Synaptic Activity Mediates Death of Hypoxic Neurons

156

Summary: The effects of magnesium, an endogenous in hibitor of calcium entry into neurons, upon ischemic brain damage were investigated using a well-character ized model of focal cerebral ischemia in rats. Infarct vol umes were determined by 2,3,5-triphenyltetrazolium chloride transcardiac perfusion 48 h after middle cerebral artery (MCA) occlusion. The area of ischemic damage was quantified by image analysis in coronal sections taken every 0.5 mm. MgCI2 (l mmol/kg) was injected inMagnesium plays an essential role in cellular physiology. It is involved in the activation of � 300 enzymes, including those catalyzing energy producing and energy-consuming reactions (Ebel and Gunther, 1980). In the extracellular space, mag nesium competes with calcium to reduce calcium entry into cells (Altura and Altura, 1981), blocks both voltage-sensitive and N-methyl-D-aspartate (NMDA)-activated channels (Iseri and French, 1984; Nowak et aI. , 1984), is implicated in the reg ulation of cerebral vascular tone (Seelig et aI. , 1983), and inhibits the release of excitatory amino acids (Rothman, 1984). These properties make mag nesium an excellent candidate for preventing brain damage.There is evidence that the neuronal death that follows cerebral ischemia may be due to a massive release of excitatory amino acids, particularly glu tamate (Rothman and Olney, 1986). Most studies suggest that a calcium influx into neurons is a cru cial step of the deleterious cascade triggered by Received March [5, 199[; revised April 29, 1991 ischemia (Schanne et aI. , 1979; Siesj6 and Bengts son, 1989). Several studies have demonstrated that magnesium can protect against anoxic damage in vitro (Ames and Nesbett, 1983;Rothman, 1983; Kass et aI. , 1988) and against applied glutamate (Gibson and Reif-Lehrer, 1985). Treatment with magnesium has also been shown to limit damage and improve outcome after global cerebral ischemia (Tsuda et aI. , 1989), brain trauma (Vink et aI. , 1988McIntosh et aI. , 1989), and spinal cord ischemia (Vacanti and Ames, 1984; Robertson et aI. , 1986).We have therefore investigated whether treat ment with MgCl 2 can reduce infarct volume in rats following focal cerebral ischemia. Intracranial oc clusion of the middle cerebral artery (MCA) in rats has been chosen because it results in highly repro ducible lesions. There is good evidence that this model is most pertinent in terms of pharmacological therapy of stroke (MacKenzie et aI. , 1986). The ef fects of administering a combination of MgCl 2 and insulin were also investigated so as to minimize any influence of magnesium-induced hyperglycemia. MATERIALS AND METHODSThe experiments were performed on 61 male Fischer-344 rats weighing 280-310 g. The rats had free access to food and water prior to experimentation. 1026Y. IZUMI ET AL. Induction of focal ischemiaThe rats were anesthetized with halothane (1.5%) in oxygen. Rectal temperature was measured and main tained within the normal physiological range during sur gery. Left MCA occlusion was performed by a subtem poral approach,...

Section: Discussionmentioning

confidence: 99%

“…, 1979; Siesj6 and Bengts son, 1989). Several studies have demonstrated that magnesium can protect against anoxic damage in vitro (Ames and Nesbett, 1983;Rothman, 1983; Kass et aI. , 1988) and against applied glutamate (Gibson and Reif-Lehrer, 1985).…”

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confidence: 99%

Reduction of Infarct Volume by Magnesium after Middle Cerebral Artery Occlusion in Rats

Izumi

Roussel

Pinard

et al. 1991

156

“…According to the concept of excitotoxicity (J�r gensen and Diemer, 1982;Rothman, 1983Rothman, , 1984Si mon et a1., 1984;Wieloch et a1., 1985), glutamate released into the extracellular space would be ex pected to influence neuronal damage in the isch emic penumbra. Nonetheless, relatively few studies of this issue have been carried out in models of focal or regional ischemia.…”

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confidence: 99%

Changes in Amino Acid Neurotransmitters and Cerebral Blood Flow in the Ischemic Penumbral Region following Middle Cerebral Artery Occlusion in the Rat: Correlation with Histopathology

