Effects of neopterin on ischemic neuronal damage in gerbils

Edaravone, a free radical scavenger, mitigates both gray and white matter damages after global cerebral ischemia in rats

Recent studies have shown that similar to cerebral gray matter (mainly composed of neuronal perikarya), white matter (composed of axons and glias) is vulnerable to ischemia. Edaravone, a free radical scavenger, has neuroprotective effects against focal cerebral ischemia even in humans. In this study, we investigated the time course and the severity of both gray and white matter damage following global cerebral ischemia by cardiac arrest, and examined whether edaravone protected the gray and the white matter. Male Sprague-Dawley rats were used. Global cerebral ischemia was induced by 5 min of cardiac arrest and resuscitation (CAR). Edaravone, 3 mg/kg, was administered intravenously either immediately or 60 min after CAR. The morphological damage was assessed by cresyl violet staining. The microtubule-associated protein 2 (a maker of neuronal perikarya and dendrites), the beta amyloid precursor protein (the accumulation of which is a maker of axonal damage), and the ionized calcium binding adaptor molecule 1 (a marker of microglia) were stained for immunohistochemical analysis. Significant neuronal perikaryal damage and marked microglial activation were observed in the hippocampal CA1 region with little axonal damage one week after CAR. Two weeks after CAR, the perikaryal damage and microglial activation were unchanged, but obvious axonal damage occurred. Administration of edaravone 60 min after CAR significantly mitigated the perikaryal damage, the axonal damage, and the microglial activation. Our results show that axonal damage develops slower than perikaryal damage and that edaravone can protect both gray and white matter after CAR in rats.

Effect of the free radical scavenger MCI-186 on spinal cord reperfusion after transient ischemia in the rabbit

OBJECTIVE

Paraplegia remains a serious complication of aortic operations. The production of free radicals during reperfusion after transient ischemia is believed to induce secondary spinal neuronal injury, resulting in paraplegia. The aim of the present study was to clarify the protective effect and method of administration of antioxidants on the neurological and histological outcome in the animal model for reperfusion injury after transient spinal cord ischemia.

METHODS

New Zealand white rabbits underwent surgical exposure of the abdominal aorta that was clamped for 15 minutes to achieve spinal cord ischemia. Group A animals received two 10 mg/kg doses of 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186) at the time of release of the aortic clamp and 30 minutes later. In group B, MCI-186, 5 mg/kg, was given three times, at the time of aorta clamp release, 30 minutes and 12 hours later. In group C (control group), one dose of vehicle was administered. Neurological status was assessed using modified Tarlov's score until 168 hours after operation. Spinal cord sections were examined microscopically to determine the extent of ischemic neuronal damage.

RESULTS

Groups A and B animals had better neurological function than group C (p < 0.001). In contrast, group C animals exhibited paraplegia or paraparesis with marked neuronal necrosis. The number of surviving neurons within examined sections of the spinal cord was significantly greater in group B than in group C (p < 0.001).

CONCLUSION

In a 15-minute ischemia-reperfusion model using rabbits, systemic repetitious administration of MCI-186, a free radical scavenger, was found to have a protective effect on the spinal cord neurons both neurologically and histologically. We postulate that the drug minimizes the delayed neuronal cell death for reperfusion injury after transient ischemia by reducing the free radical molecules. Moreover, it was thought that we could protect delayed neuronal cell death more effectively by administering MCI-186 12 hours later.

Xenon inhibits but N(2)O enhances ketamine-induced c-Fos expression in the rat posterior cingulate and retrosplenial cortices

Both nitrous oxide (N(2)O) and xenon are N:-methyl-D-aspartate receptor antagonists that have psychotomimetic effects and cause neuronal injuries in the posterior cingulate and retrosplenial cortices. We investigated the effect of xenon, xenon with ketamine, N(2)O, and N(2)O with ketamine on c-Fos expression in the rat posterior cingulate and retrosplenial cortices, a marker of psychotomimetic effects. Brain sections were prepared, and c-Fos expression was detected with immunohistochemical methods. A loss of microtubule-associated protein 2, a marker of neuronal injury, was also investigated. The number of Fos-like immunoreactivity positive cells by ketamine IV at a dose of 5 mg/kg under 70% N(2)O (128 +/- 12 cells per 0.5 mm(2)) was significantly more than those under 30% (15 +/- 2 cells per 0.5 mm(2)) and 70% xenon (2 +/- 1 cells per 0.5 mm(2)). Despite differences in c-fos immunoreactivity, there was no loss of microtubule-associated protein 2 immunoreactivity in any group examined. Xenon may suppress the adverse neuronal effects of ketamine, and combined use of xenon and ketamine seems to be safe in respect to neuronal adverse effects.

Delayed neuronal death prevented by inhibition of increased hydroxyl radical formation in a transient cerebral ischemia

The salicylate-trapping method was used to detect hydroxyl radicals by measurement of stable adduct dihydroxybenzoic acid (DHBA). Ten minutes of forebrain ischemia followed by reperfusion induced the increase in DHBA in rat hippocampal perfusates. Postischemic treatment with a free radical scavenger, 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186), significantly reduced the increase in DHBA and suppressed delayed neuronal death in the hippocampal CA1 region.