Siert Knollema

Dynamics of cerebral tissue injury and perfusion after temporary hypoxia-ischemia in the rat : evidence for region-specific sensitivity and delayed damage

BACKGROUND AND PURPOSEnSelective regional sensitivity and delayed damage in cerebral ischemia provide opportunities for directed and late therapy for stroke. Our aim was to characterize the spatial and temporal profile of ischemia-induced changes in cerebral perfusion and tissue status, with the use of noninvasive MRI techniques, to gain more insight in region-specific vulnerability and delayed damage.nnnMETHODSnRats underwent 20 minutes of unilateral cerebral hypoxia-ischemia (HI). We performed combined repetitive quantitative diffusion-weighted, T2-weighted, and dynamic susceptibility contrast-enhanced MRI from before HI to 5 hours after HI. Data were correlated with parallel blood oxygenation level-dependent MRI and laser-Doppler flowmetry. Finally, MRI and histology were done 24 and 72 hours after HI.nnnRESULTSnSevere hypoperfusion during HI caused acute reductions of the apparent diffusion coefficient (ADC) of tissue water in the ipsilateral hemisphere. Reperfusion resulted in dynamic perfusion alterations that varied spatially. The ADC recovered completely within 1 hour in the hippocampus (from 0.68 +/- 0.07 to 0.83 +/- 0.09 x 10[-3] mm2/s), cortex (from 0.56 +/- 0.06 to 0.77 +/- 0.07 x 10[-3] mm2/s), and caudate putamen (from 0.58 +/- 0.06 to 0.75 +/- 0.06 x 10[-3] mm2/s) but only partially or not at all in the thalamus (from 0.65 +/- 0.07 to 0.68 +/- 0.12 x 10[-3] mm2/s) and substantia nigra (from 0.80 +/- 0.08 to 0.76 +/- 0.10 x 10[-3] mm2/s). Secondary ADC reductions, accompanied by significant T2 elevations and histological damage, were observed after 24 hours. Initial and secondary ADC decreases were observed invariably in the hippocampus, cortex, and caudate putamen and in approximately 70% of the animals in the thalamus and substantia nigra.nnnCONCLUSIONSnRegion-specific responses and delayed ischemic damage after transient HI were demonstrated by MRI. Acute reperfusion-induced normalization of ADCs appeared to poorly predict ultimate tissue recovery since secondary, irreversible damage developed eventually.

l-Deprenyl Reduces Brain Damage in Rats Exposed to Transient Hypoxia-Ischemia

BACKGROUND AND PURPOSEnL-Deprenyl (Selegiline) protects animal brains against toxic substances such as 1-methyl-1,2,3,6-tetrahydropyridine and 6-hydroxydopamine. Experiments were conducted to test whether L-deprenyl prevents or reduces cerebral damage in a transient hypoxia/ischemia rat model.nnnMETHODSnRats were treated for 14 days with 2 mg/kg and 10 mg/kg L-deprenyl or saline. After surgery a 20-minute hypoxia/ischemia period was induced by simultaneous occlusion of the left common carotid artery and reduction of the percentage of oxygen in the gas mixture to 10%. Rats were killed 24 hours later. Silver staining was used to reveal damage in several brain regions.nnnRESULTSnIn the brain, both L-deprenyl dosages reduced damage up to 78% compared with the controls. Total brain damage was decreased from 23%-31% to 5%-9% with the L-deprenyl treatment (2 mg/kg: F1.13 = 6.956, P < .05; 10 mg/kg: F1.13 = 5.731, P < .05). In the striatum, significant treatment effects were found between both the L-deprenyl groups (2 mg/kg and 10 mg/kg, respectively) and the saline group (F1.13 = 14.870, P < .005; and F1.13 = 8.937, P = .01; respectively). In the thalamus, significant treatment effects were seen in the 2-mg/kg L-deprenyl group (F1.13 = 11.638, P < .005) and the 10-mg/kg group (F1.13 = 8.347, P < .05) compared with the control group. No significant damage decrease was seen in the hippocampus and the cortex.nnnCONCLUSIONSnThe results show that L-deprenyl is effective as a prophylactic treatment for brain tissue when it is administered before hypoxia/ischemia. Mechanisms responsible for the observed protection remain unclear. The regional differences in damage, however, are in accordance with the reported regional increase in superoxide dismutase and catalase activities after L-deprenyl treatment, suggesting the involvement of free radicals and scavenger enzymes.

