Some neurochemical aspects of pentamethylenetetrazole convulsive activity in rat brain

Brain glycogen content is increased in the acute and interictal chronic stages of the mouse pilocarpine model of epilepsy

Glucose is the main brain fuel in fed conditions, while astrocytic glycogen is used as supplemental fuel when the brain is stimulated. Brain glycogen levels are decreased shortly after induced seizures in rodents, but little is known about how glycogen levels are affected interictally in chronic models of epilepsy. Reduced glutamine synthetase activity has been suggested to lead to increased brain glycogen levels in humans with chronic epilepsy. Here, we used the mouse pilocarpine model of epilepsy to investigate whether brain glycogen levels are altered, both acutely and in the chronic stage of the model. One day after pilocarpine‐induced convulsive status epilepticus (CSE), glycogen levels were higher in the hippocampal formation, cerebral cortex, and cerebellum. Opposite to expected, this was accompanied by elevated glutamine synthetase activity in the hippocampus but not the cortex. Increased interictal glycogen amounts were seen in the hippocampal formation and cerebral cortex in the chronic stage of the model (21 days post‐CSE), suggesting long‐lasting alterations in glycogen metabolism. Glycogen solubility in the cerebral cortex was unaltered in this epilepsy mouse model. Glycogen synthase kinase 3 beta (Gsk3b) mRNA levels were reduced in the hippocampal formations of mice in the chronic stage, which may underlie the elevated brain glycogen content in this model. This is the first report of elevated interictal glycogen levels in a chronic epilepsy model. Increased glycogen amounts in the brain may influence seizure susceptibility in this model, and this warrants further investigation.

Hungry Neurons: Metabolic Insights on Seizure Dynamics

Epilepsy afflicts up to 1.6% of the population and the mechanisms underlying the appearance of seizures are still not understood. In past years, many efforts have been spent trying to understand the mechanisms underlying the excessive and synchronous firing of neurons. Traditionally, attention was pointed towards synaptic (dys)function and extracellular ionic species (dys)regulation. Recently, novel clinical and preclinical studies explored the role of brain metabolism (i.e., glucose utilization) of seizures pathophysiology revealing (in most cases) reduced metabolism in the inter-ictal period and increased metabolism in the seconds preceding and during the appearance of seizures. In the present review, we summarize the clinical and preclinical observations showing metabolic dysregulation during epileptogenesis, seizure initiation, and termination, and in the inter-ictal period. Recent preclinical studies have shown that 2-Deoxyglucose (2-DG, a glycolysis blocker) is a novel therapeutic approach to reduce seizures. Furthermore, we present initial evidence for the effectiveness of 2-DG in arresting 4-Aminopyridine induced neocortical seizures in vivo in the mouse.

Suppressive Effects of Various Amino Acids against Ouabain-Induced Seizures in Rats

The suppressive effect of various amino acids against ouabaininduced seizures was investigated in young female rats. The amino acids were injected into the left lateral ventricle 10 minutes prior to the intraventricular administration of 5 μg. of ouabain. Animals receiving 1.9 x 10-1 M solutions of hypotaurine and of β- alanine were almost completely protected from the ouabain seizures. Administration of L-alanine and of glycine was also effective, although running and leaping seizures still occurred to some extent. Betaine reduced only clonic-tonic and whole body flexion and extension seizures. In contrast, L-proline exclusively suppressed clonic-tonic and focal clonic seizures. Rats injected with isethionic acid showed increases in incidence of running and leaping seizures while L-arginine in high concentrations caused aggravation in clonic-tonic seizures. L-cysteine, even in low concentrations, also brought about an increase in the occurrence and incidence of clonic-tonic seizures. The ED50of hypotaurine was 10.11 x 10-2 M for running seizures and 4.63 x 10-2, M for clonictonic seizures; that of β -alanine was 14.01 x 10-2 M for running seizures and 5.50 x 10-2 M for clonic-tonic seizures. However, hypotaurine and β -alanine, the most effective compounds tested in the present studies, provided less protection than taurine previously examined by us under similar conditions (Izumi et al., 1973).

