differ in their growth dynamics, suggesting different roles in the parasite life-cycle. Horizontally-infected hosts harboured significantly fewer spores than vertically-infected hosts. Further, host survival was affected by infection route, with mortality being higher in horizontal infections than in vertical infections. Our results suggest that different routes of infection have an immediate effect on within-host parasite growth and thus on parasite fitness and epidemiology.

Animals↗
PubMed2004

Chronic antidopaminergic medication might affect amygdala structure in patients with schizophrenia.

BACKGROUND: Recently amygdala enlargement has been reported in patients with schizophrenia like psychosis of epilepsy. The effect of antipsychotic medication on amygdala structure has not been investigated so far. There is theoretical evidence to support the assumption that dopaminergic neurotransmission might affect neuronal plasticity. METHODS: In order to analyze the influence of chronic antidopaminergic medication on amygdala structure we compared amygdala volumes in patients with schizophrenia like psychosis of epilepsy (POE) treated with neuroleptic medication (n = 11) to patients with POE not treated with such medication (n = 15), patients with epilepsy alone (n = 24) and healthy control subjects (n = 20). RESULTS: Analyzing our data with a factorial ANOVA approach, we found a significant effect of the factor medication in that patients treated with antipsychotic medication displayed a "normalization" of the increased amygdala volumes observed in the untreated patient group. CONCLUSION: This observation supports the assumption that antidopaminergic medication might affect the amygdala structure.

Amygdala↗
PubMed2003

[Characteristics of hospitalized geriatric patients--a comparison of two cohorts using the screening of the Arbeitsgemeinschaft Geriatrisches Basisassessment (AGAST)].

The geriatric screening according to AGAST (Arbeitsgruppe Geriatrisches Basisassessment) contains functional and diagnosis related items, and risk indicators of prognostic relevance, particularly in hospitalized patients. In a retrospective, cohort study, we compared the screening results in 250 consecutive patients of geriatric in-hospital acute care, and 250 consecutive patients of geriatric in-hospital rehabilitation, as well as demographic characteristics, diagnoses, and functional status as measured by the Barthel index. There was a trend indicating the total number of positive screening findings being higher with older age. Positive correlations with age were found for hearing, leg function, and cognitive function in female patients. There were also associations between the frequencies of certain screening findings with diagnostic categories. Apart from the different official manner of admission to geriatric acute care or geriatric rehabilitation, there were differences between the cohorts in age, living place before hospitalization, discharge location, spectrum of diagnoses, and the degree of functional impairment. The screening results indicated that prognostic risk factors were not equally distributed among the study cohorts. These were, in particular, urinary incontinence, poor nutritional status, impaired cognitive function, and depressive mood. There were associations between risk frequency as indicated by the screening and complicated hospital stay, functional outcome, and death. Combined with additional data, the screening according to AGAST appears to be suitable for meaningful comparisons of different groups of geriatric patients.

Age Factors↗
PubMed2003

A voxel-based morphometric MRI study in female patients with borderline personality disorder.

Subtle prefrontal and limbic structural abnormalities have been reported in borderline personality disorder (BPD). In order to further validate the previously reported findings and to more precisely describe the nature of the structural change we performed a voxel-based morphometric (VBM) study in patients with BPD. Twenty female patients with BPD and 21 female healthy controls were investigated. High-resolution 3-D datasets were acquired and analyzed following an optimized protocol of VBM in the framework of statistical parametric mapping (SPM99). Gray matter volume loss was found in the left amygdala. No other differences in gray or white matter volume or density were found anywhere else in the brain. Our findings support the hypothesis that temporolimbic abnormalities play a role in the pathophysiology of BPD. Prefrontal structural alterations in BPD were not observed in this study.

Adult↗
PubMed2003

Psychopathological profile in patients with severe bilateral hippocampal atrophy and temporal lobe epilepsy: evidence in support of the Geschwind syndrome?

