Current Neurovascular Research - Volume 6, Issue 1, 2009

The development and distribution of secondary brain lesions, subsequent to ischemic stroke, are of considerable clinical interest but so far only a limited number of studies have investigated the distribution and development of these secondary lesions in detail. In this study, we used an animal model of focal ischemia caused by extradural compression of the sensorimotor cortex. This paradigm of focal ischemia was shown to produce a consistent pattern of secondary lesions located distally from the primary lesion. Functionally the primary brain lesion produced a transient neurological deficit, which was evaluated by daily beam walking tests. Morphological changes were assessed in parallel after the ischemic event using Fluoro-Jade (FJ) staining as a marker of neuronal cell death. Secondary brain lesions were observed in the thalamus as well as in the hippocampus. The first sign of the slowly developing secondary brain lesions was present on day 3 with subsequent lesions being identified until day 16 after the primary ischemia. In addition to the identification of neuronal cell death by the FJ assays, immunostaining for parvalbumin (PA), a marker of GABAergic interneurons, revealed a loss of PA-staining in the pyramidal layer of CA1 on day 3, thus showing a similar time pattern for loss of PA-staining as for the loss of FJ stained cells. Based upon our present results, we suggest that the current animal model of focal ischemia represents a valuable tool for studies concerning the development of secondary remote brain lesions and their association to impaired motor and cognitive functions.

Ischemic stroke causes cell necrosis with the exposure of extracellular ribonucleic acid (RNA) and other intracellular material. As shown recently, extracellular RNA impaired the blood-brain-barrier and contributed to vasogenic edema-formation. Application of ribonuclease 1 (RNase 1) diminished edema-formation and also reduced lesion volume in experimental stroke. Here we investigate whether reduction of lesion volume is due to the reduction of edema or of other neuroprotective means. Neuroprotective and edema protective effects of RNase 1 pretreatment were assessed using a temporary middle cerebral artery occlusion (MCAO) model in rats. Lesion volume was assessed on magnetic resonance imaging (MRI). T2- relaxation-time and midline-shift as well as brain water content (wet-dry-method) were measured to quantify edema formation. The impact of edema formation on infarct volume was evaluated in craniectomized animals. Exogenous RNase 1 was well tolerated and reduced edema-formation and infarct size (26.7% ± 10.7% vs. 41.0% ± 10.3%; p<0.01) at an optimal dose of 42 μg/kg as compared to placebo. Craniectomized animals displayed a comparable edema reduction but no reduction in infarct size. The present study introduces a hitherto unrecognized mechanism of ischemic brain damage and a novel neuroprotective approach towards acute stroke treatment.

Memory loss and cognitive failure are increasingly being identified as potential risks with the recognized increase in life expectancy of the general population. As a result, the development of novel therapeutic strategies for disorders such as Alzheimer's disease have garnered increased attention. The etiologies that can lead to Alzheimer's disease are extremely varied, but a number of therapeutic options are directed against amyloid-β peptide and inflammatory cell regulation to prevent or halt progressive cognitive loss. In particular, inflammatory microglial cells may have disparate functions that in some scenarios lead to disability through the removal of functional neurovascular cells and in other circumstances foster tissue repair. Given the significance microglial cells hold for neurodegenerative disorders, we therefore examined the function that amyloid (Aβ1-42) has upon the microglial cell line EOC 2 and identified a novel role for the forkhead transcription factor FoxO3a and caspase 3. Here we show that Aβ1-42 leads to progressive injury and apoptotic cell loss in microglial cells that involves both early phosphatidylserine (PS) externalization and late genomic DNA fragmentation over a 24 hour course. Prior to these injury programs, Aβ1-42 results in the activation and proliferation of microglia as demonstrated by increased proliferating cell nuclear antigen (PCNA) expression and bromodeoxyuridine (BrdU) uptake. Both apoptotic injury as well as the prior activation and proliferation of microglial cells relies upon the presence of FoxO3a, since specific gene silencing of FoxO3a promotes microglial cell protection and prevents the early activation and proliferation of these cells. Furthermore, Aβ1-42 exposure maintained FoxO3a in an unphosphorylated “active” state and facilitated the cellular trafficking of FoxO3a from the cytoplasm to the cell nucleus to potentially lead to “pro-apoptotic” programs by this transcription factor. One apoptotic program in particular appears to involve the activation of caspase 3, since loss of FoxO3a through gene silencing prevents the induction of caspase 3 activity by Aβ1-42.

Cerebral small vessel disease results in silent ischemic lesions (SIL) among which is leukoaraiosis. In this process, endothelial damage is probably involved. Endothelial progenitor cells (EPC), are involved in endothelial repair. By restoring the damaged endothelium, EPC could mitigate SIL and cerebral small vessel disease. Haptoglobin 1-1, one of three phenotypes of haptoglobin, relates to SIL and may therefore attenuate the endothelial repair by EPC. Our aim was to quantify EPC number and function and to assess haptoglobin phenotype and its effect on EPC function in patients with a high prevalence of SIL: lacunar stroke patients. We assessed EPC In 42 lacunar stroke patients and 18 controls by flow cytometry and culture with fetal calf serum, patient and control serum. We determined haptoglobin phenotype and cultured EPC with the three different haptoglobin phenotypes. We found that EPC cluster counts were lower in patients (96.9 clusters/well ± 83.4 (mean ± SD)), especially in those with SIL (85.0 ± 64.3), than in controls (174.4 ± 112.2). Cluster formation was inhibited by patient serum, especially by SIL patient serum, but not by control serum. Patients with haptoglobin 1-1 had less clusters in culture, and when haptoglobin 1-1 was added to EPC cultures, cluster numbers were lower than with the other haptoglobin phenotypes. We conclude that lacunar stroke patients, especially those with SIL, have impaired EPC cluster formation, which may point at decreased endothelial repair potential. The haptoglobin 1-1 phenotype is likely a causative factor in this impairment.

