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Notes: Abstract: To obtain direct evidence of oxygen radical activity in the course of cerebral ischemia under different intraischemic temperatures, we used a method based on the chemical trapping of hydroxyl radical in the form of the stable adducts 2,3- and 2,5-dihydroxybenzoic acid (DHBA) following salicylate administration. Wistar rats were subjected to 20 min of global forebrain ischemia by two-vessel occlusion plus systemic hypotension (50 mm Hg). Intraischemic striatal temperature was maintained as normothermic (37°C), hypothermic (30°C), or hyperthermic (39°C) but was held at 37°C before and following ischemia. Salicylate was administered either systemically (200 mg/kg, i.p.) or by continuous infusion (5 mM) through a microdialysis probe implanted in the striatum. Striatal extracellular fluid was sampled at regular intervals before, during, and after ischemia, and levels of 2,3- and 2,5-DHBA were assayed by HPLC with electrochemical detection. Following systemic administration of salicylate, stable baseline levels of 2,3- and 2,5-DHBA were observed before ischemia. During 20 min of normothermic ischemia, a 50% reduction in mean levels of both DHBAs was documented, suggesting a baseline level of hydroxyl radical that was diminished during ischemia, presumably owing to oxygen restriction to tissue at that time. During recirculation, 2,3- and 2,5-DHBA levels increased by 2.5- and 2.8-fold, respectively. Levels of 2,3-DHBA remained elevated during 1 h of reperfusion, whereas the increase in 2,5-DHBA levels persisted for 2 h. The increases in 2,3- and 2,5-DHBA levels observed following hyperthermic ischemia were significantly higher (3.8- and fivefold, respectively). In contrast, no significant changes in DHBA levels were observed following hypothermic ischemia. The postischemic changes in DHBA content observed following local administration of salicylate were comparable to the results obtained with systemic administration, thus confirming that the hydroxyl radicals arose within brain parenchyma itself. These results provide evidence that hydroxyl radical levels are increased during postischemic recirculation, and this process is modulated by intraischemic brain temperature. Hence, these data suggest a possible mechanism for the effects of temperature on ischemic outcome and support a key role for free radical-induced injury in the development of ischemic damage.

Notes: Abstract: The purpose of this investigation was to investigate pathomechanisms responsible for the deleterious effects of repeated episodes of brief forebrain ischemia. Halothane-anesthetized male Wistar rats were subjected to either (a) a single 15-min period or (b) three 5-min periods (separated by 1 h) of global forebrain ischemia by bilateral carotid artery occlusions plus hypotension (50 mm Hg), followed by various periods of recirculation. Brain temperature was normothermic throughout. In one series of rats, extracellular levels of glutamate, glycine, and γ-aminobutyric acid (GABA) were measured in the dorsolateral striatum (n = 6–8 per group) and lateral thalamus (n = 4–6 per group) by microdialysis and HPLC before and during ischemia and during 3–5 h of recirculation. In a parallel series of rats (n = 6 per group), ischemic cell change was quantified at 2 (dark neurons), 24, or 72 h following either single or multiple ischemic insults. A single 15-min ischemic period led to massive glutamate release (13-fold increase; p= 0.001), which returned to normal by 20–30 min of recirculation and remained normal thereafter. By contrast, in rats with three 5-min periods of ischemia, the glutamate level rise with each repeated insult (four- to 4.5-fold; p〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:00223042:JNC2213:les" location="les.gif"/〉 0.02) was smaller than that observed during the single 15-min insult, but a late sustained rise (five- to six-fold; p 〈 0.05) occurred at 2–3 h of recirculation. Brief ischemia-induced elevations of glycine and GABA levels were detected in both the single- and multiple-insult groups, with normalization during recirculation. In contrast, the excitotoxic index, a composite measure of neurotransmitter release ([glutamate] X [glycine]/[GABA]), differed markedly following single versus multiple insults (p= 0.002 by repeated-measures analysis of variance) and increased by seven- to 12-fold (p 〈 0.05) at 1–3 h following the third insult. The total amount of glutamate released was 3.3-fold higher in the multiple-insult than in the single-insult group (p 〈 0.02). At 2 h of recirculation, histopathological analysis of dorsolateral striatum showed a significantly greater frequency of dark neurons in the multiple- than in the single-insult group (p 〈 0.05 by analysis of variance). In the thalamus, a higher frequency of ischemic neurons was seen in the multiple- than in the single-insult group at all intervals studied. Thus, in rats with multiple ischemic insults, accelerated ischemic damage was found in the striatum, and severe ischemic injury was documented in the thalamus. These results demonstrate that multiple ischemic insults lead to a massive, sustained glutamate accumulation and to a major increase in the excitotoxic index during early recirculation, which is not seen following a single brief ischemic episode. These neurochemical changes correlate with our histopathological data showing an accelerated evolution of striatal pathology at 2 h following multiple ischemic insults.