Bilateral symmetrical hippocampal atrophy (BHA) has been implicated as a possible causal element in various neuropsychiatric disorders, in particular depressive disorder and schizophrenia. To test the hypothesis that bilateral symmetrical severe volume loss of the hippocampi is of causal relevance to these psychiatric syndromes rather than an epiphenomenon we assessed the psychopathology in a group of patients with temporal lobe epilepsy (TLE) and very severe bilateral symmetrical hippocampal atrophy and compared it with that of a patient control group. Patients with TLE and hippocampal volumes smaller than three standard deviations below the mean of a control population were identified and compared with a matched patient population with normal hippocampal volumes. Psychopathology was assessed by blinded trained psychiatrists using the Present State Examination and Neurobehavioral Inventory. The prevalence of psychiatric syndromes was high in both patient groups; however, there was no significant difference between the two groups. With use of the more specific Neurobehavioral Inventory a psychopathological pattern reminiscent of the Geschwind syndrome emerged when patients with BHA were characterized by caregivers. While BHA does not result in an increased prevalence of specific psychiatric syndromes, specific symptoms that characterize the Geschwind syndrome like hypergraphia and hyposexuality might be pathogenically related to hippocampal atrophy.

Adult↗
PubMed2003

The infection rate of Daphnia magna by Pasteuria ramosa conforms with the mass-action principle.

In simple epidemiological models that describe the interaction between hosts with their parasites, the infection process is commonly assumed to be governed by the law of mass action, i.e. it is assumed that the infection rate depends linearly on the densities of the host and the parasite. The mass-action assumption, however, can be problematic if certain aspects of the host-parasite interaction are very pronounced, such as spatial compartmentalization, host immunity which may protect from infection with low doses, or host heterogeneity with regard to susceptibility to infection. As deviations from a mass-action infection rate have consequences for the dynamics of the host-parasite system, it is important to test for the appropriateness of the mass-action assumption in a given host-parasite system. In this paper, we examine the relationship between the infection rate and the parasite inoculum for the water flee Daphnia magna and its bacterial parasite Pasteuria ramosa. We measured the fraction of infected hosts after exposure to 14 different doses of the parasite. We find that the observed relationship between the fraction of infected hosts and the parasite dose is largely consistent with an infection process governed by the mass-action principle. However, we have evidence for a subtle but significant deviation from a simple mass-action infection model, which can be explained either by some antagonistic effects of the parasite spores during the infection process, or by heterogeneity in the hosts' susceptibility with regard to infection.

Animals↗
PubMed2003

A psychopathological study into the relationship between attention deficit hyperactivity disorder in adult patients and recurrent brief depression.

OBJECTIVE: Clinical and epidemiological observations and neurobiological data suggest that there might be an inherent link between attention deficit hyperactivity disorder (ADHD) and recurrent brief depression (RBD). In this psychopathological study, we investigated the comorbidity between these two conditions. METHOD: Using an index patient approach 40 adult out-patients fulfilling the criteria for ADHD were investigated for lifetime history of RBD and another 40 out-patients with the primary diagnosis of RBD were investigated for a lifetime history of ADHD. RESULTS: We found a high prevalence of RBD in patients with ADHD (70%) while the prevalence of ADHD in the index sample with RBD was smaller (about 40%). CONCLUSION: In terms of comorbidity ADHD was the second commonest psychiatric disorder in patients with RBD next to other affective disorders. The psychopathological pattern of lifetime comorbidity might be of clinical relevance in terms of medical treatment.

Adult↗
PubMed2003

The effects of parasitism and inbreeding on the competitive ability in Daphnia magna: evidence for synergistic epistasis.

