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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The neurons that accumulate beta/A4 amyloid protein precursor (APP) after transient cerebral ischemia were characterized by comparing their distribution with those destined to suffer delayed neuronal death or those with induction of 72-kDa heat-shock protein. With immunohistochemistry of APP in gerbil brains, no alterations were detected after ischemia for 2 min and subsequent reperfusion for up to 7 days, whereas after ischemia for 3 min and reperfusion for 48 h, a small number of neurons, intensely immunoreactive for APP, were found to be scattered in the CA1 subfield of the hippocampus and the layer V/VI of the frontoparietal cortex. After reperfusion for 24 h following ischemia for 5 or 15 min, a large number of densely stained neurons appeared in the subiculum, and CA3 subfield of the hippocampus, and layers III and V/VI of the frontoparietal cortex. The majority of these neurons did not undergo delayed neuronal death after reperfusion for 72 h and thereafter. APP and heat-shock protein were upregulated in the same regions, but mostly in distinct neurons. These results indicate that APP accumulates in the neurons marginating the regions destined to die, and the majority of these neurons seem to survive after ischemic insult.
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PMID:Temporal profiles of accumulation of amyloid beta/A4 protein precursor in the gerbil after graded ischemic stress. 801 2

Glutamate is the primary excitatory amino acid in the mammalian central nervous system. Normal excitation of glutamate receptors initiates the stimulation of phospholipases and lipases with the generation of second messengers that are necessary for normal cell function. The overstimulation of glutamate receptors can initiate a cascade of biochemical events including stimulation of membrane phospholipid turnover, excessive calcium entry, abnormal phosphorylation, and proteolysis. These events may be responsible for neuronal injury and degeneration found in Alzheimer disease, ischemia, spinal cord trauma, epilepsy, and Huntington disease.
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PMID:Involvement of glutamate receptors, lipases, and phospholipases in long-term potentiation and neurodegeneration. 805 91

Proteolytic modifications of amyloid precursor protein (APP) play key roles in the development of Alzheimer's disease. However, each specific in vivo process has not yet been fully resolved in spatial terms because the orthodox approach employing electrophoretic analysis requires homogenization of samples and thus provides limited information on the localization of the process. To acquire such spatial information for the primary process involved in beta-amyloidogenesis, we have designed and developed a novel antibody exclusively specific to APP fragments possessing the exact amino terminus of the major beta-amyloid (A beta) peptide. Use of this antibody revealed that cleavage of APP at the amino terminal position of the A beta sequence is a normal steady-state process in gerbil hippocampus. Furthermore, nonfatal transient (10 min) forebrain ischemia followed by reperfusion enhanced the initial beta-amyloidogenic reaction mainly in pyramidal cells of CA1 sector and of dentate gyrus prior to and along with delayed neuronal degeneration. The APP fragments accumulated in cell bodies and dendrites of the neurons. These results suggest that beta-amyloidogenesis may involve a process that is also activated in postischemic brain and that ischemia-like conditions may contribute to pathogenic A beta accumulation.
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PMID:Spatial resolution of the primary beta-amyloidogenic process induced in postischemic hippocampus. 819 61

Throughout evolution the brain has acquired elegant strategies to protect itself against a variety of environmental insults. Prominent among these are signals released from injured cells that are capable of initiating a cascade of events in neurons and glia designed to prevent further damage. Recent research has identified a remarkably large number of neuroprotection factors (NPFs), whose expression is increased in response to brain injury. Examples include the neurotrophins (NGF, NT-3, NT-5, and BDNF), bFGF, IGFs, TGFs, TNFs and secreted forms of the beta-amyloid precursor protein. Animal and cell culture studies have shown that NPFs can attenuate neuronal injury initiated by insults believed to be relevant to the pathophysiology of traumatic brain injury (TBI) including excitotoxins, ischemia, and free radicals. Studies of the mechanism of action of these NPFs indicate that they enhance cellular systems involved in maintenance of Ca2+ homeostasis and free radical metabolism. Recent work has identified several low-molecular-weight lipophilic compounds that appear to mimic the action of NPFs by activating signal transduction cascades involving tyrosine phosphorylation. Such compounds, alone or in combination with antioxidants and calcium-stabilizing agents, have proved beneficial in animal studies of ischemic brain injury and provide opportunities for development of preventative/therapeutic approaches for TBI.
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PMID:Endogenous neuroprotection factors and traumatic brain injury: mechanisms of action and implications for therapy. 820 25

