Cerebral metabolic responses to electroconvulsive shock and their modification by hypercapnia

Fueling and imaging brain activation

Metabolic signals are used for imaging and spectroscopic studies of brain function and disease and to elucidate the cellular basis of neuroenergetics. The major fuel for activated neurons and the models for neuron–astrocyte interactions have been controversial because discordant results are obtained in different experimental systems, some of which do not correspond to adult brain. In rats, the infrastructure to support the high energetic demands of adult brain is acquired during postnatal development and matures after weaning. The brain's capacity to supply and metabolize glucose and oxygen exceeds demand over a wide range of rates, and the hyperaemic response to functional activation is rapid. Oxidative metabolism provides most ATP, but glycolysis is frequently preferentially up-regulated during activation. Underestimation of glucose utilization rates with labelled glucose arises from increased lactate production, lactate diffusion via transporters and astrocytic gap junctions, and lactate release to blood and perivascular drainage. Increased pentose shunt pathway flux also causes label loss from C1 of glucose. Glucose analogues are used to assay cellular activities, but interpretation of results is uncertain due to insufficient characterization of transport and phosphorylation kinetics. Brain activation in subjects with low blood-lactate levels causes a brain-to-blood lactate gradient, with rapid lactate release. In contrast, lactate flooding of brain during physical activity or infusion provides an opportunistic, supplemental fuel. Available evidence indicates that lactate shuttling coupled to its local oxidation during activation is a small fraction of glucose oxidation. Developmental, experimental, and physiological context is critical for interpretation of metabolic studies in terms of theoretical models.

Benefits of the laryngeal mask for airway management during electroconvulsive therapy

Accumulation of carbon dioxide (CO2) can disturb systemic hemodynamics and increase the seizure threshold in patients receiving electroconvulsive therapy (ECT). The purpose of this study was to investigate the effects of the laryngeal mask on blood gas, hemodynamics, and seizure duration during ECT under propofol anesthesia. Ventilation was assisted using either a face mask (n=23) or laryngeal mask (n=23) and 100% oxygen. There was no significant difference in PaO2 between the two groups. PaCO2 was greater in the face mask group than the laryngeal mask group at 3 minutes (54 +/- 11 mm Hg, 41 +/- 8 mm Hg, respectively) and 5 minutes (52 +/- 11 mm Hg, 43 +/- 15 mm Hg, respectively) after electrical stimulation (p<0.01). Mean blood pressure was higher than the corresponding preanesthesia value at 1 to 5 minutes after electrical stimulation in the face mask group and at 1 to 3 minutes after electrical stimulation in the laryngeal mask group. Mean seizure duration in the face mask group was significantly shorter than that in the laryngeal mask group (33 +/- 11 seconds, 42 +/- 10 seconds, respectively p<0.01). The change in PaCO2 was minor in the laryngeal mask group compared with the face mask group and seizure duration was longer in the laryngeal mask group. Laryngeal mask may be suitable for airway management during ECT anesthesia, especially when fitting a face mask is difficult.

End-tidal carbon dioxide monitoring stabilized hemodynamic changes during ECT

Accumulation of carbon dioxide (CO2) can disturb systemic and cerebral hemodynamics in patients receiving electroconvulsive therapy (ECT). The purpose of this study was to identify the effects of end-tidal CO2 monitoring on hemodynamic changes in patients who received ECT under propofol anesthesia. ECT was prescribed to 40 patients under propofol anesthesia. Ventilation was assisted using a face mask and 100% oxygen, with or without end-tidal CO2 monitoring. Heart rate was significantly increased in patients without end-tidal CO2 monitoring at 1 to 5 minutes after electrical stimulation (p < 0.01). Mean arterial blood pressure and middle cerebral artery blood flow velocity in the group without end-tidal CO2 monitoring were significantly larger than the values in the group with the monitor at 1 to 5 minutes after electrical stimulation. Arterial CO2 tension in the group without end-tidal CO2 monitoring was larger than the value in the group with the monitoring at 1 minute (45+/-5 mm Hg with the monitor and 56+/-8 without the monitor) and 5 minutes (37+/-4 mm Hg with the monitor and 51+/-8 without the monitor) after electrical stimulation (p < 0.01). Application of end-tidal CO2 monitoring is considered beneficial for safe and effective anesthesia management of patients undergoing ECT, especially patients with an intracranial disorder or ischemic heart disease.

