Expression of classical mitochondrial respiratory responses in homogenates of rat forebrain

Hippocampal Function Is Impaired by a Short-Term High-Fat Diet in Mice: Increased Blood-Brain Barrier Permeability and Neuroinflammation as Triggering Events

Worldwide, and especially in Western civilizations, most of the staple diets contain high amounts of fat and refined carbohydrates, leading to an increasing number of obese individuals. In addition to inducing metabolic disorders, energy dense food intake has been suggested to impair brain functions such as cognition and mood control. Here we demonstrate an impaired memory function already 3 days after the start of a high-fat diet (HFD) exposure, and depressive-like behavior, in the tail suspension test, after 5 days. These changes were followed by reduced synaptic density, changes in mitochondrial function and astrocyte activation in the hippocampus. Preceding or coinciding with the behavioral changes, we found an induction of the proinflammatory cytokines TNF-α and IL-6 and an increased permeability of the blood–brain barrier (BBB), in the hippocampus. Finally, in mice treated with a TNF-α inhibitor, the behavioral and BBB alterations caused by HFD-feeding were mitigated suggesting that inflammatory signaling was critical for the changes. In summary, our findings suggest that HFD rapidly triggers hippocampal dysfunction associated with BBB disruption and neuroinflammation, promoting a progressive breakdown of synaptic and metabolic function. In addition to elucidating the link between diet and cognitive function, our results might be relevant for the comprehension of the neurodegenerative process.

Mitochondrial pyruvate carrier as a key regulator of fever and neuroinflammation

The mitochondrial pyruvate carrier (MPC) is an inner-membrane transporter that facilitates pyruvate uptake from the cytoplasm into mitochondria. We previously reported that MPC1 protein levels increase in the hypothalamus of animals during fever induced by lipopolysaccharide (LPS), but how this increase contributes to the LPS responses remains to be studied. Therefore, we investigated the effect of UK 5099, a classical MPC inhibitor, in a rat model of fever, on hypothalamic mitochondrial function and neuroinflammation in LPS-stimulated preoptic area (POA) primary microcultures. Intracerebroventricular administration of UK 5099 reduced the LPS-induced fever. High-resolution respirometry revealed an increase in oxygen consumption and oxygen flux related to ATP synthesis in the hypothalamic homogenate from LPS-treated animals linked to mitochondrial complex I plus II. Preincubation with UK 5099 prevented the LPS-induced increase in oxygen consumption, ATP synthesis and spare capacity only in complex I-linked respiration and reduced mitochondrial H₂O₂ production. In addition, treatment of rat POA microcultures with UK 5099 reduced the secretion of the proinflammatory and pyrogenic cytokines TNFα and IL-6 as well as the immunoreactivity of inflammatory transcription factors NF-κB and NF-IL6 four hours after LPS stimulation. These results suggest that the regulation of mitochondrial pyruvate metabolism through MPC inhibition may be effective in reducing neuroinflammation and fever.

Mitochondrial response in a toddler-aged swine model following diffuse non-impact traumatic brain injury

Traumatic brain injury (TBI) is an important health problem, and a leading cause of death in children worldwide. Mitochondrial dysfunction is a critical component of the secondary TBI cascades. Mitochondrial response in the pediatric brain has limited investigation, despite evidence that the developing brain's response differs from that of the adult, especially in diffuse non-impact TBI. We performed a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a swine model of diffuse TBI (rapid non-impact rotational injury: RNR), and examined the cortex and hippocampus. A substrate-uncoupler-inhibitor-titration protocol examined the role of the individual complexes as well as the uncoupled maximal respiration. Respiration per mg of tissue was also related to citrate synthase activity (CS) as an attempt to control for variability in mitochondrial content following injury. Diffuse RNR stimulated increased complex II-driven respiration relative to mitochondrial content in the hippocampus compared to shams. LEAK (State 4o) respiration increased in both regions, with decreased respiratory ratios of convergent oxidative phosphorylation through complex I and II, compared to sham animals, indicating uncoupling of oxidative phosphorylation at 24h. The study suggests that proportionately, complex I contribution to convergent mitochondrial respiration was reduced in the hippocampus after RNR, with a simultaneous increase in complex-II driven respiration. Mitochondrial respiration 24h after diffuse TBI varies by location within the brain. We concluded that significant uncoupling of oxidative phosphorylation and alterations in convergent respiration through complex I- and complex II-driven respiration reveals therapeutic opportunities for the injured at-risk pediatric brain.

Persistently Altered Brain Mitochondrial Bioenergetics After Apparently Successful Resuscitation From Cardiac Arrest

BACKGROUND

Although advances in cardiopulmonary resuscitation have improved survival from cardiac arrest (CA), neurologic injury persists and impaired mitochondrial bioenergetics may be critical for targeted neuroresuscitation. The authors sought to determine if excellent cardiopulmonary resuscitation and postresuscitation care and good traditional survival rates result in persistently disordered cerebral mitochondrial bioenergetics in a porcine pediatric model of asphyxia-associated ventricular fibrillation CA.

METHODS AND RESULTS

After 7 minutes of asphyxia, followed by ventricular fibrillation, 5 female 1-month-old swine (4 sham) received blood pressure-targeted care: titration of compression depth to systolic blood pressure of 90 mm Hg and vasopressor administration to a coronary perfusion pressure >20 mm Hg. All animals received protocol-based vasopressor support after return of spontaneous circulation for 4 hours before they were killed. The primary outcome was integrated mitochondrial electron transport system (ETS) function. CA animals displayed significantly decreased maximal, coupled oxidative phosphorylating respiration (OXPHOSCI + CII) in cortex (P<0.02) and hippocampus (P<0.02), as well as decreased phosphorylation and coupling efficiency (cortex, P<0.05; hippocampus, P<0.05). Complex I- and complex II-driven respiration were both significantly decreased after CA (cortex: OXPHOSCI P<0.01, ETSCII P<0.05; hippocampus: OXPHOSCI P<0.03, ETSCII P<0.01). In the hippocampus, there was a significant decrease in maximal uncoupled, nonphosphorylating respiration (ETSCI + CII), as well as a 30% reduction in citrate synthase activity (P<0.04).

CONCLUSIONS

Mitochondria in both the cortex and hippocampus displayed significant alterations in respiratory function after CA despite excellent cardiopulmonary resuscitation and postresuscitation care in asphyxia-associated ventricular fibrillation CA. Analysis of integrated ETS function identifies mitochondrial bioenergetic failure as a target for goal-directed neuroresuscitation after CA. IACUC Protocol: IAC 13-001023.

Mitochondrial bioenergetic alterations after focal traumatic brain injury in the immature brain

Traumatic brain injury (TBI) is one of the leading causes of death in children worldwide. Emerging evidence suggests that alterations in mitochondrial function are critical components of secondary injury cascade initiated by TBI that propogates neurodegeneration and limits neuroregeneration. Unfortunately, there is very little known about the cerebral mitochondrial bioenergetic response from the immature brain triggered by traumatic biomechanical forces. Therefore, the objective of this study was to perform a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a high-fidelity large animal model of focal controlled cortical impact injury (CCI) 24h post-injury. This novel approach is directed at analyzing dysfunction in electron transport, ADP phosphorylation and leak respiration to provide insight into potential mechanisms and possible interventions for mitochondrial dysfunction in the immature brain in focal TBI by delineating targets within the electron transport system (ETS). Development and application of these methodologies have several advantages, and adds to the interpretation of previously reported techniques, by having the added benefit that any toxins or neurometabolites present in the ex-vivo samples are not removed during the mitochondrial isolation process, and simulates the in situ tricarboxylic acid (TCA) cycle by maximizing key substrates for convergent flow of electrons through both complexes I and II. To investigate alterations in mitochondrial function after CCI, ipsilateral tissue near the focal impact site and tissue from the corresponding contralateral side were examined. Respiration per mg of tissue was also related to citrate synthase activity (CS) and calculated flux control ratios (FCR), as an attempt to control for variability in mitochondrial content. Our biochemical analysis of complex interdependent pathways of electron flow through the electron transport system, by most measures, reveals a bilateral decrease in complex I-driven respiration and an increase in complex II-driven respiration 24h after focal TBI. These alterations in convergent electron flow though both complex I and II-driven respiration resulted in significantly lower maximal coupled and uncoupled respiration in the ipsilateral tissue compared to the contralateral side, for all measures. Surprisingly, increases in complex II and complex IV activities were most pronounced in the contralateral side of the brain from the focal injury, and where oxidative phosphorylation was increased significantly compared to sham values. We conclude that 24h after focal TBI in the immature brain, there are significant alterations in cerebral mitochondrial bioenergetics, with pronounced increases in complex II and complex IV respiration in the contralateral hemisphere. These alterations in mitochondrial bioenergetics present multiple targets for therapeutic intervention to limit secondary brain injury and support recovery.

