An Exploratory Report on Electrographic Changes in the Cerebral Cortex Following Mild Traumatic Brain Injury with Hyperthermia in the Rat.

Traumatic brain injury (TBI) has the potential to perturb perception by disrupting electrical propagation within and between the thalamus and cerebral cortex. Moderate and severe TBI may result in posttraumatic epilepsy, a condition characterized by convulsive tonic-clonic seizures. Spike/wave discharges (SWDs) of generalized nonconvulsive seizures, also called absence seizures, may also occur as a consequence of brain trauma. As mild hyperthermia has been reported to exacerbate histopathological and behavioral outcomes, we used an unbiased algorithm to detect periodic increases in power across different frequency bands following single or double closed head injury (CHI) under normothermia and hyperthermia conditions. We demonstrated that mild TBI did not significantly alter the occurrence of events containing increases in power between the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta1 (12-20 Hz) frequency bands in the Sprague Dawley rat 12 weeks after injury. However, when hyperthermia (39°C) was induced before and after CHI, electrographic events containing a similar waveform and harmonic frequency to SWDs were observed in a subset of animals. Further experiments utilizing chronic recordings will need to be performed to determine if these trends lead to absence seizures.

Neurotherapeutic capacity of P7C3 agents for the treatment of Traumatic Brain Injury.

Traumatic brain injury (TBI) is a significant public health problem around the world. A promising area of research is the characterization of small, drug-like molecules that have potent clinical properties. One pharmacotherapeutic agent in particular, an aminopropyl carbazole called P7C3, was discovered using an in vivo screen to identify new agents that augmented the net magnitude of adult hippocampal neurogenesis. P7C3 greatly enhanced neurogenesis by virtue of increasing survival rates of immature neurons. The potent neuroprotective efficacy of P7C3 is likely due to enhanced nicotinamide phosphoribosyltransferase (NAMPT) activity, which supports critical cellular processes. The scaffold of P7C3 was found to have favorable pharmacokinetic properties, good bioavailability, and was nontoxic. Preclinical studies have shown that administration of the P7C3-series of neuroprotective compounds after TBI can rescue and reverse detrimental cellular events leading to improved functional recovery. In several TBI models and across multiple species, P7C3 and its analogues have produced significant neuroprotection, axonal preservation, robust increases in the net magnitude of adult neurogenesis, protection from injury-induced LTP deficits, and improvement in neurological functioning. This review will elucidate the exciting and diverse therapeutic findings of P7C3 administration in the presence of a complex and multifactorial set of cellular and molecular challenges brought forth by experimental TBI. The clinical potential and broad therapeutic applicability of P7C3 warrants much needed investigation into whether these remedial effects can be replicated in the clinic. P7C3 may serve as an important step forward in the design, understanding, and implementation of pharmacotherapies for treating patients with TBI. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Automated approach to detecting behavioral states using EEG-DABS.

Electrocorticographic (ECoG) signals represent cortical electrical dipoles generated by synchronous local field potentials that result from simultaneous firing of neurons at distinct frequencies (brain waves). Since different brain waves correlate to different behavioral states, ECoG signals presents a novel strategy to detect complex behaviors. We developed a program, EEG Detection Analysis for Behavioral States (EEG-DABS) that advances Fast Fourier Transforms through ECoG signals time series, separating it into (user defined) frequency bands and normalizes them to reduce variability. EEG-DABS determines events if segments of an experimental ECoG record have significantly different power bands than a selected control pattern of EEG. Events are identified at every epoch and frequency band and then are displayed as output graphs by the program. Certain patterns of events correspond to specific behaviors. Once a predetermined pattern was selected for a behavioral state, EEG-DABS correctly identified the desired behavioral event. The selection of frequency band combinations for detection of the behavior affects accuracy of the method. All instances of certain behaviors, such as freezing, were correctly identified from the event patterns generated with EEG-DABS. Detecting behaviors is typically achieved by visually discerning unique animal phenotypes, a process that is time consuming, unreliable, and subjective. EEG-DABS removes variability by using defined parameters of EEG/ECoG for a desired behavior over chronic recordings. EEG-DABS presents a simple and automated approach to quantify different behavioral states from ECoG signals.