Immobilization stress-induced increment of lactate metabolism in the basolateral amygdaloid nucleus is attenuated by diazepam in the rat

Using in vivo microdialysis technique, extracellular lactate levels were measured in the basolateral amygdaloid nucleus of the rat under immobilization stress. Immobilization stress (40 min) led to a tetrodotoxin-reversible increase in dialysate lactate levels. Diazepam (1.0 mg/kg, i.p.) reduced the ability of immobilization stress to increase lactate levels. Furthermore, the attenuation of the immobilization stress-induced increase of lactate levels by diazepam was antagonized by pretreatment with flumazenil (15 mg/kg, i.p.), a selective antagonist at benzodiazepine receptors. These findings suggest that immobilization stress increases lactate levels in rat basolateral amygdaloid nuclei, which is attenuated by stimulation of benzodiazepine receptors.

Reversible, reproducible reduction of brain water apparent diffusion coefficient by cortical electroshocks

Rat brains were imaged after cortical electroshock pulse trains (1 ms pulses at 100 Hz) of varying durations (0.1-10 s), with diffusion-weighted echo planar imaging sequences at 2.0 T. The apparent water diffusion coefficient (ADC) decreased after either single or repeat electroshock trains. ADC reductions were observed within 6 s after the first shock. The size of the affected area of the brain increased in subsequent images during the 1st min after a 10-pulse (0.1 s) train, and also increased with the duration of electroshock trains. ADC reduction was reproducible in extent and time course after single 10-shock trains and was reversible. In the affected pixels the mean ADC reduction was 4% for a single shock train (0.1 s), and 7-8% for trains repeated once a minute, independent of electroshock train duration. The results indicate that neuronal activity associated with electrostimulation may be monitored with water diffusion measurements, and they may be useful for measuring the severity of seizure activity in patients with medically intractable epilepsy.

Repeated electroconvulsive shock selectively increases the expression of the neuron specific enolase in piriform cortex

The effect of repeated electroconvulsive shock (ECS) on the activities of the three enolase isoenzymes present in rat brain: neuron specific enolase (NSE), non-neuronal enolase (NNE) and the hybrid enolase was investigated in piriform cortex. The activities were estimated on isoenzymes separated by agarose gel electrophoresis. Whereas the specific activities of NNE and hybrid enolase were unchanged in piriform cortex or ECS-treated rats the specific activity of NSE was increased by 16.3 percent (P < 0.02). The brain enolase isoenzymes are dimers of alpha- and gamma-enolase subunits. The calculated ratio between the gamma-subunit present in both NSE and hybrid enolase and the alpha-subunits present in both NNE and hybrid enolase was increased by 11.7 percent in piriform cortex of ECS-treated rats (P < 0.05). Previously, it has been shown that the gamma-subunit is only expressed in neurons whereas the alpha-subunit is expressed in both neurons and glial cells. The selectively increased expression of the enolase gamma-subunit in ECS-treated rats might either reflect an increased transcription of a whole group of neuronal genes or rather the trophic role of NSE in ECS-enhanced synaptic remodelling of the rat brain.

Rat hippocampal lactate efflux during electroconvulsive shock or stress is differently dependent on entorhinal cortex and adrenal integrity

The role of the entorhinal cortex and the adrenal gland in rat hippocampal lactate formation was assessed during and after a short-lasting immobilization stress and electroconvulsive shock (ECS). Extracellular lactate was measured on-line using microdialysis and enzyme reactions (a technique named lactography); in some rats, unilateral lesions of the entorhinal cortex were made or the bilateral adrenal glands were removed. The stress-evoked increase in hippocampus lactate was not altered either ipsi- or contralateral to an entorhinal cortex lesion. The response to ECS was attenuated only in the hippocampus ipsilateral to the entorhinal cortex lesion. Removal of bilateral adrenal glands caused some delay in the increase in hippocampal lactate after ECS and a major reduction in the stress-evoked lactate response. These results indicate that (1) the entorhinal cortex is activated by ECS, thereby activating hippocampal lactate efflux and presumably metabolism, and (2) the adrenal gland is essential in the response to stress and, to a minor extent, in the ECS-altered hippocampal metabolism.