Central presynaptic terminals are enriched in ATP but the majority lack mitochondria

Synaptic neurotransmission is known to be an energy demanding process. At the presynapse, ATP is required for loading neurotransmitters into synaptic vesicles, for priming synaptic vesicles before release, and as a substrate for various kinases and ATPases. Although it is assumed that presynaptic sites usually harbor local mitochondria, which may serve as energy powerhouse to generate ATP as well as a presynaptic calcium depot, a clear role of presynaptic mitochondria in biochemical functioning of the presynapse is not well-defined. Besides a few synaptic subtypes like the mossy fibers and the Calyx of Held, most central presynaptic sites are either en passant or tiny axonal terminals that have little space to accommodate a large mitochondrion. Here, we have used imaging studies to demonstrate that mitochondrial antigens poorly co-localize with the synaptic vesicle clusters and active zone marker in the cerebral cortex, hippocampus and the cerebellum. Confocal imaging analysis on neuronal cultures revealed that most neuronal mitochondria are either somatic or distributed in the proximal part of major dendrites. A large number of synapses in culture are devoid of any mitochondria. Electron micrographs from neuronal cultures further confirm our finding that the majority of presynapses may not harbor resident mitochondria. We corroborated our ultrastructural findings using serial block face scanning electron microscopy (SBFSEM) and found that more than 60% of the presynaptic terminals lacked discernible mitochondria in the wild-type mice hippocampus. Biochemical fractionation of crude synaptosomes into mitochondria and pure synaptosomes also revealed a sparse presence of mitochondrial antigen at the presynaptic boutons. Despite a low abundance of mitochondria, the synaptosomal membranes were found to be highly enriched in ATP suggesting that the presynapse may possess alternative mechanism/s for concentrating ATP for its function. The potential mechanisms including local glycolysis and the possible roles of ATP-binding synaptic proteins such as synapsins, are discussed.

Neuroglobin mitigates mitochondrial impairments induced by acute inhalation of combustion smoke in the mouse brain

CONTEXT

Acute inhalation of combustion smoke adversely affects brain homeostasis and energy metabolism. We previously showed that overexpressed neuroglobin (Ngb), neuron specific globin protein, attenuates the formation of smoke inhalation-induced oxidative DNA damage, in vivo, in the mouse brain, while others reported protection by Ngb in diverse models of brain injury, mainly involving oxidative stress and hypoxic/ischemic insults.

OBJECTIVE

To determine to what extent elevated Ngb ameliorates post smoke-inhalation brain bioenergetics and homeostasis in Ngb overexpressing transgenic mouse.

METHODS

Smoke inhalation induced changes in bioenergetics were measured in the wild type and Ngb transgene mouse brain. Modulations of mitochondrial respiration were analyzed using the Seahorse XF24 flux analyzer and changes in cytoplasmic energy metabolism were assessed by measuring enzymatic activities and lactate in the course of post smoke recovery.

RESULTS

Cortical mitochondria from Ngb transgene, better maintained ATP synthesis-linked oxygen consumption and unlike wild type mitochondria did not increase futile oxygen consumption feeding the proton leak, reflecting lesser smoke-induced mitochondrial compromise. Measurements revealed lesser reduction of mitochondrial ATP content and lesser compensatory increases in cytosolic energy metabolism, involving pyruvate kinase and lactate dehydrogenase activities as well as cytosolic lactate levels. Additionally, induction of c-Fos, the early response gene and key neuronal stress sensor, was attenuated in Ngb transgene compared to wild type brain after smoke.

CONCLUSION

Considered together, these differences reflect lesser perturbations produced by acute inhalation of combustion smoke in the Ngb overexpressing mouse, suggesting that Ngb mitigates mitochondrial dysfunction and neurotoxicity and raises the threshold of smoke inhalation-induced brain injury.

Antioxidant effects of JM-20 on rat brain mitochondria and synaptosomes: mitoprotection against Ca²⁺-induced mitochondrial impairment

Because mitochondrial oxidative stress and impairment are important mediators of neuronal damage in neurodegenerative diseases and in brain ischemia/reperfusion, in the present study, we evaluated the antioxidant and mitoprotective effect of a new promising neuroprotective molecule, JM-20, in mitochondria and synaptosomes isolated from rat brains. JM-20 inhibited succinate-mediated H₂O₂ generation in both mitochondria and synaptosomes incubated in depolarized (high K(+)) medium at extremely low micromolar concentration and with identical IC₅₀ values of 0.91 μM. JM-20 also repressed glucose-induced H₂O₂ generation stimulated by rotenone or by antimycin A in synaptosomes incubated in high sodium-polarized medium at extremely low IC₅₀ values of 0.395 μM and 2.452 μM, respectively. JM-20 was unable to react directly with H₂O₂ or with superoxide anion radicals but displayed a cathodic reduction peak at -0.71V, which is close to that of oxygen (-0.8V), indicating high electron affinity. JM-20 also inhibited uncoupled respiration in mitochondria or synaptosomes and was a more effective inhibitor in the presence of the respiratory substrates glutamate/malate than in the presence of succinate. JM-20 also prevented Ca(2+)-induced mitochondrial permeability transition pore opening, membrane potential dissipation and cytochrome c release, which are key pathogenic events during stroke. This molecule also prevented Ca(2+) influx into synaptosomes and mitochondria; the former effect was a consequence of the latter because JM-20 inhibition followed the patterns of carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP), which is a classic mitochondrial uncoupler. Because the mitochondrion is considered an important source and target of neuronal cell death signaling after an ischemic insult, the antioxidant and protective effects of JM-20 against the deleterious effects of Ca(2+) observed at the mitochondrial level in this study may endow this molecule with the ability to succeed in mitochondrion-targeted strategies to combat ischemic brain damage.

Insulin prevents mitochondrial generation of H₂O₂ in rat brain

The mitochondrial electron transport system (ETS) is a main source of cellular ROS, including hydrogen peroxide (H₂O₂). The production of H₂O₂ also involves the mitochondrial membrane potential (ΔΨm) and oxygen consumption. Impaired insulin signaling causes oxidative neuronal damage and places the brain at risk of neurodegeneration. We evaluated whether insulin signaling cross-talks with ETS components (complexes I and F₀F₁ATP synthase) and ΔΨm to regulate mitochondrial H₂O₂ production, in tissue preparations from rat brain. Insulin (50 to 100 ng/mL) decreased H₂O₂ production in synaptosomal preparations in high Na(+) buffer (polarized state), stimulated by glucose and pyruvate, without affecting the oxygen consumption. In addition, insulin (10 to 100 ng/mL) decreased H₂O₂ production induced by succinate in synaptosomes in high K(+) (depolarized state), whereas wortmannin and LY290042, inhibitors of the PI3K pathway, reversed this effect; heated insulin had no effect. Insulin decreased H₂O₂ production when complexes I and F₀F₁ATP synthase were inhibited by rotenone and oligomycin respectively suggesting a target effect on complex III. Also, insulin prevented the generation of maximum level of ∆Ψm induced by succinate. The PI3K inhibitors and heated insulin maintained the maximum level of ∆Ψm induced by succinate in synaptosomes in a depolarized state. Similarly, insulin decreased ROS production in neuronal cultures. In mitochondrial preparations, insulin neither modulated H2O2 production or oxygen consumption. In conclusion, the normal downstream insulin receptor signaling is necessary to regulate complex III of ETS avoiding the generation of maximal ∆Ψm and increased mitochondrial H2O2 production.

Brain mitochondrial function in a murine model of cerebral malaria and the therapeutic effects of rhEPO

Cerebral malaria (CM) is a life-threatening complication of Plasmodium falciparum infection. The pathogenesis of CM is complex. Cerebral metabolic dysfunction is implicated in CM, which may be caused by both an impaired cerebral microcirculation and a dysregulated inflammatory response affecting cellular respiration of mitochondria. Recombinant human erythropoietin (rhEPO) is a promising new therapy that has been shown to reduce mortality in a mouse model of CM. In order to further elucidate the metabolic dysfunction in CM the objective of the present study was to assess brain mitochondrial respiratory function in CM with and without rhEPO treatment. The P. berghei ANKA - C57BL/6 murine model of CM was used. Mitochondrial respiration was analyzed in brain homogenates using high-resolution respirometry and a multiple substrate and inhibitor protocol. The animals were divided into four groups; infected injected with saline or with rhEPO, non-infected injected with saline or with rhEPO. Infected mice developed CM and treatment with rhEPO attenuated clinical signs of disease. There were no differences in respiratory parameters of brain mitochondria between infected and non-infected mice and no connection between disease severity and mitochondrial respiratory function. Treatment with rhEPO similarly had no effect on respiratory function. Thus cerebral metabolic dysfunction in CM does not seem to be directly linked to altered mitochondrial respiratory capacity as analyzed in brain homogenates ex vivo. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Bioenergetic failure of human peripheral blood monocytes in patients with septic shock is mediated by reduced F1Fo adenosine-5'-triphosphate synthase activity

OBJECTIVE

Increasing evidence points to the role of mitochondrial dysfunction in the pathogenesis of sepsis. Previous data indicate that mitochondrial function is affected in monocytes from septic patients, but the underlying mechanisms and the impact of these changes on the patients' outcome are unknown. We aimed to determine the mechanisms involved in mitochondrial dysfunction in peripheral blood mononuclear cells from patients with septic shock.

