Oxidative metabolic responses with recurrent seizures in rat cerebral cortex: role of systemic factors

Status epilepticus management and mortality risk factors: A retrospective study

INTRODUCTION

Status epilepticus (SE) is a neurological emergency with relatively high mortality rates. In this study, we analysed the management of SE and identified mortality risk factors that may be addressed with educational interventions or modifications to hospital protocols.

METHODS

In this retrospective study, we analysed demographic, treatment, and outcome data from 65 patients (mean age, 59 years [range, 44.5-77]; 53.8% women) who were admitted to our tertiary hospital during an 18-month period and met the 2015 International League Against Epilepsy criteria for SE.

RESULTS

Thirty patients (46.2%) had history of epilepsy. The most frequent causes of SE were cerebrovascular disease (27.7%) and systemic infection (16.9%). The following deviations were observed in the administration of the antiepileptic drugs: benzodiazepines were used as first option in only 33 (50.8%) patients; the combination of 2 benzodiazepines was recorded in 7 cases (10.8%); and lacosamide was used as an off-label drug in 5 patients (7.7%). Electroencephalography studies were performed in only 26 patients (40%); and only 5 studies (7.7% of patients) were performed within 12 hours of seizure onset. The mortality rate was 21.5%. Acute stroke and cerebrovascular complications were associated with higher mortality rates, while previous history of epilepsy and admission to intensive care were related to better prognosis (P <.05).

CONCLUSIONS

To improve SE management and reduce mortality rates, training activities targeting emergency department physicians should be implemented, together with elective intensive care admission for patients with multiple mortality risk factors (eg, absence of history of epilepsy, acute stroke, or cardiovascular complications).

Fluorescence lifetime microscopy of NADH distinguishes alterations in cerebral metabolism in vivo

Evaluating cerebral energy metabolism at microscopic resolution is important for comprehensively understanding healthy brain function and its pathological alterations. Here, we resolve specific alterations in cerebral metabolism in vivo in Sprague Dawley rats utilizing minimally-invasive 2-photon fluorescence lifetime imaging (2P-FLIM) measurements of reduced nicotinamide adenine dinucleotide (NADH) fluorescence. Time-resolved fluorescence lifetime measurements enable distinction of different components contributing to NADH autofluorescence. Ostensibly, these components indicate different enzyme-bound formulations of NADH. We observed distinct variations in the relative proportions of these components before and after pharmacological-induced impairments to several reactions involved in glycolytic and oxidative metabolism. Classification models were developed with the experimental data and used to predict the metabolic impairments induced during separate experiments involving bicuculline-induced seizures. The models consistently predicted that prolonged focal seizure activity results in impaired activity in the electron transport chain, likely the consequence of inadequate oxygen supply. 2P-FLIM observations of cerebral NADH will help advance our understanding of cerebral energetics at a microscopic scale. Such knowledge will aid in our evaluation of healthy and diseased cerebral physiology and guide diagnostic and therapeutic strategies that target cerebral energetics.

Determination of epileptic focus side in mesial temporal lobe epilepsy using long-term noninvasive fNIRS/EEG monitoring for presurgical evaluation

Noninvasive localization of an epileptogenic zone is a fundamental step for presurgical evaluation of epileptic patients. Here, we applied long-term simultaneous functional near-infrared spectroscopy (fNIRS)/electroencephalogram (EEG) monitoring for focus diagnosis in patients with mesial temporal lobe epilepsy (MTLE). Six MTLE patients underwent long-term (8-16 h per day for 4 days) fNIRS/EEG monitoring for the occurrence of spontaneous seizures. Four spontaneous seizures were successfully recorded out of the six patients. To determine oxy-Hb amplitude, the period-average values of oxy-Hb across 20 s from the EEG- or clinically defined epileptic onset were calculated for both hemispheres from the simultaneously recorded fNIRS data. The average oxy-Hb values for the temporal lobe at the earlier EEG- or clinically defined epileptic onsets were greater for the epileptic side than for the contralateral side after EEG activity suppression, spike train, and clinical seizure in all four cases. The true laterality was determined based on the relief of seizures by selective amygdalo-hippocampectomy. Thus, oxy-Hb amplitude could be a reliable measure for determining the epileptic focus side. Long-term simultaneous fNIRS/EEG measurement serves as an effective tool for recording spontaneous seizures. Cerebral hemodynamic measurement by fNIRS would serve as a valuable supplementary noninvasive measurement method for presurgical evaluation of MTLE.

Metabolic responses differentiate between interictal, ictal and persistent epileptiform activity in intact, immature hippocampus in vitro

Interictal spikes, ictal responses, and status epilepticus are characteristic of abnormal neuronal activity in epilepsy. Since these events may involve different energy requirements, we evaluated metabolic function (assessed by simultaneous NADH and FAD+ imaging and tissue O2 recordings) in the immature, intact mouse hippocampus (P5-P7, in vitro) during spontaneous interictal spikes and ictal-like events (ILEs), induced by increased neuronal network excitability with either low Mg2+ media or decreased inhibition with bicuculline. In low Mg2+ medium NADH fluorescence showed a small decrease both during the interictal build-up leading to an ictal event and before ILE occurrences, but a large positive response during and after ILEs (up to 10% net change). Tissue O2 recordings (pO2) showed an oxygen dip (indicating oxygen consumption) coincident with each ILE at P5 and P7, closely matching an NADH fluorescence increase, indicating a large surge in oxidative metabolism. The ILE O2 dip was significantly larger at P7 as compared to P5 suggesting a higher metabolic response at P7. After several ILEs at P7, continuous, low voltage activity (late recurrent discharges: LRDs) occurred. During LRDs, whilst the epileptiform activity was relatively small (low voltage synchronous activity) oxygen levels remained low and NADH fluorescence elevated, indicating persistent oxygen utilization and maintained high metabolic demand. In bicuculline, NADH fluorescence levels decreased prior to the onset of epileptiform activity, followed by a slow positive phase, which persisted during interictal responses. Metabolic responses can thus differentiate between interictal, ictal-like and persistent epileptiform activity resembling status epilepticus, and confirm that spreading depression did not occur. These results demonstrate clear translational value to the understanding of metabolic requirements during epileptic conditions.