Epilepsy, regulation of brain energy metabolism and neurotransmission

Seizures are the result of a sudden and temporary synchronization of neuronal activity, the reason for which is not clearly understood. Astrocytes participate in the control of neurotransmitter storage and neurotransmission efficacy. They provide fuel to neurons, which need a high level of energy to sustain normal and pathological neuronal activities, such as during epilepsy. Various genetic or induced animal models have been developed and used to study epileptogenic mechanisms. Methionine sulfoximine induces both seizures and the accumulation of brain glycogen, which might be considered as a putative energy store to neurons in various animals. Animals subjected to methionine sulfoximine develop seizures similar to the most striking form of human epilepsy, with a long pre-convulsive period of several hours, a long convulsive period during up to 48 hours and a post convulsive period during which they recover normal behavior. The accumulation of brain glycogen has been demonstrated in both the cortex and cerebellum as early as the pre-convulsive period, indicating that this accumulation is not a consequence of seizures. The accumulation results from an activation of gluconeogenesis specifically localized to astrocytes, both in vivo and in vitro. Both seizures and brain glycogen accumulation vary when using different inbred strains of mice. C57BL/6J is the most "resistant" strain to methionine sulfoximine, while CBA/J is the most "sensitive" one. The present review describes the data obtained on methionine sulfoximine dependent seizures and brain glycogen in the light of neurotransmission, highlighting the relevance of brain glycogen content in epilepsies.

Factors which abolish hypoglycemic seizures do not increase cerebral glycogen content in vitro

The brain is heavily dependant on glucose for its function and survival. Hypoglycemia can have severe, irreversible consequences, including seizures, coma and death. However, the in vivo content of brain glycogen, the storage form of glucose, is meager and is a function of both neuronal activity and glucose concentration. In the intact in vitro hippocampus isolated from mice aged postnatal days 8-13, we have recently characterized a novel model of hypoglycemic seizures, wherein seizures were abolished by various neuroprotective strategies. We had hypothesized that these strategies might act, in part, by increasing cerebral glycogen content. In the present experiments, it was found that neither decreasing temperature nor increasing glucose concentrations (above 2 mM) significantly increased hippocampal glycogen content. Preparations of isolated frontal neocortex in vitro do not produce hypoglycemic seizures yet it was found they contained significantly lower glycogen content as compared to the isolated intact hippocampus. Further, the application of either TTX, or a cocktail containing APV, CNQX and gabazine, to block synaptic activity, did not increase, but paradoxically decreased, hippocampal glycogen content in the isolated intact hippocampus. Significant decreases in glycogen were noted when neuronal activity was increased via incubation with l-aspartate (500 muM) or low Mg(2+). Lastly, we examined the incidence of hypoglycemic seizures in hippocampi isolated from mice aged 15-19 and 22-24 days, and compared it to the incidence of hypoglycemic seizures of hippocampi isolated from mice aged 8-13 days described previously (Abdelmalik et al., 2007 Neurobiol Dis 26(3):646-660). It was noted that hypoglycemic seizures were generated less frequently, and had less impact on synaptic transmission in hippocmpi from PD 22-24 as compared to hippocampi from mice PD 15-19 or PD 8-13. However, hippocampi from 8- to 13-day-old mice had significantly more glycogen than the other two age groups. The present data suggest that none of the interventions which abolish hypoglycemic seizures increases glycogen content, and that low glycogen content, per se, may not predispose to the generation of hypoglycemic seizures.

Hypoglycemic seizures during transient hypoglycemia exacerbate hippocampal dysfunction

Severe hypoglycemia constitutes a medical emergency, involving seizures, coma and death. We hypothesized that seizures, during limited substrate availability, aggravate hypoglycemia-induced brain damage. Using immature isolated, intact hippocampi and frontal neocortical blocks subjected to low glucose perfusion, we characterized hypoglycemic (neuroglycopenic) seizures in vitro during transient hypoglycemia and their effects on synaptic transmission and glycogen content. Hippocampal hypoglycemic seizures were always followed by an irreversible reduction (>60% loss) in synaptic transmission and were occasionally accompanied by spreading depression-like events. Hypoglycemic seizures occurred more frequently with decreasing "hypoglycemic" extracellular glucose concentrations. In contrast, no hypoglycemic seizures were generated in the neocortex during transient hypoglycemia, and the reduction of synaptic transmission was reversible (<60% loss). Hypoglycemic seizures in the hippocampus were abolished by NMDA and non-NMDA antagonists. The anticonvulsant, midazolam, but neither phenytoin nor valproate, also abolished hypoglycemic seizures. Non-glycolytic, oxidative substrates attenuated, but did not abolish, hypoglycemic seizure activity and were unable to support synaptic transmission, even in the presence of the adenosine (A1) antagonist, DPCPX. Complete prevention of hypoglycemic seizures always led to the maintenance of synaptic transmission. A quantitative glycogen assay demonstrated that hypoglycemic seizures, in vitro, during hypoglycemia deplete hippocampal glycogen. These data suggest that suppressing seizures during hypoglycemia may decrease subsequent neuronal damage and dysfunction.

