Hubert Korr

Time course of glial proliferation and glial apoptosis following excitotoxic CNS injury.

Activation of microglial cells and astrocytes after CNS injury results in changes in their morphology, immunophenotype and proliferative activity and has neurotrophic as well as neurotoxic consequences. However, little is known about the exact time course of glial activation as regards their proliferative activity and their fate. In this study, quantification of the densities of proliferating and non-proliferating microglial cells and astrocytes was carried out over 30 days by counting differentially labeled cells in the striatum and substantia nigra pars reticulata (SNr) after injection of quinolinic acid into the rat striatum. The TdT-mediated dUTP nick end labeling (TUNEL)-reaction was used to detect possible apoptotic mechanisms which limit the glial reaction. At 1 day post injection (p.i.) non-proliferating ameboid microglia/macrophages were seen in the striatum, but at 3 and 5 days p.i. many proliferating, ameboid microglia/macrophages and hypertrophic microglia were detected. At 10 days p.i., the time point with the highest density of hypertrophic microglia, TUNEL-positive microglial cells were observed indicating that apoptotic processes play a role in restricting this reaction. In contrast to this, at early time points, a reduction in the density and glial fibrillary acidic protein (GFAP)-immunoreactivity of astrocytes in the striatum was detected. At later time points, a dense astrogliosis with proliferating astrocytes developed in the dorsal and medial striatum. At 30 days p.i., in the entire striatum a dense astrogliosis was detected. The SNr showed a short period of microglial activation and proliferation and a long lasting astrogliosis without proliferation

Nerve cell loss in the thalamic mediodorsal nucleus in Huntington's disease

Abstract We estimated the total neurone number, glial number, and glial index (ratio glial cells/neurone) in the thalamic mediodorsal nucleus (MD) in seven patients suffering from Huntington’s disease (HD; four males, three females, mean age 52.4 ± 13.6 years) and age- and sex-matched controls (four males, three females, mean age 53.6 ± 12.1 years) by means of a stereological protocol. The mean total neurone number (NT¯) in the MD of controls was 2,985,188 ± 174,710, the mean glial number (GT¯; astrocytes, oligodendrocytes) 21,785,008 ± 2,986,678, and the glial index 7.29 ± 0.88. In HD, the average neurone number was decreased by 23.8% to 2,275,321 ± 247,162 (Mann-Whitney U-test P < 0.05), the mean glial number by 29.7 % to 15,318,895 ± 1,722,524 (Mann-Whitney U-test P < 0.05), the glial index was slightly reduced to 6.81 ± 1.06. Gallyas’ impregnation for the demonstration of fibrous astroglia gave strongly positive results in all cases with HD and negative results in the controls. The morpho-functional correlation of the results is complicated because individual variability, presence of segregated and parallel neuronal circuits, and plasticity of the adult human CNS must be considered.

Selective striatal neuron loss and alterations in behavior correlate with impaired striatal function in Huntington's disease transgenic rats

Huntingtons disease (HD) is an inherited neurodegenerative disorder characterized by selective striatal neuron loss and motor, cognitive and affective disturbances. The present study aimed to test the hypothesis of adult-onset neuron loss in striatum and frontal cortical layer V as well as alterations in behavior pointing to impaired striatal function in a recently developed transgenic rat model of HD (tgHD rats) exhibiting enlarged ventricles, striatal atrophy and pycnotic pyramidal cells in frontal cortical layer V. High-precision design-based stereological analysis revealed a reduced mean total number of neurons in the striatum but not in frontal cortical layer V of 12-month-old tgHD rats compared with age-matched wild-type controls. No alterations in mean total numbers of striatal neurons were found in 6-month-old animals. Testing 14-month-old animals in a choice reaction time task indicated impaired striatal function of tgHD rats compared with controls.

Age-related changes of DNA repair and mitochondrial DNA synthesis in the mouse brain.

