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Biomedical subjects

Andreas Hess

Publications and source records attributed to Andreas Hess.

11 recordsLinked to original sources
PubMed2006

Engineered heart tissue grafts improve systolic and diastolic function in infarcted rat hearts.

The concept of regenerating diseased myocardium by implantation of tissue-engineered heart muscle is intriguing, but convincing evidence is lacking that heart tissues can be generated at a size and with contractile properties that would lend considerable support to failing hearts. Here we created large (thickness/diameter, 1-4 mm/15 mm), force-generating engineered heart tissue from neonatal rat heart cells. Engineered heart tissue formed thick cardiac muscle layers when implanted on myocardial infarcts in immune-suppressed rats. When evaluated 28 d later, engineered heart tissue showed undelayed electrical coupling to the native myocardium without evidence of arrhythmia induction. Moreover, engineered heart tissue prevented further dilation, induced systolic wall thickening of infarcted myocardial segments and improved fractional area shortening of infarcted hearts compared to controls (sham operation and noncontractile constructs). Thus, our study provides evidence that large contractile cardiac tissue grafts can be constructed in vitro, can survive after implantation and can support contractile function of infarcted hearts.

Animals↗
PubMed2006

Imaging of hyperalgesia in rats by functional MRI.

Cerebral activation in response to sequences of temperature boosts at the hindpaw was observed in functional magnetic resonance imaging (fMRI) experiments in isoflurane anesthetized rats. Cingulate, retrosplenial, sensory-motor and insular cortex, medial and lateral posterior thalamic nuclei, pretectal area, hypothalamus and periaqueductal gray were the most consistently, often bilaterally activated regions. With the same experimental paradigm, activity changes in the brain following subcutaneous zymosan injection into one hindpaw were detected. These changes developed over time (up to 4h) in parallel with the temporal development of hyperalgesia shown by a modified Hargreaves test, thus reflecting processes of peripheral and central sensitization. When the heat stimuli were applied to the inflamed paw, the hyperalgesia manifested itself as a volume increase of the activated areas and/or an enhanced functional blood oxygenation level dependent (BOLD) signal in all the above-mentioned brain regions. Enhanced BOLD signals were also observed in response to stimulation of the contralateral non-injected paw. They were significant in higher associative regions and more pronounced in output-related than in input-related brain structures. This indicates additional sensitization processes in the brain, which we named cerebral sensitization. Long lasting zymosan-induced hyperalgesia could be monitored with high resolution fMRI in rats under isoflurane anaesthesia. This technique may provide an effective method for testing new analgesics and studying structure specific pain processing.

Afferent Pathways↗
PubMed2006

In vivo magnetic resonance imaging of dendritic cell migration into the draining lymph nodes of mice.

Dendritic cell (DC) migration into the draining lymph nodes is critical for T cell priming. Here, we show that magnetic resonance imaging (MRI) can be used to visualize DC migration in vivo. We combined clinically approved small particles of iron oxide (SPIO) with protamine sulfate to achieve efficient uptake by murine bone marrow-derived DC. SPIO-DC were largely unaltered and after injection into the footpads of mice, they migrated into the T cell areas of the draining lymph nodes, which could be visualized by MRI. Distinct MRI signal reduction patterns correlated with the detection of SPIO-DC mainly within Thy-1.2+ B220- T cell areas, as confirmed by iron staining and immunohistology. Clear signal reduction patterns could still be observed with 1x10(6) injected SPIO-DC at high resolution, resulting in the detection of about 2000 DC. Control injections of homing-incompetent SPIO-DC derived from CCR7-/- mice or SPIO alone did not reach the T cell areas. Taken together, the results demonstrate that clinically approved contrast agents allow the non-invasive visualization of DC migration into the draining lymph node by MRI in vivo at high resolution. This protocol therefore also allows dynamic imaging of immune responses and MRI-based tracking of human DC in patients.

Animals↗
PubMed2006

Engineering of vascularized transplantable bone tissues: induction of axial vascularization in an osteoconductive matrix using an arteriovenous loop.