The suspected involvement of the beta-amyloid precursor protein (beta APP) in the etiology of Alzheimer's disease (AD) has been strengthened by recent genetic evidence, but pursuit of the mechanisms involved will initially require basic cell biology approaches. Several studies have concentrated on toxic activities of beta-amyloid peptide (beta AP) itself, illuminating its contributions to excitotoxicity and calcium-mediated degeneration in general. We now know that generation of beta AP from beta APP also compromises the production of an important set of trophic factors: the secreted forms of beta APP (APPS), which may act--ironically--by conferring protection from calcium-mediated insults. Therefore, conditions which contribute to the formation of beta AP (possibly including ischemia) not only produce an agent which exacerbates calcium-mediated cell death, but also reduce the levels of one of the few factors able to rescue calcium homeostasis. The implications of these postulates and their relationship to the process of aging are discussed.
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PMID:beta-Amyloid precursor protein mismetabolism and loss of calcium homeostasis in Alzheimer's disease. 823 76

We studied changes in the spatial and temporal distribution of the beta amyloid precursor protein (APP) of Alzheimer's disease (AD) in experimental ischemic brain injury. Rats with repeated reversible occlusions of one middle cerebral artery showed striking APP reactivity in astrocytic processes in perifocal regions and adjacent white matter. APP reactive dystrophic axons and neurons were also evident in the cortex and hippocampus ipsilateral to the MCA occlusion. Such changes were similarly apparent in animals subjected to partial forebrain ischemia induced by bilateral occlusion of the carotid arteries. Our studies suggest that focal ischemic insults or chronic hypoperfusion leads to increased accumulation or induction of APP in surviving cellular elements that may relate to the processes involved in beta amyloid deposition in AD.
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PMID:The amyloid precursor protein in ischemic brain injury and chronic hypoperfusion. 823 81

Transient global forebrain ischemia induces in rat brain a large increase of expression of the immediate early genes c-fos and c-jun and of the mRNAs for the 70-kDa heat-shock protein and for the form of the amyloid beta-protein precursor including the Kunitz-type protease-inhibitor domain. At 24 hr after ischemia, this increased expression is particularly observed in regions that are vulnerable to the deleterious effects of ischemia, such as pyramidal cells of the CA1 field in the hippocampus. In an attempt to find conditions which prevent the deleterious effects of ischemia, representatives of three different classes of K+ channel openers, (-)-cromakalim, nicorandil, and pinacidil, were administered both before ischemia and during the reperfusion period. This treatment totally blocked the ischemia-induced expression of the different genes. In addition it markedly protected neuronal cells against degeneration. The mechanism of the neuroprotective effects involves the opening of ATP-sensitive K+ channels since glipizide, a specific blocker of that type of channel, abolished the beneficial effects of K+ channel openers. The various classes of K+ channel openers seem to deserve attention as potential drugs for cerebral ischemia.
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PMID:K+ channel openers prevent global ischemia-induced expression of c-fos, c-jun, heat shock protein, and amyloid beta-protein precursor genes and neuronal death in rat hippocampus. 841 18