DESIGN

A cohort of patients with septic shock to study peripheral blood mononuclear cell mitochondrial respiration by high-resolution respirometry analyses and to compare with cells from control subjects.

SETTING

Three intensive care units and an academic research laboratory.

SUBJECTS

Twenty patients with septic shock and a control group composed of 18 postoperative patients without sepsis or shock.

INTERVENTIONS

Ex vivo measurements of mitochondrial oxygen consumption were carried out in digitonin-permeabilized peripheral blood mononuclear cells from 20 patients with septic shock taken during the first 48 hrs after intensive care unit admission as well as in peripheral blood mononuclear cells from control subjects. Clinical parameters such as hospital outcome and sepsis severity were also analyzed and the relationship between these parameters and the oxygen consumption pattern was investigated.

MEASUREMENTS AND MAIN RESULTS

We observed a significant reduction in the respiration specifically associated with adenosine-5'-triphosphate synthesis (state 3) compared with the control group (5.60 vs. 9.89 nmol O2/min/10(7) cells, respectively, p < .01). Reduction of state 3 respiration in patients with septic shock was seen with increased prevalence of organ failure (r = -0.46, p = .005). Nonsurviving patients with septic shock presented significantly lower adenosine diphosphate-stimulated respiration when compared with the control group (4.56 vs. 10.27 nmol O2/min/10(7) cells, respectively; p = .004). Finally, the presence of the functional F1Fo adenosine-5'-triphosphate synthase complex (0.51 vs. 1.00 ng oligo/mL/10(6) cells, p = .02), but not the adenine nucleotide translocator, was significantly lower in patients with septic shock compared with control cells.

CONCLUSION

Mitochondrial dysfunction is present in immune cells from patients with septic shock and is characterized as a reduced respiration associated to adenosine-5'-triphosphate synthesis. The molecular basis of this phenotype involve a reduction of F1Fo adenosine-5'-triphosphate synthase activity, which may contribute to the energetic failure found in sepsis.

Methods for assessing and modulating UCP2 expression and function

Uncoupling protein 2 (UCP2) is a member of the uncoupling protein family. It is expressed in the inner mitochondrial membrane and plays a role in the control of free radical production, oxidative damage, insulin secretion, and fatty-acid peroxide exportation. Although UCP2 expression occurs in several tissues, some of its most remarkable functions are exerted in organs of difficult experimental access, such as the central nervous system, particularly the hypothalamus and the pancreatic islets. In addition, due to its low levels of expression in the mitochondrial membrane, studying UCP2 expression and function depends on specific- and well-established methods. This chapter describes methods for directly assessing UCP2 expression and function in different tissues. Purified mitochondria preparations are used for enhancing the capacity of detection of UCP2 protein or for evaluating the role of UCP2 in mitochondria respiration. Exposure of experimental animals to cold environment leads to increased UCP2 expression, while reduction of its expression can be achieved directly by targeting its mRNA with antisense oligonucleotides, or indirectly by targeting PGC-1alpha expression with antisense oligonucleotides.

Sepsis induces brain mitochondrial dysfunction

OBJECTIVE

Mitochondrial dysfunctions have been associated with the pathogenesis of sepsis. A systematic survey of mitochondrial function in brain tissues during sepsis is lacking. In the present work, we investigate brain mitochondrial function in a septic mouse model.

DESIGN

Prospective animal study.

SETTING

University research laboratory.

SUBJECTS

Male Swiss mice, aged 6-8 wks.

INTERVENTIONS

Mice were subjected to cecal ligation and perforation (sepsis group) with saline resuscitation or to sham operation (control group).

MEASUREMENTS AND MAIN RESULTS

Oxygen consumption was measured polarographically in an oximeter. Brain homogenates from septic animals presented higher oxygen consumption in the absence of adenosine 5'-diphosphate (state 4) compared with control animals. The increase in state 4 respiration in animals in the cecal ligation and perforation group resulted in a drastic decrease in both respiratory control and adenosine 5'-diphosphate/oxygen ratios, indicating a reduction in the oxidative phosphorylation efficiency. Septic animals presented a significant increase in the recovery time of mitochondrial membrane potential on adenosine 5'-diphosphate addition compared with control animals, suggesting a proton leak through the inner mitochondrial membrane. The septic group presented a general reduction in the content of cytochromes. Moreover, the activity of cytochrome c oxidase was specifically and significantly decreased in the brain during sepsis. Hydrogen peroxide generation by brain mitochondria from septic mice did not respond to substrates of electron transport chain or to adenosine 5'-diphosphate, showing that mitochondrial function may be compromised in a critical level in the brain during sepsis.

CONCLUSIONS

The mitochondrial dysfunctions demonstrated here indicate that uncoupling of oxidative phosphorylation takes place in the brain of septic mice, compromising tissue bioenergetic efficiency.

Role of mitochondrial permeability transition in the immature brain following intrauterine ischemia

Recirculation following 30 minutes of intrauterine ischemia due to uterine artery occlusion has previously been found to be accompanied by delayed deterioration of the cellular bioenergetic state and of mitochondrial function in the fetal rat brain. The objective of this study was to assess whether the delayed deterioration is due to the activation of mitochondrial permeability transition (MPT), which is observed ultrastructurally as mitochondrial swelling. The respiratory activities and ultrastructure of isolated mitochondria and the cellular bioenergetic state in the fetal rat brain were examined at the end of 30 minutes of intrauterine ischemia and after 1, 2, 3 or 4 hours of recirculation. Cyclosporin A (CsA), a potent and specific MPT blocker, or vehicle was given 1 hour after recirculation. In the vehicle-treated animals, the transient ischemia was associated with a delayed deterioration of the cellular bioenergetic state and mitochondrial activities 4 hours of recirculation. The number of swollen mitochondria increased markedly after 4 hours of recirculation. Both the deterioration and swelling were prevented by CsA. The present study indicates that treatment with CsA improves recovery of energy metabolism and inhibits mitochondrial swelling following transient intrauterine ischemia in the fetal brain. The results suggest that mitochondria and MPT may be involved in the development of ischemic brain damage in the immature rat.

Effect of the inhibitory neurotransmitter glycine on slow destructive processes in brain cortex slices under anoxic conditions

Slow destructive processes in brain cortex were studied under deep hypoxia (anoxia). Study of the character and dynamics of DNA destruction showed that apoptosis and necrosis run in parallel under the experimental conditions. These processes typically develop in tens of hours. A similar conclusion was reached from electron microscopic study of the tissue ultrastructure. More detailed study revealed that a relatively rare type of apoptosis not involving cytochrome c release from the intermembrane space of mitochondria and not associated with opening of the mitochondrial nonspecific pore occurs under the experimental conditions. As this is occurring, the process can be slowed by high concentrations of glycine, an inhibitory neurotransmitter. The study of DNA destruction demonstrated that high concentrations of glycine selectively slow apoptosis but have almost no effect on necrosis. Glycine also drastically decreases changes in the tissue ultrastructure, particularly of mitochondria, arising under anoxia. Glycine does not notably influence the mitochondrial oxidative phosphorylation system. Study of impairment of mitochondrial function demonstrated that the oxidative phosphorylation system is not disturbed for 1 h, which is several times longer than the inhibition time of brain function under deep hypoxia. The mitochondrial respiratory system is preserved for a relatively long time (24 h). Malate oxidase activity is deactivated after 48 h. The succinate oxidase fragment of the mitochondrial respiratory chain proved especially resistant; it retains activity under anoxia for more than 72 h. A possible mechanism of the effect of high glycine concentrations is discussed.

Characterization of mitochondrial respiratory chain energetics in the vestibular nucleus complex

CONCLUSIONS

Despite having very high neuronal firing rates, the VNC does not have unusually high mitochondrial activity in vitro. This study is the first in which functionally active mitochondria from the hindbrain have been isolated and characterized.

OBJECTIVE

Neurons in the vestibular nucleus complex (VNC) have exceptionally high spontaneous firing rates. Neuronal mitochondria generate adenosine triphosphate critical for maintaining the membrane potentials required for axon firing. We therefore hypothesized a high rate of mitochondrial activity in the VNC.

MATERIAL AND METHODS

To test this hypothesis, we compared mitochondrial activity in the VNC with mitochondrial activity from another area of the hindbrain, the cerebellum. Mitochondrial respiratory activity was assessed by measuring oxidative phosphorylation and mitochondrial respiratory enzyme complex activity.

RESULTS

Assay results were not significantly different in the VNC compared to those obtained with the cerebellum or with rat brain mitochondria in previous studies.

