Ganglioside receptors and induction of epileptiform activity: Cholera toxin and choleragenoid (B subunits)

The intracortical injection of cholera toxin caused recurrent epileptiform activity as recorded in the EEG of the rat. Because choleragenoid (B subunit) also induces epileptiform activity, we conclude that the induction of the epileptic discharges results from the primary action of binding to GM1 ganglioside receptors and not from the stimulation of endogenous adenylate cyclase.     

Cellular and synaptic basis of kainic acid-induced hippocampal epileptiform activity

The effects of kainic acid (KA) were studied using extracellular and intracellular recordings in the hippocampal slice preparation. In sufficient concentrations, KA led to a loss of all evoked responses. However, the amount of drug needed for this varied according to anatomic region. CA3 was more sensitive (1 microM) than CA1 or the dentate gyrus (10 microM). These results can be understood in terms of a profound and long-lasting depolarization of neurons. Lower concentrations of KA (0.05-0.1 microM) did not change the resting membrane potential or input resistance of hippocampal pyramidal cells but produced spontaneous epileptiform activity which originated in CA3 and propagated to CA1. Epileptiform discharges were not present in the dentate gyrus. Coincident with the induction of paroxysms, the following changes were observed: (1) an increase in the excitability of CA3 and CA1 pyramidal cells as measured by a left shift in the input-output curves of evoked responses and a lowered threshold stimulus intensity necessary for activation of action potentials in single neurons; (2) augmentation and synchronization of bursting in pyramidal cells; and (3) prolonged EPSPs without an increase in their amplitude. These findings indicate that multiple changes, involving both the properties of single neurons and synaptic connections, are involved in the development of hippocampal paroxysms and that CA3 and CA1 have different roles in the generation of these discharges.     

Memory deficits in an experimental hippocampal epileptiform syndrome in rats

Rats were trained on a light-discrimination task in a Y maze and 7 days later their hippocampi were injected bilaterally with about 5 mouse LD₅₀ of tetanus toxin. This leads to an epileptiform syndrome, in which the animals are hyperreactive and have complex partial seizures for about 4 weeks. When the rat's memories for the Y maze task were tested either 1, 4, 7, or 9 weeks after induction of the epilepsy, they were found to be impaired. The epilepsy thus caused amnesia both when the animals were epileptic and also at a time when the animals were no longer epileptic. It was also found, in another experiment, that similar partial amnesia at 7 weeks after operation was found whether the toxin injection was carried out 20 min, 1 day, or 1 week after initial training. Thus the susceptibility of the memory to disruption by the epilepsy was not dependent on the age of the memory. It is proposed that the amnesia found in this animal model of hippocampal epilepsy is relevant to the important question of whether memory impairments in patients with temporal lobe epilepsy are caused by the epilepsy itself or are side effects of anticonvulsant medication.     

Propagation of focal cortical epileptiform discharge to the entopeduncular nucleus: Effect of caudate lesions

Single-unit recordings were made in the entopeduncular nucleus of cats which had previously undergone ipsilateral caudate lesions. During penicillin-induced epileptiform discharge from the pericruciate cortex, the percentage of responsive entopeduncular neurons in animals with a lesion was less than 20%. In a previous study in intact cats and in control experiments in the present study the percentage of responsive entopeduncular cells was more than 75%. These results indicate that propagation of epileptic discharge through the basal ganglia depends on intact pathways from the cortex to the caudate and from the caudate to the entopeduncular nucleus.     

Effect of antiepileptic drugs and an anticonvulsant on epileptiform activity induced by antibodies to ganglioside

An immunological model of epilepsy in the rat was tested for its response to three antiepileptic drugs (phenytoin, ethosuximide, diazepam) and one anticonvulsant drug (aminooxyacetic acid). The immunologic model was produced by injection of antiganglioside serum into the sensorimotor cortex. The response in the immunologic model to these drugs was compared with that on epileptic activity induced by the implantation of cobalt powder. The two models behaved very differently with respect to the four drugs. The antiganglioside serum model responded with reduced spike frequency to phenytoin and ethosuximide but not to diazepam or aminooxyacetic acid. The cobalt powder model responded to ethosuximide, diazepam, and aminooxyacetic acid but not to phenytoin. The study concludes that the epileptiform activity induced by antibodies to ganglioside is reduced by antiepileptic drugs, and that the immunologic model differs markedly from the cobalt model in its responsiveness to antiepileptic drugs.     