Down-regulation of the hypothalamo-pituitary-adrenal axis reduces brain damage and number of seizures following hypoxia/ischaemia in rats

Several reports suggest that the activity of the hypothalamo-pituitary-adrenal axis (HPA-axis) is increased following hypoxia/ischaemia and that this might be associated with increased neuronal vulnerability. The main goal of this study was to examine the effects of down-regulation of the HPA-axis on the hypoxia/ischaemia-induced (1) rise of plasma corticosterone levels, (2) seizures, and (3) brain damage. Down-regulation of the HPA-axis was induced by prolonged corticosterone treatment lasting until 24 h before hypoxia/ischaemia exposure. When compared to 8 days vehicle (sesame oil)-treated animals (CONT), 8 days daily corticosterone (40 mg/animal)-treated animals (CORT) showed significantly reduced adrenal-and thymus weight. Shortly after hypoxia/ischaemia plasma corticosterone levels in CORT animals were significantly reduced (17.30 micrograms/dl +/- 3.50) when compared to CONT animals (54.80 micrograms/dl +/- 7.78). This correlated with the brain damage which is expressed as the ratio between the damaged area and the total area. The total brain damage was significantly less in CORT-treated animals (28% +/- 11%) than in CONT animals (69% +/- 2%). Following hypoxia/ischaemia the number of seizures was significantly reduced in CORT animals (56 +/- 26) when compared to CONT animals (217 +/- 50). We conclude that prolonged corticosterone treatment resulting in down-regulation of the HPA-axis leads to (1) lower plasma corticosterone levels during hypoxia/ischaemia, (2) a reduction in brain damage following hypoxia/ischaemia, and (3) less hypoxia/ischaemia-induced seizures.

Metyrapone reduces rat brain damage and seizures after hypoxia-ischemia: An effect independent of modulation of plasma corticosterone levels?

Hypoxia—ischemia is accompanied by abundant corticosterone secretion that could exacerbate brain damage after the insult. The authors demonstrate that the steroid synthesis inhibitor metyrapone (150 mg/kg subcutaneously) suppresses the hypoxia—ischemia-induced rise of plasma corticosterone levels (17.3 ± 3.6 μg/dL) when compared with corticosterone-treated animals (72.2 ± 4.8 μg/dL) immediately after hypoxia—ischemia. In parallel, metyrapone reduced brain damage (P < 0.05). Moreover, none of the metyrapone-treated animals displayed seizures, whereas seven of eight corticosterone-treated animals had seizures after hypoxia—ischemia. Although corticosterone administration in metyrapone-treated animals elevated plasma corticosterone levels (39.0 ± 5.3 μg/dL), this did not result in a subsequent increase in brain damage and seizures when compared with metyrapone-treated animals. The authors conclude that metyrapone reduces brain damage and the incidence of seizures after hypoxia—ischemia but that this effect might partially be independent from its effect on modulating plasma corticosterone levels.

Differential Glutathione Peroxidase mRNA Up-Regulations in Rat Forebrain Areas after Transient Hypoxia-Ischemiaa