Altered residual ATP content in rat brain cortex subcellular fractions following status epilepticus induced by lithium and pilocarpine

Changes in residual ATP concentrations were investigated following subcellular fractionation of rat brain cortex after a prolonged period of status epilepticus induced by sequential administration of lithium and pilocarpine. After 2 h of continuous high-amplitude rapid spiking on EEG, we found significantly decreased levels of residual ATP in the homogenate and mitochondria fractions from status epilepticus rat brains compared to matched controls. No difference in residual ATP level was observed in the synaptosomal preparations of status epilepticus animals compared to controls. Inorganic phosphate concentration in the status animals was higher than controls in the cytosolic fraction only. F1-ATPase activity, an enzymatic indicator of mitochondrial ATP synthesis rate, was significantly higher in the status brains, whereas other mitochondrial enzymes were not different in the status and control rat groups. These findings, together with our earlier report of reduced synaptosomal ecto-ATPase activity, suggest that either the corresponding in vivo ATP concentrations were reduced as a result of status epilepticus or other biochemical changes had occurred that facilitated the hydrolysis of ATP following decapitation. Controls for and measurement of such other changes failed to provide an explanation for the observed changes in residual ATP.

Increase in extracellular glutamate caused by reduced cerebral perfusion pressure and seizures after human traumatic brain injury: a microdialysis study

OBJECT

To determine the extent and duration of change in extracellular glutamate levels after human traumatic brain injury (TBI), 17 severely brain injured adults underwent implantation of a cerebral microdialysis probe and systematic sampling was conducted for 1 to 9 days postinjury.

METHODS

A total of 772 hourly microdialysis samples were obtained in 17 patients (median Glasgow Coma Scale score 5+/-2.5, mean age 39.4+/-20.4 years). The mean (+/-standard deviation) glutamate levels in the dialysate were evaluated for 9 days, during which the mean peak concentration reached 25.4+/-13.7 microM on postinjury Day 3. In each patient transient elevations in glutamate were seen each day. However, these elevations were most commonly seen on Day 3. In all patients there was a mean of 4.5+/-2.5 transient elevations in glutamate lasting a mean duration of 4.4+/-4.9 hours. These increases were seen in conjunction with seizure activity. However, in many seizure-free patients the increase in extracellular glutamate occurred when cerebral perfusion pressure was less than 70 mm Hg (p < 0.001). Given the potential injury-induced uncoupling of cerebral blood flow and metabolism after TBI, these increases in extracellular glutamate may reflect a degree of enhanced cellular crisis, which in severe head injury in humans appears to last up to 9 days.

CONCLUSIONS

Extracellular neurochemical measurements of excitatory amino acids may provide a marker for secondary insults that can compound human TBI.

Effect of seizures on cerebral blood flow measured with 15O-H2O and positron emission tomography

To study quantitative alterations in regional cerebral blood flow (rCBF) accompanying seizures, and to assess the utility of ictal activation PET scanning as a noninvasive clinical tool for localization of epileptogenic foci, we used pentylenetetrazole (PTZ) to induce seizures during 15O-water positron emission tomography (PET) CBF measurement in 15 patients with uncontrolled complex partial seizures (CPS) who had been referred for surgical evaluation. Continuous EEG monitoring was performed during the PET scans. After baseline scans were obtained, each patient was injected with 150-300 mg PTZ. Two patients had generalized tonic-clonic seizures (GTCs). CBF increases were asymmetrical. Two patients (in 1 the seizure occurred spontaneously, without PTZ injection) who had CPS had bitemporal 70-80% increases in CBF. Thalamic CBF increased during both CPS and GTCS. Five patients had an increase in focal EEG interictal abnormality, accompanied by focal flow decreases in 3. PTZ injection not accompanied by clinical seizures did not increase CBF. Partial seizures may be associated with bilateral increases in CBF, and subcortical gray regions are involved in ictal activation.

