Current Neurovascular Research - Volume 4, Issue 2, 2007

With the continued expansion of medical technologies and new strategies for human disease, we can sometimes fall prey to the belief that successful clinical therapies will consistently employ the desired attributes of safety and efficacy as common denominators. Yet, even for some remarkable and presumably safe diagnostic techniques such as magnetic resonance imaging, these assumptions may fall short of our actual experience. For example, there exist potential adverse effects of exposure to elevated magnetic field levels that exist during magnetic resonance imaging. It is true that magnetic fields occur naturally throughout the planet, but human derived magnetic fields can further enhance the intensity of naturally occurring magnetic fields. Industries that involve railways operating from direct current electrical supply sources or that employ magnetic levitation train systems can lead to the exposure of significant magnetic fields. In addition, commercial activities related to aluminum or steel production using intensified alternating currents also can result in magnetic fields that may be beyond normal human tolerance. In the healthcare system, magnetic resonance imaging for diagnostics can easily generate increased magnetic fields that may pose risks for both magnetic resonance imaging technicians and the patients under evaluation. Adverse affects from strong magnetic fields are multifaceted and can result in the acute onset of gastric distress, nausea, and vertigo. In regards to more long-term effects, magnetic field exposure has been tied to cerebral neoplasms, lung carcinoma, and hematological cancers. Some studies have suggested that exposure to magnetic fields can increase the risk of spontaneous abortions. More recent work involving magnetic resonance imaging previously published in this journal adds further concern to potential developmental abnormalities with magnetic field exposure by demonstrating in rodents exposed to a 1.5 T magnetic resonance image field for one week the subsequent onset of reference memory deficits (Yang et al., 2007). It should be noted that further work especially with more rigorous controls and statistically powered clinical trials is required, since some prior investigations did not exclude for the effects of confounding variables such as concurrent toxic substance exposure. So how does one develop new therapies that will offer efficacy for disease treatment, but also will not harm the afflicted individual patient? Early scientific investigation has provided us with both a clear vision and a solid foundation for future discovery. During the 1700s, Antoine Lavoisier, Karl Scheele, and Joseph Priestley independently relied upon a variety of experimental models to illustrate that air and its component oxygen were vital to sustain processes associated with combustion as well as life. Lavoisier subsequently carried this work further with animal models to illustrate that oxygen based upon concentration and duration of exposure could be either beneficial or toxic to an organism. These early models of experimentation laid some of the groundwork for today's science and the critical reliance upon both cell and animal models for the investigation of the etiology and treatment of human disease processes. Present models of human disease have become so diverse in nature that it would be almost inconceivable for one to foresee from several years past that the genetic construction of cell lines or the reliance upon aquatic animal models could for the most part accurately predict and sharply focus therapeutic strategies for a wide range of clinical disorders. This issue of Current Neurovascular Research serves to highlight the vantage points of a broad discipline of experimental models that promote the development of basic research to the realities of clinical care. In original and review articles, unique strategies describe the use of fused embryonic rodent neurons with neuroblastoma cell lines, the deployment of embryonic, neuronal, and adult mesenchymal stem cells for chronic neurodegenerative disorders, the development of ischemic animal models for furthering the understanding of the cellular pathways that occur during stroke and Alzheimer's disease, and the burgeoning reliance upon the Zebrafish model for a host of human disorders. Although it is unlikely that any single experimental model of human disease will ever be capable of replicating the complex disease processes of the human body, it is clear that the visionary minds of Lavoisier, Scheele, and Priestley have led us upon an exciting path of discovery coupled with great insight and we are enthusiastic in this issue of Current Neurovascular Research to hopefully foster this same course for our readers today.