The biological reduction of oxygen generates reactive oxygen species that are toxic to cells. To protect themselves against such toxic moieties, cells have evolved antioxidant defence mechanisms involving enzymes and vitamines. The enzymatic protection proceeds in two steps: 1) the conversion of superoxide anions (“0;) to hydrogenperoxide (HzO,) by superoxide dismutase (SOD) and (2) the subsequent conversion of hydrogenperoxide to water by glutathione peroxidase (GPx) and/or catalase (Cat). If, however, the activity or amount of SOD is increased without concomitant increase of GPx and/or Cat, then hydrogenperoxide accumulates and reacts with transition metals in the Fenton’s reaction to produce hydroxyl radicals (“OH). These hydroxyl radicals are among the most noxious radical species known and react with macromolecules, in particular with the polyunsaturated fatty acids of membrane lipids. This process, known as lipid peroxidation, initiates in the lipid bilayers cascades of free-radical-generating reactions that disrupt the membrane integrity and allow eventually entry of calcium ions into the cells. Overflow of the redundant calcium into the mitochondria generates a cellular energy crisis that leads to cell death.’.x Early and late neuronal degenerations observed in circumscribed brain regions after focal or global cerebral ischemia may be triggered by free radicals that are

Dynamics of Cerebral Tissue Injury and Perfusion After Temporary Hypoxia-Ischemia in the Rat

BACKGROUND AND PURPOSEnSelective regional sensitivity and delayed damage in cerebral ischemia provide opportunities for directed and late therapy for stroke. Our aim was to characterize the spatial and temporal profile of ischemia-induced changes in cerebral perfusion and tissue status, with the use of noninvasive MRI techniques, to gain more insight in region-specific vulnerability and delayed damage.nnnMETHODSnRats underwent 20 minutes of unilateral cerebral hypoxia-ischemia (HI). We performed combined repetitive quantitative diffusion-weighted, T2-weighted, and dynamic susceptibility contrast-enhanced MRI from before HI to 5 hours after HI. Data were correlated with parallel blood oxygenation level-dependent MRI and laser-Doppler flowmetry. Finally, MRI and histology were done 24 and 72 hours after HI.nnnRESULTSnSevere hypoperfusion during HI caused acute reductions of the apparent diffusion coefficient (ADC) of tissue water in the ipsilateral hemisphere. Reperfusion resulted in dynamic perfusion alterations that varied spatially. The ADC recovered completely within 1 hour in the hippocampus (from 0.68 +/- 0.07 to 0.83 +/- 0.09 x 10[-3] mm2/s), cortex (from 0.56 +/- 0.06 to 0.77 +/- 0.07 x 10[-3] mm2/s), and caudate putamen (from 0.58 +/- 0.06 to 0.75 +/- 0.06 x 10[-3] mm2/s) but only partially or not at all in the thalamus (from 0.65 +/- 0.07 to 0.68 +/- 0.12 x 10[-3] mm2/s) and substantia nigra (from 0.80 +/- 0.08 to 0.76 +/- 0.10 x 10[-3] mm2/s). Secondary ADC reductions, accompanied by significant T2 elevations and histological damage, were observed after 24 hours. Initial and secondary ADC decreases were observed invariably in the hippocampus, cortex, and caudate putamen and in approximately 70% of the animals in the thalamus and substantia nigra.nnnCONCLUSIONSnRegion-specific responses and delayed ischemic damage after transient HI were demonstrated by MRI. Acute reperfusion-induced normalization of ADCs appeared to poorly predict ultimate tissue recovery since secondary, irreversible damage developed eventually.

Dynamics of Cerebral Tissue Injury and Perfusion After Temporary Hypoxia-Ischemia in the Rat : Evidence for Region-Specific Sensitivity and Delayed Damage Editorial Comment: Evidence for Region-Specific Sensitivity and Delayed Damage