The effects of malignant glioma on the EEG and seizure thresholds: an experimental study

Generalised or partial seizures are a common problem with many supratentorial gliomas. Their underlying pathophysiological mechanisms are poorly understood. To investigate this problem clinical and EEG seizure thresholds were investigated in experimental rodent gliomas using the epileptogenic drug pentylenetetrazole (PTZ). Mixed C6/A15A5 malignant gliomas were grown in adult Wistar rats after unilateral stereotactic implantation of a 50:50 cell mix into the caudoputaminal region. Eleven to 14 days later EEG (raw and spectrally analysed) was recorded bilaterally from the frontal and parietal regions under mixed alpha-chloralose and urethane anaesthesia. Baseline EEG (15 minutes), EEG during and after (30 minutes) PTZ infusion (100 microliters/min) and the time to appearance of seizure manifestations after starting PTZ were recorded. Fourteen animals were studied (5 normal, 5 with tumours, 4 sham implants) and mean BP, PaCO2, PaO2 and temperature were similar in the three groups. Baseline raw EEG showed predominate slow wave activity with lower amplitude and less spontaneous activity overlying tumours. Following PTZ infusion a sequence of vibrissal twitching (following a mean of 14.5 mg/kg PTZ in control and sham animals); jaw/nasal twitches (17.5 mg/kg); fore and hind limb jerking (46 mg/kg); myoclonic jerking (47 mg/kg); and status (77.5 mg/kg) was observed. The seizure thresholds for all PTZ induced seizure phenomena were, except for status epilepticus, highest in the tumour bearing animals. The time to 70% seizure activity on the EEG was also significantly longer in the tumour bearing animals. Spectral analysis of the EEG, although showing increased alpha and theta activity after PTZ infusion, did not discriminate between the three experimental groups either before or after PTZ activation. These studies have confirmed that experimental gliomas alter baseline EEG and both the EEG and behavioural response to PTZ. The reasons for the raised seizure threshold in the glioma bearing animals and the relevance of this experimental paradigm to human tumour associated epilepsy are discussed.

GABA metabolism in the substantia nigra, cortex, and hippocampus during status epilepticus

The metabolism of GABA and other amino acids was studied in the substantia nigra, the hippocampus and the parietal cortex of rats following microinjections of GAMMA-vinyl-GABA during status epilepticus induced by lithium and pilocarpine. GABA metabolism showed striking regional variations. In controls, both GABA concentration and rate of GABA synthesis were highest in the substantia nigra and lowest in cortex, as expected. In substantia nigra, status epilepticus resulted in a 2 1/2 fold decline in the rate of GABA synthesis and in a 307% increase in the turnover time of the GABA pool. In hippocampus, the rate of GABA synthesis was not altered significantly, but the turnover time of the GABA pool was 284% of controls, and the size of that pool increased to 208% of controls. By contrast, in cortex, where seizure activity is limited in this model, the rate of GABA synthesis increased to 230% of controls while pool size and turnover time did not change. Aspartate concentration decreased in all three brain regions. These data suggest that the observed reduction of the rate of GABA synthesis in substantia nigra could play a key role in seizure spread in this model of status epilepticus.

An experimental model of generalized seizures for the measurement of local cerebral glucose utilization in the immature rat. I. Behavioral characterization and determination of lumped constant

An experimental model of status epilepticus has been developed in the immature rat by administration of pentylenetetrazol (PTZ) using repetitive, timed intraperitoneal injections of subconvulsive doses. The pattern of behavioral signs has been well characterized in each age group, i.e. 10 (P10), 14 (P14), 17 (P17) and 21 postnatal days (P21). In this model, the dose of convulsant could be adjusted as a function of interindividual sensitivity and status epilepticus lated for quite a long duration to allow the measurement of local cerebral metabolic rates for glucose (LCMRglc) by means of the [14C]2-deoxyglucose method [J. Neurochem., 28 (1977) 897-916]. To estimate LCMRglc during status epilepticus, the lumped constant (LC) was re-calculated in controls and PTZ-treated rats. The control LC was 0.54 at P10 and 0.50-0.51 at the three older ages studied (P14, P17 and P21). During status epilepticus, it increased to 0.64 in P10 rats and decreased to 0.42 and 0.40, respectively, in P17 and P21 animals. At P14, LC was not affected by seizures. The measurements of brain lactate levels showed a large 4.5-10-fold increase in PTZ-treated rats as compared to controls at all ages. The results of the present study show that the immature brain responds to sustained seizure activity in a specific way according to its postnatal age. Moreover, our results underscore the necessity of re-calculation of LC to the quantification of LCMRglc in such pathological states, particularly in immature animals.