Effect of temperature on kainic acid-induced seizures

The effects of body temperature on kainic acid-induced seizures and seizure-related brain damage were examined in rats. In rats with status epilepticus induced by intraperitoneal injection of 12 mg/kg of kainic acid (KA), ictal discharges were decreased by 50% when body temperature was lowered to 28°C and nearly abolished when body temperature was lowered to 23°C. In rats with mild hypothermia (28°C), the duration of ictal discharges following KA injection was significantly lower than in rats with normal body temperature. No detectable hippocampal cell loss was observed in rats with hypothermia to 28°C whereas gross cell loss in the hippocampus was observed in all rats with KA injection at normal body temperature. In contract to hypothermia, hyperthermia markedly aggravated the seizures and hippocampal damage induced by KA. Following elevation of body temperature to 42°C KA (12 mg/kg) resulted in severe seizures and all rats died of tonic seizures within 2 h. Furthermore, 6 mg/kg of KA administered to rats with a body temperature of 41–42°C, resulted in up to 4 h of continuous ictal discharges whereas no continuous ictal discharges were observed after the same injections in rats with normal body temperature. Histological examination in rats receiving 6 mg/kg of KA revealed severe cell loss in the hippocampus in rats with hyperthermia but not in rats with normal temperature. These results demonstrate that body temperature plays an important role in the control of epileptic seizures and seizure-related brain damage. These data suggest that hypothermia may be useful in reducing seizures and associated brain damage and that hyperthermia should be avoided in status epilepticus.     

Prognostic interictal electroencephalographic biomarkers and models to assess antiseizure medication efficacy for clinical practice: A scoping review

Antiseizure medication (ASM) is the primary treatment for epilepsy. In clinical practice, methods to assess ASM efficacy (predict seizure freedom or seizure reduction), during any phase of the drug treatment lifecycle, are limited. This scoping review identifies and appraises prognostic electroencephalographic (EEG) biomarkers and prognostic models that use EEG features, which are associated with seizure outcomes following ASM initiation, dose adjustment, or withdrawal. We also aim to summarize the population and context in which these biomarkers and models were identified and described, to understand how they could be used in clinical practice. Between January 2021 and October 2022, four databases, references, and citations were systematically searched for ASM studies investigating changes to interictal EEG or prognostic models using EEG features and seizure outcomes. Study bias was appraised using modified Quality in Prognosis Studies criteria. Results were synthesized into a qualitative review. Of 875 studies identified, 93 were included. Biomarkers identified were classed as qualitative (visually identified by wave morphology) or quantitative. Qualitative biomarkers include identifying hypsarrhythmia, centrotemporal spikes, interictal epileptiform discharges (IED), classifying the EEG as normal/abnormal/epileptiform, and photoparoxysmal response. Quantitative biomarkers were statistics applied to IED, high-frequency activity, frequency band power, current source density estimates, pairwise statistical interdependence between EEG channels, and measures of complexity. Prognostic models using EEG features were Cox proportional hazards models and machine learning models. There is promise that some quantitative EEG biomarkers could be used to assess ASM efficacy, but further research is required. There is insufficient evidence to conclude any specific biomarker can be used for a particular population or context to prognosticate ASM efficacy. We identified a potential battery of prognostic EEG biomarkers, which could be combined with prognostic models to assess ASM efficacy. However, many confounders need to be addressed for translation into clinical practice.     