Neurospheres can be generated from the mouse fetal forebrain by exposing multipotent neural stem cells (NSCs) to epidermal growth factor (EGF). In the presence of EGF, NSCs can proliferate continuously while retaining the potential to differentiate into neurons, astrocytes and oligodendrocytes. We examined the expression pattern of the neurotrophin (NT) receptors tropomysin-related kinase (TRK)-A, TRK-B, TRK-C and p75 neurotrophin receptor (p75NTR) in NSCs and the corresponding lineage cells. Furthermore, we analyzed the action of the NT Brain-Derived Neurotrophic Factor (BDNF) on NSCs' behavior. The effects of BDNF on NSC proliferation and differentiation were examined together with the signaling pathways by which BDNF receptors transduce signaling effects. We found that all the known NT receptors, including the truncated isoforms of TRK-B (t-TRK-B) and TRK-C (t-TRK-C), were expressed by Nestin-positive cells within the neurosphere. Proliferation was enhanced in Nestin-positive and BrdU-positive cells in the presence of BDNF. In particular, we show that t-TRK-B was abundantly expressed in NSCs and the corresponding differentiated glia cells while full length TRK-B (fl-TRK-B) was expressed in fully differentiated post-mitotic neurons such as the neuronal cells of the newborn mouse cortex, suggesting that BDNF may exert its proliferative effects on NSCs through the t-TRK-B receptor. Finally, we analyzed the cell fates of NSCs differentiated with BDNF in the absence of EGF and we demonstrate that BDNF stimulated the formation of differentiated cell types in different proportions through the MAP kinase, AKT and STAT-3 signaling pathways. Thus, the in-vivo regulation of neurogenesis may be mediated by the summation of signals from the BDNF receptors, in particular the t-TRK-B receptor, regulating physiological fates as diverse as normal neural replacement, excessive neural loss, or tumor development.

An increasing number of applications use nanospecie-fluorescent labeling technology; however, no established guidelines are available to warrant their safety for potential clinical use. Here, rTg4510 transgenic mice and their littermate controls were injected with fluorogold, a nanospecie tracer, or phosphate buffered saline (PBS) targeted to the right amygdala. No significant abnormal behavior was detected in any mice injected with PBS. After fluorogold injection, however, rTg4510 mice displayed persistent left-sided neurological deficits and left circling behavior for up to 14 days post-injection, while control mice demonstrated a transient syndrome. Mortality occurred only in rTg4510 mice and statistically significant differences appeared independent of age. An immunofluorescent study revealed TUNEL positive cells that were heavily and extensively distributed in the periamygdalar region that overlapped with the fluorogold deposit region in rTg4510 mice, whereas control mice showed only sporadic distribution of TUNEL-positive cells. Colocalization of TUNEL and caspase-3 active peptide immunoreactivity was identified in a subset of the cells, indicating an involvement of caspase-dependent apoptotic mechanisms. In conclusion, fluorogold induces damage in the central nervous system most noticeably in mice over-expressing human mutant tau.

Stroke and traumatic brain injuries often lead to cerebral edema and persistent elevations in intracranial pressure (ICP) that can be life threatening. Thus, rodent models would benefit from a simple and reliable method to measure ICP in awake, mobile animals. Up to now most techniques have been limited to anesthetized or immobile animals, which is not practical for following the prolonged elevations in ICP that follow stroke and traumatic brain injury. With an initial set of data, we describe a simple method that uses blood pressure telemetry sensors, which are commercially available (Data Sciences Int.) to measure ICP in freely moving rats for several days following implantation. Basically, an epidural cannula is secured to the skull and connected to the catheter of the telemetry probe, which is then secured inside a protective plastic shield on the skull. We confirm the sensitivity of our measurements by experimentally modifying ICP by either the Valsalva maneuver (abdominal compression) or a large ischemic brain injury. The Valsalva maneuver caused a small brief spike in ICP (lasting about 2-3 sec), whereas a transient middle cerebral artery occlusion substantially increased ICP (up to 50 mmHg) for approximately 3 days post-surgery. In summary, the current method allows for ICP to be continuously monitored in rats for several days, and thus is suitable for studies investigating mechanisms of raised ICP and in testing experimental treatments that mitigate it.

One of the current problems in medicine research is the development of safe drugs for the treatment of neurological disorders. Furthermore, there is a close relationship between the process of aging and the appearance of neurological disorders, particularly Parkinson's disease and Alzheimer's disease. Therefore, an ideal compound would have two characteristics: neuroprotective action and an anti-aging effect. The natural compound resveratrol is a suitable candidate for this purpose due to its low toxicity and antioxidant properties. In addition, recent research has shown that it has an anti-aging effect in rat, yeast, Caenorhabditis elegans, and Drosophila, although the mechanism involved in this process remains to be clarified. One hypothesis is that by activating Sirtuin 1, resveratrol modulates the activity of numerous proteins, including peroxisome proliferator-activated receptor coactivator-1α (PGC-1 alpha), the FOXO family, Akt (protein kinase B) and nuclear factor-κβ (NFκβ). This review summarises recent research on the molecular mechanisms through which resveratrol might exert its therapeutic effects via the interaction with Sirtuin 1, as well as other targets. In addition, we discuss the possibility of using resveratrol in the treatment of neurodegenerative diseases.