The Role of Reactive Oxygen Species in the Light-Induced Deformation of DNA

Dimerizations and reactions with water of pyrimidine bases are the primary steps held respon­sible for the deformation of DNA at short wavelengths in vitro and in vivo experiments. However the influence of oxygen in combination with water on the UV deformation at wavelengths rep­resentative for troposphere is evident from the observed data and both together are needed to change the DNA structure. The only plausible explanation for the effect of oxygen is the forma­tion of reactive oxygen species during the UV irradiation of DNA. In the present work the deformation of DNA by different oxygen species like singlet oxygen (1O2), superoxideanion (O2 -), hydroxyradical (·OH), ozone (O3) and hydrogenperoxide (H2O2) is excluded with the help of chemical-trapping experiments. The photo-induced transformation proceeds via excited states of DNA. which react with groundstate oxygen to afford peroxide.

Preferential host switching and codivergence shaped radiation of bark beetle symbionts, nematodes of Micoletzkya (Nematoda: Diplogastridae)

Host-symbiont systems are of particular interest to evolutionary biology because they allow testable inferences of diversification processes while also providing both a historical basis and an ecological context for studies of adaptation. Our investigations of bark beetle symbionts, predatory nematodes of the genus Micoletzkya, have revealed remarkable diversity of the group along with a high level of host specificity. Cophylogenetic analyses suggest that evolution of the nematodes was largely influenced by the evolutionary history of beetles. The diversification of the symbionts, however, could not be attributed to parallel divergence alone; our results indicate that adaptive radiation of the nematodes was shaped by preferential host shifts among closely related beetles along with codivergence. Whereas ecological and geographic isolation have played a major role in the diversification of Micoletzkya at shallow phylogenetic depths, adaptations towards related hosts have played a role in shaping cophylogenetic structure at a larger evolutionary scale.

Ageing differentially affects neural processing of different conflict types-an fMRI study

Interference control and conflict resolution is affected by ageing. There is increasing evidence that ageing does not compromise interference control in general but rather shows distinctive effects on different components of interference control. Different conflict types, [e.g., stimulus-stimulus (S-S) or stimulus-response (S-R) conflicts] trigger different cognitive processes and thus activate different neural networks. In the present functional magnetic resonance imaging (fMRI) study, we used a combined Flanker and Stimulus Response Conflict (SRC) task to investigate the effect of ageing on S-S and S-R conflicts. Behavioral data analysis revealed larger SRC effects in elderly. fMRI Results show that both age groups recruited similar regions [caudate nucleus, cingulate gyrus and middle occipital gyrus (MOG)] during Flanker conflict processing. Furthermore, elderly show an additional activation pattern in parietal and frontal areas. In contrast, no common activation of both age groups was found in response to the SRC. These data suggest that ageing has distinctive effects on S-S and S-R conflicts.

Detection of nosocomial Clostridium difficile infections with toxigenic strains despite negative toxin A and B testing on stool samples

A two-step diagnostic algorithm is recommended to detect Clostridium difficile infections; however, samples are regularly found that are glutamate dehydrogenase (GDH) positive but stool toxin negative. In the present single-centre prospective study we focused on these 'difficult-to-interpret' samples and characterized them by anaerobic culture, toxigenic culture, slpA sequence typing and multiplex PCR (GenoType CDiff). The majority of stool toxin A and B-negative samples have been caused by toxigenic strains including ribotype 027. The multiplex PCR was faster and more sensitive compared with culture and allowed preliminary identification of hypervirulent strains in stool samples on the same day.

The perception of dynamic and static facial expressions of happiness and disgust investigated by ERPs and fMRI constrained source analysis

A recent functional magnetic resonance imaging (fMRI) study by our group demonstrated that dynamic emotional faces are more accurately recognized and evoked more widespread patterns of hemodynamic brain responses than static emotional faces. Based on this experimental design, the present study aimed at investigating the spatio-temporal processing of static and dynamic emotional facial expressions in 19 healthy women by means of multi-channel electroencephalography (EEG), event-related potentials (ERP) and fMRI-constrained regional source analyses. ERP analysis showed an increased amplitude of the LPP (late posterior positivity) over centro-parietal regions for static facial expressions of disgust compared to neutral faces. In addition, the LPP was more widespread and temporally prolonged for dynamic compared to static faces of disgust and happiness. fMRI constrained source analysis on static emotional face stimuli indicated the spatio-temporal modulation of predominantly posterior regional brain activation related to the visual processing stream for both emotional valences when compared to the neutral condition in the fusiform gyrus. The spatio-temporal processing of dynamic stimuli yielded enhanced source activity for emotional compared to neutral conditions in temporal (e.g., fusiform gyrus), and frontal regions (e.g., ventromedial prefrontal cortex, medial and inferior frontal cortex) in early and again in later time windows. The present data support the view that dynamic facial displays trigger more information reflected in complex neural networks, in particular because of their changing features potentially triggering sustained activation related to a continuing evaluation of those faces. A combined fMRI and EEG approach thus provides an advanced insight to the spatio-temporal characteristics of emotional face processing, by also revealing additional neural generators, not identifiable by the only use of an fMRI approach.

Multiple routes to mental animation: language and functional relations drive motion processing for static images

When looking at static visual images, people often exhibit mental animation, anticipating visual events that have not yet happened. But what determines when mental animation occurs? Measuring mental animation using localized brain function (visual motion processing in the middle temporal and middle superior temporal areas, MT+), we demonstrated that animating static pictures of objects is dependent both on the functionally relevant spatial arrangement that objects have with one another (e.g., a bottle above a glass vs. a glass above a bottle) and on the linguistic judgment to be made about those objects (e.g., "Is the bottle above the glass?" vs. "Is the bottle bigger than the glass?"). Furthermore, we showed that mental animation is driven by functional relations and language separately in the right hemisphere of the brain but conjointly in the left hemisphere. Mental animation is not a unitary construct; the predictions humans make about the visual world are driven flexibly, with hemispheric asymmetry in the routes to MT+ activation.