Cholinergic cell lines were established by fusion of embryonic day 17 wild-type neurons from rat basal forebrain (BF) and upper brainstem (BS) with N18tg neuroblastoma cells. Isolated clones expressed choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS) activities that were increased upon differentiation with retinoic acid. Clones from the BF expressed high levels of the tyrosine kinase type A (TrkA) receptor expression and activation of the mitogen-activated kinase ERK2 upon treatment with nerve growth factor. Like wild-type cholinergic populations, the six clones studied were variably resistant to nitric oxide (NO) excess from addition of S-nitroso-N-acetyl-D, L-penicillamine (SNAP). Of these, the BS2 clone exhibited resistance like in vivo BS cholinergic neurons, while the MS10 clone mimicked in vivo BF vulnerability. Apoptosis in response to NO excess was preceded by increases in mitochondrial responses bax/bcl-2 ratios, but cytochrome C was not released. Mitochondrial levels of apoptosis initiating factor (AIF) were either unchanged or increased, and only in MS clones was endonuclease G (EndoG) released. Microarray data indicated the existence of endoplasmic reticular (ER) stress and caspase-4 and caspase-12 were involved in the pathway to DNA fragmentation. The array data also indicated a survival role for mdm2, and its blockade rendered vulnerable the brainstem survivor clone BS2. Akt and ERK1/2 pathways were activated in response to NO and their blockade increased DNA fragmentation. Blockade of GSK-3α/β, a downstream target of Akt, reduced SNAP toxicity and this was more prominent in basal forebrain clones. We have identified two cholinergic cell lines useful for molecular studies of cholinergic vulnerability. We hypothesize that, in cholinergic neurons, control of ER stress signaling may be a major factor in differential vulnerability.

Atherosclerosis may cause severe stenosis of the arteries supplying the brain, which induces chronic cerebral hypoperfusion. Although an infarction often occurs in the chronically hypoperfused brain area, it has been uncertain whether the stroke severity is attenuated or increased when further decrease of blood flow occurs. To test the hypothesis that chronic cerebral hypoperfusion is protective against the subsequent severe ischemia, we examined the effect of chronic cerebral hypoperfusion on brains subjected to acute focal ischemia. Spontaneous hypertensive rats were subjected to middle cerebral artery occlusion/reperfusion four weeks after bilateral common carotid artery ligation (BCAL) or sham operation. The rats with BCAL had smaller infarctions, determined by 2,3,5- triphenyltetrazolium hydrochloride staining, and less severe neurologic deficits than those with sham operation. The number of DNAdamaged cells, examined by the in situ nick translation study, was significantly reduced in animals with BCAL. Immunoreactivity for apurinic/apyrimidinic endonuclease/redox factor-1, which plays a role in cellular defense mechanism, was markedly increased in those with BCAL. Indirect evidence of extracellular matrix remodeling, which might be associated with adaptive arteriogenesis or angiogenesis, was obtained in the form of increased matrix metalloproteinase-2 activity in them. These findings provide experimental evidence that chronic cerebral hypoperfusion would be protective against subsequent severe ischemic insults.

Stem cell replacement has emerged as the novel therapeutic strategy for Parkinson's disease (PD). Control of motor behavior is lost in PD due to the selective degeneration of mesencephalic dopamine neurons (DA) in the substantia nigra. This progressive loss of DA neurons results in devastating symptoms for which there is no cure. Debilitating side effects often result from chronic pharmacological treatment, hence current investigations into cell transplantation therapy as a substitute and/or adjuvant to other therapeutics. Clinical trials with fetal DA tissue have provided evidence that cell transplantation could be a viable alternative. Limited availability of fetal tissue, combined with variable outcome led to emphasis on other sources of cells, such as stem cells. This review focuses on three stem cell sources (embryonic, neural, and adult mesenchymal). Also discussed is the molecular differentiation into mature DA neurons, the various protocols that have been developed to generate DA neurons from various stem cells, and the current state of stem cell therapy for PD.

