Christoph Redecker

Widespread and Long-Lasting Alterations in GABAA-Receptor Subtypes after Focal Cortical Infarcts in Rats: Mediation by NMDA-Dependent Processes

Impairment of inhibitory neurotransmission has been reported to occur in widespread, structurally intact brain regions after focal ischemic stroke. These long-lasting alterations contribute to the functional deficit and influence long-term recovery. Inhibitory neurotransmission is primarily mediated by γ-aminobutyric acid (GABA)A receptors assembled of five subunits that allow a variety of adaptive changes. In this study, the regional distribution of five major GABAA-receptor subunits (α1, α2, α3, α5, and γ2) was analyzed immunohistochemically 1, 7, and 30 days after photochemically induced cortical infarcts. When compared with sham-operated controls, a general and regionally differential reduction in immunostaining was found within the cortex, hippocampus, and thalamus of both hemispheres for almost all subunits. Within ipsilateral and contralateral neocortical areas, a specific pattern of changes with a differential decrease of subunits α1, α2, α5, and γ2 and a significant upregulation of subunit α3 was observed in the contralateral cortex homotopic to the infarct. This dysregulation was most prominent at day 7 and still present at day 30. Interestingly, a single application of the noncompetitive N-methyl-D-aspartate–receptor antagonist MK-801 during lesion induction completely blocked these bihemispheric alterations. Cortical spreading depressions induced by topical application of KCl do not change GABAA-receptor subunit expression. As alterations in subtype distribution crucially influence inhibitory function, ischemia-induced modifications in GABAA-receptor subtype expression may be of relevance for functional recovery after stroke.

Effects of Skilled Forelimb Training on Hippocampal Neurogenesis and Spatial Learning After Focal Cortical Infarcts in the Adult Rat Brain

Background and Purpose— Environmental stimulation consistently increases dentate neurogenesis in the adult brain and improves spatial learning. We tested the hypothesis whether specific rehabilitative training of an impaired forelimb influences these processes after focal cortical infarcts. Methods— Focal cortical infarcts were induced in the forelimb sensorimotor cortex using the photothrombosis model. One group of infarcted animals and sham-operated controls housed in standard cages received one daily session of skilled reaching training of the impaired or dominant forelimb, respectively. A second group was transferred to an enriched environment, whereas a third group remained in the standard cages without further treatment. Bromodeoxyuridine was administered from day 2 until day 6 postinfarct. Proliferation and differentiation of newborn cells was analyzed at day 10 and 42 using immunocytochemistry with neuronal and glial markers and confocal laser scanning microscopy. Spatial learning was tested in the Morris water maze between days 35 and 41. Results— After cortical infarcts in the forelimb sensorimotor cortex, environmental enrichment as well as daily reaching training of the impaired paw both increase dentate neurogenesis and improve functional performance in the Morris water maze. Nevertheless, the reaching training-induced neurogenic response was significantly greater in nonlesioned controls associated with the best spatial learning performance in the water maze. Conclusions— Skilled forelimb training effectively stimulates dentate neurogenesis and spatial learning in the infarcted and healthy brain. However, this reaching training-induced increase in neurogenesis was reduced after cortical infarcts.

Rat focal cerebral ischemia induced astrocyte proliferation and delayed neuronal death are attenuated by cyclin-dependent kinase inhibition

Astroglial proliferation and delayed neuronal death are two common pathological processes in the ischemic brain. However, it is not clear if astrogliosis causes delayed neuronal death. In this study, we addressed this potential linkage by examining the relationship between attenuated astrocyte proliferation, induced by cyclin-dependent kinase (CDK) inhibition, and delayed neuronal death in rat ischemic hippocampus. Our results show that following middle cerebral artery occlusion (MCAO), astrocyte hypertrophy and proliferation were closely associated with delayed neuronal death. Importantly, administration of olomoucine, a selective CDK inhibitor, not only suppressed astroglial proliferation and glial scar formation, but also decreased neuronal cell death in the ischemic boundary zone and hippocampal CA1 region at days 1 and 30 after MCAO. These results indicate that reactive astrogliosis and delayed neuronal death, at least in rat hippocampus, are sequential pathological events following MCAO. Therefore, suppressing astroglial cell cycle progression in acute focal cerebral ischemia may be beneficial to neuronal survival. Our study also implies that cell cycle regulation should be considered as a promising future therapeutic intervention in treating those neurological diseases characterized by an excessive astrocyte proliferation.

