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Objective: To establish a neonatal rat model of hypoxic-ischemic encephalopathy and clarify the changing features of neural stem cells (NSCs) in episodes of hypoxic-ischemic encephalopathy (HIE) so as to provide experimental and theoretical evidences for treating HIE by applying NSCs at the appropraite time., Methods: Totally 210 neonatal rats aged 7 d were divided randomly into three groups, normal control group, hypoxic group and hypoxic-ischemic group with 70 rats in each. According to the time of sacrefice, 70 rats of every group were further divided randomly into seven groups including third hour (3 h), the sixth hour (6 h), first day (1 d), third day (3 d), the seventh day (7 d), the fourteenth day (14 d) and the twenty-first day (21 d), with 10 rats in each subgroup. The left common carotid artery of the neonatal rats in hypoxic-ischemic group was ligated and those in the hypoxic group were subjected to inhalation of 8% oxygen for 2.5 h. NSCs from brain tissues of the rats of the three groups were determined with HE staining and immunohistochemical method under light microscope., Results: Most of neonatal rats in hypoxic-ischemic group behaved turning to the left stably 1 h after normal concentration of oxygen was given. In hypoxic-ischemic group, slight brain injury occurred at 3 h, severe brain injury appeared at 1 d, glial cells proliferated at 3 d and 7 d, brain atrophy was found at 14 d and 21 d. NSCs existed in brain tissues of rats in all the three groups. NSCs in normal control and the hypoxic group mainly distributed in hippocampus, subventricular tissues, striatum and cortex. But NSCs in hippocampus located in layers of molecule, cone cell and inner granular cell. NSCs in hypoxic-ischemic group showed obvious regional distribution, less in the regions with pathological changes. At 3 h, 6 h and 14 d, there was no difference in the number of NSCs between hypoxi and hypoxic-ischemic group. At 1 d, 3 d and 7 d, there was a highly significant difference in the number of NSCs between hypoxic and hypoxic-ischemic group. At 21 d, there was a significant difference in the number of NSCs between hypoxic and hypoxic-ischemic group, meanwhile, there was a significant difference in the number of NSCs between control and hypoxic group. At 3 d, there was a very significant difference in the number of NSCs between control and hypoxic-ischemic group. At 7 d and 21 d points, there was a highly significant difference in the number of NSCs between control and hypoxic group., Conclusion: The neonatal rat model of HIE was successfully established. NSCs increased in earlier period and decreased in later period of HIE, ultimately, NSCs located in the injured regions died one after anotner. Hypoxia induces NSCs' proliferation.

Inspired oxygen (FiO2) was manipulated during the early reperfusion period after global cerebral ischemia (four-vessel occlusion of 20 or 30 min duration) in anesthetized rats. The goal was to determine whether oxygen availability during the early reperfusion period alters recovery of mitochondrial redox state and evoked electrical activity. The effectiveness of post-ischemic oxygen treatment was monitored at the tissue level with oxygen sensitive microelectrodes, and at the mitochondrial level by reflection spectrophotometry of the redox state of cytochrome oxidase. Transiently decreasing FiO2 from 0.3 to 0.15 limited reperfusion-induced hyperoxygenation and post-ischemic mitochondrial hyperoxidation (PIMHo). Evoked potential recovery was improved by this treatment after 20 min ischemia but not after 30 min ischemia. Increasing FiO2 from 0.3 to 1.0 exacerbated PIMHo and tissue hyperoxygenation. Transient elevation of tissue oxygen tension after 30 min of global ischemia inhibited recovery of evoked potentials. These data suggest that a period of heightened vulnerability to oxidative stress occurs within the first 10 min of reperfusion after global ischemia. This period is characterized by tissue hyperoxygenation and mitochondrial hyperoxidation. Limiting oxygen availability during this period may improve the outcome while conversely elevating oxygenation may be detrimental.

The purposes of this study were to determine whether cortical spreading depression occurs outside of the infarct produced by photothrombotic vascular occlusion, and also the direction of spreading. Focal cerebral thrombotic infarction was produced by irradiating the exposed skull of anesthetized rats with green light (560 nm) following systemic injection of rose bengal dye. At proximal sites (approximately 2 mm anterior to the infarct border), transient, severe hyperemic episodes (THEs) lasting 1-2 min were intermittently recorded. THE frequency was greatest in the first hour and declined over a 3-h period. THEs were accompanied (and usually preceded) by a precipitous rise in [K+]0 (from approximately 3 to > 40 mM) and were associated with increases in local tissue oxygen tension (tPO2). Following the rise in [K+]0, clearance of [K+]0 to its pre-THE baseline preceded baseline recovery of CBF. These data indicate that THEs were reactive to physiologic events resembling cortical spreading depression (CSD), which provoked increased demand for oxygen and blood flow, and which spread from proximal sites to areas more distal (approximately 4 mm) from the rim of the evolving infarct. MK-801 (1 mg/kg, i.v.) inhibited subsequent CSD-like episodes. We conclude that photothrombosis-induced ischemia provoked CSD which was triggered either within the infarct core or in the infarct rim and spread to more distal sites. Whether multiple episodes of CSD during infarct generation are responsible for the remote consequences of focal brain injury remains to be determined.