Onset of insensibility at slaughter in calves: effects of electroplectic seizure and exsanguination on spontaneous electrocortical activity and indices of cerebral metabolism

Cerebral venous and femoral arterial blood samples were collected from 21 young calves either during electrical stunning and recovery or electrical stunning and slaughter by carotid severance or slaughter without stunning. The blood samples were analysed for PO2, PCO2, pH, glucose and lactate. The results were compared with simultaneous recordings of spontaneous electrocortical (ECOG) activity. Calves subjected to head-only electrical stunning and slaughter became permanently insensible at the time of the stun. The six calves slaughtered without stunning lost sensibility within 10 seconds. One calf, in which a clot formed in the carotid arteries inhibiting bleeding, maintained some evidence of cortical activity beyond 52 seconds; this was high amplitude low frequency activity and analysis by Fast Fourier Transform showed sensibility was not regained. In the remaining calves the ECOG activity was lost on average within 49 +/- 3.5 (SEM) seconds after slaughter. The cerebral extraction of metabolites increased after carotid severance, indicating inadequacy of cerebral bloodflow after slaughter. No correlations were found between indices of cerebral metabolism and the time of loss of cortical function.

Dichloroacetate increases glucose use and decreases lactate in developing rat brain

Dichloroacetate (DCA) activates pyruvate dehydrogenase (PDH) by inhibiting PDH kinase. Neutralized DCA (100 mg/kg) or saline was intravenously administered to 20 to 25-day-old rats (50-75g). Fifteen minutes later a mixture of [6-14C]glucose and [3H]fluorodeoxyglucose (FDG) was administered intravenously and the animals were sacrificed by microwave irradiation (2450 MHz, 8.0 kW, 0.6-0.8 sec) after 2 or 5 min. Brain regional rates of glucose use and metabolite levels were determined. DCA-treated rats had increased rates of glucose use in all regions studied (cortex, thalamus, striatum, and brain stem), with an average increase of 41%. Lactate levels were lower in all regions, by an average of 35%. There were no significant changes in levels of ATP, creatine phosphate, or glycogen in any brain region. Blood levels of lactate did not differ significantly between the DCA- and the saline-treated groups. Blood glucose levels were higher in the DCA group. In rats sacrificed by freeze-blowing, DCA treatment caused lower brain levels of both lactate and pyruvate. These results cannot be explained by any systemic effect of DCA. Rather, it appears that in the immature rat, DCA treatment results in activation of brain PDH, increased metabolism of brain pyruvate and lactate, and a resulting increase in brain glycolytic rate.

Mild stress stimulates rat hippocampal glucose utilization transiently via NMDA receptors, as assessed by lactography

Lactography is a novel technique that allows the continuous on-line registration of brain extracellular lactate in the freely behaving animal and that is based on a fluorimetric enzymatic assay of brain dialysates. Electroconvulsive shock, activation of the glutamate receptor (NMDA-type) and mild stress (immobilization, cold stress or handling) result in transient increases in the efflux of lactate from the rat hippocampus. The increase following immobilization stress was attenuated by the NMDA-receptor antagonist 2-amino-5-phosphopentanoic acid and after several pre-exposures to this stressor. These experiments suggest that mild stress activates glutamatergic neurons, which may be less after habituation to stress.

In vivo identification and quantitative evaluation of carrier-mediated transport of lactate at the cellular level in the striatum of conscious, freely moving rats

Intracerebral dialysis has allowed the continuous, on-line measurement of lactate in the extracellular fluid (ECF) of conscious, freely moving rats. The rapid time response of the technique allows the direct determination of the time course of changes in lactate in ECF following externally imposed stimuli. The time course of lactate appearance in ECF was found to be considerably slower than that observed in tissue following electroconvulsive shock or during ischemia following cardiac arrest. The ECF data could be fit to an integrated Michaelis-Menten model that assumed reversible transport of lactate across the cell membrane. This transport was found to act only when energy supplies could maintain membrane integrity and function, since ECF levels of lactate failed to follow tissue levels after cardiac arrest when energy resources are depleted. The calculated rate of cellular lactate transport was two orders of magnitude faster than transport of lactate across the blood-brain barrier in the adult rat, and passive diffusion of lactate was not found to contribute significantly across either cell or blood-brain barriers. Probenecid, an inhibitor of acid transport, was able to block both the efflux of lactate from cell to ECF and the consequent reuptake of lactate by cells in the striatum of the rat following electroconvulsive shock or ischemia.