Induction of Neurogenesis in the Adult Dentate Gyrus by Cortical Spreading Depression

Background and Purpose— Spreading depression (SD) is an epiphenomenon of neurological disorders, like stroke or traumatic brain injury. These diseases have been associated with an increased neurogenesis in the adult rodent dentate gyrus. Such proliferative activity can also be induced by conditions that—like SD—coincide with a disturbed neuronal excitability, eg, epilepsy. Thus we hypothesized that SD might likewise influence hippocampal neurogenesis and potentially act as mediator of injury-induced neurogenesis. Methods— Repetitive cortical SD were induced by epidural application of 3 mol/L KCl. At different time points thereafter dentate gyrus neurogenesis was investigated by means of intraperitoneal bromodeoxyuridine injections and immunocytochemistry. Spatial learning and memory was tested in a Morris water maze. Results— Cortical SD significantly increased proliferative activity in the ipsilateral subgranular zone on days 2 and 4. We detected about 280% more newborn cells in the dentate gyrus of rats that received bromodeoxyuridine during the first week after SD and were allowed to recover for 6 weeks. Most of these cells expressed the mature neuronal marker NeuN. The mitogenic action of SD was suppressed by systemic administration of the NMDA receptor antagonist MK-801. Behavioral performance of SD animals in the Morris water maze did not improve significantly. Conclusions— From our data we postulate that the increased dentate gyrus neurogenesis observed after brain injury may at least partly be mediated by SD-like epiphenomena. Furthermore they indicate that even a strongly enhanced dentate gyrus neurogenesis may occur without significant improvements in hippocampus-dependent spatial learning and memory.

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.

Immunocytochemical Detection of Newly Generated Neurons in the Perilesional Area of Cortical Infarcts After Intraventricular Application of Brain-Derived Neurotrophic Factor

The adult brain responds to focal infarction with proliferation of glial subpopulations. In addition, cells that express the immature neuronal marker doublecortin have been found consistently in the perileisonal zone. We investigated whether application of brain-derived neurotrophic factor (BDNF) would influence this perilesional proliferative response. Photothrombotic infarcts were induced in the sensorimotor forelimb and hindlimb cortex of adult rats. Brain-derived neurotrophic factor or vehicle was continuously infused intraventricularly for 2 weeks after the infarct using osmotic minipumps. Proliferating cells were labeled by daily intraperitoneal injections of bromodeoxyuridine during the first 2 weeks and were quantified at days 14 and 42 using semiautomatic stereology. Triple immunofluorescence with antibodies against immature and mature neuronal and glial markers was used to identify the proliferating cell populations. On day 14 after intraventricular BNDF application, the numbers of doublecortin-positive cells were doubled in the perilesional zone. On day 42, BDNF-treated animals had a small number of mature neurons in these areas, whereas vehicle-treated controls did not. Behavioral analysis with a battery of sensorimotor tests revealed, however, that the alterations in the perilesional cellular response were not associated with an improved functional outcome.

CXCR4 prevents dispersion of granule neuron precursors in the adult dentate gyrus.

Neurogenesis in the adult dentate gyrus (DG) generates new granule neurons that differentiate in the inner one‐third of the granule cell layer (GCL). The migrating precursors of these neurons arise from neural stem cells (NSCs) in the subgranular zone (SGZ). Although it is established that pathological conditions, including epilepsy and stroke, cause dispersion of granule neuron precursors, little is known about the factors that regulate their normal placement. Based on the high expression of the chemokine CXCL12 in the adult GCL and its role in guiding neuronal migration in development, we addressed the function of the CXCL12 receptor CXCR4 in adult neurogenesis. Using transgenic reporter mice, we detected Cxcr4‐GFP expression in NSCs, neuronal‐committed progenitors, and immature neurons of adult and aged mice. Analyses of hippocampal NSC cultures and hippocampal tissue by immunoblot and immunohistochemistry provided evidence for CXCL12‐promoted phosphorylation/activation of CXCR4 receptors in NSCs in vivo and in vitro. Cxcr4 deletion in NSCs of the postnatal or mature DG using Cre technology reduced neurogenesis. Fifty days after Cxcr4 ablation in the mature DG, the SGZ showed a severe reduction of Sox2‐positive neural stem/early progenitor cells, NeuroD‐positive neuronal‐committed progenitors, and DCX‐positive immature neurons. Many immature neurons were ectopically placed in the hilus and inner molecular layer, and some developed an aberrant dendritic morphology. Only few misplaced cells survived permanently as ectopic neurons. Thus, CXCR4 signaling maintains the NSC pool in the DG and specifies the inner one‐third of the GCL as differentiation area for immature granule neurons.