Enhanced astrocytic d-serine underlies synaptic damage after traumatic brain injury.

After traumatic brain injury (TBI), glial cells have both beneficial and deleterious roles in injury progression and recovery. However, few studies have examined the influence of reactive astrocytes in the tripartite synapse following TBI. Here, we have demonstrated that hippocampal synaptic damage caused by controlled cortical impact (CCI) injury in mice results in a switch from neuronal to astrocytic d-serine release. Under nonpathological conditions, d-serine functions as a neurotransmitter and coagonist for NMDA receptors and is involved in mediating synaptic plasticity. The phasic release of neuronal d-serine is important in maintaining synaptic function, and deficiencies lead to reductions in synaptic function and plasticity. Following CCI injury, hippocampal neurons downregulated d-serine levels, while astrocytes enhanced production and release of d-serine. We further determined that this switch in the cellular source of d-serine, together with the release of basal levels of glutamate, contributes to synaptic damage and dysfunction. Astrocyte-specific elimination of the astrocytic d-serine-synthesizing enzyme serine racemase after CCI injury improved synaptic plasticity, brain oscillations, and learning behavior. We conclude that the enhanced tonic release of d-serine from astrocytes after TBI underlies much of the synaptic damage associated with brain injury.

Increased Expression of Epileptiform Spike/Wave Discharges One Year after Mild, Moderate, or Severe Fluid Percussion Brain Injury in Rats.

In this study, we describe increased expression of cortical epileptiform spike/wave discharges (SWD) in rats one year after mild, moderate, or severe fluid percussion traumatic brain injury (fpTBI). Groups of rats consisted of animals that had received mild, moderate, or severe fpTBI, or sham operation one year earlier than electrocorticography (ECoG) recordings. In addition, we included a group of age-matched naïve animals. ECoG was recorded from awake animals using epidural electrodes implanted on the injured hemisphere (right), sham-operated hemisphere (right), or right hemisphere in naïve animals. The SWDs were detected automatically using Fast Fourier Transformation and a novel algorithm for comparing changes in spectral power to control (nonepileptical) ECoG. The fpTBI resulted in increased expression of SWDs one year after injury compared with sham-operated or naïve animals. The number of SWD-containing ECoG epochs recorded in a 1 h recording session were: naïve 12.9 ± 10.3, n = 8, sham 23.6 ± 8.2, n = 10, mild TBI 78.9 ± 23.9, n = 10, moderate TBI 61.3 ± 32.5, n = 12, severe TBI 72.5 ± 28.3, n = 11 (mean ± standard error of the mean). Increased expression of SWDs was not related to injury severity. SWDs were observed to a lesser extent even in sham-operated and naïve animals. The data indicate that fpTBI exacerbates expression of SWDs in the rat and that this increase may be observed at least one year after injury. As others have discussed, the spontaneous occurrence of these epileptiform events in rodents limits the use of this model for investigations of acquired epilepsy, at least of the nonconvulsive type, after TBI.

EphB3 signaling propagates synaptic dysfunction in the traumatic injured brain.

Traumatic brain injury (TBI), ranging from mild concussion to severe penetrating wounds, can involve brain regions that contain damaged or lost synapses in the absence of neuronal death. These affected regions significantly contribute to sensory, motor and/or cognitive deficits. Thus, studying the mechanisms responsible for synaptic instability and dysfunction is important for protecting the nervous system from the consequences of progressive TBI. Our controlled cortical impact (CCI) injury produces ~20% loss of synapses and mild changes in synaptic protein levels in the CA3-CA1 hippocampus without neuronal losses. These synaptic changes are associated with functional deficits, indicated by >50% loss in synaptic plasticity and impaired learning behavior. We show that the receptor tyrosine kinase EphB3 participates in CCI injury-induced synaptic damage, where EphB3(-/-) mice show preserved long-term potentiation and hippocampal-dependent learning behavior as compared with wild type (WT) injured mice. Improved synaptic function in the absence of EphB3 results from attenuation in CCI injury-induced synaptic losses and reduced d-serine levels compared with WT injured mice. Together, these findings suggest that EphB3 signaling plays a deleterious role in synaptic stability and plasticity after TBI.

