Silvio Schmidt

Accumulation of secondary carotenoids in flagellates of Haematococcus pluvialis (Chlorophyta) is accompanied by an increase in per unit chlorophyll productivity of photosynthesis

Flagellates of Haematococcus pluvialis accumulate secondary carotenoids (mainly astaxanthin and its esters) under nitrogen deficiency in combination with exposure to stronger light. Our cultivation scheme allows the characterization of metabolic activities during the accumulation process without interference by formation of the resting state (aplanospores). The highest rate of secondary carotenoid biosynthesis (0.046 h−1) was observed almost simultaneously with the highest rates of cell division (0.027 h−1) and of chlorophyll biosynthesis (0.015 h−1) after 1.5 days of exposure to nitrogen limitation and higher irradiance. Photosynthetic activity was studied by oxygen evolution and chlorophyll fluorescence measurements; changes in protein components of the photosynthetic apparatus were quantified by gel electrophoresis and immunoblot analysis. Accumulation of secondary carotenoids was accompanied by an increase in photosynthetic productivity expressed on a unit chlorophyll basis. Changes in the photosynthetic apparatus occurring mainly during the first 2 days of exposure to nitrogen limitation and stronger light can be interpreted as acclimation to the increased cultivation irradiance. Photoprotective action of secondary carotenoids as a ‘sunshade’ was demonstrated in red flagellates exhibiting a lower blue-light-induced decrease in photosystem II efficiency as compared with red actinic light.

Global impairment and therapeutic restoration of visual plasticity mechanisms after a localized cortical stroke

We tested the influence of a photothrombotic lesion in somatosensory cortex on plasticity in the mouse visual system and the efficacy of anti-inflammatory treatment to rescue compromised learning. To challenge plasticity mechanisms, we induced monocular deprivation (MD) in 3-mo-old mice. In control animals, MD induced an increase of visual acuity of the open eye and an ocular dominance (OD) shift towards this eye. In contrast, after photothrombosis, there was neither an enhancement of visual acuity nor an OD-shift. However, OD-plasticity was present in the hemisphere contralateral to the lesion. Anti-inflammatory treatment restored sensory learning but not OD-plasticity, as did a 2-wk delay between photothrombosis and MD. We conclude that (i) both sensory learning and cortical plasticity are compromised in the surround of a cortical lesion; (ii) transient inflammation is responsible for impaired sensory learning, suggesting anti-inflammatory treatment as a useful adjuvant therapy to support rehabilitation following stroke; and (iii) OD-plasticity cannot be conceptualized solely as a local process because nonlocal influences are more important than previously assumed.

Age dependence of excitatory-inhibitory balance following stroke.

The mechanisms which mediate cortical map plasticity and functional recovery following stroke remain a matter of debate. Readjustment of the excitatory-inhibitory balance may support cortical map plasticity in perilesional areas. Here we studied cortical net inhibition in the vicinity of photothrombotically-induced cortical lesions in young adult (3 months) and aged (24 months) male rats. Field potentials were recorded in cortical layer II/III following application of paired-pulse stimulation at layer VI/white matter in coronal brain slices. Additionally, we analyzed the regional distribution of 5 major gamma-aminobutyric acid A (GABA(A)) receptor subunits (α1, α2, α3, α5, and γ2) by immunohistochemistry. Paired-pulse inhibition in the perilesional parietal cortex was decreased in young rats but was increased in aged rats. As a consequence of the diminished intrinsic net inhibition in aged control animals, the excitatory-inhibitory balance was readjusted to an age-independent similar level in young and aged lesioned rats in a homeostatic-like fashion. These physiological changes in neuronal activity were accompanied by age-specific laminar alterations of the gamma-aminobutyric acid A (GABA(A)) receptor subunit composition, most prominently of the subunit α5. The present study suggests that the mechanisms underlying functional reorganization in aged animals may be distinctly different from those in young animals.

Magnetic resonance imaging of the mouse visual pathway for in vivo studies of degeneration and regeneration in the CNS.

Traditionally, depiction of isolated CNS fiber tracts is achieved by histological post mortem studies. As a tracer-dependent strategy, the calcium analog manganese has proved valuable for in vivo imaging of CNS trajectories, particularly in rats. However, adequate protocols in mice are still rare. To take advantage of the numerous genetic mouse mutants that are available to study axonal de- and regeneration processes, a MnCl2-based protocol for high-resolution contrast-enhanced MRI (MEMRI) of the visual pathway in mice acquired on a widely used clinical 3 Tesla scanner was established. Intravitreal application of MnCl2 significantly enhanced T1-weighted contrast and signal intensity along the retino-petal projection enabling its reconstruction in a 3D mode from a maximum intensity projection (MIP) calculated dataset. In response to crush injury of the optic nerve, axonal transport of MnCl2 was diminished and completely blocked proximal and distal to the lesion site, respectively. Conditions of Wallerian degeneration after acute optic nerve injury accelerated Mn2+-enhanced signal fading in axotomized projection areas between 12 and 24 h post-injury. In long-term regeneration studies 12 months after optic nerve injury, the MRI protocol proved highly sensitive and discriminated animals with rare spontaneous axonal regrowth from non-regenerating specimens. Also, structural MRI aspects shared high correlation with histological results in identical animals. Moreover, in a model of chronic neurodegeneration in p50/NF-κB-deficient mice, MnCl2-based neuron-axonal tracing supported by heat map imaging indicated neuropathy of the visual pathway due to atrophy of optic nerve fiber projections. Toxic effects of MnCl2 at MRI contrast-relevant dosages in repetitive administration protocols were ruled out by histological and optometric examinations. At higher dosages, photoreceptors, not retinal ganglion cells, turned out as most susceptible to the well-known toxicity of MnCl2. Our data accentuate in vivo MEMRI of the murine visual system as a highly specific and sensitive strategy to uncover axonal degeneration and restoration processes, even in a functional latent state. We expect MEMRI to be promising for future applications in longitudinal studies on development, aging, or regeneration of CNS projections in mouse models mimicking human CNS pathologies.

