Cerebral Dysfunction Related to Local and Global Ischemia of the Brain. In: Hoffmeister F, Müller C, editors. Brain Function in Old Age. Berlin: Springer Berlin Heidelberg; 1979. pp. 385-93. [DOI: 10.1007/978-3-642-67304-7_27]

Cerebral ischemia in gerbils: postischemic administration of cyclohexyl adenosine and 8-sulfophenyl-theophylline

Adenosine agonists have now been shown by several laboratories to have profound neuroprotective effects when administered either pre- or postischemia. In an effort to determine whether these effects are centrally mediated, the effects of the non-brain-permeable adenosine receptor antagonist 8-sulfophenyl-theophylline (8-SPTH) on cyclohexyladenosine (CHA) -mediated protection was determined. Both survival and neurologic outcome were assessed in gerbils following 30 minutes of bilateral carotid occlusion. A dose of 2 mg/kg of CHA 5 minutes postreperfusion resulted in highly significant increases in survival relative to saline injected controls. Administration of doses of 8-SPTH sufficient to normalize the hypotension observed with CHA resulted in the same degree of postischemic protection. Similar results were obtained when neurologic status was evaluated. The results indicate that the neuroprotective effects of CHA are apparently centrally mediated.

Local cerebral glucose utilization in chronic middle cerebral artery occlusion in the cat

This study examines the correlation between local CMRglc (LCMRglc) alterations and clinicopathological changes in a chronic middle cerebral artery (MCA) occlusion model in the cat. The left MCA was occluded for a period of 2 h. The animals were grouped into mild, moderate, and severe ischemia based on the depression of the EEG 30 min after the MCA occlusion. Following release of the clip, the animals were allowed to recover for a week during which time daily neurological examinations were performed. On the seventh day [14C]2-deoxyglucose was injected for the determination of LCMRglc. Alternative blocks were processed for histological evaluation in which both neuronal and phagocytic changes were graded into four categories (0 = normal to 3 = severe). LCMRglc (mumol/100 g/min) in the ischemic hemisphere (all histological grades) was significantly lower than the metabolic rate in comparable regions of the sham MCA occlusion group. Regions with significant phagocytosis (grade 2 and 3) invariably exhibited activated glucose metabolism (57.4 +/- 8.4 and 105.9 +/- 6.8 mumol/100 g/min, respectively), which was significantly higher than in regions without phagocytosis (30.4 +/- 0.8 mumol/100 g/min). There was a significant gradient of metabolism in the central, peripheral, and boundary zone and the non-MCA territory in the animals with severe ischemic lesions. LCMRglc in the central MCA territory was well correlated with the EEG amplitude changes (r = 0.82, p less than 0.05) and the morphological score (r = -0.89, p less than 0.05). The metabolic rate was significantly depressed in both the ipsilateral and the contralateral central MCA territories in comparison with the sham occlusion animals. The depression in LCMRglc in the contralateral hemisphere correlated well with the concomitant depression in the contralateral EEG amplitude. These studies demonstrate that local heterogeneous metabolic alterations and contralateral cortical diaschisis exist chronically following temporary MCA occlusion and that the increases in local cerebral glucose metabolism seen in chronic stroke may be due to phagocytotic activity.

Role of circulatory disturbances in the development of post-ischemic brain edema

Two post-ischemic circulatory disturbances that play a significant role in pathophysiology of an ischemic lesion are: (1) reactive hyperemia or hyperperfusion and (2) hypoperfusion. The reactive hyperemia promptly follows release of major cerebral artery occlusion, and it is associated with the opening of the blood-brain barrier to serum proteins and ensuing edema. Prevention or reduction of reactive hyperemia results in significant amelioration of edema and the resulting ischemic brain tissue injury. The post-ischemic hypoperfusion, studied in gerbils, develops soon after recirculation and usually lasts up to 6 h. Its relationship to post-ischemic edema is evident in repeated ischemic insults. In these studies, three ischemic insults of 5 min duration when applied at 1 h intervals, i.e., during the period of hypoperfusion, resulted in a cumulative effect, post-ischemic edema and tissue injury becoming considerably more pronounced that those following a single 15 min ischemia. There was no cumulative effect when the ischemic insults were spaced 3 min or longer than 6 h apart. These observations indicate that repeated ischemic insults taking place during the phase of post-ischemic hypoperfusion may significantly increase the development of edema and brain tissue injury.