Thyroid hormone influences antioxidant defense system in adult rat brain

The objective of the current study was to find out whether thyroid hormone influences antioxidant defense parameters of rat brain. Several oxidative stress and antioxidant defense parameters of mitochondrial (MF) and post-mitochondrial (PMF) fractions of cerebral cortex (CC) of adult rats were compared among euthyroid (control), hypothyroid [6-n-propylthiouracil (PTU)-challenged], and hyperthyroid (T3-treatment to PTU-challenged rats) states. Oxidative stress parameters, such as thiobarbituric acid-reactive substances (TBA-RS) and protein carbonyl content (PC), in MF declined following PTU challenge in comparison to euthyroid rats. On the other hand, when PTU-challenged rats were treated with T3, a significant increase in the level of oxidative stress parameters in MF was recorded. Hydrogen peroxide content of MF as well as PMF of CC was elevated by PTU-challenge and brought to normal level by subsequent treatment of T3. Although mitochondrial glutathione (reduced or oxidized) status did not change following PTU challenge, a significant reduction in oxidized glutathione (GSSG) level was noticed in PMF following the treatment. T3 administration to PTU-challenged rats had no effect on mitochondrial glutathione status. Total and CN-resistant superoxide dismutase (SOD) activities in MF of CC augmented following PTU challenge. CN-resistant SOD activity did not change when PTU-challenged rats were treated with T3. Although CN-sensitive SOD activity of PMF remained unaltered in response to PTU challenge, its activity increased when PTU-challenged rats were treated with T3. Catalase activity in PMF of CC of PTU-challenged rats increased, whereas the activity was decreased when hypothyroid rats were treated with T3. Similarly, total and Se-dependent glutathione peroxidase (GPx) activities of MF increased following PTU challenge and reduced following administration of T3. Se-independent GPx activity of MF and PMF and glutathione reductase activity of PMF decreased following PTU challenge and did not change further when rats were treated with T3. On the other hand, glutathione S-transferase activity of MF and PMF of CC did not change following PTU challenge but decreased below detectable level following T3 treatment. Results of the current investigation suggest that antioxidant defense parameters of adult rat brain are considerably influenced by thyroid states of the body.

Evidence for chronic mitochondrial impairment in the cervical spinal cord of a murine model of motor neuron disease

Profound alteration of the oxygen consumption rate (QO2) is present in the cervical spinal cord (CS) of the wobbler mice aged 12 weeks (wr12). Early symptomatic mice at 4 weeks (wr4) show less pronounced changes with decreases of basal QO2 (P < 0.03) and of QO2 through complex I (P < 0.04). Mitochondrial respiratory enzyme activities, measured spectrophotometrically in the CS homogenate, show no difference between wr12 and controls, whereas complex I is reduced in the wr4 CS (P < 0.0003). Complex I activity is lower than normal both in wr12 and wr4 CS when measured in motor neurons by mean of a histochemical technique. Electron microscopy (EM) reveals a mixture of normal and morphologically altered mitochondria in wr4 motor neurons. The wobbler lumbar spinal cord is spared even at 12 weeks. Our results demonstrate the presence of mitochondrial abnormalities in the wobbler CS since the first manifestations of the disease. Thus, chronic mitochondrial dysfunction has a contributory role in motor neuron degeneration in the wobbler disease.

Role of mitochondrial permeability transition in fetal brain damage in rats

Recirculation after transient in utero ischemia has previously been found to be accompanied by delayed deterioration of cellular bioenergetic state and of mitochondrial function in the fetal rat brain. Our objective was to assess whether the delayed deterioration is a result of the activation of mitochondrial permeability transition which is observed ultrastructurally as mitochondrial swelling. The respiratory activities and ultrastructure of isolated mitochondria and the cellular bioenergetic state in fetal rat brain were examined at the end of 30 minutes of in utero ischemia and after 1, 2, 3 and 4 hours of recirculation. Cyclosporin A, a potent and virtually specific mitochondrial permeability transition blocker, or vehicle was administered 1 hour after recirculation. In the vehicle-treated animals, the transient ischemia was associated with a delayed deterioration of cellular bioenergetic state and mitochondrial activities at 4 hours of recirculation. The number of swollen mitochondria increased markedly after 4 hours of recirculation. The deterioration and the swelling were prevented by cyclosporin A. The present study indicates that cyclosporin A treatment improves recovery of fetal brain energy metabolism and inhibits the mitochondrial swelling after transient in utero ischemia. The results suggest that mitochondria and mitochondrial permeability transition may be involved in the development of ischemic brain damage in the immature rat.

Mitochondrial oxidative stress and increased seizure susceptibility in Sod2(-/+) mice

Epileptic seizures can occur as a result of mitochondrial dysfunction. Mitochondria have vital functions such as energy generation, control of cell death, neurotransmitter synthesis, and free radical production. Which of these critical mitochondrial functions contributes to epileptic seizures is unknown. We demonstrate here that a subset of mice with partial deficiency of the mitochondrial superoxide dismutase (Sod2(-/+)) show increased incidence of spontaneous and handling-induced seizures that correlates with chronic mitochondrial oxidative stress (increased aconitase inactivation and 8-hydroxy-2'-deoxyguanosine formation in mitochondria) and diminished mitochondrial oxygen utilization. Before the age at which spontaneous seizures appear in a subset of the mice, Sod2(-/+) mice demonstrated increased susceptibility to behavioral seizures, mitochondrial aconitase inactivation, and neurodegeneration induced by the administration of kainate. These data suggest that chronic mitochondrial oxidative stress initiated by superoxide (O(2)(.-)) radicals is sufficient to increase seizure susceptibility due to aging, environmental stimulation, or excitotoxin administration. Sod2(-/+) mice showed an age-related decrease in the expression of glial glutamate transporters (GLT-1 and GLAST), suggesting that oxidant-induced inhibition of glutamate transport may play a mechanistic role in rendering some Sod2(-/+) mice susceptible to seizures. In summary, mitochondrial oxidative stress and resultant dysfunction may be an important mechanism underlying certain seizure disorders.

Short therapeutic window for nifedipine in transient intrauterine ischemia in fetal rat brain

The aim of this study was to explore whether nifedipine influences the secondary deterioration of cerebral mitochondrial function after transient intrauterine ischemia in fetal rats. Intrauterine ischemia was induced by a 30-min occlusion of the right uterine artery at 20 days of gestation in Wistar rats. Nifedipine (1 mg kg(-1)) or vehicle was injected subcutaneously before the onset of ischemia or 1 h after the start of recirculation. Fetuses were delivered by cesarean section at the end of ischemia (n=6 with vehicle; n=6 with nifedipine pretreatment) or at 4 h of recirculation (n=6 with vehicle; n=6 with nifedipine pretreatment; n=6 with nifedipine posttreatment), and the cerebral mitochondrial respiration was measured polarographically. Tissue oxygen tension was evaluated in placental and fetal cerebral tissues (n=5 with vehicle; n=5 with nifedipine pretreatment). The vehicle treated animals showed a significant decrease in mitochondrial activities at the end of ischemia and 4 h of recirculation. Nifedipine attenuates the secondary deterioration at 4 h of recirculation when given just prior to ischemia, but had no neuroprotective activity when given 1 h after the start of recirculation. Nifedipine pretreatment had no influence on oxygen delivery in placenta and fetal cerebrum during and after ischemia. Despite the short therapeutic window, the treatment of nifedipine attenuates the secondary deterioration of cerebral mitochondrial function after transient intrauterine ischemia in fetal rats when given just prior to ischemia.

Vitamins ameliorate secondary mitochondrial failure in neonatal rat brain

Recirculation after transient intrauterine ischemia has previously been found to be accompanied by secondary mitochondrial dysfunction in the immature rat brain. This study was performed to assess the efficacy of combined treatment with ascorbic acid and alpha-tocopherol in improving secondary brain damage. On the 17th day of gestation, transient intrauterine ischemia was induced by 30 minutes of uterine artery occlusion. Either vehicle, ascorbic acid, alpha-tocopherol, or combination of ascorbic acid and alpha-tocopherol was randomly administered to pregnant rats before and after occlusion. The pups were delivered by cesarean section at 21 days of gestation, and cerebral neocortical tissue was sampled. The mitochondrial respiration was measured polarographically in homogenates. In the ischemia uterine horn, mitochondrial activity of the vehicle treatment decreased significantly to 56% of nonischemic controls. Treatment with ascorbic acid or alpha-tocopherol alone demonstrated a moderate improvement of the secondary mitochondrial dysfunction to 64% and 62% of nonischemic controls, respectively. The combined treatment caused a normalization of mitochondrial activity to 91% of nonischemic controls. These results indicate that combined treatment with ascorbic acid and alpha-tocopherol has a more protective effect against secondary mitochondrial dysfunction after transient intrauterine ischemia compared with the administration of ascorbic acid or alpha-tocopherol alone.