Protein kinase C epsilon regulates mitochondrial pools of Nampt and NAD following resveratrol and ischemic preconditioning in the rat cortex.

Preserving mitochondrial pools of nicotinamide adenine dinucleotide (NAD) or nicotinamide phosphoribosyltransferase (Nampt), an enzyme involved in NAD production, maintains mitochondrial function and confers neuroprotection after ischemic stress. However, the mechanisms involved in regulating mitochondrial-localized Nampt or NAD have not been defined. In this study, we investigated the roles of protein kinase C epsilon (PKCɛ) and AMP-activated protein kinase (AMPK) in regulating mitochondrial pools of Nampt and NAD after resveratrol or ischemic preconditioning (IPC) in the cortex and in primary neuronal-glial cortical cultures. Using the specific PKCɛ agonist ψɛRACK, we found that PKCɛ induced robust activation of AMPK in vitro and in vivo and that AMPK was required for PKCɛ-mediated ischemic neuroprotection. In purified mitochondrial fractions, PKCɛ enhanced Nampt levels in an AMPK-dependent manner and was required for increased mitochondrial Nampt after IPC or resveratrol treatment. Analysis of intrinsic NAD autofluorescence using two-photon microscopy revealed that PKCɛ modulated NAD in the mitochondrial fraction. Further assessments of mitochondrial NAD concentrations showed that PKCɛ has a key role in regulating the mitochondrial NAD(+)/nicotinamide adenine dinucleotide reduced (NADH) ratio after IPC and resveratrol treatment in an AMPK- and Nampt-dependent manner. These findings indicate that PKCɛ is critical to increase or maintain mitochondrial Nampt and NAD after pathways of ischemic neuroprotection in the brain.

Oral contraceptives and nicotine synergistically exacerbate cerebral ischemic injury in the female brain.

Oral contraceptives (OC) and smoking-derived nicotine (N) are known to synergistically increase the risk and severity of cerebral ischemia in women. Although it has been known for some time that long-term use of OC and nicotine will have an increased risk of peripheral thrombus formation, little is known about how the combination of OC and nicotine increases severity of brain ischemia. Recent laboratory studies simulating the conditions of nicotine exposure produced by cigarette smoking and OC regimen of women in female rats confirms that the severity of ischemic hippocampal damage is far greater in female rats simultaneously exposed to OC than to nicotine alone. These studies also demonstrated that the concurrent exposure of OC and nicotine reduces endogenous 17ß-estradiol levels and inhibits estrogen signaling in the brain of female rats. The endogenous 17ß-estradiol plays a key role in cerebrovascular protection in women during their pre-menopausal life and loss of circulating estrogen at reproductive senescence increases both the incidence and severity of cerebrovascular diseases. Therefore, OC and nicotine induced severe post-ischemic damage might be a consequence of lack of estrogen signaling in the brain. In the present review we highlight possible mechanisms by which OC and nicotine inhibits estrogen signaling that could be responsible for severe ischemic damage in females.

EEGgui: a program used to detect electroencephalogram anomalies after traumatic brain injury.