Rapid antiepileptic drug withdrawal may obscure localizing information obtained during presurgical EEG recordings

Withdrawal of antiepileptic drugs (AEDs) is a standard procedure during presurgical epilepsy assessment. Rapid and, at times, even pre‐hospital withdrawal of medication is performed in some centres to enhance the yield of recorded seizures during video‐EEG monitoring. AED withdrawal, however, affects the propensity and speed of propagation of epileptic activity, may evoke more severe seizures, and may cause pitfalls in EEG interpretation. We report a case which had been recommended to undergo intracranial EEG recordings in order to clarify apparently discordant MRI findings and ictal EEG patterns when monitoring was performed following complete AED withdrawal. Re‐evaluation to assess scalp EEG patterns at several drug levels during slow AED tapering showed a loss of localizing information with AED withdrawal due to contralateral and bitemporal spread of frontal epileptic activity. Our report demonstrates that in individual cases, rapid AED withdrawal during presurgical video‐EEG monitoring can impair the validity of EEG recordings and lead to unnecessary risks and investigations during workup.     

Sparing of rhythmic slow activity (RSA or theta) in two hippocampal generators after kainic acid CA3 and CA4 lesions

The contribution of the CA3 and CA4 fields of the hippocampus to hippocampal rhythmical slow activity (RSA or theta rhythm) was examined in freely moving or anesthetized rats. The pyramidal cells in CA3-CA4 were selectively destroyed unilaterally and bilaterally by means of intrahippocampal injections of 0.1 μg kainic acid at several sites. Immediately after the cessation of kainic acid-induced epileptiform activity and for longer than 30 days thereafter, RSA amplitude and frequency were normal. Hippocampal depth profiles with microelectrodes in urethane-anes-thetized rats and EEG recordings in freely moving undrugged and atropine-drugged rats conducted after kainic acid injections revealed that RSA amplitudes, frequency, loci of maxima and null zones, and phase coupling between the dorsal and ventral generators were all normal despite virtually complete removal of the CA3-CA4 fields. Both the atropine-resistant and atropine-sensitive forms of RSA were also present. These results suggest that transmission through the basic hippocampal circuit involving the CA3 pyramidal cells is not necessary for the maintenance of normal hippocampal RSA. The synchronous input to both generators possibly from the medial septum and entorhinal cortex is sufficient to maintain normal RSA types, frequency, and phase coupling.     

Convulsive activity in gerbils subjected to cerebral ischemia.

Convulsive activity observed in the mongolian gerbil following carotid artery occlusion is of extracerebral origin. The clinical discharge is demonstrated to be primarily in the spinal cord.     

Postnatal challenge dose of methamphetamine amplifies anticonvulsant effects of prenatal methamphetamine exposure on epileptiform activity induced by electrical stimulation in adult male rats

Administration of psychostimulants is often associated with increased seizure susceptibility. In our previous studies prenatal methamphetamine (MA) exposure increased seizure susceptibility of adult rats in models of primarily or secondarily generalized seizures induced by convulsant drugs. The effect of a single MA challenge dose in adulthood on chemically induced generalized seizures however, depends on the prenatal MA exposure history. Thus, the present study used a model of focal electrical stimulation to determine whether prenatal MA exposure with or without the adult challenge MA dose has the same outcome in a focal seizure model. Total of six groups of adult male rats were tested (prenatally MA-exposed, prenatally saline-exposed and rats without prenatal injections), each of these groups was either postnatally challenged with MA or with vehicle injection (MA-MA, MA-S; S-MA, S-S; C-MA, C-S). Seizures were induced by repetitive electrical stimulation (15 s/8 Hz) of sensorimotor cortex. Stimulation threshold, duration of afterdischarges (ADs), and presence and duration of spontaneous ADs (SAD) were evaluated. Additionally, behaviors associated with stimulation and ADs, and occurrence of wet-dog shakes (WDS) were analyzed. Our data demonstrate that daily injection of MA (5 mg/kg) within prenatal period decreased the occurrence of WDS and SADs, and shortened the duration of ADs and SADs suggesting anticonvulsant effects. Moreover, the challenge dose of MA (1 mg/kg) increased seizure threshold in all groups of rats, shortened duration of ADs in controls and prenatally saline-exposed animals, shortened duration of SADs in prenatally saline-exposed rats and totally eliminated WDS in all groups. Thus, the present study demonstrates that both chronic prenatal MA exposure and a single dose of MA in adulthood decrease focally induced epileptiform activity in adult male rats.     