Extracellular lactic acid as an indicator of brain metabolism: continuous on-line measurement in conscious, freely moving rats with intrastriatal dialysis

Lactic acid was measured continuously in the dialysis perfusate emerging from the striatum of conscious, freely moving rats. The continuous measurement utilized a specific enzymatic/fluorometric detector that provided temporal information about the changes in the concentration of lactate in extracellular fluid (ECF). The level of lactate in extracellular fluid was found to be directly linked to local cellular metabolism. Inhibition of glycolysis with 2-deoxyglucose decreased the ECF level of lactate, whereas increased lactate production was observed after uncoupling mitochondrial electron transport with 2,4-dinitrophenol. A transient increase in the extracellular level of lactate was found after neuronal stimulation (e.g., electroconvulsive shock or local administration of kainic acid). The response to electroconvulsive shock could be attenuated by inhibiting the electrical activity of neurons with tetrodotoxin. Thus, this system is capable of providing novel information about transient changes in the extracellular concentration of lactic acid in real time, and these changes can be related to changes in metabolism and neuronal activity.

Status epilepticus-induced changes in primate cortical energy metabolism

The objective of this study was to evaluate changes in cortical energy metabolism in experimentally induced seizures in the primate. Cynamologus fascicularis monkeys were anesthetized, and a craniotomy was performed. Small samples from the motor cortex were removed for measurement of energy metabolites just prior to intravenous bicuculline infusion (0.6 mg/kg), 20 min after the onset of seizures, and 2 h after the second sample. Samples were also taken for electron microscopy. Results showed decreased phosphocreatine values 20 min after the onset of seizures, whereas ATP levels were normal. Two hours after the onset of seizures, phosphocreatine had returned to normal, but ATP levels were below normal. Examination of tissue by electron microscopy showed evidence of cell damage 2 h, 20 min after the onset of seizures. These findings are consistent with the concept that sustained seizures may lead to irreversible cell damage and that alterations in energy metabolism may contribute to the cell death.

Combined 1H and 31P nuclear magnetic resonance spectroscopic studies of bicuculline-induced seizures in vivo

Using a 1.89-Tesla spectrometer, 1H and 31P nuclear magnetic resonance spectra were acquired from the brains of paralyzed rabbits ventilated with 30% oxygen in nitrous oxide. Intracellular pH and changes in lactate concentration in the cerebrum were monitored by nuclear magnetic resonance methods during and after bicuculline-induced seizures, together with the electroencephalogram, heart rate, and arterial blood pressure. During seizures lasting more than an hour, cerebral intracellular pH became acidic, the cerebral lactate level rose rapidly, and both changes persisted as long as 2 hours without signs of recovery. After less prolonged seizures, lactate elevations were no less persistent, despite nearly complete recovery of intracellular pH and the electroencephalogram.