Effect of NXY-059 on secondary mitochondrial dysfunction after transient focal ischemia; comparison with cyclosporin A

The free radical trapping agents NXY-059 and alpha-phenyl-N-tert.-butylnitrone (PBN) markedly reduce infarct volume, even when given 1 or 3 h after the start of recirculation, following 2 h of middle cerebral artery (MCA) occlusion in rats. Their anti-ischemic effects are shared by the two immunosuppressants cyclosporin A (CsA) and FK506. Interestingly, CsA causes an additional reduction in infarct volume when given after only 5 min of recirculation, possibly reflecting blockade of a mitochondrial permeability transition (MPT) pore. PBN, CsA and FK506 are known to ameliorate the secondary dysfunction of mitochondrial function, as assessed in vitro, which occurs during the first 4-6 h of recirculation. The present experiments were undertaken to assess whether NXY-059 reduces tissue damage by acting directly on mitochondrial membranes, and provided that this is the case, if blockade of an MPT is involved. The results were compared to those of CsA, which thus served as a reference compound. NXY-059 was given i.v. after 5 min and 1 h, and CsA after 5 min of recirculation. Both NXY-059 and CsA reduced infarct volumes to about 30% of control, prevented the secondary decline in mitochondrial respiratory function during recirculation, and reduced the mitochondrial release of cytochrome c after 6 and 24 h of recirculation. However, NXY-059 failed to block the effect of Ca(2+) on mitochondrial swelling in vitro, as CsA did. Furthermore, NXY-059, given after 5 min of recirculation, did not reproduce the effects of CsA. The results thus suggest that NXY-059 exerts its effects on mitochondria by indirect mechanisms.

Seizure-dependent modulation of mitochondrial oxidative phosphorylation in rat hippocampus

Mitochondrial function is a key determinant of both excitability and viability of neurons. Here, we demonstrate seizure-dependent changes in mitochondrial oxidative phosphorylation in the epileptic rat hippocampus. The intense pathological neuronal activity in pilocarpine-treated rats exhibiting spontaneous seizures resulted in a selective decline of the activities of NADH-CoQ oxidoreductase (complex I of the respiratory chain) and cytochrome c oxidase (complex IV of respiratory chain) in the CA3 and CA1 hippocampal pyramidal subfields. In line with these findings, high-resolution respirometry revealed an increased flux control of complex I on respiration in the CA1 and CA3 subfields and decreased maximal respiration rates in the more severely affected CA3 subfield. Imaging of mitochondrial membrane potential using rhodamine 123 showed a lowered mitochondrial membrane potential in both pyramidal subfields. In contrast to the CA1 and CA3 subfields, mitochondrial oxidative phosphorylation was unaltered in the dentate gyrus and the parahippocampal gyrus. The changes of oxidative phosphorylation in the epileptic rat hippocampus cannot be attributed to oxidative enzyme modifications but are very likely related to a decrease in mitochondrial DNA copy number as shown in the more severely affected CA3 subfield and in cultured PC12 cells partially depleted of mitochondrial DNA. Thus, our results demonstrate that seizure activity downregulates the expression of mitochondrial-encoded enzymes of oxidative phosphorylation. This mechanism could be invoked during diverse forms of pathological neuronal activity and could severely affect both excitability and viability of hippocampal pyramidal neurons.

Effect of dexamethasone on mitochondrial maturation in the fetal rat brain

OBJECTIVE

The objective of the present study was to explore whether prenatal dexamethasone treatment influences mitochondrial maturation in the fetal rat brain.

STUDY DESIGN

Mitochondrial respiration was measured polarographically with homogenates of fetal cerebral cortical tissues on day 16 (with saline solution, n = 8; with dexamethasone, n = 8), day 18 (with saline solution, n = 8; with dexamethasone, n = 8), and day 20 (with saline solution, n = 8; with dexamethasone,n = 8) of gestation. Four doses of dexamethasone (0.1 mg small middle dot kg) or vehicle (saline solution) were given, with an interval of 12 hours, until 12 hours before each measurement.

RESULTS

In the vehicle-treated animals, mitochondrial respiratory activity was increased significantly after day 18 of gestation. Dexamethasone-treated animals showed a significant increase in mitochondrial activity at day 16 of gestation compared with vehicle-treated animals.

CONCLUSION

The results indicate that prenatal dexamethasone treatment contributes to the precocious maturation of mitochondrial activity in the fetal rat brain. Because acceleration in cerebral mitochondrial activities is required immediately after birth to maintain high-energy phosphate levels, the precocious maturation may be crucial for the successful outcome of the preterm infant.

Influence of mild hypothermia on delayed mitochondrial dysfunction after transient intrauterine ischemia in the immature rat brain

The aim of this study was to determine the effect of different maternal thermal conditions during transient intrauterine ischemia on the mitochondrial respiratory activities in the immature rat brain. On 17 days of gestation, transient intrauterine ischemia was induced by 30 min of right uterine artery occlusion under hypothermic (33.5-34.5 degrees C, n=6), normothermic (36.5-37.5 degrees C, n=6), and hyperthermic conditions (39.5-40.5 degrees C, n=6). All of the pups were delivered by cesarean section at 21 days of gestation and cerebral neocortical tissue was sampled 1 h after delivery. The mitochondrial respiration was measured polarographically in homogenates. In the ischemic uterine horn, ADP-stimulated respiration of the normothermia and the hyperthermia groups decreased significantly to 73 and 74% of the non-ischemic controls, respectively. Since non-stimulated respiration remained unchanged, the respiratory control ratio (RCR) of the normothermia and the hyperthermia groups decreased significantly to 59 and 54% of the non-ischemic levels, respectively. In contrast, the mitochondrial respiratory activities of the hypothermia group showed no differences between the non-ischemic and the ischemic uterine horns. The results demonstrate that mild maternal hypothermia ameliorates the cerebral mitochondrial dysfunction in neonatal rats after intrauterine ischemia due to transient uterine artery occlusion and suggest that maternal thermal conditions, particularly during uteroplacental insufficiency, have important implications for the neuropathological outcome of the newborn.

Developmental changes in tolerance to transient intrauterine ischemia in rat cerebral mitochondria

OBJECTIVE

Mitochondfial respiratory activities were measured in neonatal rat brain to compare the influence of transient intrauterine ischemia in the preterm fetus with that in the term fetus and to evaluate the effect of alpha-phenyl-N -tert-butyl-nitrone treatment.

STUDY DESIGN

Intrauterine ischemia was induced by a 30-minute occlusion of the right uterine artery. The control group consisted of term fetuses (20 days old) exposed to normoxia (n = 8) and ischemia (n = 8). For the investigation into maturity effect, preterm fetuses (14 days old) were exposed to normoxia (n = 8) or ischemia (n = 8), and for the alpha-phenyl-N -tert-butyl-nitrone treatment investigation, term fetuses were exposed to ischemia with alpha-phenyl-N -tert-butyl-nitrone (n = 8). All subjects underwent cesarean delivery at 21 days of gestation, and the mitochondrial respiration was measured polarographically 1 hour after delivery.

RESULTS

In the control group the neonatal cortical tissue exposed to ischemia showed a significant decrease in mitochondrial activities compared with those in normoxic control animals. In the preterm group the mitochondrial activities of ischemic fetuses were maintained close to normoxic levels. The neonatal mitochondrial deterioration caused by term ischemia was prevented by alpha-phenyl-N -tert-butyl-nitrone.

CONCLUSION

The results indicate that preterm fetuses are more capable than term fetuses of maintaining mitochondrial function under conditions of transient intrauterine ischemia and suggest that oxygen derived free radicals may play a crucial role in the development of neonatal neurologic deficit.

Effect of the immunosuppressant drug FK506 on neonatal cerebral mitochondrial function and energy metabolism after transient intrauterine ischemia in rats

Mitochondrial respiratory activities and energy metabolism were measured in neonatal rat brains to evaluate the influence of transient intrauterine ischemia on the near-term fetus and to assess the effect of the immunosuppressant drug FK506 treatment. Transient intrauterine ischemia was induced by 30 min of right uterine artery occlusion at 17 days of gestation in Wistar rats. The vehicle or 1.0 mg/kg of FK506 was administered after 1 h of recirculation. All of the pups were delivered by cesarean section at 21 days of gestation and samples of cerebral cortical tissue were obtained from pups at 1 h after birth. The mitochondrial respiration was measured polarographically in homogenates. For the analysis of ATP, ADP, and AMP, neonatal brains were frozen in situ and fluorometric enzymatic techniques were used. In the neonatal cortical tissue exposed to ischemia, mitochondrial respiratory activities and ATP concentrations decreased significantly to approximately 59 and 67% of those in normoxic controls, respectively. The deterioration of both mitochondrial respiratory activities and high-energy phosphates was prevented by FK506, given 1 h after the start of recirculation. The present results indicate that transient intrauterine ischemia is accompanied by mitochondrial dysfunction and cellular bioenergetic failure in the neonatal rat brain and suggest that treatment with FK506 prevents the deterioration, even when administered after the ischemic periods.

Potassium channel openers depolarize hippocampal mitochondria

We investigated the effect of the potassium channel openers diazoxide and RP66471 on mitochondrial membrane potential and mitochondrial respiration in digitonin-treated rat hippocampal homogenates. Both diazoxide and RP66471 induced a dose-dependent decrease of mitochondrial membrane potential. Concomitant with the depolarization was an increase of mitochondrial respiration. Furthermore, the mitochondrial membrane depolarization induced by diazoxide and RP66471 was significantly larger in the presence of potassium ions than in the presence of sodium ions. The diazoxide-induced (but not RP66471-induced) mitochondrial membrane depolarization was partially inhibited by blockers of the ATP-regulated potassium channel, 5-hydroxydecanoic acid or the antidiabetic sulfonylurea glibenclamide. In addition, the potassium channel openers diazoxide and RP66471 increased mitochondrial matrix volume and induced a release of cytochrome c from hippocampal mitochondria. These results indicate the presence of a mitochondrial ATP-regulated potassium channel in rat hippocampus being a target for potassium channel openers.