Pial artery pressure after one hour of global ischemia

Pial artery pressure was measured in anesthetized control cats and in animals subjected to 1 h of global ischemia and 6 h of recirculation. Cerebral blood flow (CBF) was measured with the intraarterial 133Xe technique before and after ischemia, and lumped segmental resistances upstream and downstream to the pial artery were calculated. In the control brain, upstream resistance was 1.30 +/- 0.28 and downstream resistance 0.94 +/- 0.1 mm Hg ml-1 100 g min. During the postischemic hypoperfusion period, both resistances significantly increased, indicating that hypoperfusion constitutes a dysregulation of both large extracerebral and small intracerebral vessels. Hypercapnia induced an increase of CBF in the control brain and was accompanied by a fall in downstream resistance, demonstrating intracortical vasodilation. By contrast, hypercapnia did not provoke changes in either CBF or segmental resistances in the hypoperfusion period. In conclusion, during the postischemic hypoperfusion period, both extra- and intracortical resistances are increased and vascular reactivity to CO2 is abolished.

Effects of hypoxia and anoxia on the ex vivo release of prostaglandins from mouse cortical slices

Arachidonic acid is transiently accumulated in the brain as a result of a variety of pathological conditions. The synthesis and release of some of its metabolites, namely, prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from cortical slices of mice were studied following exposure to 6 min of hypoxia (7% O2), 45 s of anoxia, and 5 min-4 h of reoxygenation following anoxia. Hypoxia induced a slight increase in the rate of TXB2 release and a slight decrease in the rate of PGE2 release, whereas 6-keto-PGF1 alpha was unaffected. Anoxia (45 s) followed by reoxygenation induced a transient increase in the release of PGE2 and of 6-keto-PGF1 alpha with a return to the normal rate at 30 min and 2 h of recovery, respectively. However, the rate of TXB2 synthesis and release reached its peak (twofold increase) after 1 h and remained significantly higher than the control rate even after 4 h of normal air breathing. Our results demonstrate that hypoxia and anoxia, even of short duration, selectively trigger the activity of thromboxane synthetase and that this elevated rate of synthesis and release persists long after normal oxygen supply is restored. We suggest that enhanced thromboxane synthesis, with normal prostacyclin levels, might have a role in the pathophysiology of ischemic cell damage.

Delayed recovery of CO2 reactivity after one hour's complete ischaemia of cat brain

The cerebrovascular CO2 reactivity was examined after 6 h, 1, 2, and 3 days and 1 year following 1 h complete brain ischaemia in the cat. After 6 h recirculation, the CO2 reactivity was completely suppressed although major EEG activity had recovered. After 2 days, CO2 reactivity began to reappear, but even after 1 year restitution was not complete. The prolonged (though partly reversible) attenuation of CO2 responsiveness suggests that ischaemia is followed by a long-lasting state of haemodynamic imbalance, which may be responsible for the slow progress of post-ischaemic recovery processes.

Cerebral glucose metabolism during the recovery period after ischemia--its relationship to NADH-fluorescence, blood flow, EcoG and histology

Local cerebral glucose utilization (lCMRgl), NADH fluorescence, cerebral blood flow (CBF), electrocortical activity (ECoG) and histology were studied during a 4 hr recovery period following 2 hrs of left middle cerebral artery (MCA) occlusion in cats. Changes in relative reduced pyridine nucleotides and CBF were measured by fluororeflectometry, ECoG was obtained from the left middle ectosylvian gyrus (MEG), and lCMRgl was measured at the end of the recovery period autoradiographically with 14-C-2-deoxyglucose. A sham group was comprised of 4 cats. The ten animals subjected to the stroke were classified into 3 groups based on the mean amplitude of the ECoG at the end of the ischemic period. At the end of the recovery period, the relative reduced pyridine nucleotides showed a 22.5% oxidation (oxidation of NADH), a 66.2% reduction (reduction of NAD) and a 3.0% reduction compared to the sham group in the severe, moderate and mild groups, respectively. LCMRgl of the left MEG in the severe group was 64.2% of the corresponding sham value, whereas lCMRgl in the moderate and mild groups were 124.8% and 132.0% of the sham, respectively. CBF at the end of the recovery period ranged from 28.1% to 83.0% of the sham value, although there was no significant difference among these groups. Histologically, a large portion of the neurons in the left MEG in the severe group showed ischemic neuronal changes, while the damage was less severe in the moderate and mild groups. On the basis of these data, it is suggested that a relative substrate deficiency and/or a loss of mitochondrial enzymatic pool size may occur in the animals comprizing the severe group. Conversely, anaerobic glycolysis may be activated in the moderate group, while the mild group exhibits an increase in glucose metabolism that is most likely aerobic. A gradient in the magnitude of changes in lCMRgl was noted from the central MCA territory to the surrounding brain regions in the ischemic hemisphere. In addition, there was a mild, but statistically significant (p less than 0.05), depression in lCMRgl with no histological damage in the non-ischemic hemisphere of the severe group.