BACKGROUND: Identifying and quantifying pathological changes in brain electrical activity is important for investigations of brain injury and neurological disease. An example is the development of epilepsy, a secondary consequence of traumatic brain injury. While certain epileptiform events can be identified visually from electroencephalographic (EEG) or electrocorticographic (ECoG) records, quantification of these pathological events has proved to be more difficult. In this study we developed MATLAB-based software that would assist detection of pathological brain electrical activity following traumatic brain injury (TBI) and present our MATLAB code used for the analysis of the ECoG. METHODS: Software was developed using MATLAB(™) and features of the open access EEGLAB. EEGgui is a graphical user interface in the MATLAB programming platform that allows scientists who are not proficient in computer programming to perform a number of elaborate analyses on ECoG signals. The different analyses include Power Spectral Density (PSD), Short Time Fourier analysis and Spectral Entropy (SE). ECoG records used for demonstration of this software were derived from rats that had undergone traumatic brain injury one year earlier. RESULTS: The software provided in this report provides a graphical user interface for displaying ECoG activity and calculating normalized power density using fast fourier transform of the major brain wave frequencies (Delta, Theta, Alpha, Beta1, Beta2 and Gamma). The software further detects events in which power density for these frequency bands exceeds normal ECoG by more than 4 standard deviations. We found that epileptic events could be identified and distinguished from a variety of ECoG phenomena associated with normal changes in behavior. We further found that analysis of spectral entropy was less effective in distinguishing epileptic from normal changes in ECoG activity. CONCLUSION: The software presented here was a successful modification of EEGLAB in the Matlab environment that allows detection of epileptiform ECoG signals in animals after TBI. The code allows import of large EEG or ECoG data records as standard text files and uses fast fourier transform as a basis for detection of abnormal events. The software can also be used to monitor injury-induced changes in spectral entropy if required. We hope that the software will be useful for other investigators in the field of traumatic brain injury and will stimulate future advances of quantitative analysis of brain electrical activity after neurological injury or disease.

Phosphodiesterase inhibition rescues chronic cognitive deficits induced by traumatic brain injury.

Traumatic brain injury (TBI) modulates several cell signaling pathways in the hippocampus critical for memory formation. Previous studies have found that the cAMP-protein kinase A signaling pathway is downregulated after TBI and that treatment with a phosphodiesterase (PDE) 4 inhibitor rolipram rescues the decrease in cAMP. In the present study, we examined the effect of rolipram on TBI-induced cognitive impairments. At 2 weeks after moderate fluid-percussion brain injury or sham surgery, adult male Sprague Dawley rats received vehicle or rolipram (0.03 mg/kg) 30 min before water maze acquisition or cue and contextual fear conditioning. TBI animals treated with rolipram showed a significant improvement in water maze acquisition and retention of both cue and contextual fear conditioning compared with vehicle-treated TBI animals. Cue and contextual fear conditioning significantly increased phosphorylated CREB levels in the hippocampus of sham animals, but not in TBI animals. This deficit in CREB activation during learning was rescued in TBI animals treated with rolipram. Hippocampal long-term potentiation was reduced in TBI animals, and this was also rescued with rolipram treatment. These results indicate that the PDE4 inhibitor rolipram rescues cognitive impairments after TBI, and this may be mediated through increased CREB activation during learning.

Chronic nicotine exposure inhibits estrogen-mediated synaptic functions in hippocampus of female rats.

Nicotine, the addictive agent in cigarettes, reduces circulating estradiol-17ß (E2) and inhibits E2-mediated intracellular signaling in hippocampus of female rats. In hippocampus, E2-signaling regulates synaptic plasticity by phosphorylation of the N-methyl-D-aspartic acid receptor subunit NR2B and cyclic-AMP response element binding protein (pCREB). Therefore, we hypothesized that chronic nicotine exposure induces synaptic dysfunction in hippocampus of female rats. Female rats were exposed to nicotine or saline for 16 days followed by electrophysiological analysis of hippocampus. Briefly, population measurements of excitatory post-synaptic field potentials (fEPSPs) were recorded from stratum radiatum of the CA1 hippocampal slice subfield. A strict software-controlled protocol was used which recorded 30 min of baseline data (stimulation rate of 1/min), a paired-pulse stimulation sequence followed by tetanic stimulation, and 1h of post-tetanus recording. EPSP amplitude and the initial EPSP slope were measured off-line. We then investigated by Western blot analysis the effects of nicotine on hippocampal estrogen receptor-beta (ER-ß), NR2B and pCREB. The results demonstrated significantly decreased post-tetanic potentiation and paired-pulse facilitation at the 40, and 80 ms interval in nicotine-exposed rats compared to the saline group. Western blot analysis revealed that nicotine decreased protein levels of ER-ß, NR2B, and pCREB. We also confirmed the role of E2 in regulating NR2B and pCREB phosphorylation by performing Western blots in hippocapmal tissue obtained from E2-treated ovariectomized rats. In conclusion, chronic nicotine exposure attenuates short-term synaptic plasticity, and the observed synaptic defects might be a consequence of loss of estradiol-17ß-signaling. However, determining the exact molecular mechanisms of chronic nicotine exposure on synaptic plasticity specific to the female brain require further investigation.