INTRODUCTION: Vascularization remains an obstacle to engineering of larger volume bone tissues. Our aim was to induce axial vascularization in a processed bovine cancellous bone (PBCB) matrix using an arteriovenous (AV) loop (artery, vein graft, and vein). METHODS: Custom-made PBCB discs (9 x 5 mm) were implanted into rats. In group A (n = 19), the matrices were inserted into microsurgically constructed AV loops between the femoral vessels using a vein graft from the contralateral side. In group B (n = 19), there was no vascular carrier. The matrices were encased in isolation chambers. After 2, 4, and 8 weeks, the animals were perfused with India ink via the abdominal aorta. Matrices were explanted and subjected to histological and morphometric analysis. Results were compared with intravital dynamic micro & magnetic resonance imaging and scanning electron microscopy images of vascular corrosion replicas. RESULTS: In group A, significant vascularization of the matrix had occurred by the 8th week. At this time, vascular remodeling with organization into vessels of different sizes was evident. Blood vessels originated from all 3 zones of the AV loop. Group A was significantly superior to group B in terms of vascular density and vascularization kinetics. DISCUSSION: This study demonstrates for the first time successful vascularization of solid porous matrices by means of an AV loop. Injection of osteogenic cells into axially prevascularized matrices may eventually create functional bioartificial bone tissues for reconstruction of large defects.

Animals↗
PubMed2004

A method for the automatic segmentation of autoradiographic image stacks and spatial normalization of functional cortical activity patterns.

This paper introduces two new methods for the automatic anatomical and functional analysis of neurobiological autoradiographic image stacks, such as 2-fluoro-deoxyglucose (2FDG) images. The difficulty in the evaluation of these "2(1/2)D" datasets is that they do not inherently represent a continuous 3D data volume (as generated by MRI or CT), but consist of a stack of images from single tissue slices, suffering from unavoidable preparation artifacts. In the first part of the paper, a semi-automatic segmentation method is presented which generates a 3D surface model of certain brain structures and which is robust against different cutting directions with respect to the brain coordinate system. The method saves man-hours compared to manual segmentation and the results are highly reproducible. In the second part, a fully automatic method for the extraction, analysis and 3D visualization of functional information is described, which allows not only a more accurate localization of activation sites, but also greatly enhances the comparability of different individuals. Results are shown for 2FDG autoradiographs from rat brains under acoustical stimulation.

Animals↗
PubMed2003

A new point-based warping method for enhanced and simplified analysis of functional brain image data.

Comparison of brain imaging data requires the exact matching of data sets from different individuals. Warping methods, used to optimize matching of data sets, can exploit either local gray value distribution or identifiable reference points within the images to be compared. Gray value-based warping, which is more comfortable, cannot be used if gray values include functional information that should be compared between images. A major drawback in the use of point-based warping methods is the lack of methods for efficient and precise definition of reference points (landmarks) within comparable data sets. Here, we present a novel approach to automatically detect sufficient numbers of landmarks, which is based on 3D differential operators. In addition, we have developed a new distance-weighted warping method, which optimizes individual local weighting factors of displacement vectors. The quality of the methods was evaluated using a set of autoradiographs documenting the metabolic activity of gerbil brains after acoustic stimulation. The new warping method was compared with known methods of landmark-based warping, i.e., warping with radial basis functions and with distance-weighted methods. For the data sets presented in this study our new optimized warping method produced an increase in linear cross correlation of 4.44%, an increase in volume overlap index of 1.55%, and a decrease in the registration error of 36.2%. In addition, the detection of functional differences was improved after warping. Therefore, the new method is a powerful tool, which enhances the comparison of complex biological structures and the quantitative evaluation of functional imaging data.

Algorithms↗
PubMed2003

Noncontact mapping of ventricular tachycardia in a closed-chest animal model of chronic myocardial infarction.

Treatment of ventricular tachyarrhythmias in the setting of chronic myocardial infarction requires accurate characterization of the arrhythmia substrate. New mapping technologies have been developed that facilitate identification and ablation of critical areas even in rapid, hemodynamically unstable ventricular tachycardia. A noncontact mapping system was used to analyze induced ventricular tachycardia in a closed-chest sheep model of chronic myocardial infarction. Twelve sheep were studied 96 +/- 10 days after experimental myocardial infarction. During programmed stimulation, 15 different ventricular tachycardias were induced in nine animals. Induced ventricular tachycardia had a mean cycle length of 190 +/- 30 ms. In 12 ventricular tachycardias, earliest endocardial activity was recorded from virtual electrodes, preceding the surface QRS onset by 30 +/- 7 ms. Noncontact mapping identified diastolic activity in ten ventricular tachycardias. Diastolic potentials were recorded over a variable zone, spanning more than 30 mm. Timing of diastolic potentials varied from early to late diastole and could be traced back to the endocardial exit site. Entrainment with overdrive pacing was attempted in nine ventricular tachycardias, with concealed entrainment observed in seven. Abnormal endocardium in the area of chronic myocardial infarction identified by unipolar peak voltage mapping was confirmed by magnetic resonance imaging. These data suggest that induced ventricular tachycardia in the late phase of myocardial infarction in the sheep model is due to macroreentry involving the infarct borderzone. The combination of this animal model with noncontact mapping technology will allow testing of new strategies to cure and prevent ventricular tachycardia in the setting of chronic myocardial infarction.