Focal Increases in Perfusion and Decreases in Hemoglobin Oxygenation Precede Seizure Onset in Spontaneous Human Epilepsy

PURPOSE

Optical recording of intrinsic signals provides the highest combined spatial and temporal resolution with broad spatial sampling for measuring cerebral blood volume (CBV) and hemoglobin oxygenation in cerebral cortex. Few opportunities arise to apply this laboratory method to record spontaneous seizures in unanesthetized human brain during neurosurgery. We report such a rare opportunity in a man with recurrent focal epilepsy arising from a cavernous malformation.

METHODS

We recorded intrinsic optical signals (IOS) from human cortex intraoperatively during spontaneous seizures arising from brain surrounding a small cavernous malformation in an awake patient using only local anesthesia with simultaneous electrocorticography. The IOS was recorded at two wavelengths, one an isosbestic point for hemoglobin to measure CBV (570 nm) and the other at a wavelength more sensitive to deoxygenated hemoglobin (Hbr) (610 nm). A modified Beer-Lambert calculation was used on two separate but similar seizures to approximate changes in Hbr, CBV as well as oxygenated hemoglobin (HbO(2)).

RESULTS

Electrographically recorded seizures (n = 3) elicited a focal increase in both Hbr and CBV that lasted for the duration of the seizure, indicating that perfusion was inadequate to meet metabolic demand. Remarkably, these hemodynamic changes preceded the onset of the seizures by approximately 20 s and occurred focally over the known location of the lesion and the seizure onsets.

DISCUSSION

These findings demonstrate that the hemoglobin becomes deoxygenated in spite of large increase in CBV during spontaneous human focal seizures and that optically recorded hemodynamic events can be used both to predict and localize human focal epilepsy. Such data may someday be useful to assist in the presurgical evaluation of patients considered for epilepsy surgery and to predict the timing and location of seizure onsets.

Differences in O2 availability resolve the apparent discrepancies in metabolic intrinsic optical signals in vivo and in vitro

Monitoring changes in the fluorescence of metabolic chromophores, reduced nicotinamide adenine dinucleotide and flavin adenine dinucleotide, and the absorption of cytochromes, is useful to study neuronal activation and mitochondrial metabolism in the brain. However, these optical signals evoked by stimulation, seizures and spreading depression in intact brain differ from those observed in vitro. The responses in vivo consist of a persistent oxidized state during neuronal activity followed by mild reduction during recovery. In vitro, however, brief oxidation is followed by prolonged and heightened reduction, even during persistent neuronal activation. In normally perfused, oxygenated and activated brain tissue in vivo, partial pressure of oxygen (P(O2)) levels often undergo a brief 'dip' that is always followed by an overshoot above baseline, due to increased blood flow (neuronal-vascular coupling). By contrast, in the absence of blood circulation, tissue P(O2)in vitro decreases more markedly and recovers slowly to baseline without overshooting. Although oxygen is abundant in vivo, it is diffusion-limited in vitro. The disparities in mitochondrial and tissue oxygen availability account for the different redox responses.

Hemodynamic and metabolic responses to activation, deactivation and epileptic discharges

To investigate the coupling between the hemodynamic and metabolic changes following functional brain activation as well as interictal epileptiform discharges (IEDs), blood oxygenation level dependent (BOLD), perfusion and oxygen consumption responses to a unilateral distal motor task and interictal epileptiform discharges (IEDs) were examined via continuous EEG-fMRI. Seven epilepsy patients performed a periodic (1 Hz) right-hand pinch grip using approximately 8% of their maximum voluntary contraction, a paradigm previously shown to produce contralateral MI neuronal excitation and ipsilateral MI neuronal inhibition. A multi-slice interleaved pulsed arterial spin labeling and T(2)*-weighted gradient echo sequence was employed to quantify cerebral blood flow (CBF) and BOLD changes. EEG was recorded throughout the imaging session and reviewed to identify the IEDs. During the motor task, BOLD, CBF and cerebral metabolic rate of oxygen consumption (CMR(O(2))) signals increased in the contra- and decreased in the ipsilateral primary motor cortex. The relative changes in CMR(O(2)) and CBF were linearly related, with a slope of 0.46 +/- 0.05. The ratio of contra- to ipsilateral CBF changes was smaller in the present group of epilepsy patients than in the healthy subjects examined previously. IEDs produced both increases and decreases in BOLD and CBF signals. In the two case studies for which the estimation criteria were met, the coupling ratio between IED-induced CMR(O(2)) and CBF changes was estimated at 0.48 +/- 0.17. These findings provide evidence for a preserved coupling between hemodynamic and metabolic changes in response to both functional activation and, for the two case studies available, in response to interictal epileptiform activity.