Notes: Abstract Recent experimental investigations have emphasized the importance of assessing both acute and chronic histopathological changes occurring after cerebral ischemia. The purpose of this study was to evaluate the temporal profile of neuronal, astrocytic and microglial alterations within vulnerable regions (striatum and CA1 sector of hippocampus) following transient global ischemia. Anesthetized Wistar rats underwent 10 min of normothermic (37° C) ischemia induced by bilateral carotid ligations plus hypotension (45–50 mm Hg) and were allowed to survive for periods ranging from 1 to 10 weeks (n = 4–6/ group) prior to quantitative histopathological analysis. Adjacent sections were examined by hematoxylin-and-eosin histopathology, immunostaining for glial fibrillary acidic protein, and B4-isolectin immunochemistry for microglia. In the striatum, normal-neuron counts were first decreased significantly at 2 weeks after the ischemic insult. Neuronal loss was associated with the proliferation of reactive microglia, which peaked at 1 week. By contrast, reactive astrocytosis displayed a more protracted pattern, with peak activation at 2 weeks. In the CA1 hippocampus, a decreased number of normal neurons was seen at 1 week post ischemia, together with a significant increase in immunoreactive microglia at that time; the latter normalized after 2 weeks. Reactive astrocytes in the CA1 hippocampus were significantly increased at 1–2 weeks after ischemia. In a subgroup of severely injured animals, foci of frank striatal infarction were associated with early and severe microglial and astrocytic proliferation at week 4 or later. Finally, cerebrovascular changes included endothelial disruption within affected areas. These observations document a subacute and chronic sequence of cellular responses following brief periods of global ischemia, involving both neurons, glia and vascular endothelium.

Notes: Abstract In addition to producing acute neuronal necrosis within selectively vulnerable brain regions, our recent studies have shown that global cerebral ischemia may also be followed by protracted degenerative changes occurring over the course of 10 weeks. Chronic brain pathology may be associated with the abnormal deposition of β-amyloid precursor protein (βAPP). In the present study, we used a monoclonal antibody to the N-terminal portion of βAPP to characterize the brains of rats surviving 1–10 weeks following 10 min of global brain ischemia produced by bilateral carotid artery occlusions plus systemic hypotension. After ischemia, increased βAPP immunolabeling emerged in several brain regions. In the hippocampus, granular deposits appeared in the damaged CA1 area by 2 weeks, and by 4–10 weeks the remnants of necrotic CA1 neurons were also immunolabeled. In striatum and thalamus, regions with necrotic cell death also revealed granular βAPP deposits. The neocortex was devoid of overt ischemic neuronal damage but revealed prominent βAPP immunoreactivity. Large ovoid deposits of low-density βAPP immunostaining occurred in cortical neurons at 1–2 weeks. At 4–10 weeks, large round or oval deposits immunoreactive for βAPP appeared in several cortical regions. The highest density of deposits was seen in the temporal and piriform cortices. Our results indicate that abnormal βAPP deposition may result from ischemic as well as chronic neurodegenerative processes.

Notes: Abstract We undertook a detailed characterization of the cellular responses to acute global cerebral ischemia complicated by hyperglycemia. Anesthetized, physiologically monitored male Wistar rats received 12.5 min of global forebrain ischemia by bilateral common carotid artery occlusions plus hemorrhagic hypotension to 45 mm Hg. Cranial temperature was maintained at normothermic levels. Hyperglycemic animals received dextrose (2.5 ml of a 25% solution, intraperitoneally) prior to ischemia; this doubled the mean plasma glucose concentration to 296 mg/100 ml. At 3 days (n = 10) or 24 h (n = 4) after ischemia, brains were perfusion-fixed and paraffin-embedded for light microscopic histopathology and for the histochemical visualization of activated microglia and the immunocytochemical visualization of glial fibrillary acid protein. Normal-neuron counts in the vulnerable hippocampal CA1 sector of hyperglycemic-ischemic (HI) rats were reduced to one-third the number observed in normoglycemic-ischemic (NI) animals. Ischemic cell counts in the striatum were increased fivefold or more in HI compared to NI rats, and normal small-neuron counts were reduced by two-thirds. The neocortex and striatum of NI rats showed only mild damage, while the majority of HI rats had extensive lesions, and several showed large cortical, striatal or thalamic infarcts. In addition, widespread cortical ischemic neuronal changes were evident in HI animals. No endothelial alterations were present in NI rats. By contrast, HI rats showed prominent peri- and intravascular polymorphonuclear and monocytic accumulation evident at 24 h; frequent white cell thrombi in pial arterioles on day 3; and thickening of vascular endothelium, with foci of parenchymal rarefaction or microinfarction adjacent to occluded vessels. Prominent microglial activation, often along the course of penetrating blood vessels, was common in the striatum and neocortex of HI animals but was much less extensive in the NI group. Activated microglia in HI rats were typically hypertrophic and amoeboid. These results suggest that the detrimental influence of hyperglycemia in ischemia is initially mediated by an action on vascular endothelium, which in turn leads to widespread foci of infarction and neuronal loss.