Abstract Using quantitative autoradiography, both nuclear DNA repair – measured as nuclear unscheduled DNA synthesis (UDS) – and mitochondrial (mt) DNA synthesis were evaluated in situ for several types of cells in the brains of untreated mice of various age. It was found that distinct types of neuronal cells showed a decline of both UDS and mtDNA synthesis with age, whereas – except for glial cells of the cerebral cortex – no glial or endothelial cells showed age-related alterations of UDS. Together with various data reported in the literature, these patterns of a cell type-specific decrease of UDS and mtDNA synthesis with age in the mouse brain lead to an improved understanding of the complex interrelationships between the molecular events associated with the phenomenon of aging as well as to a new idea regarding the cause of the specific distribution pattern of those cells in the human brain that are affected by the formation of paired helical filaments in Alzheimer’s disease.

Tau-4R suppresses proliferation and promotes neuronal differentiation in the hippocampus of tau knockin/knockout mice

Differential isoform expression and phosphorylation of protein tau are believed to regulate the assembly and stabilization of microtubuli in fetal and adult neurons. To define the functions of tau in the developing and adult brain, we generated transgenic mice expressing the human tau‐4R/2N (htau‐4R) isoform on a murine tau null background, by a knockout/ knockin approach (tau‐KOKI). The main findings in these mice were the significant increases in hippocam‐pal volume and neuronal number, which were sustained throughout adult life and paralleled by improved cognitive functioning. The increase in hippocampal size was found to be due to increased neurogenesis and neuronal survival. Proliferation and neuronal differentiation were further analyzed in primary hippocampal cultures from tau‐KOKI mice, before and after htau‐4R expression onset. In absence of tau, proliferation increased and both neurite and axonal outgrowth were reduced. Htau‐4R expression suppressed proliferation, promoted neuronal differentiation, and restored neu‐rite and axonal outgrowth. We suggest that the tau‐4R isoform essentially contributes to hippocampal development by controlling proliferation and differentiation of neuronal precursors.–Sennvik K., Boekhoorn, K., Lasrado, R., Terwel, D., Verhaeghe, S., Korr, H., Schmitz, C., Tomiyama, T., Mori, H., Krugers, H., Joels, M., Ramakers, G. J. A., Lucassen, P. J., Van Leuven F. Tau‐4R suppresses proliferation and promotes neuronal differentiation in the hippocampus of tau knockin/knockout mice. FASEB J. 21, 2149–2161 (2007)

The aging brain: accumulation of DNA damage or neuron loss?

Age-related molecular and cellular alterations in the central nervous system are known to show selectivity for certain cell types and brain regions. Among them age-related accumulation of nuclear (n) DNA damage can lead to irreversible loss of genetic information content. In the present study on the aging mouse brain, we observed a substantial increase in the amount of nDNA single-strand breaks in hippocampal pyramidal and granule cells as well as in cerebellar granule cells but not in cerebellar Purkinje cells. The reverse pattern was found for age-related reductions in total numbers of neurons. Only the total number of cerebellar Purkinje cells was significantly reduced during aging whereas the total numbers of hippocampal pyramidal and granule cells as well as of cerebellar granule cells were not. This formerly unknown inverse relation between age-related accumulation of nDNA damage and age-related loss of neurons may reflect a fundamental process of aging in the central nervous system.

Selective loss of unmyelinated nerve fibers after extracorporeal shockwave application to the musculoskeletal system

Application of extracorporeal shockwaves (ESW) to the musculoskeletal system may induce long-term analgesia in the treatment of chronic tendinopathies of the shoulder, heel and elbow. However, the molecular and cellular mechanisms behind this phenomenon are largely unknown. Here we tested the hypothesis that long-term analgesia caused by ESW is due to selective loss of nerve fibers in peripheral nerves. To test this hypothesis in vivo, high-energy ESW were applied to the ventral side of the right distal femur of rabbits. After 6 weeks, the femoral and sciatic nerves were investigated at the light and electron microscopic level. Application of ESW resulted in a selective, substantial loss of unmyelinated nerve fibers within the femoral nerve of the treated hind limb, whereas the sciatic nerve of the treated hind limb remained unaffected. These data might indicate that alleviation of chronic pain by selective partial denervation may play an important role in the effects of clinical ESW application to the musculoskeletal system.