Correlation between carbohydrate and catecholamine level impairments in methionine sulfoximine epileptogenic rat brain

This work shows that the convulsant methionine sulfoximine induces an increase in glucose and glycogen levels and a parallel decrease in norepinephrine and dopamine levels in rat brain. Among the epileptogenic agents, methionine sulfoximine is known to have a glycogenic property in the central nervous system. The aim of this work is to look for the neurochemical mechanism underlying this property. For this, catecholamines, glucose, and glycogen were measured at the same time in different areas of the brain in rats submitted to methionine sulfoximine. The convulsant induced an increase in glucose and glycogen levels as previously described and a decrease in dopamine and norepinephrine levels in all the areas of the rat brain. These changes were roughly dose dependent. When L-dihydroxyphenylalanine and benserazide (a decarboxylase inhibitor) were administered with methionine sulfoximine, the latter failed to induce seizures in rat up to 8 h after dosing. Moreover, the glucose and glycogen amounts did not increase. In all these experiments, there was an obvious evidence of parallelism between seizures, increase in carbohydrate levels, and decrease in catecholamine levels. These results allow to conclude that the glycogenic property of methionine sulfoximine in the central nervous system probably results from its ability to decrease norepinephrine and dopamine levels. Because the effect of the convulsant on the catecholamine levels persisted for long, it is normal that glucose and glycogen levels increased during preconvulsive, convulsive and postconvulsive period. Methionine sulfoximine is probably glycogenic in rat brain because it decreases catecholamine levels for a long time.

Local cerebral glucose utilization during status epilepticus in newborn primates

The effect of bicuculline-induced status epilepticus (SE) on local cerebral metabolic rates for glucose (LCMRglc) was studied in 2-wk-old ketamine-anesthetized marmoset monkeys, using the 2-[14C]-deoxy-D-glucose autoradiographical technique. To estimate LCMRglc in cerebral cortex and thalamus during SE, the lumped constant (LC) for 2-deoxy-D-glucose (2-DG) and the rate constants for 2-DG and glucose were calculated for these regions. The control LC was 0.43 in frontoparietal cortex, 0.51 in temporal cortex, and 0.50 in thalamus; it increased to 1.07 in frontoparietal cortex, 1.13 in temporal cortex, and 1.25 in thalamus after 30 min of seizures. With control LC values, LCMRglc in frontoparietal cortex, temporal cortex, and dorsomedial thalamus appeared to increase four to sixfold. With seizure LC values, LCMRglc increased 1.5- to 2-fold and only in cortex. During 45-min seizures, LCMRglc in cortex and thalamus probably increases 4- to 6-fold initially and later falls to the 1.5- to 2-fold level as tissue glucose concentrations decrease. Together with our previous results demonstrating depletion of high-energy phosphates and glucose in these regions, the data suggest that energy demands exceed glucose supply. The long-term effects of these metabolic changes on the developing brain remain to be determined.

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.

Differential changes in the content of amino acid neurotransmitters in discrete regions of the rat brain prior to the onset and during the course of homocysteine-induced seizures

Changes in amino acid concentrations were investigated in selected regions of rat brain prior to the onset and during the course of epileptiform seizures induced by L-homocysteine. The concentration of gamma-aminobutyric acid (GABA) decreased preictally in substantia nigra (-18%), caudate putamen (-26%), and inferior colliculus (-46%). After seizure onset, the GABA content was further reduced in substantia nigra (-31%) and additionally in hippocampus (-18%). Preictal taurine levels were elevated in globus pallidus (+26%) and caudate putamen (+13%) but returned to normal after seizure onset. However, in hippocampus, taurine decreased both preictally (-22%) and after seizure onset (-56%). Glycine was reduced preictally only in globus pallidus (-13%). After seizure onset the direction of its concentration change varied in the brain regions studied. Glutamate levels decreased preictally in hippocampus (-10%) and hypothalamus (-46%) but increased in globus pallidus (+14%). Normal levels were detectable after seizure onset in hypothalamus and globus pallidus but a further reduction in hippocampus (-59%) and significant reductions in substantia nigra (-15%) and caudate putamen (-17%) were detected. Aspartate was elevated in hippocampus, both preictally (+49%) and after seizure onset (+21%) while at the same phases in globus pallidus a consistent reduction (-30%) was observed. The glutamine content increased preictally in globus pallidus (+41%) and hypothalamus (+36%), and in all brain areas during the ictal phase of seizure, the hippocampus exhibiting a dramatic increase (approximately 300%). The contents of serine and alanine were altered in most regions studied only after seizure onset, with the exception of the hippocampus, where a decrease (-41%) of serine was observed preictally.