Cerebral metabolic effects of organophosphorus anticholinesterase compounds

Rats treated intravenously with an organophosphorus anticholinesterase compound, paraoxon or soman, were sacrificed 2 to 131 min later, using 0.7 sec of focused microwave irradiation (25 kW at 915 MHz). Brain regional rates of glucose utilization during 3-min intervals were determined with labeled glucose and fluorodeoxyglucose as tracers. Levels of glucose, lactate, ATP, and creatine phosphate were assayed in the same samples. The two compounds differed markedly in their effects on brain metabolism. Paraoxon (0.8 LD50) depressed rates of glucose use in all brain regions, without causing consistent changes in brain metabolite levels. This depressant effect was most pronounced during the first 30 min after toxin exposure and had largely disappeared by 2 hr. Soman (0.8-0.95 LD50) was variable in its effects. Animals that showed seizure-like behavior had marked increases in glucose use in diencephalon and cerebrum but no changes in cerebellum or brain stem. Rapid rates of glucose use were associated with high levels of lactic acid and lower levels of creatine phosphate. In cerebrum, but not diencephalon, levels of ATP fell by as much as 50% in strongly affected animals by 30-130 min after soman. All of these effects were reversible with atropine. Soman-treated animals that did not have seizure-like activity did not exhibit these brain metabolic changes. These results and those of others show that cholinergic compounds vary greatly in their effects on brain glucose and energy metabolism. Although noncholinergic mechanisms are a possibility, the most parsimonious explanation for these findings is that cholinesterase inhibitors vary in their affinity for different central nervous system (CNS) acetylcholine receptor populations.

Regional glucose and beta-hydroxybutyrate use by developing rat brain

Rates of glucose and D-beta-hydroxybutyrate use were determined in five brain regions of 20-day-old rats. The regions studied were cerebral cortex, thalamus, striatum, cerebellum, and brain stem. The tracers for determining rates of substrate use were [3H]fluorodeoxyglucose and [3-14C]-D-beta-hydroxybutyrate. Two or five minutes after isotope administration the animals were sacrificed in a 6-kW, 2450-MHz focused microwave device. Ten minutes prior to isotope administration the animals were injected intraperitoneally with normal saline or DL-beta-hydroxybutyrate (10 mmol/kg). Blood D-beta-hydroxybutyrate levels averaged 0.21 mumol/ml in saline-injected and 3.13 mumol/ml in hyperketonemic rats. Rates of glucose utilization were significantly heterogeneous between regions in both groups: thalamus greater than cerebral cortex greater than or equal to striatum greater than brain stem greater than cerebellum. These rates were 20-35% lower in hyperketonemic rats. Rates of D-beta-hydroxybutyrate use varied significantly between regions only in the saline group, with the brain stem rate being significantly lower than that in cortex or cerebellum. Regional rates of D-beta-hydroxybutyrate use did not correlate significantly with regional rates of glucose use in either the saline or the hyperketonemic groups. Regional rates of glucose use were strongly and positively correlated between conditions, as were regional rates of D-beta-hydroxybutyrate use. Thus, in 20-day-old rats, the regional heterogeneity of brain glucose use is similar to that in adult rats. D-beta-Hydroxybutyrate use is much less regionally heterogeneous.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the novel compound aniracetam (Ro 13-5057) upon impaired learning and memory in rodents

The effect of aniracetam (Ro 13-5057, 1-anisoyl-2-pyrrolidinone) was studied on various forms of experimentally impaired cognitive functions (learning and memory) in rodents and produced the following effects: (1) almost complete prevention of the incapacity to learn a discrete escape response in rats exposed to sublethal hypercapnia immediately before the acquisition session; (2) partial (rats) or complete (mice) prevention of the scopolamine-induced short-term amnesia for a passive avoidance task; (3) complete protection against amnesia for a passive avoidance task in rats submitted to electroconvulsive shock immediately after avoidance acquisition; (4) prevention of the long-term retention- or retrieval-deficit for a passive avoidance task induced in rats and mice by chloramphenicol or cycloheximide administered immediately after acquisition; (5) reversal, when administered as late as 1 h before the retention test, of the deficit in retention or retrieval of a passive avoidance task induced by cycloheximide injected 2 days previously; (6) prevention of the deficit in the retrieval of an active avoidance task induced in mice by subconvulsant electroshock or hypercapnia applied immediately before retrieval testing (24 h after acquisition). These improvements or normalizations of impaired cognitive functions were seen at oral aniracetam doses of 10-100 mg/kg. Generally, the dose-response curves were bell-shaped. The mechanisms underlying the activity of aniracetam and its 'therapeutic window' are unknown. Piracetam, another pyrrolidinone derivative was used for comparison. It was active only in six of nine tests and had about one-tenth the potency of aniracetam. The results indicate that aniracetam improves cognitive functions which are impaired by different procedure and in different phases of the learning and memory process.