Deformation-based brain morphometry in rats

Magnetic resonance imaging (MRI)-based morphometry provides in vivo evidence for macro-structural plasticity of the brain. Experiments on small animals using automated morphometric methods usually require expensive measurements with ultra-high field dedicated animal MRI systems. Here, we developed a novel deformation-based morphometry (DBM) tool for automated analyses of rat brain images measured on a 3-Tesla clinical whole body scanner with appropriate coils. A landmark-based transformation of our customized reference brain into the coordinates of the widely used rat brain atlas from Paxinos and Watson (Paxinos Atlas) guarantees the comparability of results to other studies. For cross-sectional data, we warped images onto the reference brain using the low-dimensional nonlinear registration implemented in the MATLAB software package SPM8. For the analysis of longitudinal data sets, we chose high-dimensional registrations of all images of one data set to the first baseline image which facilitate the identification of more subtle structural changes. Because all deformations were finally used to transform the data into the space of the Paxinos Atlas, Jacobian determinants could be used to estimate absolute local volumes of predefined regions-of-interest. Pilot experiments were performed to analyze brain structural changes due to aging or photothrombotically-induced cortical stroke. The results support the utility of DBM based on commonly available clinical whole-body scanners for highly sensitive morphometric studies on rats.

Changes in the Photosynthetic Apparatus During Accumulation of Secondary Carotenoids in Flagellates of Haematococcus Pluvialis

The unicellular volvocalean green alga Haematococcus pluvialis as one of the astaxanthinsynthesising organisms receives close attention from a biotechnological point of view [1]. In previous studies it was proposed that secondary carotenoid (SC) synthesis is related to the formation of resting cells [2]. However, SC accumulation was clearly shown in flagellates demonstrating this process as independent of senescence [3, 4].

Transcriptomic alterations during ageing reflect the shift from cancer to degenerative diseases in the elderly

Disease epidemiology during ageing shows a transition from cancer to degenerative chronic disorders as dominant contributors to mortality in the old. Nevertheless, it has remained unclear to what extent molecular signatures of ageing reflect this phenomenon. Here we report on the identification of a conserved transcriptomic signature of ageing based on gene expression data from four vertebrate species across four tissues. We find that ageing-associated transcriptomic changes follow trajectories similar to the transcriptional alterations observed in degenerative ageing diseases but are in opposite direction to the transcriptomic alterations observed in cancer. We confirm the existence of a similar antagonism on the genomic level, where a majority of shared risk alleles which increase the risk of cancer decrease the risk of chronic degenerative disorders and vice versa. These results reveal a fundamental trade-off between cancer and degenerative ageing diseases that sheds light on the pronounced shift in their epidemiology during ageing.Ageing is associated with a pronounced shift in mortality from cancer to degenerative diseases. Here, the authors show that in concordance with this shift, conserved transcriptional alterations during ageing across four vertebrates align with degenerative diseases but are opposite to those in cancer.

Non-invasive monitoring of cortical volume alterations in rat brains using a clinical 3T whole body MRI scanner

Research on neurodegenerative disorders is increasingly important in an aging population. Therefore, noninvasive detection of local changes in cerebral volume which can be accomplished by MRI, is in focus of clinical investigations. Animal models are playing a pivotal role in geriatric research, but many labs do not have access to dedicated animal MRI scanners. In this study we show that deformation based morphometry of the rat brain can be achieved with data acquired on a human 3T whole body system using a multi purpose 8-channel coil with overlapping coil elements of 5 cm diameter for optimized SNR. For the morphometric evaluation a T2-weighted hyperecho based TSE sequence (SPACE) was employed with an isotropic resolution of 0.33 mm. Deformation based morphometry, a fully automatic intensity based method, was used to detect the cerebral volume changes on 3 and 26 months old rats. On animals, a cortical dysplasia was induced on the day of birth by freeze lesions in the right-hemispheric motor cortex. We found a volume decrease in the lesion surrounding the primary somatosensory cortex with progression in aging animals. The volume changes are in accordance with age-dependent reduced performance in a dexterity test.

In vivo1H-MRS of the rat brain with a clinical 3 T whole-body MR Scanner: Estimation of absolute metabolic concentrations and T2 values

In vivo single voxel 1H-MR measurements were performed in a rat’s brain on a clinical whole-body 3 T MR scanner by using a dedicated small animal head RF-coil. Spectroscopic experiments were performed with and without water suppression as well as with different echo times (TE) by placing a 0.5 ml voxel in the rat cerebrum. Absolute concentrations of tNAA, tCr, tCho, mIns, Lac and Glu were estimated by applying the internal tissue water reference technique. In addition, T2 values for tNAA, tCr and tCho were determined by mono-exponential fitting of metabolite intensities sampled at the different echo times.