Although the zebrafish model provides an important platform for the study of developmental biology, recent work with the zebrafish model has extended its application to a wide variety of experimental studies relevant to human disease. Currently, the zebrafish model is used for the study of human genetic disease, caveolin-associated muscle disease, homeostasis, kidney development and disease, cancer, cardiovascular disorders, oxidative stress, caloric restriction, insulin-like pathways, angiogenesis, neurological diseases, liver disease, hemophilia, bacterial pathogenesis, apoptosis, osteoporosis, immunological studies, germ cell study, Bardet-Biedl syndrome gene (BBS11), Alzheimer's disease, virology studies and vaccine development. Here we describe the essential use of the zebrafish model that applies to several clinical diseases. With increased understanding of the cellular mechanisms responsible for disease, we can use knowledge gained from the zebrafish model for the development of therapeutics.

This review demonstrated that ischemic brain injury induces chronic changes in blood-brain barrier in the gray and white matter. This insufficiency of blood-brain barrier may allow entry of uncellular blood components such as different fragments of amyloid precursor protein and cellular blood components like leukocytes and platelets into the brain parenchyma. These blood components may have chronic harmful effects on the ischemic neuronal cells, axons and myelin and can intensify and finish the neuropathology in ischemic brain parenchyma. Pathological accumulation of different toxic fragments of amyloid precursor protein in extracellular space and myelinated axons appears after ischemic blood-brain barrier injury and seem to be concomitant with, but independent of neuronal ischemic cytoplasmic injury. It seems that ischemic blood-brain barrier disturbances may play an important, both direct and indirect role in the pathogenesis of extra- and intracellular space in gray and white matter lesions following ischemic episode. This neuropathology appears to have similar character and distribution as in sporadic Alzheimer's disease. This review presented chronic micro-blood-brain barrier openings in ischemic gray and white matter lesions that probably would act as seeds of future Alzheimer’s amyloid plaques.

Although alcohol is believed to exert deleterious effects on the nervous system in general, its specific effect on the brain's immune system remains poorly understood. In particular, the effects of alcohol consumption on the immune and inflammatory responses in the central nervous system (CNS) have not been extensively investigated. Here, reviewed is the recent progress on how ethanol influences the signal transduction pathways of the inflammatory activation of brain microglia, which are thought to function as the resident immune defense system of the brain. Microglia are the CNS representatives of macrophages, which have the ability to clean up cellular debris. Microglia participate in neuroinflammation in response to various intrinsic or extrinsic stimuli. It has been recently suggested that microglial signal transduction is one of the main targets of ethanol action in the brain: ethanol exposure selectively modulates the intracellular signal transductions of microglia, rather than globally inhibiting signaling pathways in a nonspecific manner. Deregulation by ethanol of the inflammatory activation signaling of microglia may contribute to the derangement of CNS immune and inflammatory responses.

Neurotrophins are proteins that regulate neuronal survival, axonal growth, synaptic plasticity and neurotransmission. They are members of the neurotrophic factors family and include factors such as the nerve growth factor (NGF), the brain derived neurotrophic factor (BDNF), the neurotrophin-3 (NT-3), and the neurotrophin-4/5 (NT-4/5). These molecules bind to two types of receptors: i) tyrosine kinase receptors (TrkA, TrkB, TrkC) and ii) a common neurotrophin receptor (p75NTR). The two receptor types can either suppress or enhance each other's actions. Neurotrophins have a multifunctional role both in the central and peripheral nervous system. They have been suggested as axonal guidance molecules during the growth and regeneration of nerves. It has also been proven that they stimulate axonal growth by mediating the polymerization and accumulation of F-actin in growth cones and axon shafts. Neurotrophins, as other neurotrophic factors, have been shown that they reduce neuronal injury by exposure to excitotoxins, glucose deprivation, or ischemia. Furthermore, the nerve regeneration promoting effect of these growth factors is well documented for many different models of central or peripheral nervous system injury. Several studies have shown that exogenous administration of these factors has protective properties for injured neurons and stimulates axonal regeneration. Based on these properties, these molecules may be used as therapeutic agents for treating degenerative diseases and traumatic injuries of both the central and peripheral nervous system.