Impairment of mitochondrial respiration after cerebral hypoxia-ischemia in immature rats: relationship to activation of caspase-3 and neuronal injury

Mitochondrial damage may play a key role in the development of necrotic and apoptotic hypoxic-ischemic (HI) brain damage. It has previously been shown that mitochondrial respiration is depressed in the cerebral cortex after HI in neonatal animals. The aim of the present study was to further characterize the time course of the mitochondrial impairment during reperfusion and the correlation between the respiratory control ratio and brain injury and activation of caspase-3. Rat pups were subjected to unilateral carotid artery ligation and exposed to hypoxia (7.7% oxygen). Mitochondrial respiration was measured 0-72 h after HI in a mitochondrial fraction isolated from cerebral cortex. Microtubule associated protein-2 (MAP2) and caspase-3 were analyzed with immunoblotting in cerebral cortex homogenates. In addition, the time course of caspase-3 activation was measured as DEVD cleavage. The mitochondrial respiratory control ratio in cerebral cortex decreased immediately after HI followed by a partial recovery at 3-8 h. Thereafter, a secondary drop occurred with a minimum reached at 24 h of reperfusion. The secondary loss of respiratory function was accompanied by depletion of MAP2, cleavage of caspase-3 and an increased caspase-3 -like activity at 3-24 h after the insult. In conclusion, the primary phase of mitochondrial dysfunction was paralleled by a moderate decrease of MAP2 and a limited activation of caspase-3. The secondary mitochondrial impairment was associated with neuronal injury and pronounced activation of caspase-3.

Alterations in glutathione and amino acid concentrations after hypoxia-ischemia in the immature rat brain

Hypoxic-ischemic brain injury involves an increased formation of reactive oxygen species. Key factors in the cellular protection against such agents are the GSH-associated reactions. In the present study we examined alterations in total glutathione and GSSG concentrations in mitochondria-enriched fractions and tissue homogenates from the cerebral cortex of 7-day-old rats at 0, 1, 3, 8, 14, 24 and 72 h after hypoxia-ischemia. The concentration of total glutathione was transiently decreased immediately after hypoxia-ischemia in the mitochondrial fraction, but not in the tissue, recovered, and then decreased both in mitochondrial fraction and homogenate after 14 h, reaching a minimum at 24 h after hypoxia-ischemia. The level of GSSG was approximately 4% of total glutathione and increased selectively in the mitochondrial fraction immediately after hypoxia-ischemia. The decrease in glutathione may be important in the development of cell death via impaired free radical inactivation and/or redox related changes. The effects of hypoxia-ischemia on the concentrations of selected amino acids varied. The levels of phosphoethanolamine, an amine previously reported to be released in ischemia, mirrored the changes in glutathione. GABA concentrations initially increased (0-3 h) followed by a decrease at 72 h. Glutamine levels increased, whereas glutamate and aspartate were unchanged up to 24 h after the insult. The results on total glutathione and GSSG are discussed in relation to changes in mitochondrial respiration and microtubule associated protein-2 (MAP2) which are reported on in accompanying paper [64].

Secondary mitochondrial dysfunction after transient intrauterine ischemia in the fetal rat brain

OBJECTIVE

Recirculation following transient intrauterine ischemia has previously been found to cause partial recovery and secondary deterioration of cellular bioenergetic states in the fetal rat brain. Our objective was to assess whether secondary bioenergetic failure is due to mitochondrial dysfunction.

STUDY DESIGN

Cerebral cortical tissues were obtained from 20-day-old fetal rats at the end of 30 minutes of intrauterine ischemia (n = 6) and after 1 hour (n = 6), 2 hours (n = 6), and 4 hours (n = 6) of recirculation. Mitochondrial respiratory activities were measured polarographically using homogenates.

RESULTS

Mitochondrial activities decreased to 45% of sham-operated controls at the end of ischemia. Recirculation (1 hour) brought about partial recovery, but continued reflow (2 hours and 4 hours) was associated with a secondary deterioration of mitochondrial activities.

CONCLUSION

The results indicate that although during the early time period after ischemia mitochondrial respiratory capacity is restored, secondary mitochondrial dysfunction develops in the immature rat brain.

Quantitative biochemical and ultrastructural comparison of mitochondrial permeability transition in isolated brain and liver mitochondria: evidence for reduced sensitivity of brain mitochondria

Opening of the mitochondrial permeability transition pore has increasingly been implicated in excitotoxic, ischemic, and apoptotic cell death, as well as in several neurodegenerative disease processes. However, much of the work directly characterizing properties of the transition pore has been performed in isolated liver mitochondria. Because of suggestions of tissue-specific differences in pore properties, we directly compared isolated brain mitochondria with liver mitochondria and used three quantitative biochemical and ultrastructural measurements of permeability transition. We provide evidence that brain mitochondria do not readily undergo permeability transition upon exposure to conditions that rapidly induce the opening of the transition pore in liver mitochondria. Exposure of liver mitochondria to transition-inducing agents led to a large, cyclosporin A-inhibitable decrease in spectrophotometric absorbance, a loss of mitochondrial glutathione, and morphologic evidence of matrix swelling and disruption, as expected. However, we found that similarly treated brain mitochondria showed very little absorbance change and no loss of glutathione. The absence of response in brain was not simply due to structural limitations, since large-amplitude swelling and release of glutathione occurred when membrane pores unrelated to the transition pore were formed. Additionally, electron microscopy revealed that the majority of brain mitochondria appeared morphologically unchanged following treatment to induce permeability transition. These findings show that isolated brain mitochondria are more resistant to induction of permeability transition than mitochondria from liver, which may have important implications for the study of the mechanisms involved in neuronal cell death.

Developmental changes in mitochondrial activity and energy metabolism in fetal and neonatal rat brain

Experiments were undertaken to investigate mitochondrial activity and energy metabolism in the developing rat brain from the late fetal stage to the neonatal stage. Samples of cerebral cortical tissue were obtained from fetuses at 14, 16, 18, and 20 days of gestation, and from pups at 1 h, 1 day and 7 days after birth. Mitochondrial respiration was measured polarographically using homogenates. Fetal and neonatal brains were frozen in situ and fluorometric enzymatic techniques were used for the analysis of ATP, ADP, AMP, and lactate. In the fetal brain, there was a gradual increase in stimulated (+ADP) and uncoupled respiratory rates using glutamate and malate as substrates, from 14 days to 20 days of gestation, together with a moderate increase in ATP concentration and in the sum total of adenine nucleotides, and a significant decrease in lactate. Since non-stimulated (-ADP) respiratory rates did not change with increasing gestational age, the respiratory control ratio appeared to increase over the same period. An increase in mitochondrial activity was more pronounced immediately after birth, together with a marked increase in ATP concentration and in the sum total of adenine nucleotides. The highest rate of mitochondrial respiration was observed in 1-hour-old pups. These results indicate that, in the rat brain, there is maturation of oxidative metabolism in mitochondria that is initiated in late gestation. Acceleration in mitochondrial respiration occurs immediately after birth in order to maintain high-energy phosphate levels, and this may be crucial for the successful outcome of the newborn.

Improved recovery of highly enriched mitochondrial fractions from small brain tissue samples

The investigation of mitochondrial abnormalities in brain commonly requires isolation of these organelles from small tissue samples. We have modified a mitochondrial isolation procedure based on Percoll density gradient centrifugation to increase the proportion of the total mitochondrial pool recovered while reducing contamination with synaptosomes and related structures containing cytoplasm. Initially, myelin was removed by centrifugation in 12% Percoll in isotonic buffer. The pellet was resuspended, treated with digitonin to break up synaptosomes and similar structures and subjected to discontinuous Percoll density gradient centrifugation. The mitochondrial fraction obtained from this procedure was highly metabolically active and well coupled, exhibiting respiratory control ratios above 5. The recovery of mitochondrial markers using a single rat forebrain as starting material was approximately 18% to 21%. When small tissue samples (approximately 50 mg wet weight) were used as starting material the recovery of the mitochondrial marker was approximately 16%. The ratio of recovery of a mitochondrial marker to the cytoplasmic marker lactate dehydrogenase exceeded 200 in preparations from a single rat forebrain. This is substantially greater than values reported for previously published procedures reflecting both an improved yield of mitochondria and a reduction in cytoplasmic contamination.