Takagi

Ginsberg

Globus

et al. 1993

218

Summary: We simultaneously measured neurotransmit ter amino acids by the microdialysis technique and corti cal CBP by laser-Doppler flowmetry in the ischemic pen umbral cortex of rats subjected to 2-h normothermic (36.5-37SC) transient middle cerebral artery (MCA) clip occlusion. Brains were perfusion-fixed 3 days later and infarct volume measured. CBP (% of preischemic values) fell to 32 ± 2% (mean ± SD) during ischemia and rose to 157 ± 68% during recirculation. Extracellular glutamate levels increased from a baseline value of 7 ± 3 f.LM to a peak value of 180 ± 247 f.LM 20-30 min following onset of ischemia but subsequently returned to near baseline lev els after 70 min of ischemia despite ongoing MCA occlu sion. The threshold CBP for moderate glutamate release was 48%. Massive glutamate release was seen during the first 60 min of MCA occlusion in the two animals showing Glutamate-mediated excitotoxicity, though not the sole factor, is now accepted as a major mecha nism of ischemic neuronal damage. In in vitro cell culture studies, the vulnerability of both hippocam pal and cortical neurons to anoxia has been related to glutamate release from presynaptic terminals (Rothman, 1984; Choi et aI., 1987). In in vivo stud ies of both global and focal ischemia, extracellular glutamate levels increase massively during the isch emic period (Benveniste et aI., 1984; Hagberg et aI., Abbreviations used: EI, excitotoxic index; GABA, -y-ami nobutyrate; MeA, middle cerebral artery. 575the largest infarcts and occurred at CBP values .,;20% of control levels. Mean CBP during ischemia exhibited an inverse relationship with infarct volume, and the magni tude of glutamate release during ischemia was positively correlated with infarct volume. Extracellular -y-aminobu tyrate and glycine changes were similar to those of glu tamate but showed no significant correlation with infarct volume. These results suggest that (a) accumulation of extracellular glutamate is an important determinant of in jury in the setting of reversible MCA occlusion and (b) reuptake systems for neurotransmitter amino acids may be functional in the penumbra during transient focal isch emia.

“…Most notable among them is glutamate, which is presumed to be a major contributor to cell death in hypoxia (Jorgensen and Diemer, 1982; Rothmann and Olney, 1986). In vitro, extracellular glutamate concentrations exceeding 100 jl-M kill cultured neuronal cells even under normoxic con ditions (Rothman, 1984), but neurons can survive anoxia when synaptic activity is blocked (Rothman, 1983). Recent microdialysis studies in ischemic brain confirmed the direct relationship between the increase in extracellular glutamate concentration and cell death (Benveniste et aI., 1984; Hagberg et aI., 1985; Hillered et aI., 1989), and a number of investigators have suggested that excessive influx of calcium may be the mechanism by which gluta mate leads to injury and cell death (Simon, 1984;Stein and Vannucci, 1988 Abbreviations used: CCA, ipsilateral common carotid artery; MCA, middle cerebral artery.…”

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confidence: 99%

Relevance of Interstitial Glutamate to Selective Vulnerability in Focal Cerebral Ischemia

Osuga

Hakim

1994

Summary: Glutamate concentrations in striatum and cor tex were measured by means of in vivo cerebral microdi alysis before and for 4 h after middle cerebral and ipsi lateral common carotid artery occlusion in rats. The peak glutamate concentration reached 7.28 ± 3.60 11M in dial ysate from striatum and 5.64 ± 2.24 11M in that fromcortex. An index of exposure of each region to glutamate was calculated by integrating glutamate concentrations Massive release of a number of neurotransmitters during ischemia causes neuronal injury (Erecinska et aI., 1984; Globus et aI., 1988;Hillered et at., 1989). Most notable among them is glutamate, which is presumed to be a major contributor to cell death in hypoxia (Jorgensen and Diemer, 1982; Rothmann and Olney, 1986). In vitro, extracellular glutamate concentrations exceeding 100 jl-M kill cultured neuronal cells even under normoxic con ditions (Rothman, 1984), but neurons can survive anoxia when synaptic activity is blocked (Rothman, 1983). Recent microdialysis studies in ischemic brain confirmed the direct relationship between the increase in extracellular glutamate concentration and cell death (Benveniste et aI., 1984; Hagberg et aI., 1985; Hillered et aI., 1989), and a number of investigators have suggested that excessive influx of calcium may be the mechanism by which gluta mate leads to injury and cell death (Simon, 1984;Stein and Vannucci, 1988 Abbreviations used: CCA, ipsilateral common carotid artery; MCA, middle cerebral artery. 343after occlusion. During ischemia the striatum was ex posed to statistically higher cumulative concentrations of glutamate than the cortex (p < 0.01). The difference in vulnerability between striatum and cortex may arise from the additional time needed for the cortex to be exposed to cumulative threshold levels of glutamate. Key Words: Fo cal ischemia-Glutamate-Time course.on cell survival is clear, the relevance of the in crease in glutamate concentrations to regional cere bral vulnerability in focal ischemia has not been studied extensively. Extracellular glutamate rises when CBF falls below 20 m1l100 glmin (Shimada et aI., 1989), and its concentration increases with the severity of ischemia (Ueda et aI., 1992), but Globus et ai. (1991) showed that differences in extracellular glutamate concentration could not explain the re gional differences in vulnerability to global isch emia. Focal ischemia produced by simultaneous oc clusion of the middle cerebral artery (MCA) and ipsilateral common carotid artery (CCA) in rats re sults in a lower CBF and an earlier appearance of histologic damage in the striatum than in the over lying cortex (Hakim et aI., 1992). Since both struc tures eventually infarct, we explored the possibility that vulnerability in the early ischemic phase may be determined by glutamate time-concentration re lationships different from those that ultimately de termine cell death. We used in vivo microdialysis in the rat, measured the glutamate concentration in dialysates from both striatum and cortex before and after per...