Simultaneous electroencephalographic recording and functional magnetic resonance imaging during pentylenetetrazol-induced seizures in rat

Truly simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) were registered in curarized rats injected with convulsive doses of pentylenetetrazol (PTZ, 65 mg/kg, sc). Rigorous control of physiological parameters like body temperature and ventilation with control of blood gasses helped to avoid potential interference between systemic parameters, and central PTZ-induced blood oxygenation level-dependent (BOLD) changes. Simultaneous EEG/fMRI recordings demonstrated progressive epileptiform EEG discharges with concomitant BOLD changes, the latter gradually affecting most of the fore- and midbrain. Approximately 15 min after PTZ injection, the first BOLD contrast changes mainly occurred in neocortex, and coincided with the first minor EEG alterations. Most regions that displayed BOLD changes were regions with reportedly high GABA(A) receptor densities. Full-blown epileptiform discharges occurred on the EEG tracing, approximately 30 min after PTZ injection, and coincided with bilateral positive and/or negative BOLD contrast changes in cortical and subcortical regions. Behavioral observations demonstrated the first of several generalized clonic or clonic-tonic seizure episodes to occur also around this time. Approximately 90 min after injection, the electrographic paroxysms gradually decreased in amplitude and duration, whereas the BOLD signal changes still extended with alternating positive and negative traces, and spread to subcortical regions like caudate-putamen and globus pallidus.

Altered brain phosphocreatine and ATP regulation when mitochondrial creatine kinase is absent

In cerebral gray matter, ATP concentration is closely maintained despite rapid, large increases in turnover and low substrate reserves. As seen in vivo by (31)P nuclear magnetic resonance (NMR) spectroscopy, brain ATP is stable early in seizures, a state of high energy demand, and in mild hypoxia, a state of substrate deficiency. Like other tissues with high and variable ATP turnover, cerebral gray matter has high phosphocreatine (PCr) concentration and both cytosolic and mitochondrial creatine kinase (UbMi-CK) isoenzymes. To understand the physiology of brain creatine kinases, we used (31)P NMR to study PCr and ATP regulation during seizures and hypoxia in mice with targeted deletion of the UbMi-CK gene. The baseline CK reaction rate constant (k) was higher in mutants than wild-types. During seizures, PCr and ATP decreased in mutants but not in wild-types. The k-value for the CK catalyzed reaction rate increased in wild-types but not in the mutants. Hypoxic mutants and wild-types showed similar PCr losses and stable ATP. During recovery from hypoxia, brain PCr and ATP concentrations returned to baseline in wild-types but were 20% higher than baseline in the mutants. We propose that UbMi-CK couples ATP turnover to the CK catalyzed reaction rate and regulates ATP concentration when synthesis is increased.

Vagal and sciatic nerve stimulation have complex, time-dependent effects on chemically-induced seizures: a controlled study

Previous studies of the effects of electrical vagus stimulation on experimental seizures were without suitable controls or statistical validation, and ignored the potential role of vagally-induced hemodynamic depression on seizure expression. This study addresses these limitations. The effects of periodic left vagus nerve stimulation (LVNS) on chemically-induced seizures in rats were compared with control groups receiving no stimulation (NoS), left sciatic nerve stimulation (LSNS) and LVNS after pretreatment with methyl atropine (MA-LVNS). Stimulation followed a 30 s on-120 s off cycle over 130 min. Seizures were scored visually and the temporal variation of their probability P(s) across the stimulation cycle was measured statistically. P(s) was significantly different (P<0.01) for all groups: LSNS had the highest and MA-LVNS the lowest seizure probability; LVNS and NoS had intermediate values. While LVNS blocked seizures, it also precipitated them, explaining why its anti-seizure effect was only slightly greater than NoS. Neither LVNS nor MA-LVNS induced changes in cortical rhythms ('activation') associated with decreased P(s), unlike LSNS which increased cortical rhythm synchrony and with it, P(s). LVNS alone induced marked bradycardia and moderate hypoxemia. In conclusion, cranial and peripheral nerve stimulation have complex, time-varying effects on cerebral excitability: low frequency LSNS facilitated seizures, while LVNS both suppressed and facilitated them. The anti-seizure effect of LVNS was small and may have, in part, been due to a hemodynamically-induced deficit in energy substrates. The effects of MA-LVNS on seizure duration and P(s) raise the possibility that, in the absence of hemodynamic depression, stimulation of this nerve does not have a strong anti-seizure effect.

Status epilepticus

Status epilepticus is a serious medical emergency that requires prompt and appropriate intervention. Maintenance of adequate vital function with attention to airway, breathing, and circulation; prevention of systemic complications; and rapid termination of seizures must be coupled with investigating and treating any underlying cause. In most patients with SE, the use of adequate dosages of first-line antiepileptic agents allows for the successful and rapid termination of SE and avoidance of potential neurologic complications. Refractory SE requires more aggressive treatment, often the use of intravenous anesthetic agents and intense monitoring, and therefore must be managed in a pediatric intensive care unit with a multidisciplinary approach. Large, controlled, multicenter, comparative studies are needed urgently to clarify better the optimal management of these patients.

The effect of hyperglycemia on cocaine neurotoxicity and death in mice

OBJECTIVE

Cocaine toxicity frequently manifests as seizures and status epilepticus. Frequently, dextrose is administered to patients with cocaine-induced seizures. The objective of this study was to examine the effect of pre-existing hyperglycemia on cocaine neurotoxicity and death in mice.

METHODS

Swiss albino mice received intraperitoneal dextrose at a dose of 1 g/kg (12.5%) (hyperglycemic group, n = 98). The euglycemic group (n = 98) received an equal volume of 0.9% saline. After 60 minutes, all the animals received intraperitoneal cocaine at a dose of 90 mg/kg. The times to onset of ataxia, seizure, and death were recorded in seconds. Times to events were compared using a Kaplan-Meier method and results were compared using the logrank test. The overall percentage outcomes were compared using chi-square.