Effects of two convulsant beta-carboline derivatives, DMCM and beta-CCM, on regional neurotransmitter amino acid levels and on in vitro D-[3H]aspartate release in rodents

Clonic seizures were induced in Swiss or DBA/2 mice by methyl-6-7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), 0.048 mmol/kg i.p., or by methyl-beta-carboline-3-carboxylate (beta-CCM), 0.044 mmol/kg i.p. Measurement of regional brain (cortex, hippocampus, striatum, and cerebellum) amino acid levels after 15 min of seizure activity showed increases in gamma-aminobutyric acid (GABA) (in all regions after beta-CCM, and in cortex and hippocampus after DMCM), and an increase in glycine in the striatum after beta-CCM. Aspartate levels fell (in cortex and hippocampus) after DMCM, but were unchanged in all regions after beta-CCM. Glutamate levels fell in cortex after beta-CCM and in striatum after DMCM. Pretreatment with the excitatory amino acid receptor antagonist, 2-amino-7-phosphonoheptanoic acid, 0.5 mmol/kg i.p., 45 min prior to the beta-carboline, significantly increased the ED50 for DMCM-induced clonic seizures (4.68 mumol/kg vs. 9.39 mumol/kg). Similar pretreatment did not significantly alter the ED50 for beta-CCM (4.22 mumol/kg vs. 6.6 mumol/kg). Pretreatment with 2-amino-7-phosphonoheptanoic acid, 1.0 mmol/kg, blocked the increase in GABA content produced by DMCM but not the fall in cortical aspartate content. Potassium-induced release of preloaded D-[3H]aspartate from rat cortical or hippocampal minislices was enhanced in the presence of DMCM (100 microM). In contrast, stimulated release of D-[3H]aspartate (from cortex or hippocampus) was not altered in the presence of beta-CCM (100 microM). Although DMCM and beta-CCM are both considered to induce convulsion by acting at the GABA--benzodiazepine receptor complex, the convulsions differ in several pharmacological and biochemical respects. It is suggested that enhanced release of excitatory amino acid neurotransmitters plays a more important role in seizures induced by DMCM.

In vivo phosphorus nuclear magnetic resonance spectroscopy in status epilepticus

Bicuculline-induced status epilepticus was studied in paralyzed rabbits ventilated with an oxygen and nitrous oxide mixture. An Oxford Instruments TMR 32-200 spectrometer was used to record phosphorus 31 nuclear magnetic resonance spectra of the in vivo brain. An array of conventional physiological variables including the electroencephalogram was simultaneously recorded. Several features were consistently observed during status epilepticus: (1) Phosphocreatine levels fell to about two-thirds of their control values and remained at that level despite a gradual decline in seizure activity; (2) intracellular pH declined and then remained constant, whereas seizure discharges declined; (3) adenosine triphosphate levels remained constant at their control values. These new, lower levels of brain phosphocreatine and intracellular pH were largely unaffected by increases in seizure activity brought about by elevation of blood pressure from levels too low to support adequate cerebral perfusion, by waning of anticonvulsant drug effect, or by repeated doses of bicuculline.

Cerebral metabolic responses to electroconvulsive shock and their modification by hypercapnia