Cell-Type-Specific Differences in Age-Related Changes of DNA Repair in the Mouse Brain - Molecular Basis for a New Approach to Understand the Selective Neuronal Vulnerability in Alzheimer's Disease

Despite intensive research over the last decades, the molecular basis of the selective neuronal vulnerability in Alzheimers disease (AD) is still largely unknown. In this context we have recently shown by means of quantitative autoradiography that presumably all types of neurons in the mouse brain suffer an age-related decrease in the rate of mitochondrial DNA synthesis, while in contrast only some distinct types of neurons showed a decrease in the rate of spontaneous overall nuclear DNA repair measured as unscheduled nuclear DNA synthesis. Most strikingly, there was a highly positive correlation to be found between that group of neurons in the mouse brain showing the age-related decrease in the rate of spontaneous overall nuclear DNA repair (pattern X) and the pattern of neurons in the human brain which - according to the literature - are affected by the formation of neurofibrillary tangles in AD (pattern Y). To minimize the risk that this correlation was a result of mere chance based on the selection of the nine types of neurons investigated thus far, in the present study nine further types of neurons in phylogenetically different regions of the mouse brain were investigated by using the same method. An age-related decrease in the rate of spontaneous overall nuclear DNA repair was found only for projection neurons of brain areas with a more plastic, variable and/or malleable structure over phylogenesis but neither for projection neurons of brain areas with a more rigid, invariant and/or conservative structure over phylogenesis nor for interneurons. The obtained results confirmed the highly positive correlation between the aforementioned patterns X and Y. Together with a wealth of data from the literature regarding age-related neuron loss in both the rodent and the human brain, these results may indeed indicate a new approach for understanding the selective neuronal vulnerability in AD.

Antioxidants and Alzheimerʼs disease: from bench to bedside (and back again)

Purpose of reviewAccumulating evidence from both animal and human studies indicates a major role for oxidative damage in the pathogenesis of Alzheimers disease, occurring even before symptoms arise and both β-amyloid-containing plaques and neurofibrillary tangles are formed. This raises the possibility of preventing, or at least slowing down, the progression of Alzheimers disease by the use of antioxidants. In this review, we present recent studies on the association between oxidative stress and Alzheimers disease pathology, and on the efficacy of dietary, exogenous antioxidants to prevent or attenuate the progression of Alzheimers disease. Recent findingsRecent prospective studies have indicated that dietary intake of several exogenous antioxidants is associated with a lower risk for Alzheimers disease. This suggests that people at risk for developing Alzheimers disease or being in the early phases of this disease may benefit from intervention with exogenous antioxidants. The clinical studies carried out so far, however, do not provide the final answer to whether antioxidants are truly protective against Alzheimers disease. SummaryThere is compelling evidence that oxidative stress is involved in Alzheimers disease pathogenesis, and several lines of evidence indicate that administration of antioxidants may be useful in prevention and treatment of Alzheimers disease. Further clinical studies, based on larger cohorts studied over a longer period of time, are needed, however, to test this hypothesis. Furthermore, for the future one might expect balanced upregulation of both exogenous and endogenous antioxidants as one of the best treatment strategies for preventing or at least slowing down the progression of Alzheimers disease.

Use of cryostat sections from snap-frozen nervous tissue for combining stereological estimates with histological, cellular, or molecular analyses on adjacent sections.

Adequate tissue preparation is essential for both modern stereological and immunohistochemical investigations. However, combining these methodologies in a single study presents a number of obstacles pertaining to optimal histological preparation. Tissue shrinkage and loss of nuclei/nucleoli from the unprotected section surfaces of unembedded tissue used for immunohistochemistry may be problematic with regard to adequate stereological design. In this study, frozen cryostat sections from hippocampal and cerebellar regions of two rat strains and cerebellar and cerebral regions from a human brain were analyzed to determine the potential impact of these factors on estimates of neuron number obtained using the optical disector. Neuronal nuclei and nucleoli were clearly present in thin sections of snap-frozen rat (3 microm) and human (6 microm) tissue, indicating that neuronal nuclei/nucleoli are not unavoidably lost from unprotected section surfaces of unembedded tissue. In order to quantify the potential impact of any nuclear loss, optical fractionator estimates of rat hippocampal pyramidal cells in areas CA1-3 and cerebellar granule and Purkinje cells were made using minimal (1 microm) upper guard zones. Estimates did not differ from data reported previously in the literature. This data indicates that cryostat sections of snap-frozen nervous tissue may successfully be used for estimating total neuronal numbers using optical disectors.