RESULTS

The ataxia rates (hyperglycemic 97%, euglycemic 97%, chi(2) = 0, p = 1), seizure rates (hyperglycemic 85%, euglycemic 82%, chi(2) = 0.292, p = 0.589), and survival rates (hyperglycemic 62%, euglycemic 51%, chi(2) = 0.2514, p = 0.113) were similar between the groups. The survival following a seizure was significantly higher in the hyperglycemic group (hyperglycemic 57%, euglycemic 41%, chi(2) = 4.439, p = 0.035). The median ataxia time was earlier in the hyperglycemic group (190 sec) than in the euglycemic group (166 sec) (p = 0.031). Seizures occurred no earlier in the hyperglycemic group (331 sec) than in the euglycemic group (342 sec) (p = 0.207). Survival times were not different for the hyperglycemic group (9,133 sec) and the euglycemic group (7,593 sec) (p = 0.394). Survival times following seizures were not different for the hyperglycemic group (8,095 sec) and the euglycemic group (5,816 sec) (p = 0.0752).

CONCLUSIONS

In mice with pre-existing hyperglycemia, ataxia occurred earlier and survival following cocaine-induced seizures was longer than for euglycemic mice. No significant difference in the overall percentage of seizures and death was detected. Pre-existing hyperglycemia had minimal effect on worsening cocaine toxicity in mice.

In vivo development of brain phosphocreatine in normal and creatine-treated rabbit pups

To study the effects of creatine (Cr) on brain energy metabolism and on hypoxia-induced seizures, 5- to 30-day-old rabbit pups were given subcutaneous Cr (3 g/kg) for 3 days before exposure to 4% O2 for 8 min. In saline-treated controls, hypoxic seizures were most frequent at 15 days (80% of pups) and 20 days (60%) of age. Seizures were prevented at 15 days and reduced 60% at 20 days in Cr-treated pups. In surface coil-localized brain 31P nuclear magnetic resonance spectra, with signal from both cerebral gray (GM) and white (WM) matter, the phosphocreatine (PCr)/nucleoside triphosphate (NTP) ratio doubled between 5 and 30 days of age in controls. In all Cr-injected pups, brain PCr/NTP increased to values seen in 30-day-old controls. When spectra were acquired in predominantly GM and WM slices in vivo, the PCr/NTP ratio was very low in GM at 5 days but reached adult levels by 15 days in controls. In WM, the ratio increased steadily from 5 to 30 days of age. In Cr-injected pups, PCr/NTP increased to mature levels in WM and in GM at all ages. In conclusion, hypoxic seizures occur midway in the time course of brain PCr/NTP increase in rabbit pups as previously described in rat pups. In both altricial pups, systemic Cr increases brain PCr/NTP ratio and prevents hypoxic seizures. These results suggest that mature levels of PCr and/or Cr in brain limit EEG activation either directly or indirectly by preventing hypoxic metabolic changes.

In vivo phosphocreatine and ATP in piglet cerebral gray and white matter during seizures

The creatine kinase (CK) reaction is thought to be important in coupling ATP metabolism and regulating ADP concentration in tissues with high and variable ATP turnover, including cerebral gray matter (GM). There is low phosphocreatine (PCr), low CK reaction rates, and high mitochondrial CK (MiCK) isoenzyme activity in GM compared to white matter (WM). To compare the CK reaction in GM and WM when ATP metabolism is high, CK reactants and reaction rates were measured in predominantly GM and WM slices in vivo in 2 and 14-day old piglets during pentylenetetrazole (PTZ) seizures using 31P nuclear magnetic resonance (NMR) 1-dimensional chemical shift imaging (CSI). Arterial pressure, temperature, and blood gasses were stable at both ages. Before seizures, the PCr/nucleoside triphosphate (NTP) ratio was higher in WM than GM at both ages with a developmental increase seen in WM. The CK reaction rate constant increased in both regions between 2 and 14 days. During seizures, PCr/NTP increased in GM at 14 days due to increased PCr while the ratio and PCr decreased in WM. The NTP was more stable in WM and GM at both ages. The CK reaction rate decreased in both regions more at 2 than at 14 days. Thus, brain ATP, deduced from NTP, is stable during seizures in the piglet. In GM stable ATP is associated with a unique increase in PCR concentration.

Co-variation of free amino acids in brain interstitial fluid during pentylenetetrazole-induced convulsive status epilepticus

Effects of pentylenetetrazole (PTZ)-induced convulsive status epilepticus on free amino acids changes in venous blood, CSF and interstitial fluid (IF) of the brain were examined in dogs. A volume of brain IF sufficient for analysis was obtained by chronically implanted tissue cages. The onset of PTZ-induced convulsive seizures seemed mainly related to a marked increase of glutamate, aspartate, taurine, glycine and phosphoserine while, the maintenance and frequency of seizures seemed related to a marked increase of serine and glycine, in combination with a moderate rise of glutamate. L-alpha-Aminoadipate was recovered in moderate amount in epileptic brain IF, while, in controls, this compound was present in minimal amount. The observed complex temporal variation of the amino acidic pattern may play a role in PTZ-induced seizures and, possibly, in pharmacological kindling and brain structural alterations induced by PTZ.