Mitochondrial respiratory function and cell death in focal cerebral ischemia

Pyruvate-supported oxygen uptake was determined as a measure of the functional capacity of mitochondria obtained from rat brain during unilateral middle cerebral artery occlusion and reperfusion. During ischemia, substantial reductions developed in both ADP-stimulated and uncoupled respiration in tissue from the focus of the affected area in the striatum and cortex. A similar pattern of change but with lesser reductions was seen in the adjacent perifocal tissue. Succinate-supported respiration was more affected than that with pyruvate in perifocal tissue at 2 h of ischemia, suggesting additional alterations to mitochondrial components in this tissue. Mitochondrial respiratory activity recovered fully in samples from the cortex, but not the striatum, within the first hour of reperfusion following 2 h of ischemia and remained similar to control values at 3 h of reperfusion. In contrast, impairment of the functional capacity of mitochondria from all three regions was seen in the first 3 h of reperfusion following 3 h of ischemia. Extensive infarction generally affecting the cortical focal tissue with more variable involvement of the perifocal tissue developed following 2 h of focal ischemia. Thus, mitochondrial impairment during the first 3 h of reperfusion was apparently not essential for tissue infarction to develop. Nonetheless, the observed mitochondrial changes could contribute to the damage produced by permanent focal ischemia as well as the larger infarcts produced when reperfusion was initiated following 3 h of ischemia.

Metabolic consequences of the cytochrome c oxidase deficiency in brain of copper-deficient Mo(vbr) mice

Biochemical micromethods were used for the investigation of changes in mitochondrial oxidative phosphorylation associated with cytochrome c oxidase deficiency in brain cortex from Mo(vbr) (mottled viable brindled) mice, an animal model of Menkes' copper deficiency syndrome. Enzymatic analysis of cortex homogenates from Mo(vbr) mice showed an approximately twofold decrease in cytochrome c oxidase and a 1.4-fold decrease in NADH:cytochrome c reductase activities as compared with controls. Assessment of mitochondrial respiratory function was performed using digitonin-treated homogenates of the cortex, which exhibited the main characteristics of isolated brain mitochondria. Despite the substantial changes in respiratory chain enzyme activities, no significant differences were found in maximal pyruvate or succinate oxidation rates of brain cortex homogenates from Mo(vbr) and control mice. Inhibitor titrations were used to determine flux control coefficients of NADH:CoQ oxidoreductase and cytochrome c oxidase on the rate of mitochondrial respiration. Application of amobarbital to titrate the activity of NADH:CoQ oxidoreductase showed very similar flux control coefficients for control and mutant animals. Alternately, titration of respiration with azide revealed for Mo(vbr) mice significantly sharper inhibition curves than for controls, indicating a more than twofold elevated flux control coefficient of cytochrome c oxidase. Owing to the reserve capacity of respiratory chain enzymes, the reported changes in activities do not seem to affect whole-brain high-energy phosphates, as observed in a previous study using 31P NMR.

Mitochondrial function and energy metabolism after hypoxia-ischemia in the immature rat brain: involvement of NMDA-receptors

Treatment after hypoxia-ischemia (HI) in immature rats with the N-methyl-D-aspartate receptor (NMDAR) antagonist dizocilpine maleate (MK-801) reduces areas with high glucose utilization and reduces brain damage. The object was to study the metabolic effects of MK-801 treatment after HI. Seven-day-old rats were randomized to the following groups: non-HI, HI, or HI plus MK-801 (0.5 mg/kg immediately after HI). In the parietal cortex, the mitochondrial respiration was measured in homogenates 1 to 4 hours, and the energy metabolites at 3 and 8 hours after HI. The energy use was calculated from changes in energy metabolites after decapitation at 3 hours after HI. State 3 respiration was reduced by 46%, 32%, and 25% after HI compared with non-HI with pyruvate plus malate, glutamate plus malate, or glutamate plus succinate as substrates, respectively. Uncoupler-stimulated but not state 4 respiration was similarly reduced. The MK-801 augmented pyruvate plus malate-supported state 3 respiration after HI by 42%. The energy utilization was not affected by HI but was reduced by MK-801 treatment in the ipsilateral cortex from 4.6 +/- 2.3 to 2.6 +/- 1.8 micromol high-energy phosphate bond/min/g. The levels of ATP and phosphocreatine did not differ between the HI and HI plus MK-801 groups at 3 hours, but were lower in the HI than in the HI plus MK-801 group at 8 hours after HI. In conclusion, treatment with MK-801 reduced energy utilization and improved mitochondrial function and energy status after HI, suggesting a linkage between NMDAR activation and impaired energy metabolism during reperfusion.

The immunosuppressant drug FK506 ameliorates secondary mitochondrial dysfunction following transient focal cerebral ischemia in the rat

Recirculation following 2 h of focal ischemia due to transient middle cerebral artery (MCA) occlusion has previously been found to be accompanied by an initial, partial recovery of the cellular bioenergetic state and of mitochondrial respiratory functions, with secondary deterioration during the first 2-4 h of reflow. Both the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN) and the immunosuppressant drug FK506 ameliorate the damage incurred by the 2-h period of focal ischemia, even when given 1-3 h after the start of the recirculation. The primary objective of this study was to find out if FK506, like PBN, prevents the secondary deterioration of mitochondrial function, as this can be studied in vitro. Since this proved to be the case, we addressed the question of whether the secondary mitochondrial dysfunction and bioenergetic failure were related to a secondary compromise of microcirculation and cellular oxygen delivery. Six groups of male Wistar rats were studied for measurement of mitochondrial respiratory activity (total, n = 36). One group was used as control (n = 6). In the other groups of animals, MCA occlusion of 2 h duration was induced by an intraluminal filament technique, Neocortical focal and perifocal ("penumbra") tissues were sampled after 2 h of ischemia (n = 6) and after 1 h (n = 6), 2 h (n = 6 with vehicle), and 4 h (n = 6 with vehicle; n = 6 with FK506) of recirculation. The vehicle or 1.0 mg.kg-1 of FK506 was injected intravenously after 1 h of recirculation. Homogenates were prepared, and stimulated (+ADP), nonstimulated (-ADP), and uncoupled respiratory rates were measured polarographically. The uncoupling agent used was carbonyl cyanide m-chlorophenylhydrazone. Local CBF and tissue oxygen tension were evaluated by laser-Doppler flowmetry and PO2 microelectrodes, respectively, throughout the whole periods of 2 h of ischemia and 4 h of recirculation, using a remote MCA occlusion technique. After 2 h of ischemia, the penumbra showed a moderate decrease and the focus a marked decrease in ADP-stimulated and uncoupled respiratory rates, with a marked fall in the respiratory control ratio, defined as ADP-stimulated divided by nonstimulated respiration. Recirculation (1 h) brought about partial recovery, but continued reflow (2 and 4 h) was associated with a secondary deterioration of respiratory functions. The secondary deterioration was prevented by FK506. The results thus confirm previous findings showing that secondary mitochondrial dysfunction occurs following transient focal cerebral ischemia and demonstrate that FK506, like PBN, improves the in vitro performance of mitochondria in focal and penumbral areas. Following MCA occlusion, local CBF in a penumbral area and tissue PO2 in a focal area decreased to about 30 and 5% of control, respectively. However, recirculation brought about rapid recovery of blood flow and oxygen delivery. During the whole 4-h period of recirculation, local CBF and tissue PO2 were maintained close to 100% and at about 160% of the preischemic level, respectively. The results make it highly unlikely that the secondary bioenergetic failure during recirculation is due to a compromised microcirculation. It follows that oxygen delivery is not rate-limiting for recovery events. Very likely, FK506 (and PBN) acts at the cellular level to improve mitochondrial energy functions.

Quantitative mapping of cytochrome oxidase activity in the central auditory system of the gerbil: a study with calibrated activity standards and metal-intensified histochemistry

The objective was to obtain detailed topographic determinations of cytochrome oxidase activity in the gerbil central auditory system at the light microscopic level. Quantitative techniques were developed using (1) tissue standards calibrated to express histochemical measures as actual enzyme activity units, (2) densitometry and image analysis of histochemical reaction product formation, (3) spectrophotometry of cytochrome oxidase activity, and (4) a cobalt-intensified staining procedure compatible with autoradiography and other techniques requiring fresh-frozen brains without perfusion-fixation. Linear relationships between incubation time, section thickness, and activity of dissected brain regions, with their reaction product measured densitometrically were determined. Auditory structures with the high activities showed about 8 times the labeling intensity of the white matter or control sections inhibited with cyanide, glutaraldehyde, or heat. This indicated the high sensitivity of the method without loss of specificity. Specific activity for each of the 18 auditory structures measured were all above the units measured for whole brain homogenates, supporting the notion that basal levels of oxidative metabolism are greater for the auditory system. There was a progressive decrement in activity from brain stem to forebrain auditory structures. The more peripheral nuclei also showed a higher proportion of somatic as compared to neuropil reactivity. In contrast, auditory midbrain and thalamocortical regions were characterized primarily by neuropil reactivity. Comparison of intrinsic patterns of activity with morphological schemes to subdivide nuclei, showed a good correspondence with classical subdivisions derived from Golgi studies. The reported activities may provide a base of normative data in the gerbil for subsequent studies of central auditory functions. The method presented fulfilled established quantitative criteria and provided a more sensitive approach for regional mapping studies of brain cytochrome oxidase activity.

