Biomedical subjects

Dieter Ebert

Publications and source records attributed to Dieter Ebert.

32 records · Page 2Linked to original sources

PubMed2004

Absence of cortical gray matter abnormalities in psychosis of epilepsy: a voxel-based MRI study in patients with temporal lobe epilepsy.

The authors retrospectively explored cortical differences between 26 patients with temporal lobe epilepsy and psychosis of epilepsy (POE), 24 patients with temporal lobe epilepsy (TLE) alone, and 20 healthy comparison subjects. Using voxel-based morphometry based on statistical parametric mapping (SPM99), which is an unbiased and fully automated technique to test for morphometric differences, magnetic resonance imaging (MRI) 3D-datasets were acquired and analyzed. There were no significant cortical gray matter differences between the POE and the TLE group. Since cortical pathology is prominent in schizophrenia, POE may be a clinical entity separate from schizophrenia.

Adult↗

PubMed2003

Attention deficit hyperactivity disorder in adults-early vs. late onset in a retrospective study.

Attention deficit hyperactivity disorder (ADHD) is a severe and often debilitating mental disorder, which begins in childhood and can persist into adulthood. Both major classificatory systems, ICD-10 and DSM-IV, include the age-of-onset criterion (AOC) requiring clinically relevant symptoms before the age of 7 years. In clinical practice, particularly in adult psychiatry, it is often difficult to establish this AOC when ADHD remained unrecognized in childhood. In the literature, there is controversy about the validity of this criterion. In order to explore the validity of the AOC, we performed a retrospective study in adult patients with ADHD. Fifty consecutively diagnosed patients were subjected to a standardized diagnostic procedure. Depending on the onset of clinical symptoms, patients were divided in an early onset and in a late onset ADHD subgroup. Fourteen patients (28%) described late onset ADHD. In four of these patients (8% of the total sample), this assessment was confirmed by parent ratings. There was no difference between early onset and late onset ADHD groups in terms of psychopathology or psychiatric comorbidity.

Adult↗

PubMed2003

Frontolimbic brain abnormalities in patients with borderline personality disorder: a volumetric magnetic resonance imaging study.

BACKGROUND: Dual frontolimbic brain pathology has been suggested as a possible correlate of impulsivity and aggressive behavior. One previous study reported volume loss of the hippocampus and the amygdala in patients with borderline personality disorder. We measured limbic and prefrontal brain volumes to test the hypothesis that frontolimbic brain pathology might be associated with borderline personality disorder. METHODS: Eight unmedicated female patients with borderline personality disorder and eight matched healthy controls were studied. The volumes of the hippocampus, amygdala, and orbitofrontal, dorsolateral prefrontal, and anterior cingulate cortex were measured in the patients using magnetic resonance imaging volumetry and compared to those obtained in the controls. RESULTS: We found a significant reduction of hippocampal and amygdala volumes in borderline personality disorder. There was a significant 24% reduction of the left orbitofrontal and a 26% reduction of the right anterior cingulate cortex in borderline personality disorder. Only left orbitofrontal volumes correlated significantly with amygdala volumes. CONCLUSIONS: While volume loss of a single brain structure like the hippocampus is quite an unspecific finding in neuropsychiatry, the patterns of volume loss of the amygdala, hippocampus, and left orbitofrontal and right anterior cingulate cortex might differentiate borderline personality disorder from other neuropsychiatric conditions.

Adult↗

PubMed2003

Challenging the trade-off model for the evolution of virulence: is virulence management feasible?

Progress in understanding the evolution of infectious diseases has inspired proposals to manage the evolution of pathogen (including parasite) virulence. A common view is that social interventions that lower pathogen transmission will indirectly select lower virulence because of a trade-off between transmission and virulence. Here, we argue that there is little theoretical justification and no empirical evidence for this plan. Although a trade-off model might apply to some pathogens, the mechanism appears too weak for rapid selection of substantial changes in virulence. Direct selection against virulence itself might be a more rewarding approach to managing the evolution of virulence.

Animals↗

PubMed2003

Parasite-mediated selection in experimental Daphnia magna populations.

It has been suggested that parasites are a strong selecting force for their hosts and therefore may alter the outcome of competition among host genotypes. We tested the extent to which parasite-mediated selection by different parasite species influenced competition among clones of the cyclic parthenogen Daphnia magna. We monitored clone frequency changes in laboratory microcosm populations consisting of 21 D. magna clones. Parasite treatments (two microsporidians, Glugoides intestinalis and Ordospora colligata) and a parasite-free control treatment were followed over a nine-month period. A further treatment with the bacterium Pasteuria ramosa failed. We found significant differences in clonal success among the treatments: the two parasite treatments differed from the control treatment and from each other. Additionally, we measured the clone-specific population carrying capacity, competitive ability against tester clones, and reproductive success of infected and uninfected females to test whether they correlate with clonal success in the microcosms. The clone-specific competitive ability was a good predictor of clonal success in the microcosms, but clonal carrying capacity and host reproductive success were not. Our study shows that parasite-mediated selection can strongly alter the outcome of clonal competition. The results suggest that parasites may influence microevolution in Daphnia populations during periods of asexual reproduction.