Brain creatine kinase reaction rates and reactant concentrations during seizures in developing rats

Brain creatine kinase (CK) catalyzed phosphorus fluxes between phosphocreatine (PCr) and ATP and changes in reactant concentrations were measured using [31P] nuclear magnetic resonance spectroscopy ([31P]NMR) before and during pentylenetetrazole-induced seizures in 7 and 21 day old rats. The CK rate constants measured before seizures were three times higher in the older than in the younger rats. The rate constants increased 60% during seizures in the older rats but did not change or decreased in the younger. Small decreases in PCr were seen during seizures at both ages. A small decrease in ATP was seen at 7 days but not at 21 days.

Neuronal injury in experimental status epilepticus in the rat: role of hypoxia

While it seems axiomatic that hypoxia is a risk factor for neuronal death during prolonged seizures, the classic neuropathologic literature does not confirm such an association. We investigated this issue by inducing status epilepticus in normoxic (PaO2 approximately 100 mmHg) and hypoxia (PaO2 approximately 50 mmHg) rats, using heat-shock protein (HSP) expression as an index of early cell injury and acid fuchsin staining to detect cell death. Neither stress protein induction nor neuronal death was increased in the selectively vulnerable CA3c region of hippocampus, or in cerebral cortex, of hypoxic compared to normoxic animals. These data support the concept that moderate hypoxia is not a risk factor for brain injury from status epilepticus.

Status epilepticus

Generalised convulsive status epilepticus is a medical emergency. Knowledge of the pathophysiology of status epilepticus and the pharmacology of the medications used to treat it allow one to devise a rational protocol for management. Anticipation of medical complications facilitates intervention when required. Prognosis depends largely on the underlying causes.

Seizure-induced c-fos expression in rat medulla oblongata is not dependent on associated elevation of blood pressure

This study was performed to determine whether c-fos immunoreactivity (IR) induced in medulla oblongata by pentylenetetrazole seizures is a consequence of seizure-associated blood pressure elevation and activation of baroreceptor afferent pathways, or occurs independently of hypertension. Immunohistochemical study of sections of medulla oblongata revealed that seizures are followed by induction of c-fos IR in nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (DMN 10), and ventrolateral medulla (VLM), while there is negligible c-fos IR after saline sham injections. Seizures were associated with blood pressure elevation peaking at 31 +/- 17% (+/- SD) above baseline. Experimental hypertension at a similar level induced by i.p. phenylephrine also resulted in induction of c-fos IR in NTS. When seizures were preceded by antihypertensive treatment with the alpha-adrenergic antagonist, phentolamine, peak blood pressure tended to remain near the baseline level and lower than sham-injected controls. Normotensive seizures were associated with c-fos IR in NTS, DMN 10, and VLM similar to the pattern following hypertensive seizures. Seizure-induced activation of c-fos IR occurred despite normal blood pressure, and thus can be attributed to a direct effect of the seizure, and not to an indirect effect mediated by hypertension.

Membrane lipid degradation is related to interictal cortical activity in a series of seizures

Brain levels of free fatty acids (FFA) and diacylglycerols (DAG) rise rapidly with the onset of seizures, reflecting activation of phospholipases A2 (PLA2) and C (PLC), respectively. However, the ictal/interictal accumulation of FFA attenuates as recurrent seizures continue. To assess the role of neuronal activity in stimulating PLA2 and C, we compared FFA and DAG in rat cerebral cortex during recurrent ictal periods as a function of associated levels of interictal activity. Pentobarbital-anesthetized rats were paralyzed, ventilated with 30% O2 and subjected to periodic pentylenetetrazol seizures at intervals of 5 min. Animals were killed with focused-microwave irradiation during either the 3rd or 15th seizure. The rise in cortical FFA levels during early seizures for 20:4, 22:6, and 18:0 was 3.6-, 2.5-, and 2.2-fold greater, respectively, when adjacent interictal activity was intense as compared to weak activity. During late seizures, this difference dropped to 2.2-fold for 20:4, the only FFA that showed a significantly higher value between robust versus weak interictal activity. In contrast, accumulation of DAG during early and late seizures was observed only when adjacent interictal activity was high. These results indicate that the cortical accumulation of FFA and DAG during ictal periods of similar intensity and duration depends upon the electrocortical activity during adjacent interictal periods.

Free fatty acid and diacylglycerol accumulation in the rat brain during recurrent seizures is related to cortical oxygenation

Cerebral blood flow and oxygenation increase during the early seizures of a series, but the increase in cerebral blood flow attenuates during late seizures, sometimes resulting in decreased cortical oxygenation. Cortical free fatty acids (FFA) and diacylglycerols also increase during early seizures and the increase attenuates during late seizures. We analyzed the correlation between lipid accumulation and cortical O2 during periodic pentylenetetrazol-induced seizures. During early seizures, both FFA and diacylglycerols increased in the cerebral cortex, particularly arachidonate (20:4) and stearate (18:0). Changes in lipids were different during late seizures, depending on cortical O2 levels. An increase in cortical O2 during late seizures was associated with lower FFA levels compared with early seizures, and FFA levels recovered to basal levels during interictal periods. A decline in cortical O2 was associated with a further increase in FFA, which remained elevated during interictal periods. Our results indicate that periseizure lipid accumulation is related to cortical oxygenation.

