Development of a piglet model of status epilepticus: preliminary results

Mammalian models of status epilepticus - Their value and limitations

Status epilepticus (SE) is a medical and neurologic emergency that may lead to permanent brain damage, morbidity, or death. Animal models of SE are particularly important to study the pathophysiology of SE and mechanisms of SE resistance to antiseizure medications with the aim to develop new, more effective treatments. In addition to rodents (rats or mice), larger mammalian species such as dogs, pigs, and nonhuman primates are used. This short review describes and discusses the value and limitations of the most frequently used mammalian models of SE. Issues that are discussed include (1) differences between chemical and electrical SE models; (2) the role of genetic background and environment on SE in rodents; (3) the use of rodent models (a) to study the pathophysiology of SE and mechanisms of SE resistance; (b) to study developmental aspects of SE; (c) to study the efficacy of new treatments, including drug combinations, for refractory SE; (d) to study the long-term consequences of SE and identify biomarkers; (e) to develop treatments that prevent or modify epilepsy; (e) to study the pharmacology of spontaneous seizures; (4) the limitations of animal models of induced SE; and (5) the advantages (and limitations) of naturally (spontaneously) occurring SE in epileptic dogs and nonhuman primates. Overall, mammalian models of SE have significantly increased our understanding of the pathophysiology and drug resistance of SE and identified potential targets for new, more effective treatments. This paper was presented at the 9th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures held in April 2024.

Challenges and future directions of SUDEP models

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among patients with epilepsy, causing a global public health burden. The underlying mechanisms of SUDEP remain elusive, and effective prevention or treatment strategies require further investigation. A major challenge in current SUDEP research is the lack of an ideal model that maximally mimics the human condition. Animal models are important for revealing the potential pathogenesis of SUDEP and preventing its occurrence; however, they have potential limitations due to species differences that prevent them from precisely replicating the intricate physiological and pathological processes of human disease. This Review provides a comprehensive overview of several available SUDEP animal models, highlighting their pros and cons. More importantly, we further propose the establishment of an ideal model based on brain-computer interfaces and artificial intelligence, hoping to offer new insights into potential advancements in SUDEP research. In doing so, we hope to provide valuable information for SUDEP researchers, offer new insights into the pathogenesis of SUDEP and open new avenues for the development of strategies to prevent SUDEP.

The Extracellular Vesicle Citrullinome and Signature in a Piglet Model of Neonatal Seizures

Neonatal seizures are commonly associated with acute perinatal brain injury, while understanding regarding the downstream molecular pathways related to seizures remains unclear. Furthermore, effective treatment and reliable biomarkers are still lacking. Post-translational modifications can contribute to changes in protein function, and post-translational citrullination, which is caused by modification of arginine to citrulline via the calcium-mediated activation of the peptidylarginine deiminase (PAD) enzyme family, is being increasingly linked to neurological injury. Extracellular vesicles (EVs) are lipid-bilayer structures released from cells; they can be isolated from most body fluids and act as potential liquid biomarkers for disease conditions and response to treatment. As EVs carry a range of genetic and protein cargo that can be characteristic of pathological processes, the current study assessed modified citrullinated protein cargo in EVs isolated from plasma and CSF in a piglet neonatal seizure model, also following phenobarbitone treatment. Our findings provide novel insights into roles for PAD-mediated changes on EV signatures in neonatal seizures and highlight the potential of plasma- and CSF-EVs to monitor responses to treatment.

Intracranial electrophysiological recordings on a swine model of mesial temporal lobe epilepsy

Objective

To test the feasibility and reliability of intracranial electrophysiological recordings in an acute status epilepticus model on laboratory swine.