Energy metabolism and selective neuronal vulnerability following global cerebral ischemia

A short period of global ischemia results in the death of selected subpopulations of neurons. Some advances have been made in understanding events which might contribute to the selectivity of this damage but the cellular changes which culminate in neuronal death remain poorly defined. This overview examines the metabolic state of tissue in the post-ischemic period and the relationship of changes to the development of damage in areas containing ischemia-susceptible neurons. During early recirculation there is substantial recovery of ATP, phosphocreatine and related metabolites in all brain regions. However, this recovery does not signal restitution of normal energy metabolism as reductions of the oxidative metabolism of glucose are seen in many areas and may persist for several days. Furthermore, decreases in pyruvate-supported respiration develop in mitochondria from at least one ischemia-susceptible region at times coincident with the earliest histological evidence of ischemia-induced degeneration. These mitochondrial changes could simply be an early marker of irreversible damage but the available evidence is equally consistent with these contributing to the degenerative process and offering a potential site for therapeutic intervention.

Selective impairment of respiration in mitochondria isolated from brain subregions following transient forebrain ischemia in the rat

Using Percoll density gradient centrifugation, free (nonsynaptosomal) mitochondria were isolated from the dorsal-lateral striatum and paramedian neocortex of rats during complete forebrain ischemia and reperfusion. Mitochondria prepared from either region after 30 min of ischemia showed decreased state 3 (ADP and substrate present) and uncoupled respiration rates (19-45% reductions) with pyruvate plus malate as substrates, whereas state 4 respiration (no ADP present) was preserved. At 6 h of recirculation, state 3 and uncoupled respiration rates for mitochondria from the paramedian neocortex (a region resistant to ischemic damage) were similar to or even increased compared with control values. By contrast, in mitochondria from the dorsal-lateral striatum (a region containing neurons susceptible to global ischemia), decreases in state 3 and uncoupled respiration rates (25 and 30% less than control values) were again observed after 6 h of recirculation. With succinate as respiratory substrate, however, no significant differences from control values were found in either region at this time point. By 24 h of recirculation, respiratory activity with either pyruvate plus malate or succinate was greatly reduced in samples from the dorsal-lateral striatum, probably reflecting complete loss of function in some organelles. In contrast with these marked changes in free mitochondria, the respiratory properties of synaptosomal mitochondria, assessed from measurements in unfractionated homogenates, were unchanged from controls in the dorsal-lateral striatum at each of the time points studied, but showed reductions (19-22%) during ischemia and after 24 h of recirculation in the paramedian neocortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed decreases in specific brain mitochondrial electron transfer complex activities and cytochrome concentrations following anoxia/ischemia

Hyperglycemic, but not normoglycemic cats exposed to anoxia develop neurologic signs following reoxygenation including fasciculations, focal and tonic-clonic seizures and coma after a symptom-free period. These symptomatic hyperglycemic cats may develop brain edema and will show diffuse neuronal injury or brain infarction depending on length of survival. Brain mitochondria isolated from symptomatic but not asymptomatic cats have decreased ADP- and uncoupler-stimulated oxygen consumption rates. Since impaired respiration could result from altered electron transport chain function, we measured cytochrome c, b, and aa3 concentrations and the activities of the five electron transfer complexes in isolated brain mitochondria. In symptomatic cats marked alterations were present in particular in complex IV, cytochrome oxidase, with a 57% reduction in activity and a 45% reduction in prosthetic group (cytochrome aa3) concentrations. Less marked reductions in other segments of the chain included 27% and 41% decreases, respectively, in cytochrome c concentrations and in electron transfer complex II, succinate:ubiquinone oxidoreductase activity. Cytochrome b concentrations and complex I, II and V activities were unchanged. Small but significant decreases in cytochrome aa3 concentrations (18%) and cytochrome oxidase activity (20%) were also present in mitochondria from postanoxic hyperglycemic cats prior to appearance of neurologic signs. These results indicate that delayed decreases in the activities of specific electron transfer complexes are correlated with impaired mitochondrial respiration and neurologic deterioration in postanoxic hyperglycemic cats. However, it is presently unclear if these postanoxic brain mitochondrial alterations are primary or secondary events in the development of brain injury.

Rapid isolation of metabolically active mitochondria from rat brain and subregions using Percoll density gradient centrifugation

Two procedures are described for isolating free (nonsynaptosomal) mitochondria from rat brain. Both procedures employ a discontinuous Percoll gradient and yield well coupled mitochondria which exhibit high rates of respiratory activity and contain little residual contamination by synaptosomes or myelin. The procedures are considerably more rapid than methods described previously for the isolation of brain mitochondria and do not require an ultracentrifuge or swing-out rotor. The first method separates mitochondria by gradient centrifugation from a P2 (crude mitochondrial) fraction and is likely to be widely applicable for studies in which at least 500 mg of tissue are available as starting material. In the second method, the unfractionated homogenate is subjected directly to gradient centrifugation. This method requires the preparation of more gradients (per gram of tissue) than the first method and yields a subcellular fraction with slightly more synaptosomal contamination. However, this second procedure is more rapid, requires less manipulation of the tissue, and is suitable for obtaining mitochondria with well preserved metabolic characteristics from subregions of single rat brains.

Delayed onset of neurologic deterioration following anoxia/ischemia coincides with appearance of impaired brain mitochondrial respiration and decreased cytochrome oxidase activity

We previously demonstrated markedly inhibited brain mitochondrial respiration only in cats that (a) were hyperglycemic at anoxia and (b) had neurologic signs, i.e., fasciculations in tongue or facial muscles or focal seizures following reoxygenation. However, since the relationship between time of onset of mitochondrial dysfunction and neurologic signs was unclear, in the present study we killed postanoxic cats immediately when signs first appeared. Cerebrocortical homogenates and isolated brain mitochondria only from symptomatic cats showed markedly inhibited substrate-, ADP-, and uncoupler-stimulated respiration rates. Cytochrome oxidase activity and cytochrome aa3 concentrations were also markedly reduced in these mitochondria. Since brain mitochondrial function was impaired when neurologic signs first appeared, mitochondrial alterations are an important early organellar change correlated with development of neurologic deterioration following anoxia.

Cytosolic-free calcium and neurotransmitter release with decreased availability of glucose or oxygen

Exposing brain slices to reduced oxygen tensions or impairing their ability to utilize oxygen with KCN decreases acetylcholine (ACh) but increases dopamine (DA) and glutamate in the medium at the end of a release incubation. To determine if these changes are due to alterations in the presynaptic terminals, release from isolated nerve endings (i.e. synaptosomes) was determined during histotoxic hypoxia (KCN). KCN reduced potassium-stimulated synaptosomal ACh release and increased dopamine and glutamate release. Since several lines of evidence suggest that altered calcium homeostasis underlies these changes in release, the effects of reducing medium calcium concentrations from 2.3 to 0.1-mM were determined. In low calcium medium, KCN still increased dopamine and glutamate release, but had no effect on ACh release. Hypoxia increased cytosolic-free calcium in both the normal and low calcium medium, although the elevation was less in the low calcium medium. Thus, the effects of histotoxic hypoxia on cytosolic free calcium concentration paralleled those on glutamate and dopamine release. Reducing the glucose concentration of the medium also increased cytosolic-free calcium. The data are consistent with the hypothesis that hypoxia and hypoglycemia increase cytosolic-free calcium, which stimulates the release of dopamine and glutamate, whose excessive release may lead to subsequent cellular damage postsynaptically.

Delayed neurologic deterioration following anoxia: brain mitochondrial and metabolic correlates

Hyper- but not normoglycemic cats exposed to 8 min of anoxia show neurologic signs (fasciculations, myoclonic jerks, seizures) that develop after a symptom-free period. We examined brain mitochondrial function and metabolite concentrations at 0, 1, 3, and 5 h following exposure to anoxia, to correlate biochemical findings with the presence ("symptomatic") or absence ("presymptomatic") of neurologic signs. Brain mitochondria isolated postexposure only from symptomatic cats showed markedly decreased (-50%), state 3 (ADP-stimulated), and uncoupler-stimulated respiration rates with NAD- and FAD-linked substrates. Respiratory control and ADP/oxygen (ADP/O) ratios remained unchanged, indicating, respectively, that coupling and efficiency of ATP synthesis were preserved. Thus, inhibition of electron transport chain function, not phosphorylative activity, may be rate limiting for respiration. During anoxia, hyperglycemic cats showed higher brain lactate levels (26 versus 20 mumol/g), but similar ATP and phosphocreatine concentrations, compared with normoglycemic cats. After exposure, in all animals lactate and phosphocreatine were restored to control levels, whereas ATP remained at 85%. Cats that became symptomatic demonstrated four- to sixfold increases in lactate and 50% reductions in phosphocreatine. At 3 and 5 h postexposure, symptomatic animals showed significant reductions in ATP concentrations. We conclude that although initially asymptomatic, hyperglycemic cats exposed to anoxia undergo a neurologic deterioration over several hours following reoxygenation that is correlated with inhibition of mitochondrial respiration, increases in tissue lactate, and decreases in energy state.