BACKGROUND AND PURPOSEnSelective regional sensitivity and delayed damage in cerebral ischemia provide opportunities for directed and late therapy for stroke. Our aim was to characterize the spatial and temporal profile of ischemia-induced changes in cerebral perfusion and tissue status, with the use of noninvasive MRI techniques, to gain more insight in region-specific vulnerability and delayed damage.nnnMETHODSnRats underwent 20 minutes of unilateral cerebral hypoxia-ischemia (HI). We performed combined repetitive quantitative diffusion-weighted, T2-weighted, and dynamic susceptibility contrast-enhanced MRI from before HI to 5 hours after HI. Data were correlated with parallel blood oxygenation level-dependent MRI and laser-Doppler flowmetry. Finally, MRI and histology were done 24 and 72 hours after HI.nnnRESULTSnSevere hypoperfusion during HI caused acute reductions of the apparent diffusion coefficient (ADC) of tissue water in the ipsilateral hemisphere. Reperfusion resulted in dynamic perfusion alterations that varied spatially. The ADC recovered completely within 1 hour in the hippocampus (from 0.68 +/- 0.07 to 0.83 +/- 0.09 x 10[-3] mm2/s), cortex (from 0.56 +/- 0.06 to 0.77 +/- 0.07 x 10[-3] mm2/s), and caudate putamen (from 0.58 +/- 0.06 to 0.75 +/- 0.06 x 10[-3] mm2/s) but only partially or not at all in the thalamus (from 0.65 +/- 0.07 to 0.68 +/- 0.12 x 10[-3] mm2/s) and substantia nigra (from 0.80 +/- 0.08 to 0.76 +/- 0.10 x 10[-3] mm2/s). Secondary ADC reductions, accompanied by significant T2 elevations and histological damage, were observed after 24 hours. Initial and secondary ADC decreases were observed invariably in the hippocampus, cortex, and caudate putamen and in approximately 70% of the animals in the thalamus and substantia nigra.nnnCONCLUSIONSnRegion-specific responses and delayed ischemic damage after transient HI were demonstrated by MRI. Acute reperfusion-induced normalization of ADCs appeared to poorly predict ultimate tissue recovery since secondary, irreversible damage developed eventually.

Long-Term Food Restriction, Deprenyl, and Nimodipine Treatment on Life Expectancy and Blood Pressure of Stroke-Prone Rats

We determined whether food restriction or the drugs nimodipine (Ca2+ antagonist) and deprenyl (a MAO-B inhibitor) prevent the development of stroke in the spontaneously hypertensive stroke-prone rat (SHR-SP). Forty male SHR-SP rats, in the age of 34 weeks, were exposed to various treatments. During a period of 27 weeks, survival and blood pressure were followed. In the control and deprenyl group, the blood pressure values remained unchanged; 50% had died after 27 weeks. All rats that were treated with nimodipine survived. After food restriction, 7/8 rats survived and showed a lower blood pressure. This study in SHR-PR rats shows the superiority of nimodipine on survival, and the potential of food restriction as a stroke-preventing measure.

The number of insults and the cerebral damage after hypoxia/ischemia are altered after acute pretreatment with corticosterone and metyrapone

The role of glucocorticoids in neuronal viability is controversial. Most studies which describe the effects of glucocorticoids on ischemic brain damage use surgical adrenalectomy to induce a reduction in plasma corticosterone levels. In the present study we used metyrapone, a corticosterone synthesis inhibitor, to examine the effects of acute manipulation of corticosterone levels on neuronal damage and seizures. Shortly before transient hypoxia/ischemia, animals were subcutaneously injected with sesame oil, metyrapone, corticosterone or corticosterone + metyrapone. Both the neuronal damage and the percentage animals with seizures were found to correlate well with plasma corticosterone levels. This relation between affected area, seizures and corticosterone levels was confirmed when the rats were re-arranged into animals with and without seizures. However, Corticosterone administration in metyrapone treated rats did not result (compared to MET treatment) in an increased neuronal damage. This suggests that the beneficial effects of metyrapone may be regulated by a corticosterone independent mechanism.

Glia and the development of brain damage

Transient cerebral hypoxia/ischemia triggers a differential sequence of damage development, which can be distinguished on the basis of the duration of both the period of oxygen shortage and the post-ischemic reperfusion period (figure 1). Development of neuronal damage can be divided into three main patterns; Acute(infarction), early and delayed neuronal damage. Long ischemic periods cause acute (after 3 hours) neuronal and astroglial cell death (1,2), possibly as a consequence of high intracellular acidosis by ionic pump failure. Early damage occurs after 3 hours and is characterized by selective neuronal degeneration most likely a consequence of progressing depolarization events due to a decreased activity of the enzyme Na+/K+ ATP-ase (3,4). Delayed damage becomes apparent between 24 and 72 hours and is also selective neuronal (5,6).