Cytochrome oxidase is decreased in piglet hippocampus following hypoxia-ischemia

Mitochondrial function in rat cerebral cortex and hippocampus after short- and long-term hypobaric hypoxia

Taking into account the importance of aerobic metabolism in brain, the aim of the present work was to evaluate mitochondrial function in cerebral cortex and hippocampus in a model of sustained hypobaric hypoxia (5000 m simulated altitude) during a short (1 mo) and a long (7 mo) term period, in order to precise the mechanisms involved in hypoxia acclimatization. Hippocampal mitochondria from rats exposed to short-term hypobaric hypoxia showed lower respiratory rates than controls in both states 4 (45%) and 3 (41%), and increased NO production (1.3 fold) as well as eNOS and nNOS expression associated to mitochondrial membranes, whereas mitochondrial membrane potential decreased (7%). No significant changes were observed in cortical mitochondria after 1 mo hypobaric hypoxia in any of the mitochondrial functionality parameters evaluated. After 7 mo hypobaric hypoxia, oxygen consumption was unchanged as compared with control animals both in hippocampal and cortical mitochondria, but mitochondrial membrane potential decreased by 16% and 8% in hippocampus and cortex respectively. Also, long-term hypobaric hypoxia induced an increase in hippocampal NO production (0.7 fold) and in eNOS expression. A clear tendency to decrease in H2O2 production was observed in both tissues. Results suggest that after exposure to hypobaric hypoxia, hippocampal mitochondria display different responses than cortical mitochondria. Also, the mechanisms responsible for acclimatization to hypoxia would be time-dependent, according to the physiological functions of the brain studied areas. Nitric oxide metabolism and membrane potential changes would be involved as self-protective mechanisms in high altitude environment.

Two free radical pathways mediate chemical hypoxia-induced glutamate release in synaptosomes from the prefrontal cortex

It has been known that the inhibition of mitochondrial cytochrome c oxidase is one of the earliest events occurring under hypoxia and this inhibition can lead to neuronal damages. Thus, the cytochrome c oxidase inhibitor sodium cyanide (NaCN) is widely used to produce a model of chemical hypoxia by inhibiting this enzyme. However, the downstream signaling pathways of the inhibition of the cytochrome c oxidase remain to be studied. In the present paper, we used sodium cyanide to mimic the inhibition of the mitochondrial cytochrome c oxidase and studied its effect on glutamate release in synaptosomes from the prefrontal cortex using on-line fluorimetry. We also further investigated the mechanisms underlying the enhancing effect of sodium cyanide on glutamate release using pharmacological approaches combined with other techniques. The results showed that sodium cyanide significantly increased glutamate release from synaptosomes of prefrontal cortex; the broad-spectrum free radical scavenger MnTBAP and melatonin completely abolished the effect of sodium cyanide on glutamate release; the H2O2-NMDA receptor pathway mediated one part, whereas the lipid peroxyl radicals-ATP synthase pathway mediated another part of the sodium cyanide-induced glutamate release; scavenging H2O2 and enhancing ATP synthase activity could completely abolish the sodium cyanide-induced glutamate release.

Neonatal hypoxia triggers transient apoptosis followed by neurogenesis in the rat CA1 hippocampus

Continuous generation of new neurons has been demonstrated in the adult mammalian brain, and this process was shown to be stimulated by various pathologic conditions, including cerebral ischemia. Because brain oxygen deprivation is particularly frequent in neonates and represents the primary event of asphyxia, we analyzed long-term consequences of transient hypoxia in the newborn rat. Within 24 h after birth, animals were exposed to 100% N(2) for 20 min at 36 degrees C, and temporal changes in the vulnerable CA1 hippocampus were monitored. Cell density measurements revealed delayed cell death in the pyramidal cell layer reflecting apoptosis, as shown by characteristic nuclear morphology and expression levels of Bcl-2, Bax, and caspase-3. Neuronal loss was confirmed by reduced density of neuron-specific enolase (NSE)-labeled cells, and peaked by 1 wk post insult, to reach 27% of total cells. A gradual recovery then occurred, and no significant difference in cell density could be detected between controls and hypoxic rats at postnatal d 21. Repeated injections of bromodeoxyuridine (50 mg/kg) showed that newly divided cells expressing neuronal markers increased by 225% in the germinative subventricular zone, and they tended to migrate along the posterior periventricle toward the hippocampus. Therefore, transient hypoxia in the newborn rat triggered apoptosis in the CA1 hippocampus followed by increased neurogenesis and apparent anatomical recovery, suggesting that the developing brain may have a high capacity for self-repair.