Brain glucose metabolism was studied in paralyzed, ventilated rats given electroconvulsive shock (ECS) under normocapnic and hypercapnic conditions. Brains were obtained with a freeze-blowing apparatus. Rates of glucose utilization were determined with [2-14C]glucose and [3H]deoxyglucose as tracers. In normocapnic rats, ECS caused a large increase in the rate of glycolysis to 5--6 mumol/g/min. Brain lactate levels increased three- to fourfold. The stimulation of glucose metabolism was reflected in decreased brain glucose 6-phosphate concentration as early as 2--3 s after ECS. There were significant decreases in brain glucose and glycogen levels at 20 and 30 s after ECS. The decreases in endogenous brain glucose accounted for most of the increases in glucose utilization measured isotopically, implying that influx of glucose from blood into brain did not increase greatly over these time periods. Animals made hypercapnic by respiration with 10% CO2 for 2 min prior to ECS were different in their metabolic responses to ECS in several ways. The increases in glycolytic rate and lactate content of brain were half of those found in normocapnic rats. Brain glycogen and glucose concentrations did not change significantly in the hypercapnic rats during seizure activity. Thus, hypercapnia lessened the stimulation of glycolysis caused by ECS, but increased net influx of glucose from blood to brain. The mechanisms of these effects of hypercapnia are uncertain, but it is postulated that the effect on glycolytic activity is due to the acidosis and that the effect on glucose transport is due to an increase in capillary surface area.

Anticonvulsant activity of cyclopentano amino acids

The hypothesis that certain amino acid analogues possessing a five-membered ring structure or amino acid analogues that can be viewed as fragments derived from such a ring would have anticonvulsant activity was proposed and tested. The compounds 1-aminocyclopentane carboxylic acid, 1-amino-3-methylcyclopentane carboxylic acid, 3-aminotetrahydrothiophene carboxylic acid, and alpha-aminoisobutyric acid were found to protect rats against seizures in the maximal electroshock test but offered no protection against metrazol- (pentylenetetrazol) induced seizures in mice. The structural feature of this class of anticonvulsants that allows for hydrophobic interactions at the receptor site is considered to be a major physical factor necessary in promoting the activity of this class of anticonvulsants.

Cerebral metabolic and circulatory changes in the rat during sustained seizures induced by DL-homocysteine

Sustained, generalized seizure activity was induced in anaesthetized (70% N2O), paralyzed and artifically ventilated rats by i.p. DL-homocysteine thiolactone in a dose of 11 mmol/kg. Epileptic discharges in the EEG were accompanied by marked perturbation of tissue metabolites. There was a fall in phosphocreatine concentration to 40% of control but only moderate changes in adenine nucleotides, a marked rise in lactate concentration, and a pronounced increase in the lactate/pyruvate ratio. Excessive amounts of dihydroxyacetone phosphate (and glyceraldehyde phosphate) accumulated, indicating that depletion of NAD+ occurred. There was marked accumulation of ammonia, glutamine and alanine, and reduction in glutamate and aspartate concentrations. Administration of a subconvulsive dose of homocysteine (7.5 mmol/kg) gave rise to changes in ammonia and amino acids, qualitatively similar to those occurring during seizures. It is concluded that although changes in the metabolites of the energy reserve were mainly caused by the induced seizures, those affecting amino acid concentrations were significantly influenced by accumulation of ammonia, secondary to metabolism of injected homocysteine. Cerebral blood flow (CBF) and oxygen utilization (CMRO2) were measured during sustained seizures. CMRO2 rose to 150% of control, with a corresponding increase in CBF.

Effect of insulin-induced epileptic seizures on neutral glycolipids of rabbit cerebral cortex

The neutral glycolipids of rabbit central cortex were analyzed during epileptic seizures produced by insulin or pentetrazol injection. The two agents gave similar results. A decrease of glycolipid content occurred in the cortex and in the neuronal fraction during seizures. The normal glycolipid level was restored during the recovery phase.

Longitudinal changes of brain amino acid content occurring before, during and after epileptic activity

In cats affected with cortical epileptogenic foci induced by penicillin application to and cobalt implantation into the pericruciate area, the brain amino acids contents were determined in the focus as well as in extrafocal areas. In different groups of animals, brain removal for biochemical determinations was performed at different times before, during and after epilepsy and the values compared to controls. The only amino acid to show a significant change before appearance of spikes in both types of epilepsy was taurine, which decreased. Cobalt epilepsy was accompanied by changes in a larger number of amino acids than penicillin epilepsy: in the former the brain content of taurine, GABA, aspartate, glutamate, serine, threonine, glycine and alanine was altered. The changes were proportional to the severity of epilepsy and more prominent in the focus area. After disappearance of spikes the levels of most amino acids returned to normal except for some amino acids, previously unaffected by penicillin epilepsy, which were decreased. It is proposed that the decrease in brain taurine, occurring before the appearance of penicillin and cobalt epilepsy, could increase the excitability of a certain neuronal population and thus, by potentiating the effects on neurons of penicillin and cobalt, contribute to the initiation of epilepsy.