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Caspase Inhibitors Reduce Neuronal Injury After Focal but Not Global Cerebral Ischemia in Rats

BACKGROUND AND PURPOSE Studies show that blocking the activation of caspases by the caspase inhibitors z-VAD.FMK and z-DEVD.FMK can reduce ischemic neuronal injury after cerebral ischemia. Because the severity of ischemia was mild in some studies, we tested the efficacy of these caspase inhibitors on moderately severe but transient forebrain and focal ischemic insults in the rat. METHODS Various regimens of z-VAD, z-DEVD, and control DMSO were given to rats subjected to either 4-vessel occlusion ischemia (4-VO, 10-minute occlusion, 7-day survival) or distal middle cerebral artery occlusion (MCAo, 90-minute occlusion, 22.5-hour survival). In global ischemia, treatments were given immediately after ischemia (experiment 1) or as preischemic and postischemic treatments (experiment 2). Three focal ischemia experiments were done. Injection times were 60 minutes into ischemia (experiment 1) and 60 minutes into ischemia plus 30 and 120 minutes after ischemia (experiment 2). Experiment 3 was identical to experiment 2 except that a 30-minute preischemia treatment was instituted. Core normothermia was maintained in all experiments during ischemia. However, in the last focal and global experiments, core and brain temperatures, respectively, were also measured after ischemia with telemetry probes. Because hyperthermia accompanied z-DEVD treatment, an extra z-DEVD-treated group (MCAo) was included with temperature clamped at normothermia. RESULTS Neither z-VAD nor z-DEVD significantly reduced CA1 injury after global ischemia. In focal ischemia, both drugs significantly reduced infarction, but only in the third experiment, and the prevention of hyperthermia that accompanied z-DEVD treatment did not alter this. CONCLUSIONS These results suggest a detrimental role of caspases in moderately severe focal but not global cerebral ischemia.

Dehydroepiandrosterone (DHEA) reduces neuronal injury in a rat model of global cerebral ischemia

INTRODUCTION Many studies report an inverse correlation between levels of DHEA and neurological diseases. Exogenous DHEA protects hippocampal neurons against excitatory amino acid induced neurotoxicity. The purpose of this experiment is to evaluate the effect of DHEA in an animal model of transient but severe forebrain ischemia. METHODS At thirteen days prior to induction of ischemia, male Wistar rats were implanted with various doses of DHEA-placebo, 25 mg, 50 mg or 100 mg. Forebrain ischemia was induced for 10 min using a modified four-vessel occlusion technique, with hippocampal neuronal injury assessed at 7 days post-ischemically and expressed as a percentage of total cells. RESULTS Both normal and necrotic hippocampal CA(1) cells were counted. Percentages of hippocampal injury observed were 88+/-13% in animals treated with placebo, 84+/-8% in the 25 mg DHEA group, and 60+/-7% in the 50 mg DHEA group. Animals treated with 100 mg DHEA displayed a significant (P<0.05) reduction of hippocampal CA(1) cell injury at 60+/-7% CONCLUSION Treatment with a high dose, but not a low or moderate dose, of DHEA implantation reduces hippocampal CA(1) neuronal injury following severe but transient forebrain ischemia.

Tissue plasminogen activator does not increase neuronal damage in rat models of global and focal ischemia