Cardiac output and regional hemodynamics during recurrent seizures in rats

Altered cardiovascular function in status epilepticus may contribute to mortality and morbidity in patients. We investigated changes in cardiac output and regional hemodynamics during 2 h of recurrent PTZ-induced seizures in anesthetized, paralyzed rats using radioactive microspheres, thermodilution methods, and the pulsed Doppler technique. Cardiac output fell 30-60% during recurrent seizures in 17 of 27 animals. The fall in cardiac output was sudden in onset and occurred primarily in association with seizures accompanied by prolonged increases in MABP but no change in central venous pressure. Total peripheral resistance (TPR) rose during early seizures in association with vasoconstriction of renal and certain splanchnic vascular beds. Ictal increases in TPR became attenuated during late seizures, due to failure of renal and splanchnic beds to constrict. Therefore, derangements in both cardiac and vascular function occur during late seizures. These derangements may contribute to both cerebral hypoperfusion and sudden death in status epilepticus.

Dynamic changes in cerebral oxygenation in chemically induced seizures in rats: study by near-infrared spectrophotometry

Using near-infrared spectrophotometry, the redox state of copper in cytochrome oxidase, and the hemoglobin oxygenation state were measured in the rat brain in situ during and after chemically induced seizures. Pentylentetrazol (PTZ) administration caused the partial reduction of cytochrome oxidase in the brain just before the electroencephalogram (EEG) showed desynchronization, and then blood pressure was elevated concomitantly with an increase in cerebral blood volume. When blood pressure reached a maximum, bursts of spikes appeared on the EEG and cytochrome oxidase was reoxidized to reach the initial oxidation level, giving a rapid, transient reduction of cytochrome oxidase in the preictal period. Hemoglobin was more oxygenated than before the administration throughout the seizure. In the late postictal phase, cytochrome oxidase was partially reduced again, while blood pressure remained high and hemoglobin was more oxygenated than initially. The second administration of PTZ in the late postictal phase induced the same responses as observed after the first administration. By decreasing oxygen concentrations in the inspired gas during the seizure, cytochrome oxidase was more reduced than in the non-epileptic rat, and spike activity was observed until about 85% of cytochrome oxidase was reduced. The transient cerebral hypoxia reflected by the reduction of cytochrome oxidase in the preictal period may be a trigger for an increase in cerebral blood flow rather than the result of a delayed autonomic response. The second reduction of cytochrome oxidase observed in the late postictal phase may be due to a lasting arterio-venous shunt that opens during seizures. These results revive the classical theory that cellular hypoxia is responsible for epileptic brain damage.

Systemic effects of generalized convulsive status epilepticus

Generalized convulsive status epilepticus (GCSE) is accompanied by a marked increase in plasma catecholamines. This produces a number of changes in general systemic physiology including hypertension, tachycardia, cardiac arrhythmias, hyperglycemia, acidosis, and hyperpyrexia. If SE is stopped quickly, these changes are self-correcting and do not produce an increased risk of neuropathology. However, if seizures continue, many of the early physiologic changes reverse, and late status epilepticus is marked by hypotension, hypoglycemia, pulmonary edema and a continued acidosis and elevation of body temperature. Prevention of serious hypoglycemia, maintenance of adequate systemic blood pressure to provide adequate cerebral perfusion, and normalizing the body temperature will minimize or prevent neuropathologic sequelae to SE of extended duration.

Cerebral oxygenation state in chemically-induced seizures in the rat--study by near infrared spectrophotometry

The hemoglobin oxygenation state and the redox state of Cyt.ox. in the rat brain during and after seizure induced by PTZ were measured by using near-infrared spectrophotometry. PTZ administration caused transient reduction of Cyt.ox. in the brain, which might be a trigger for the increase of CBF during seizure. In postictal phase, although BP remained high, Cyt.ox. was in the certain reduced state, which might be due to A-V shunt. Hypoxic loading during seizure caused more reduction of Cyt.ox. than under non-epileptic conditions, which meant that seizure even under mild hypoxic conditions could cause severe hypoxic brain damage.

Relative hypoperfusion in rat cerebral cortex during recurrent seizures

Focal cortical CBF and oxygenation were measured in rats during repetitive seizures to determine whether CBF is maintained above a critical level for adequate delivery of O2. Cerebral oxygenation was determined by measuring relative changes in the oxidation/reduction level of cytochrome aa3 and CBF was measured by the washout of H2. During early seizures, cortical CBF increased to 350% of control and cortical oxygenation also rose markedly. During later seizures, both the increases in CBF and in cortical oxygenation were attenuated progressively. This was accompanied also by attenuation of the associated increases in MABP. Cortical oxygenation decreased during a seizure if the increase in CBF failed to exceed 150-200% of control, defining the critical CBF value. Ventilating the rats on 97% O2 resulted in restoration of the seizure-associated increases in cortical oxygenation in 50% of the cases. The elevation of inspired O2 was effective only if CBF increased once again above 150-200% of control, confirming that the critical CBF lies within this range of values. We conclude that CBF must rise greater than 200% of control levels to provide sufficient O2 to meet the enhanced metabolic requirements of repetitive seizures.

Hypoxia prevents seizures and neuronal damages of the hippocampus induced by kainic acid in rats

The effects of hypoxia on the epileptic seizures and neuronal damages induced by kainic acid were studied in rats using hypoxic chamber equipment. Rats treated with kainic acid and placed in atmospheric pressure showed typical limbic seizures and regressive neuronal changes in CA3 and CA4 of the hippocampus, while those kept in a hypoxic chamber with 8.5% O2 and 91.5% N2 showed moderate hypoxia and a slight decline of mean arterial blood pressure. In these hypoxic rats, seizures were completely prevented and there was remarkably less regressive neuronal injury of the hippocampus. Thus hypoxia has a rather ameliorative effect on the occurrence of seizures and excitotoxic neuronal injuries induced by kainic acid. The contribution of oxygen radicals and endogenous adenosine to preventing excitotoxic neuronal damages by kainic acid was discussed.