EphrinBs regulate D-serine synthesis and release in astrocytes.

There is growing evidence that astrocytes play critical roles in neuron-glial interactions at the synapse. Astrocytes are believed to regulate presynaptic and postsynaptic structures and functions, in part, by the release of gliotransmitters such as glutamate, ATP, and d-serine; however, little is known of how neurons and astrocytes communicate to regulate these processes. Here, we investigated a family of transmembrane proteins called ephrinBs and Eph receptors that are expressed in the synapse and are known to regulate synaptic transmission and plasticity. In addition to their presence on CA1 hippocampal neurons, we determined that ephrins and Eph receptors are also expressed on hippocampal astrocytes. Stimulation of hippocampal astrocytes with soluble ephrinB3, known to be expressed on CA1 postsynaptic dendrites, enhanced d-serine synthesis and release in culture. Conversely, ephrinB3 had no effect on d-serine release from astrocytes deficient in EphB3 and EphA4, which are the primary receptors for ephrinB3. Eph receptors mediate this response through interactions with PICK1 (protein interacting with C-kinase) and by dephosphorylating protein kinase C α to activate the conversion of l-serine to d-serine by serine racemase. These findings are supported in vivo, where reduced d-serine levels and synaptic transmissions are observed in the absence of EphB3 and EphA4. These data support a role for ephrins and Eph receptors in regulating astrocyte gliotransmitters, which may have important implications on synaptic transmission and plasticity.

Post-traumatic seizure susceptibility is attenuated by hypothermia therapy.

Traumatic brain injury (TBI) is a major risk factor for the subsequent development of epilepsy. Currently, chronic seizures after brain injury are often poorly controlled by available antiepileptic drugs. Hypothermia treatment, a modest reduction in brain temperature, reduces inflammation, activates pro-survival signaling pathways, and improves cognitive outcome after TBI. Given the well-known effect of therapeutic hypothermia to ameliorate pathological changes in the brain after TBI, we hypothesized that hypothermia therapy may attenuate the development of post-traumatic epilepsy and some of the pathomechanisms that underlie seizure formation. To test this hypothesis, adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury, and were then maintained at normothermic or moderate hypothermic temperatures for 4 h. At 12 weeks after recovery, seizure susceptibility was assessed by challenging the animals with pentylenetetrazole, a GABA(A) receptor antagonist. Pentylenetetrazole elicited a significant increase in seizure frequency in TBI normothermic animals as compared with sham surgery animals and this was significantly reduced in TBI hypothermic animals. Early hypothermia treatment did not rescue chronic dentate hilar neuronal loss nor did it improve loss of doublecortin-labeled cells in the dentate gyrus post-seizures. However, mossy fiber sprouting was significantly attenuated by hypothermia therapy. These findings demonstrate that reductions in seizure susceptibility after TBI are improved with post-traumatic hypothermia and provide a new therapeutic avenue for the treatment of post-traumatic epilepsy.

Increased seizure duration and slowed potassium kinetics in mice lacking aquaporin-4 water channels.