Teratogenicity of the newer antiepileptic drugs - the Australian experience

Data on the use in pregnancy of the new antiepileptic drugs (AED) are limited. We analysed data collected by the Australian Pregnancy Register to provide information on their relative teratogenicity. The database containing pregnancy outcomes from 1317 women with epilepsy (WWE) was examined for three widely used new AED in monotherapy in the first trimester - lamotrigine, levetiracetam and topiramate. This was compared with outcomes of pregnant WWE on monotherapy with three traditional AED, and with untreated women. The incidence of malformations associated with lamotrigine monotherapy was 12/231 (5.2%), with topiramate 1/31 (3.2%) and with levetiracetam 0/22 (0%). This compares with rates of 1/35 (2.9%) for phenytoin, 35/215 (16.3%) for valproate (VPA), 19/301 (6.3%) for carbamazepine and 6/116 (5.2%) for untreated women. There was no evidence of dose-dependent risks of foetal malformation, except with VPA monotherapy. We conclude that the new AED appear no more teratogenic than traditional drugs in monotherapy.     

Electrophysiological effects of guanosine and MK-801 in a quinolinic acid-induced seizure model

Quinolinic acid (QA) is an N-methyl-d-aspartate receptor agonist that also promotes glutamate release and inhibits glutamate uptake by astrocytes. QA is used in experimental models of seizures studying the effects of overstimulation of the glutamatergic system. The guanine-based purines (GBPs), including the nucleoside guanosine, have been shown to modulate the glutamatergic system when administered extracellularly. GBPs were shown to inhibit the binding of glutamate and analogs, to be neuroprotective under excitotoxic conditions, as well as anticonvulsant against seizures induced by glutamatergic agents, including QA-induced seizure. In this work, we studied the electrophysiological effects of guanosine against QA-induced epileptiform activity in rats at the macroscopic cortical level, as inferred by electroencephalogram (EEG) signals recorded at the epidural surface. We found that QA disrupts a prominent basal theta (4–10 Hz) activity during peri-ictal periods and also promotes a relative increase in gamma (20–50 Hz) oscillations. Guanosine, when successfully preventing seizures, counteracted both these spectral changes. MK-801, an NMDA-antagonist used as positive control, was also able counteract the decrease in theta power; however, we observed an increase in the power of gamma oscillations in rats concurrently treated with MK-801 and QA. Given the distinct spectral signatures, these results suggest that guanosine and MK-801 prevent QA-induced seizures by different network mechanisms.     

Peri‐ictal headache due to epileptiform activity in a disconnected hemisphere

A 4‐year‐old girl with intractable epilepsy due to left‐side hemispheric cortical dysplasia underwent a hemispherotomy. She was seizure‐free after the surgery. EEG showed persistent abundant epileptiform activity over the left (disconnected) hemisphere, including ictal patterns that neither generalised nor had clinical correlates. Antiepileptic medication was completely withdrawn four years following the surgery. One week after the withdrawal, she developed episodes of intense left‐sided hemicranias (ipsilateral to the surgery) with vomiting and photophobia that did not resemble her habitual seizures and were unresponsive to non‐steroidal anti‐inflammatory drugs. Video‐EEG showed association of the headache attacks with ictal patterns over the disconnected hemisphere. Brain MRI revealed increased signal changes in the left hemisphere. Attacks responded promptly to i.v. midazolam and carbamazepine at a low dose. Mechanisms underlying peri‐ictal headache originating in the disconnected hemisphere are discussed. [Published with video sequences]     

Suppression of epileptiform activity by increased intracranial pressure in cat.