Generalized seizures deplete brain energy reserves in normoxemic newborn monkeys

The cerebral metabolic response to bicuculline (BC)-induced status epilepticus (SE) was studied in two-week-old ketamine-anesthetized marmoset monkeys. During 30-min clonic seizures, mean blood pressure, plasma glucose and paO2 did not decrease and plasma lactate doubled. Brains were funnel-frozen and punch biopsies of frontoparietal cortex, temporal cortex and thalamus were analyzed for ATP, phosphocreatine (PCr), glucose and lactate. There were marked reductions of ATP (to 56-77% of controls), PCr (to 23-28% of controls) and glucose (to 1-4% of controls), and lactate increased 3- to 6-fold in seizure animals. NADH fluorescence increased during seizures in cerebral cortex, thalamus, amygdaloid nuclei, hippocampus, posterior striatum and hemispheric white matter. This suggests a reduced tissue redox state in these regions and is correlated with the high energy phosphate depletion and elevated lactate in cortex and thalamus. Our results demonstrate a significant depletion of energy reserves and glucose in cerebral cortex and thalamus during neonatal seizures in the absence of adverse systemic factors. These seizure-induced metabolic changes in brain could have adverse long-term effects on brain development and function.

Detection of an oxidizable fraction of cytochrome oxidase in intact rat brain

Rapid-scanning reflectance spectrophotometry was used to evaluate the reduction-oxidation state of cytochrome oxidase in normoxic rat brain. Reflectance spectra were recorded from intact blood-perfused cerebral cortices after increased oxidative metabolic activity induced by direct cortical stimulation. Reflectance spectra taken from blood-free rat brain and from the rat ear vascular bed were used to identify cytochrome and hemoglobin components of spectra taken from intact brain. Cortical stimulation provoked shifts toward increased oxidation of cytochrome oxidase that were detectable in reflectance spectra. Observations of an oxidizable fraction of cytochrome oxidase demonstrate that a fraction of the cytochrome oxidase pool exists in a reduced state in normoxic brain. The presence of reduced cytochrome oxidase suggests that oxygen delivery to the brain is restricted by microvascular control mechanisms either as a function of brain metabolic physiology or as protection against oxygen toxicity.

Role of pulmonary edema in phasic changes of cerebral oxygenation during serial seizures

To examine whether pulmonary dysfunction leads to episodes of cerebral hypoxia during recurrent seizures, measurements were made of arterial blood pressure, blood-gases, cerebral pO2, and relative changes in cytochrome a,a3 redox levels in anesthetized, paralyzed rats. Seizures were induced serially with bicuculline (BIC) or pentylenetetrazol (PTZ). During early seizures, cerebral oxygenation increased phasically. As seizures continued, a transition often occurred following which seizures were accompanied by phasic decreases in cerebral oxygenation. In addition, pulmonary edema often occurred at an unpredictable point during a series of seizures. Seizure-associated pulmonary edema was less likely to occur with pentobarbital anesthesia and PTZ seizures, than with nitrous oxide anesthesia and BIC seizures. Pulmonary edema was always accompanied by prolonged increases in blood pressure and paroxysmal electrocortical activity, and by hypoxemia, acidemia, and decreased cerebral oxygen supply. Despite the severity of these physiological changes, the transition from phasic increases to decreases in cerebral oxygenation during serial seizures occurred with virtually the same frequency in rats with and without pulmonary edema. This indicates that this transition is independent of pulmonary edema.

Cytochrome reduction induced by increase in extracellular potassium and by electrical stimulation in isolated perifused neurohypophysis of guinea pig under mild hypoxic conditions

Parallel reduction of cytochromes, a(a3), b and c + c1 was recorded under mild hypoxic conditions when the neurohypophysis was electrically stimulated and extracellular KCl concentration was increased. The electrically stimulated reduction was abolished by tetrodotoxin and by replacement of NaCl with LiCl. The reduction was not influenced by removal of extracellular Ca2+, or by application of a Ca ionophore, A23187. These results show that cytochrome reduction correlates with K+-influx in the resting state, and with Na+-influx followed by activation of the neurosecretory terminals contained in the neurohypophysis.

Cytochrome reduction coincides with electrical activity in perfused bullfrog brain

The redox states of cytochromes a(a3), b and c + c1 were continuously measured on the surface of the perfused bullfrog brain with the aid of a scanning spectrophotometer. To correlate with changes of the redox state, electrical activity was simultaneously recorded in the vicinity of the tip of the light guide of the spectrophotometer. In most cases, parallel reduction of the cytochromes was recorded in concordance with burst activity when the third or the fourth dorsal root of the spinal cord was electrically stimulated for 2 min. Recurrent cytochrome reduction and burst activity were produced by stimulation for a longer period, 5 or 10 min. Both the cytochrome reduction and burst activity were abolished when 1 microM tetrodotoxin was added to the perfusing solution. These results suggest that the cytochrome reduction coinciding with electrical activity in the brain may correlate with the Na+-influx followed by the activation of Na+,K+-adenosine triphosphatase in the neurons.