Animals↗

PubMed2003

Test of synergistic interaction between infection and inbreeding in Daphnia magna.

It has been proposed that parasitic infections increase selection against inbred genotypes. We tested this hypothesis experimentally using pairs of selfed and outcrossed sibling lines of the freshwater crustacean Daphnia magna, which can be maintained clonally. We studied the performance of selfed relative to outcrossed sibling clones during repeated pairwise clonal competition in the presence and absence of two species of microsporidian parasites. In 13 of the 14 pairs, the selfed clones did worse than the outcrossed ones in the control treatment, but the presence of either parasite did not result in an overall increase in this difference. Rather, it decreased the performance of the selfed relative to the outcrossed sibling in some pairs and increased it in others. Moreover, the two parasite species did not have the same effect in a given pair. This indicates that, contrary to the hypothesis that parasites generally lead to a decreased performance of inbred genotypes, their effect may depend on the genetic background of the host as well as on the parasite species, and suggests that inbreeding can lead to reduced or increased resistance to parasites. Our findings also indicate that there is variation for specific resistance to different species of parasites in the meta-population from which the hosts for this study were obtained.

Analysis of Variance↗

PubMed2003

Evidence for strong host clone-parasite species interactions in the Daphnia microparasite system.

Organisms are often confronted with multiple enemy species. Defenses against different parasite species may be traded off against each other. However, if resistance is based on (potentially costly) general defense mechanisms, it may be positively correlated among parasites. In an experimental study, we confronted 19 clones from one Daphnia magna population with two bacterial and three microsporidian parasite species. All parasites were isolated from the same pond as the hosts. Host clones were specific in their susceptibility towards different parasite species, and parasite species were host-clone specific in their infectivity, spore production, and virulence, resulting in highly significant host-parasite interactions. Since the Daphnia's resistance to different parasite species showed no obvious correlation, neither general defense mechanisms nor trade-offs in resistance explain our findings. None of the Daphnia clones were resistant to all parasite species, and the average level of resistance was quite similar among clones. This may reflect a cost of defense, so that the cumulative cost of being resistant to all parasite species might be too high.

Analysis of Variance↗

PubMed2002

In deep trouble: habitat selection constrained by multiple enemies in zooplankton.

Habitat selection behavior is an important predator-avoidance strategy for many organisms. Its particular expression is often explained as the result of a tradeoff between avoiding antagonists and acquiring resources. However, there is need for a broader perspective on this behavior, as organisms are often simultaneously involved in complex antagonistic relationships with multiple types of enemies. We show experimentally that a tradeoff between predator and parasite avoidance may be important in the evolution of habitat selection behavior in the waterflea, Daphnia magna. In this species, negatively phototactic clones suffer less from visually hunting predators by residing in deeper and darker portions of the water column during the day. However, this behavior increases the risk of parasitic infections when the Daphnia are exposed to pond sediments containing parasite spores. Positively phototactic clones, which are at a higher risk of predation, are less exposed to parasite spores in the sediment and consequently suffer less from parasitic infection. We show that the increased risk of infection remains even if the animals change their phototactic behavior on exposure to chemical cues from fish. This tradeoff highlights a substantial cost of predator-induced changes in habitat selection behavior. Tradeoffs caused by multiple enemies may explain genetic polymorphism for habitat selection behavior in many natural populations.

Analysis of Variance↗

PubMed2002

Dose-dependent infection rates of parasites produce the Allee effect in epidemiology.

In many epidemiological models of microparasitic infections it is assumed that the infection process is governed by the mass-action principle, i.e. that the infection rate per host and per parasite is a constant. Furthermore, the parasite-induced host mortality (parasite virulence) and the reproduction rate of the parasite are often assumed to be independent of the infecting parasite dose. However, there is empirical evidence against those three assumptions: the infection rate per host is often found to be a sigmoidal rather than a linear function of the parasite dose to which it is exposed; and the lifespan of infected hosts as well as the reproduction rate of the parasite are often negatively correlated with the parasite dose. Here, we incorporate dose dependences into the standard modelling framework for microparasitic infections, and draw conclusions on the resulting dynamics. Our model displays an Allee effect that is characterized by an invasion threshold for the parasite. Furthermore, in contrast to standard epidemiological models a parasite strain needs to have a basic reproductive rate that is substantially greater than 1 to establish an infection. Thus, the conditions for successful invasion of the parasite are more restrictive than in mass-action infection models. The analysis further suggests that negative correlations of the parasite dose with host lifespan and the parasite reproduction rate helps the parasite to overcome the invasion constraints of the Allee-type dynamics.

Animals↗

PubMed2002

A selective advantage to immigrant genes in a Daphnia metapopulation.