Animals↗
PubMed2002

Cardiac grafting of engineered heart tissue in syngenic rats.

BACKGROUND: Cell grafting has emerged as a novel approach to treat heart diseases refractory to conventional therapy. We hypothesize that survival and functional and electrical integration of grafts may be improved by engineering cardiac tissue constructs in vitro before grafting. METHODS AND RESULTS: Engineered heart tissue (EHT) was reconstituted by mixing cardiac myocytes from neonatal Fischer 344 rats with liquid collagen type I, matrigel, and serum-containing culture medium. EHTs were designed in circular shape (inner/outer diameter: 8/10 mm; thickness: 1 mm) to fit around the circumference of hearts from syngenic rats. After 12 days in culture and before implantation on uninjured hearts, contractile function of EHT was measured under isometric conditions. Baseline twitch tension amounted to 0.34+/-0.03 mN (n=33) and was stimulated by Ca(2+) and isoprenaline to 200+/-12 and 185+/-10% of baseline values, respectively. Despite utilization of a syngenic model immunosuppression (mg/kg BW: azathioprine 2, cyclosporine A 5, methylprednisolone 2) was necessary for EHT survival in vivo. Echocardiography conducted 7, 14, and 28 days after implantation demonstrated no change in left ventricular function compared with pre-OP values (n=9). Fourteen days after implantation, EHTs were heavily vascularized and retained a well organized heart muscle structure as indicated by immunolabeling of actinin, connexin 43, and cadherins. Ultrastructural analysis demonstrated that implanted EHTs surpassed the degree of differentiation reached before implantation. Contractile function of EHT grafts was preserved in vivo. CONCLUSIONS: EHTs can be employed for tissue grafting approaches and might serve as graft material to repair diseased myocardium.

Animals↗
PubMed2002

Superposition of horseshoe-like periodicity and linear tonotopic maps in auditory cortex of the Mongolian gerbil.

The segregation of an individual sound from a mixture of concurrent sounds, the so-called cocktail-party phenomenon, is a fundamental and largely unexplained capability of the auditory system. Speaker recognition involves grouping of the various spectral (frequency) components of an individual's voice and segregating them from other competing voices. The important parameter for grouping may be the periodicity of sound waves because the spectral components of a given voice have one periodicity, viz. fundamental frequency, as their common denominator. To determine the relationship between the representations of spectral content and periodicity in the primary auditory cortex (AI), we used optical recording of intrinsic signals and electrophysiological mapping in Mongolian gerbils (Meriones unguiculatus). We found that periodicity maps as an almost circular gradient superimposed on the linear tonotopic gradient in the low frequency part of AI. This geometry of the periodicity map may imply competitive signal processing in support of the theory of "winner-takes-all".

Acoustic Stimulation↗
PubMed2002

Auditory activation of "visual" cortical areas in the blind mole rat (Spalax ehrenbergi).

The mole rat (Spalax ehrenbergi) is a subterranean rodent whose adaptations to its fossorial life include an extremely reduced peripheral visual system and an auditory system suited for the perception of vibratory stimuli. We have previously shown that in this blind rodent the dorsal lateral geniculate nucleus, the primary visual thalamic nucleus of sighted mammals, is activated by auditory stimuli. In this report we focus on the manifestation of this cross-modal compensation at the cortical level. Cyto- and myeloarchitectural analyses of the occipital area showed that despite the almost total blindness of the mole rat this area has retained the organization of a typical mammalian primary visual cortex. Application of the metabolic marker 2-deoxyglucose and electrophysiological recording of evoked field potentials and single-unit activity disclosed that a considerable part of this area is activated by auditory stimuli. Previous neuronal tracing studies had revealed the origin of the bulk of this auditory input to be the dorsal lateral geniculate nucleus which itself receives auditory input from the inferior colliculus.

Acoustic Stimulation↗