Reperfusion after cerebral ischemia: influence of duration of ischemia

The influence of the duration of ischemia on the pattern of cerebral blood flow in recirculation was studied in anesthetised rats. Severe incomplete cerebral ischemia (mean ischemic flow = 5.8 +/- 0.4 ml/100 g/min) was produced by four-vessel occlusion and recirculation permitted after 15, 30 or 60 minutes ischemia. All three groups showed an immediate hyperemia followed by hypoperfusion. Hyperemia was maximal following 15 minutes ischemia and least pronounced following 60 minutes ischemia (p = 0.0249). Hypoperfusion started most quickly following 15 minutes ischemia and was delayed following 60 minutes ischemia (p less than 0.001). In established hypoperfusion there was no difference in flow between the three groups. The possible mechanisms of these changes in flow are discussed.

Regional flow-metabolism couple following middle cerebral artery occlusion in cats

The regional flow-metabolism couple was studied during the recovery period after 1 h of left middle cerebral artery (MCA) occlusion in cats. Local CBF (LCBF) was assessed at the end of ischemia as well as at the end of 4 h of recirculation by the microsphere technique. Local CMRgl (LCMRgl) was measured at the end of the recirculation period with [14C]2-deoxyglucose. Histology was evaluated by light microscopy from coronal brain blocks adjacent to those used for the determination of LCBF and LCMRgl. When LCBF in the central and peripheral MCA territories during the recovery period was between 40 and 115% of the value in sham occlusion studies, LCMRgl was greater than the control level found in the sham studies, and was accompanied by slight histological damage. This finding suggests that anaerobic glycolysis may persist after transient ischemia in spite of the recovery of LCBF to a level that is normally greater than the threshold for the activation of anaerobic glycolysis (less than 40% of the control). Persistent anaerobic glycolysis in the reperfusion period following an ischemic insult may be a sign of early tissue damage. Some of the regions in the peripheral MCA territory with LCBF between 40 and 110% of the levels during the recovery period in the sham studies showed a mild to moderate depression in LCMRgl so that the flow-metabolism ratio remained normal. These regions did not exhibit histological damage. This possible protective mechanism of the tissue in response to ischemia is discussed from the standpoint of the relationship between flow and metabolism.

CBF and time thresholds for the formation of ischemic cerebral edema, and effect of reperfusion in baboons

Ischemic cerebral edema has been studied in 41 baboons, with regional cerebral blood flow (CBF) determined by hydrogen clearance, and edema measured by microgravimetry. A threshold of ischemia has been identified for baboon cortex and subcortical white matter, which has to be crossed before edema formation begins. This threshold is 40.5% of normal CBF in cortex, and 34.4% of normal flow in subcortical white matter. A time threshold has also been determined, and the baboon brain can withstand 30 minutes of ischemia of the middle cerebral artery without significant edema formation. Reperfusion of ischemic brain has no effect on tissue water if the ischemic flow and time thresholds have not been crossed. Reperfusion of cortex, where water has begun to accumulate, exacerbates the water accumulation in proportion to the extent of the reperfusion. If these results are applicable to man, restoration of flow should not be attempted after an ischemic insult that reduces flow to less than 40% of normal unless it can be accomplished within 30 minutes of the insult. Provided CBF can be restored to above the 40% threshold within 30 minutes, reversal of the neurological deficit and prevention of ischemic edema can be expected.

The effects of 5-minute ischemia in Mongolian gerbils: I. Blood-brain barrier, cerebral blood flow, and local cerebral glucose utilization changes

Changes in morphology, behavior of the blood-brain barrier (BBB), regional cerebral blood flow (rCBF), and local cerebral glucose utilization (LCGU) were assessed and correlated in Mongolian gerbils following 5 min cerebral ischemia, produced by bilateral clamping of the common carotid arteries. The morphological changes were confined to the hippocampus and revealed a conspicuously delayed destruction of the CA1 neurons, occurring after 3 days. Following release of carotid occlusions, there were two separate openings of the BBB. One, occurring shortly after recirculation, was associated with focal hyperemia in the cerebral cortex, hippocampus and basal ganglia; the second opening was observed after several days and was associated with severe neuronal destruction in the CA1 sector. Correlation of quantitative and qualitative rCBF assays with 14C-deoxyglucose autoradiographic observations indicated an uncoupling between blood flow and glucose metabolism, observed in the hippocampus at 10 min after recirculation. The described changes provide a further insight into the post-ischemic events which determine the outcome of ischemic injury.