Immigrants to habitats occupied by conspecific organisms are usually expected to be competitively inferior, because residents may be locally adapted. If residents are inbred, however, mating between immigrants and residents results in offspring that may enjoy a fitness advantage from hybrid vigor. We demonstrate this effect experimentally in a natural Daphnia metapopulation in which genetic bottlenecks and local inbreeding are common. We estimate that in this metapopulation, hybrid vigor amplifies the rate of gene flow several times more than would be predicted from the nominal migration rate. This can affect the persistence of local populations and the entire metapopulation.

Alleles↗

PubMed2002

Psychotherapy of attention deficit hyperactivity disorder in adults--a pilot study using a structured skills training program.

In clinical practice many adult patients with attention deficit hyperactivity disorder (ADHD) ask for an additional psychotherapeutic intervention besides the medical therapy. In this paper we present a structured skill training program particularly tailored for adult patients with ADHD. The program is based on the principles of cognitive-behavioral treatment for borderline personality disorder developed by M. Linehan. It was modified to suit the special needs of adult patients with ADHD. In this exploratory pilot study we tested this program in a group setting. The following elements were presented: neurobiology of ADHD, mindfulness, chaos and control, behavior analysis, emotion regulation, depression, medication in ADHD, impulse control, stress management, dependency, ADHD in relationship and self respect. In an open study design patients were assessed clinically using psychometric scales (Attention Deficit Hyperactivity Disorder Checklist according to DSM-IV, 16 items of the SCL-90-R, Beck-Depression Inventory, visual analogue scale) prior to and following group therapy. This treatment resulted in positive outcomes in that patients improved on all psychometric scales.

Adult↗

PubMed2002

On the role of quantitative brain imaging in the differential diagnosis of speech disorders.

We present the case of a 71-year-old woman with an 11-year history of slowly progressive decline of motor speech. Normal clinical investigations including routine magnetic resonance imaging (MRI) at 7, 8 and 10 years after the onset of speech dysfunction led to the suggestion of a psychogenic disorder. Extensive clinical, neuropsychological and neuroimaging investigations including 18F-desoxyglucose-positron emission tomography (PET), quantitative MRI and MR spectroscopy were performed to look for subtle brain pathology. Quantitative assessment of 3D-MRI, F-desoxyglucose-PET and magnetic resonance spectroscopy all demonstrated clear evidence of multifocal frontotemporal brain pathology that had not been picked up on routine MRI investigations on previous admissions. This is the longest benign history of slowly progressive anarthria reported so far. It demonstrates a possible role of quantitative neuroimaging techniques in the diagnosis of complex neuropsychiatric disorders.

Aged↗

PubMed2002

Strong inbreeding depression in a Daphnia metapopulation.

The deleterious effects of inbreeding have long been known, and inbreeding can increase the risk of extinction for local populations in metapopulations. However, other consequences of inbreeding in metapopulations are still not well understood. Here we show the presence of strong inbreeding depression in a rockpool metapopulation of the planktonic freshwater crustacean Daphnia magna, which reproduces by cyclical parthenogenesis. We conducted three experiments in real and artificial rockpools to quantify components of inbreeding depression in the presence and the absence of competition between clonal lines of selfed and outcrossed genotypes. In replicated asexual populations, we recorded strong selection against clones produced by selfing in competition with clones produced by outcrossing. In contrast, inbreeding depression was much weaker in single-clone populations, that is, in the absence of competition between inbred and outbred clones. The finding of a competitive advantage of the outbred genotypes in this metapopulation suggests that if rockpool populations are inbred, hybrid offspring resulting from crosses between immigrants and local genotypes might have a strong selective advantage. This would increase the effective gene flow in the metapopulation. However, the finding of low inbreeding depression in the monoclonal populations suggests that inbred and outbred genotypes might have about equal chances of establishing new populations.

Animals↗

PubMedDate not supplied

Physiology of immunity in the water flea Daphnia magna: environmental and genetic aspects of phenoloxidase activity.

In an attempt to understand the ecological correlates of immunocompetence in Daphnia magna (Crustacea, Cladocera), we tested for variation in immune function in relation to feeding conditions, host conditions, and host genotype. We investigated both phenotypic (environmental dependent and condition dependent) as well as genotypic aspects of the prophenoloxidase activating system (Pro-POAS), which has been described as a key factor in invertebrate immunity. Daphnia magna is an ideal study system to disentangle phenotypic and genetic variation because females can reproduce clonally. Well-fed Daphnia showed higher phenoloxidase (PO) activity than Daphnia kept at a low food level. Wounding provoked a higher level of PO activity, indicating that the Pro-POAS was condition dependent. Further, we found clonal variation in PO activity among four clones of D. magna isolated from four different populations. The same four clones were tested for their resistance to the bacterial pathogen Pasteuria ramosa. High resistance corresponded to high PO activity. Our results suggest adaptive variation in PO activity and suggest that its expression is costly. These costs may influence the evolution of the PO activity level and the maintenance of its genotypic variation.

Animals↗