A combined treatment with 1α,25-dihydroxy-vitamin D3 and 17β-estradiol reduces the expression of heat shock protein-32 (HSP-32) following cerebral cortical ischemia

1alpha,25-(OH)(2)-vitamin D(3) (1,25-D(3)) and 17beta-estradiol are both known to act neuroprotectively in certain experimental in vitro and in vivo settings and it has been noted that both steroids lead to an upregulation of certain neurotrophic factors. Here, we studied the effects of 1alpha,25-(OH)(2)-vitamin D(3) or 17beta-estradiol or their combined application on heat shock protein-32 (HSP-32) distribution after focal cortical ischemia using the well established photothrombosis model. Heat shock protein-32 is a well-established marker of the cerebral oxidative stress response and contributes to neuroprotection by metabolising cytotoxic free heme to carbon monoxide, iron and biliverdin. Photothrombotically lesioned rats were injected i.p. 1h after injury with either 1 microg 1alpha,25-(OH)(2)-vitamin D(3)/kg or 7 microg 17beta-estradiol/kg or a combination of both steroids. Groups of non-lesioned steroid-treated rats and lesioned, solvent-treated rats served as controls. In contrast to non-lesioned rats, in lesioned animals a significant increase in heat shock protein-32 expression occurred which was slightly, but non-significantly altered in the groups treated either with 1alpha,25-(OH)(2)-vitamin D(3) or 17beta-estradiol alone when compared to the solvent-treated control group. Only the combined treatment with 1alpha,25-(OH)(2)-vitamin D(3) and 17beta-estradiol resulted in a significant reduction of glial heat shock protein-32 immunoreactivity within the lesion-remote cortical areas supplied by the affected middle cerebral artery (MCA), indicating that both steroids act synergistically in a protective manner.

Enhanced Neurogenesis in the Hippocampal Dentate Gyrus during Antigen-Induced Arthritis in Adult Rat – A Crucial Role of Immunization

Neurogenesis in the subgranular zone of the mammalian hippocampal dentate gyrus contributes significantly to brain neuroplasticity. There is evidence that inflammation of the central nervous system inhibits neurogenesis but peripheral inflammation such as antigen-induced arthritis may rather enhance neurogenesis. Manifest arthritis is associated with symptoms such as pain and altered locomotion indicating that peripheral inflammation is associated with changes of both the immune system and the nervous system. This raises the intriguing question whether immune or neuronal factors or both actually drive changes of neurogenesis. Here we explored hippocampal neurogenesis in the rat during chronic antigen-induced arthritis in the knee joint. We analyzed neurogenesis in control rats, and in rats which were immunized for the antigen producing arthritis but which did not show arthritis and neurological symptoms, and in rats in which antigen injection into the knee produced manifest local inflammation and symptoms such as pain at the inflamed knee and altered locomotor behavior. Neurogenesis was assessed by quantifying bromodeoxyuridine-positive cells in sections of the complete hippocampal dentate gyrus. Compared to control animals, rats with antigen-induced arthritis presenting manifest local inflammation, hyperalgesia at the inflamed knee and significantly altered locomotion exhibited a significant increase of bromodeoxyuridine-positive cells. However, a similar increase in the number of such cells was found in rats which were only immunized against the antigen, but in which no local inflammatory response was induced and which thereby neither showed hyperalgesia nor alterations of locomotion. Thus we conclude that in peripheral immune-mediated arthritis the activation of the immune system in the process of immunization is the causal factor driving enhanced neurogenesis, and neither the local enhancement of inflammation nor the activation of the nervous system leading to neurological symptoms such as pain and altered locomotion. It seems noteworthy to further explore the clinical importance of this neuroimmune interaction.

Stroke-like onset of brain stem degeneration presents with unique MRI sign and heterozygous NMNAT2 variant: a case report

BackgroundAcute-onset neurodegenerative diseases in older patients are rare clinical cases, especially when the degeneration only affects specific regions of the nervous system. Several neurological disorders have been described in which the degeneration of brain parenchyma originates from and/or primarily affects the brain stem. Clinical diagnosis in these patients, however, is often complicated due to a poor understanding of these diseases and their underlying mechanisms.Case presentationIn this manuscript we report on a 73-year-old female who had experienced a sudden onset of complex neurological symptoms that progressively worsened over a period of 2xa0years. Original evaluation had suggested a MRI-negative stroke as underlying pathogenesis. The combination of patient’s medical history, clinical examination and exceptional pattern of brain stem degeneration presenting as “kissing swan sign” in MR imaging was strongly suggestive of acute onset of Alexander’s disease. This leukoencephalopathy is caused by GFAP (glial fibrilary acidic protein) gene mutations and may present with brain stem atrophy and stroke-like onset of symptoms in elderly individuals. However, a pathognomonic GFAP gene mutation could not be identified by Sanger sequencing.ConclusionsAfter an extended differential diagnosis and exclusion of other diseases, a definite diagnosis of the patient’s condition presently remains elusive. However, whole-exome sequencing performed from patient’s blood revealed 12 potentially disease-causative heterozygous variants, amongst which several have been associated with neurological disorders in vitro and in vivo – in particular the axon degeneration-related NMNAT2 gene.