Background: Intravenous tissue plasminogen activator (tPA) is the only approved treatment for acute ischemic stroke. Recent results from both in vitro and in vivo animal model experiments suggest the possibility that tPA is neurotoxic. Methods: The authors evaluated the putative neurotoxicity of tPA in both global and focal animal models of ischemic stroke. Global ischemia was induced in male Wistar rats using a modified four-vessel occlusion technique, with percentage neuronal injury assessed at 7 days through necrotic and normal cell count in the CA1 region. Transient focal ischemia was induced in male spontaneously hypertensive rats subjected to middle cerebral artery clipping, with measurement of cortical infarct volume at 24 hours. tPA was administered in 1, 5, or 10 mg/kg doses given intravenously as a 10% bolus, 90% over the following hour, analogous to current human treatment protocols. Results: In the global model, percent hippocampal injury was 60% ± 23%, 66% ± 26%, 55% ± 26%, and 52% ± 12% in the saline control, 1, 5, and 10 mg/kg tPA groups, respectively. In the focal model, after 120 minutes of ischemia, the control infarct size was 151 ± 39 mm3, and for the group given 10 mg/kg of tPA, it was 158 ± 28 mm3. Conclusions: Despite sublethal insults, with moderate injury induced by ischemia, there was no evidence that increasing doses of tPA exacerbated ischemic injury.

CoQ10 fails to protect brain against focal and global ischemia in rats.

OBJECTIVE Release of oxygen free radicals occurs following cerebral ischemia. Studies show that oxygen free radicals mediate ischemic brain injury. CoQ10 is a potent free radical scavenger and may offset brain injury associated with reperfusion. We tested exogeneous CoQ10 as a neuroprotectant in rats following both global and focal ischemic insults. METHODS Rats were subjected to either 4-vessel occlusion ischemia (4-VO, 10 min occlusion, 7-day survival) or middle cerebral artery occlusion (MCAO, 120 min-occlusion, 22.5 h survival). Regional cerebral blood flows (rCBF) and physiological variables such as blood pressure, pO2, pCO2, plasma glucose and hematocrit were monitored and measured in focal ischemia. The animals were randomized to receive treatments of either phosphate buffered saline (PBS) vehicle or CoQ10 following global or focal ischemia. Injection times were at the end of ischemia and 3 h later for both models of ischemia. Histological outcomes are expressed as a percentage of hippocampal CA(1) cell injury in global ischemia or percentage of cortical infarct over that of non-ischemic hemisphere in focal ischemia. RESULTS In global ischemia, animals treated with PBS vehicle and CoQ10 had 86+/-5% (n=8) and 83+/-10% (n=8), respectively, of hippocampal CA(1) cell injury (P>0.05). The percentage of infarct volumes in animals following focal ischemia were 23+/-9% (control, n=10) and 25+/-9% (CoQ10, n=10). There were no temperature or physiological differences between the two treatment groups. CONCLUSION Acute treatment with CoQ10 via intraperitoneal injection does not prevent neuronal injuries following global and focal ischemia.

Neuroprotection and neurogenesis: Modulation of cornus ammonis 1 neuronal survival after transient forebrain ischemia by prior fimbria-fornix deafferentation

Severe transient forebrain ischemia causes selective neuronal death in the hippocampal cornus ammonis 1 region. We tested the hypothesis that fimbria-fornix deafferentation can provide long-term protection to cornus ammonis 1 neurons and modulate neurogenesis following ischemia. Fimbria-fornix lesion or sham-fimbria-fornix lesion was performed on Wistar rats 13 days prior to 10 min forebrain ischemia or sham ischemia. Temperature was regulated and rats survived for 7, 14 or 28 days. Immunofluorescent bromodeoxyuridine and neuron specific nuclear protein staining and immunochemistry terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining were performed. At 7 days after ischemia, 73%+/-14% of cornus ammonis 1 neurons were damaged, while deafferentation reduced the injury to 36%+/-17% of cornus ammonis 1 neurons. This protection persisted for at least 28 days. Ischemia significantly increased the number of bromodeoxyuridine-positive cells (85-90 cells/section in stroke group vs. 6 to 11 cells/section in normal or sham stroke group), with very few terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-stained cells adjacent to the hippocampal cornus ammonis 1. Fimbria-fornix lesioning followed by ischemia increased the percentage of new neurons 13-fold over ischemia alone and 6.5-fold over sham lesion plus ischemia. The results indicate that fimbria-fornix deafferentation provides long-term neuroprotection in cornus ammonis 1 following forebrain ischemia and promotes neurogenesis after ischemic insults.