To evaluate the contribution of extracellular H+ activity toward depression of brain electrical activity during anoxia, extracellular pH (pHe) and field potentials were measured in turtle and rat olfactory bulbs with ion-selective microelectrodes. This study tests the hypothesis that unique regulation of pHe contributes to the remarkable tolerance of turtle brain to prolonged anoxia. Hypercapnea (20% CO2 ventilation) depressed olfactory bulb evoked potentials 25-30% in both rat and turtle. During anoxia, evoked potentials were completely abolished within 1 min in rat olfactory bulb but decreased to only 40% of control after 4 h in the turtle despite similar changes in brain pHe. Anoxia-induced acidification of turtle brain was exacerbated by hypercapnea and was attenuated by hypocapnea or by hypocapnea plus intravenous infusion of sodium bicarbonate. However, these manipulations of pHe during anoxia in turtle brain had little effect on depression of evoked potentials. We conclude that energy failure, rather than extracellular acidification, is the major contributor toward suppression of electrical activity in mammalian brain and that preservation of energy balance, rather than unique pH regulation, is responsible for protection of turtle brain during anoxia.

A key to turtle brain survival during anoxia is continued ion transport and avoidance of anoxic depolarization. Previous findings that ATP concentration remained constant during prolonged anoxia and calculations that ATP production decreased indicate that compensatory processes, other than consumption of energy stores or increased anaerobic glycolysis, must also contribute to ion homeostasis and brain survival. To determine whether preservation of ion transport is associated with changes in electrophysiology during loss of oxidative metabolism, the brains of pentobarbital sodium-anesthetized turtles were electrically stimulated 1) to provoke measurable increments in extracellular K+ activity (a degrees k) for determination of rates of K+ reaccumulation at the stimulus site and 2) to elicit polysynaptic extracellular field potentials (evoked potentials) recordable in the olfactory bulb. During anoxia, base-line a degrees k rose only a few millimolar, and rates of reaccumulation of K+, incremented by stimulation were slightly but not significantly slowed. In contrast, postsynaptic orthodromic responses of olfactory bulb granule cells were markedly depressed by anoxia. Monosynaptic responses of granule cells to antidromic stimulation of the lateral olfactory tract were less affected, and compound action potentials in the olfactory nerve were unchanged by anoxia. These data suggest that synaptic transmission in turtle brain, as in that of mammal, is highly dependent on oxidative metabolism and that the turtle brain may effectively conserve energy for ion transport during anoxia by depression of electrical activity.

Recent evidence suggests that suppression of electrical activity, with the likely reduction of energy use, provides a necessary strategy for prolonged anoxic tolerance of turtle brain. The present study was aimed toward defining mechanisms underlying anoxia-induced suppression of electrical activity in turtle brain. Goals were to determine whether effects of anoxia were selective to excitatory or inhibitory processes and to test the hypothesis that enhanced inhibition underlies suppression of orthodromic field potentials in olfactory bulb. Amplitudes of "conditioning" and "test" responses, provoked by pairs of stimulus pulses to the olfactory nerve, were evaluated before, during, and after anoxic insults in the brains of turtles anesthetized with pentobarbital sodium. Suppression of conditioning responses was proportionally greater than that of test responses, indicating that inhibition was decreased and that enhanced inhibitory activity is not responsible for suppression of field potentials in turtle olfactory bulb during anoxia. When normoxia was restored, conditioning responses recovered but test responses remained suppressed. These data confirm that the inhibitory effect of a conditioning pulse on responses to a second pulse of stimulation results from a recurrent circuit and suggest that anoxia-induced changes in field potentials are independent of this recurrent circuit. Enhanced inhibition during the early period of recovery after anoxic insults may provide advantages for restoring energy status and cell physiology by suppressing electrical activity and energy use.

Unlike the mammalian brain, the turtle brain maintains ion homeostasis and avoids anoxic depolarization during prolonged anoxia. The mechanisms by which turtle brains avoid and recover from anoxic depolarization were investigated by relating changes in cellular ATP levels to extracellular K+ (K+o) and evoked potential activities after 6 h of anoxia and during anoxic depolarization induced by superfusion of the brain surface with iodoacetate during anoxia. ATP levels were maintained during 6 h of anoxia despite marked decreases in energy production, but ATP was lowered during inhibition of both oxidative phosphorylation and glycolysis. K+o activity was unchanged during 6 h of anoxia but increased when ATP levels decreased. Ion homeostasis in the turtle brain appears to be linked to ATP levels but is unaffected by rate of energy production. In contrast, amplitudes of evoked potentials decreased when ATP levels were maintained, but rate of energy production declined. ATP and K+o levels recovered after anoxic depolarization, but evoked potential activity was not restored. These data suggest that the basic strategy for turtle brain to survive anoxia is to avoid anoxic depolarization by maintaining ATP levels.