The glial water channel aquaporin-4 (AQP4) has been hypothesized to modulate water and potassium fluxes associated with neuronal activity. In this study, we examined the seizure phenotype of AQP4 -/- mice using in vivo electrical stimulation and electroencephalographic (EEG) recording. AQP4 -/- mice were found to have dramatically prolonged stimulation-evoked seizures after hippocampal stimulation compared to wild-type controls (33 +/- 2 s vs. 13 +/- 2 s). In addition, AQP4 -/- mice were found to have a higher seizure threshold (167 +/- 17 microA vs. 114 +/- 10 microA). To assess a potential effect of AQP4 on potassium kinetics, we used in vivo recording with potassium-sensitive microelectrodes after direct cortical stimulation. Although there was no significant difference in baseline or peak [K(+)](o), the rise time to peak [K(+)](o) (t(1/2), 2.3 +/- 0.5 s) as well as the recovery to baseline [K(+)](o) (t(1/2), 15.6 +/- 1.5 s) were slowed in AQP4 -/- mice compared to WT mice (t(1/2), 0.5 +/- 0.1 and 6.6 +/- 0.7 s, respectively). These results implicate AQP4 in the expression and termination of seizure activity and support the hypothesis that AQP4 is coupled to potassium homeostasis in vivo.

Quantitative analysis of brain NADH in the presence of hemoglobin using microfiber spectrofluorometry: a pre-calibration approach.

Dysfunction of mitochondria links a variety of central nervous system disorders and other neurodegenerative diseases. The primary respiratory chain substrate reduced-form nicotinamide adenine dinucleotide (NADH) is an important regulator of respiratory chain function in mitochondria and, because of its fluorescent properties, has been used to assess mitochondrial pathophysiology in cells and tissues. However, assessment of changes in tissue NADH has been limited to qualitative analysis primarily because hemoglobin (Hb) interferes with NADH fluorescence measurements by absorbing both excitation and emission light. This report presents a computer-assisted approach to estimate tissue NADH and Hb concentrations quantitatively at the same time. The method is based on a two-dimensionally interpolated database model that is calibrated by fluorescence emission spectra with known-value standard chemical solutions. Quantitative concentrations for NADH and Hb can be determined by the corresponding known-value spectral data that have the minimum error to the sample spectrum obtained from an experiment. Repeatability and reliability tests are also presented in this report. Results demonstrate that this method can feasibly quantify the NADH content regardless of the Hb background in living hippocampal cells during hypoxia, suggesting that it has the potential to be applied to in vivo experiments in the future.

Protein kinase C delta cleavage initiates an aberrant signal transduction pathway after cardiac arrest and oxygen glucose deprivation.

Protein kinase C (PKC) isozymes have been known to mediate a variety of complex and diverse cellular functions. deltaPKC has been implicated in mediating apoptosis. Using two models of cerebral ischemia, cardiac arrest in rats and oxygen glucose deprivation (OGD) in organotypic hippocampal slices, we tested whether an ischemic insult promoted deltaPKC cleavage during the reperfusion and whether the upstream pathway involved release of cytochrome c and caspase 3 cleavage. We showed that cardiac arrest/OGD significantly enhanced deltaPKC translocation and increased its cleavage at 3 h of reperfusion. Since deltaPKC is one of the substrates for caspase 3, we next determined caspase 3 activation after cardiac arrest and OGD. The maximum decrease in levels of procaspase 3 was observed at 3 h of reperfusion after cardiac arrest and OGD. We also determined cytochrome c release, since it is upstream of caspase 3 activation. Cytochrome c in cytosol increased at 1 h of reperfusion after cardiac arrest/OGD. Inhibition of either deltaPKC/caspase 3 during OGD and early reperfusion resulted in neuroprotection in CA1 region of hippocampus. Our results support the deleterious role of deltaPKC in reperfusion injury. We propose that early cytochrome c release and caspase 3 activation promote deltaPKC translocation/cleavage.

Changes in trkB-ERK1/2-CREB/Elk-1 pathways in hippocampal mossy fiber organization after traumatic brain injury.