This study investigated the relationships between changes in intracranial pressure and the activity of cortical epileptogenic foci in cats. Epileptiform spiking was produced by focal freezing and/or topical application of penicillin. Increases in intracranial pressure were produced by infusion of mock cerebrospinal fluid into the cisterna magna. We found that increases in intracranial pressure always produced decreases in epileptiform spike discharge rate. Some preparations also showed an enhancement or “rebound” of spike discharge rate soon after the intracranial pressure was returned to normal. We concluded that it is unlikely that compression or distortion of cerebral tissue play any role in these results. Decreases in cerebral blood flow may be a factor but only for the higher values of intracranial pressure in the less sensitive preparations. We suggest that the most important mechanism responsible for these findings is the desynchronizing effect of afferent input related to increased intracranial pressure. The source of this sensory activity may be from receptors in the cerebrospinal meninges and blood vessels.     

Effect of barbiturate on epileptiform activity: comparison between intravenous and oral administration

The present study was performed in order to compare: 1) the differences between oral and intravenous barbiturate on interictal epileptiform activity (sharp-waves and spikes) in the EEG, and 2) interictal epileptiform activity in the sphenoidal electrode compared to the temporal and zygomatic electrodes (an electrode placed at the cutaneous entry of the sphenoidal electrode) during intravenous barbiturate administration in patients with epilepsy. Two procedures were performed: 1) an oral pentobarbital sleep induction with 10–20 electrode placement including a zygomatic electrode, and 2) an intravenous thiopental sleep induction with the same electrode placement including a sphenoidal electrode. Thirty eight patients with complex partial seizures were included. During the oral pentobarbital procedure 34 of 38 (90%) patients showed interictal epileptiform activity compared with 22 of 38 (55%) patients during the intravenous thiopental procedure (p<0.005). A interictal epileptiform focus was observed in 33 (87%) patients in the oral procedure and in 19 (50%) patients in the intravenous procedure (p<0.01). Interictal epileptiform activity recorded in the sphenoidal electrode was also recorded in the zygomatic electrode. Except from two patients a good correlation was observed between the zygomatic electrodes and the F7/F8 electrodes. We conclude that administration of intravenous thiopental offers no advantage compared to the administration of oral pentobarbital as an activating procedure, and for standard interictal EEG recordings with sleep activation procedures, suitable places scalp electrodes including a zygomatic electrode with the use of oral pentobarbital may be sufficient.     

Pharmacological monitoring of antiepileptic drugs in epilepsy patients on haemodialysis

Aims: To retrospectively evaluate the pharmacological profiles of antiepileptic drugs (AEDs) in epilepsy patients during haemodialysis using therapeutic drug monitoring data. Methods: The serum concentration of AEDs was collected before and after haemodialysis, and the clearance rate and concentration‐to‐dose ratio were calculated as pharmacological parameters. Results: Thirty‐six patients were enrolled in the study (25 males, 11 females; age: 65.3 ± 14.8 years). In 24 of the 36 patients, epilepsy was associated with cerebrovascular disorders, and diabetes was the most common reason for haemodialysis in 16 patients. With regards to seizure type, focal aware seizures were less frequent than focal impaired awareness seizures and focal‐to‐bilateral tonic‐clonic seizures. Interictal EEG showed intermittent rhythmic slow waves and intermittent slow waves more often than spikes or sharp waves. Levetiracetam was the most commonly used AED and led to the highest percentage of responders (80%; 16/20 patients). However, the clearance rate of levetiracetam during dialysis was highest among the antiepileptic drugs used, requiring supplementary doses after haemodialysis in all 20 patients. Valproic acid was not effective for focal epilepsy for patients on haemodialysis, and non‐responders to phenytoin had low serum concentration of phenytoin both before and after haemodialysis. The pre‐haemodialysis concentration of levetiracetam tended to be higher than the reference range, suggesting a potential risk of overdosing before haemodialysis. The pre‐ and post‐haemodialysis concentrations of valproic acid tended to be lower than the reference range, suggesting a potential risk of underdosing. The concentration‐to‐dose ratios for levetiracetam, valproic acid, phenytoin, and carbamazepine were significantly lower after than before haemodialysis. Conclusions: The majority of patients with epilepsy on haemodialysis had cerebrovascular diseases, and therapeutic drug monitoring for levetiracetam, valproic acid, and phenytoin, before and after haemodialysis, is needed to ensure proper dosing.