Oxygen insufficiency during hypoxic hypoxia in rat brain cortex

To relate cerebral oxygen sufficiency and insufficiency with arterial oxygen tension, reduction/oxidation responses of the initial and terminal members of the mitochondrial respiratory chain (NADH and cytochrome c oxidase) were recorded in situ by optical techniques when increased cerebral energy use was provoked by direct electrical stimulation. Small decreases in paO2, produced by forced ventilation of hypoxic gas mixtures, resulted in decreased amplitude of the characteristic negative shift in extracellular potential which accompanies such stimulation and smaller oxidative response of NADH and cytochrome oxidase. When paO2 fell below 40-50 Torr, stimulation produced reductive rather than oxidative shifts of the mitochondrial respiratory chain components. The data suggest that when arterial oxygen tension is slightly decreased, compensating mechanisms allow brain function to continue with minimal changes in cortical metabolites and high energy phosphate compounds. When arterial oxygen falls below 40-50 Torr, however, compensation can no longer prevent tissue hypoxia during times of increased energy demand. Thus, hypoxemia is not necessarily synonymous with oxygen insufficiency, but oxygen sufficiency must be defined with due regard to the degree of energy demand.

Concepts of brain oxygen sufficiency during seizures

To resolve conflicting evidence of oxygen sufficiency or insufficiency during seizures, signals of metabolic and circulatory function were monitored in rat cerebral cortex during recurrent seizures. Early seizures were accompanied by increased blood volume, increased tPO2, and oxidative shifts of cytochrome a,a3, indicative of oxygen sufficiency. Later seizures were accompanied by a smaller increment in blood volume, a fall in tPO2, and shifts toward reduction of cytochrome a,a3, suggesting that cerebral oxygen supply became insufficient to meet demand. Responses suggesting oxygen insufficiency occurred during short duration ictal bursts, interictal spikes or electrocortical stimulation at times when longer duration ictal episodes still were accompanied by responses signalling oxygen sufficiency. These data indicate that there is a progressive dissociation of the normally tight couple between neuronal activity, energy demand, and cerebral blood flow during status epilepticus. Systemic derrangements that often accompanied recurrent seizures also contributed to decreased cerebral oxygenation. These factors may cause the neuronal damage reported to follow prolonged status epilepticus.

Importance of vascular responses in determining cortical oxygenation during recurrent paroxysmal events of varying duration and frequency of repetition

Cerebral oxygenation initially increases and later decreases in rats subjected to experimental status epilepticus. In this study, we have compared cerebral oxygen supply and vascular changes during paroxysmal events of different durations and at different time intervals to test the hypothesis that oxygen insufficiency is associated more readily with paroxysmal events of greater intensity. Continuous measurements were made of local changes in cortical blood volume, redox levels of cytochrome a, a3, cortical Po2, and systemic arterial blood pressure during recurrent seizures induced by pentylenetetrazol or bicuculline. In contrast to expectations, systemic and cerebral vascular responses and associated increases in cerebral oxygenation were better maintained during long-duration ictal episodes than during short-duration ictal bursts, interictal spikes, or evoked potentials. Short-duration paroxysmal events were often accompanied by decreases in cerebral oxygenation, whereas long-duration events were still accompanied by increases in oxygenation. Ictal bursts occurring with short interburst intervals caused a more rapid failure of vascular responsiveness than those occurring at longer intervals. These relationships of intensity and frequency of repetition of seizures to changes in vascular responses indicate progressive dissociation of the normally tight couple between neuronal activity, energy demand, and cerebral blood flow during status epilepticus.

Influence of systemic factors on experimental epileptic brain injury. Structural changes accompanying bicuculline-induced seizures in rats following manipulations of tissue oxygenation or alpha-tocopherol levels

A previous study from the laboratory showed that status epilepticus induced by bicuculline administration to ventilated rats produced astrocytic swelling and nerve cell changes ("type 1 and 2 injury") particularly in layers 3 and 5 of the neocortex (Söderfeldt et al. 1981). The type 1 injured neurons were characterized by condensation of cyto- and karyoplasm and the less common type 2 cells were characterized by swelling of endoplasmic reticulum including the nuclear envelope. In the present study we explored whether changes in cerebral oxygen availability altered the extent or character of the cellular alterations. Animals with 2 h of status epilepticus were made either hyperoxic (administration of 100% O2), hypoxic (arterial pO2 50 mm Hg) or hypotensive (arterial blood pressure of either 70-75 or 50 mm Hg). Furthermore, we explored whether "oxidative" damage occurred by manipulating tissue levels of alpha-tocopherol, a known free radical scavenger. Non-epileptic control animals exposed to comparable degrees of hypoxia or hypotension showed no or minimal structural alterations. In the epileptic animals the results were as follows. Hyperoxia did not change the quality or extent of the structural alterations previously observed in normoxic epileptic animals. Neither administration nor deficiency of vitamin E did modify this pattern of alterations. In hypoxia the extent of cell damage was the same or somewhat larger than in normoxic, epileptic animals. In addition, neurons often showed cytoplasmic microvacuoles due to swelling of mitochondria. The hypoxic animals also showed swelling of astrocytic nuclei with clumped chromatin. Changes similar to those observed in hypoxic animals also appeared in moderate hypotension (mean arterial blood pressure 50 mm Hg), whereas mild hypotension (70-75 mm Hg) did not change the character of the tissue injury from that seen in hyperoxic or normoxic epileptic rats. The present results demonstrate that the neuronal cell damage that can be observed when the brain is fixed by perfusion after status epilepticus of 2 h duration is not exaggerated by hyperoxia or vitamin E deficiency nor is it ameliorated by a moderate restriction in cerebral oxygen supply or by vitamin E administration. If anything, hypoxia (or moderate hypotension) appears to increase the extent of damage and it clearly alters its ultrastructural characteristics. However, although the results fail to support the notion that epileptic cell damage is "oxidative", definite conclusions must await information on the cell damage that remains upon arrest of the epileptic activity.