Traumatic brain injury (TBI) leads to mossy fiber reorganization, which is considered to be a causative factor in the development of temporal lobe epilepsy. However, the underlying mechanism is not fully understood. Emerging evidence suggests that TrkB-ERK1/2-CREB/Elk-1 pathways are highly related to synaptic plasticity. This study used the rat fluid-percussion injury model to investigate activation of TrkB-ERK1/2-CREB/Elk-1 signaling pathways after TBI. Rats were subjected to 2.0-atm parasagittal TBI followed by 30 minutes, 4 hours, 24 hours, and 72 hours of recovery. After TBI, striking activation of TrkB-ERK1/2-CREB/Elk-1 signaling pathways in mossy fiber organization were observed with confocal microscopy and Western blot analysis. ERK1/2 was highly phosphorylated predominantly in hippocampal mossy fibers, whereas TrkB was phosphorylated both in the mossy fibers and the dentate gyrus region at 30 minutes and 4 hours of recovery after TBI. CREB was also activated at 30 minutes, peaked at 24 hours of recovery, and returned to the control level at 72 hours of recovery in dentate gyrus granule cells. Elk-1 phosphorylation was seen in CA3 neurons at 4 hours after TBI. The results suggest that the signaling pathways of TrkB-ERK1/2-CREB/Elk-1 are highly activated in mossy fiber organization, which may contribute to mossy fiber reorganization seen after TBI.

Mitochondria consume energy and compromise cellular membrane potential by reversing ATP synthetase activity during focal ischemia in rats.

The direction of the chemical reaction of ATP synthetase is reversible. The present study was designed to determine whether mitochondria produce or consume ATP during ischemia. For this purpose, changes in mitochondrial membrane potential were measured in vivo at the site of a direct current (DC) electrode using a potentiometric dye, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1), and a rat model of focal ischemia. Two microL of dye (control group) or dye with oligomycin, an ATP synthetase inhibitor (oligomycin group), was injected into the parietotemporal cortex through the DC electrode. With the initiation of ischemia, a decrease in mitochondrial potential was observed within 20 seconds in the oligomycin group (earlier than the onset of DC deflection, P = 0.02). In contrast, in the control group, mitochondrial potential was maintained at 91 +/- 5% of the preischemia level for 118 +/- 38 seconds before showing full depolarization simultaneously with DC deflection. During the period of ischemia, the mitochondrial potential was higher in the control group (66 +/- 9%) than in the oligomycin group (46 +/- 8%, P = 0.0002), whereas DC potential was lower in the control group (-18 +/- 3) than in the oligomycin group (-15 +/- 2 mV, P = 0.04). These observations suggest that mitochondria consume ATP during ischemia by reversing ATP synthetase activity, which compromises cellular membrane potential by consuming ATP.

Mild cardiopulmonary arrest promotes synaptic dysfunction in rat hippocampus.

Cardiac arrest (CA) patients exhibit learning and memory disabilities. These deficits suggest that synaptic dysfunction may underlie such disabilities. The hypothesis of the present study was that synaptic dysfunction occurs following CA and that this precedes cell death. To test this hypothesis, we used histopathological and electrophysiological markers in the hippocampus of rats subjected to CA. Evoked potentials (EP) were determined in the CA1 region of hippocampal slices harvested from animals subjected to CA or sham-operated rats by stimulating the Schaffer collaterals and recording in the CA1 pyramidal region. EP amplitudes were significantly attenuated by approximately 60% in hippocampal slices harvested from animals subjected to CA. Hippocampal slices harvested from sham rats exhibited normal long-term potentiation (LTP). In contrast, hippocampal slices harvested 24 h after CA exhibited no LTP response, even when no histopathological abnormalities were observed. These data suggest that synaptic dysfunction occurs before and without overt histopathology. We suggest that the synaptic dysfunction precedes and may be an early marker for delayed neuronal cell death in the hippocampus after CA.