We used various antibodies to the beta amyloid precursor protein (APP) of Alzheimer's disease to study changes in the cellular distribution of APP in experimental ischemic brain injury. In contrast to sham operated controls, rats with repeated reversible occlusions of one middle cerebral artery showed striking APP reactivity in astrocytic processes in perifocal regions and white matter tracts. Dystrophic axons and neurons with accumulated APP were also evident in the ipsilateral neocortex and hippocampus. Such changes were also apparent in rats subjected to partial forebrain ischemia by bilateral occlusion of the carotid arteries. Our studies suggest that focal ischemic insults or chronic hypoperfusion leads to increased accumulation of APP in surviving brain cells that may pertain to enhanced beta amyloid deposition in Alzheimer's disease.
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PMID:Accumulation of the beta amyloid precursor protein at sites of ischemic injury in rat brain. 845 62

We have studied amyloid precursor protein (APP) expression in rat brain following transient global ischemia. Ischemic damage 24 h after 30 min of four-vessel occlusion (4VO) was limited to the caudate nucleus; hippocampal pyramidal neurons appeared histologically normal by light microscopy. Consistent with ongoing neurodegeneration in the caudate nucleus, microtubule-associated protein-2 (MAP-2) levels assessed by immunoblots were significantly reduced in homogenates of caudate nucleus after 4VO. MAP-2 levels In the hippocampus were comparable to control values. In contrast, full length APP levels in both the caudate nucleus and hippocampal homogenates were significantly decreased following 4VO despite normal hippocampal morphology at 24 h. These findings suggest that decrements in full length APP precede overt neuronal damage and may play a role in the subsequent delayed neurodegeneration in the hippocampus.
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PMID:Decrease in amyloid precursor protein precedes hippocampal degeneration in rat brain following transient global ischemia. 849 67

Several cellular signaling systems have been implicated in the neuronal death that occurs both in development ("natural" cell death) or in pathological conditions such as stroke and Alzheimer's disease (AD). Here we consider the possibility that neuronal degeneration in an array of disorders including stroke and AD arises from one or more alterations in calcium-regulating systems that result in a loss of cellular calcium homeostasis. A long-standing hypothesis of neuronal injury, the excitatory amino acid (EAA) hypothesis, is revisited in light of new supportive data concerning the roles of EAAs in stroke and the neurofibrillary degeneration in AD. Two quite new concepts concerning mechanisms of neuronal injury and death are presented, namely: 1) growth factors normally "stabilize" intracellular free calcium levels ([Ca2+]i) and protect neurons against ischemic/excitotoxic injury, and 2) aberrant processing of beta-amyloid precursor protein (APP) can cause neurodegeneration by impairing a neuroprotective function of secreted forms of APP (APPs) which normally regulate [Ca2+]i. Altered APP processing also results in the accumulation of beta-amyloid peptide which contributes to neuronal damage by destabilizing calcium homeostasis; in AD beta-amyloid peptide may render neurons vulnerable to excitotoxic conditions that accrue with increasing age (e.g., altered glucose metabolism, ischemia). Growth factors may normally protect neurons against the potentially damaging effects of calcium influx resulting from energy deprivation and overexcitation. For example, bFGF, NGF and IGFs can protect neurons from several brain regions against excitotoxic/ischemic insults. Growth factors apparently stabilize [Ca2+]i by several means including: a reduction in calcium influx; enhanced calcium extrusion or buffering; and maintenance or improvement of mitochondrial function. For example, bFGF can suppress the expression of a N-methyl-D-aspartate (NMDA) receptor protein that mediates excitotoxic damage in hippocampal neurons. Growth factors may also prevent the loss of neuronal calcium homeostasis and the increased vulnerability to neuronal injury caused by beta-amyloid peptide. Since elevated [Ca2+]i can elicit cytoskeletal alterations similar to those seen in AD neurofibrillary tangles, we propose that neuronal damage in AD results from a loss of calcium homeostasis. The data indicate that a variety of alterations in [Ca2+]i regulation may contribute to the neuronal damage in stroke and AD, and suggest possible means of preventing neuronal damage in these disorders.
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PMID:Altered calcium signaling and neuronal injury: stroke and Alzheimer's disease as examples. 851 77


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