Synergistic epistasis for fitness is often assumed in models of how selection acts on the frequency and distribution of deleterious mutations. Evidence for synergistic epistasis would exist if the logarithm of fitness declines more quickly with number of deleterious mutations, than predicted by a linear decline. This can be studied indirectly by quantifying the effect of different levels of inbreeding on fitness. Here, six sets (different genetic backgrounds) of three increasingly inbred Daphnia magna clones were used to assess their relative fitness according to changes in frequency in a competition experiment against a tester clone. A novelty of the mating procedure was that the inbreeding coefficients (F) of the three clones belonging to each set increased in steps of 0.25 independent of the (unknown) inbreeding coefficient of the common ancestor. The equal increase of the inbreeding coefficients is important, because deviations influence the quantification of inbreeding depression, its variance and the detection of epistasis. In a simple mathematical model we show that when working with a partially inbred population inbreeding depression is underestimated, the variance of fitness is increased, and the detection of epistasis more difficult. Further, to examine whether an interaction between inbreeding and parasitism exists, each inbred clone was tested with and without a microsporidium infection (Octosporea bayeri). We found a nonlinear decrease of the logarithm of fitness across the three levels of inbreeding, indicating synergistic epistasis. The interaction term between parasitism and inbreeding was not significant. Our results suggest that deleterious mutations may be purged effectively once the level of inbreeding is high, but that parasitism seems not to influence this effect.

Animals↗
PubMed2002

Frontoorbital volume reductions in adult patients with attention deficit hyperactivity disorder.

Attention deficit hyperactivity disorder (ADHD) is a common psychiatric disorder in childhood and adolescence and in a considerable number of patients it persists into adulthood. A network of brain regions have been shown to be abnormal in ADHD. In the present study we used magnetic resonance volumetry to investigate a possible role of the orbitofrontal cortex (OFC). Eight never medicated male patients fulfilling diagnostic criteria for ADHD and 17 male healthy controls were investigated. There was a significant reduction of the volume of the left OFC in patients with ADHD. It remains unknown whether small volumes are a primary deficit or a result of dysfunctional activation during childhood in terms of a residual deficit or a specific type of adult outcome of the disease.

Adult↗
PubMed2002

Different striatal dopamine D2 receptor occupancy in alcohol dependent patients with or without physical withdrawal symptoms --a study using IBZM-SPECT.

Ten male patients with type I alcohol dependency fulfilling DSM-IV criteria for alcohol dependency were investigated twice using IBZM-SPECT after alcohol withdrawal (day 2 and day 28 after withdrawal). Five patients had a history of physical withdrawal symptoms, 5 patients had no such history. The group with physical withdrawal symptoms showed higher IBZM binding in both scans indicating differences of dopaminergic neurotransmission in different subtypes of alcohol dependency.

Adult↗
PubMed2002

Small subunit ribosomal DNA phylogeny of microsporidia that infect Daphnia (Crustacea: Cladocera).

Glugoides intestinalis, Microsporidium sp., Ordospora colligata, Gurleya vavrai, Larssonia obtusa and Flabelliforma magnivora are microsporidian parasites of planctonic freshwater crustaceans Daphnia spp. We performed a phylogenetic analysis of the small subunit ribosomal DNA which revealed their positions as polyphyletic. G. intestinalis, Microsporidium sp. and O. colligata, which are horizontally transmitted gut parasites with small spores and low virulence, group with different lineages. G. intestinalis is related to 2 microsporidia infecting lepidopterans and to Vittaforma corneae, which has been described as a human pathogen. It is thought that V. corneae may have an invertebrate as its natural host. Microsporidium sp. is a relative of the genera Enterocytozoon and Nucleospora, pathogens of man and fish respectively. O. colligata is the first species found to be closely related to the genus Encephalitozoon, which is comprised of 3 species that are parasites of homeothermic vertebrates. G. vavrai and L. obtusa are sister taxa that branch close to the Amblyosporidae, the only microsporidia with known intermediate hosts. This finding supports the presumption of secondary hosts for G. vavrai and L. obtusa, as it has not been possible to maintain these species in Daphnia in the laboratory. F. magnivora roots deep at the base of the phylum microsporidia with no close relative found so far.

Animals↗