Method

Intrahippocampal injection of kainic acid (KA) was performed on 17 male Bama pigs (Sus scrofa domestica) weighing between 25 and 35 kg. Two stereoelectroencephalography (SEEG) electrodes with a total of 16 channels were implanted bilaterally along the sensorimotor cortex to the hippocampus. Brain electrical activity was recorded 2 h daily for 9-28 days. Three KA dosages were tested to evaluate the quantities capable of evoking status epilepticus. Local field potentials (LFPs) were recorded and compared before and after the KA injection. We quantified the epileptic patterns, including the interictal spikes, seizures, and high-frequency oscillations (HFOs), up to 4 weeks after the KA injection. Test-retest reliability using intraclass correlation coefficients (ICCs) were performed on interictal HFO rates to evaluate the recording stability of this model.

Results

The KA dosage test suggested that a 10 μl (1.0 μg/μl) intrahippocampal injection could successfully evoke status epilepticus lasting from 4 to 12 h. At this dosage, eight pigs (50% of total) had prolonged epileptic events (tonic-chronic seizures + interictal spikes n = 5, interictal spikes alone n = 3) in the later 4 weeks of the video-SEEG recording period. Four pigs (25% of total) had no epileptic activities, and another four (25%) had lost the cap or did not complete the experiments. Animals that showed epileptiform events were grouped as E + (n = 8) and the four animals showing no signs of epileptic events were grouped as E- (n = 4). A total of 46 electrophysiological seizures were captured in the 4-week post-KA period from 4 E + animals, with the earliest onset on day 9. The seizure durations ranged from 12 to 45 s. A significant increase of hippocampal HFOs rate (num/min) was observed in the E+ group during the post-KA period (weeks 1, 2,4, p < 0.05) compared to the baseline. But the E-showed no change or a decrease (in week 2, p = 0.43) compared to their baseline rate. The between-group comparison showed much higher HFO rates in E + vs. E - (F = 35, p < 0.01). The high ICC value [ICC (1, k) = 0.81, p < 0.05] quantified from the HFO rate suggested that this model had a stable measurement of HFOs during the four-week post-KA periods.

Significance

This study measured intracranial electrophysiological activity in a swine model of KA-induced mesial temporal lobe epilepsy (mTLE). Using the clinical SEEG electrode, we distinguished abnormal EEG patterns in the swine brain. The high test-retest reliability of HFO rates in the post-KA period suggests the utility of this model for studying mechanisms of epileptogenesis. The use of swine may provide satisfactory translational value for clinical epilepsy research.

An on demand macaque model of mesial temporal lobe seizures induced by unilateral intra hippocampal injection of penicillin

PURPOSE

Our objective was to propose a new on demand non-human primate model of mesial temporal lobe seizures suitable for pre-clinical innovative therapeutic research.

METHODS

Five macaques were stereotaxically implanted unilaterally with a deep recording electrode in the hippocampus. For each experiment, penicillin was injected into the hippocampus and animals were monitored during five consecutive hours. A total of 12-27 experiments with a mean cumulative dose of 162644 ± 70190 UI of penicillin have been performed per animal Injections were repeated at least once a week over a period of 98-276 days. The time-course of electro-clinical seizures and the response to diazepam have been quantified from, respectively, 84 and 11 experiments randomly selected. To evaluate brain injury produced by several penicillin injections and to characterize the changes occurring into the hippocampus, we performed an histological analysis, including neuronal nuclei and glial fibrillary acid protein immunostaining and electron microscopy.

RESULTS

After each penicillin injection, we observed that the electro-clinical characteristics were reproducible among non-human primates and experiments. Seizures duration was stable (29.60 ± 6.62 s) and the frequency of seizures reached a plateau with about 3 seizures/20 min during 180 min and that could be useful to test new treatments. Diazepam did not modify the course of the seizures. Hippocampal sclerosis was found similar to that encountered in epileptic patients with a neuronal loss and a glial cells proliferation. Electron microscopy analysis of CA1 revealed a decreased number of synapses and a large amount of glial fibrillary filaments in the injected hippocampus. Interestingly, this on-demand model of seizure, turned into a chronic model with spontaneous occurrence of seizures after a cumulative amount ranging from 119 to 145 KIU of penicillin injected.

CONCLUSION

The present study shows that an on-demand model of mesial temporal lobe seizure can be developed by intra-hippocampal injection of penicillin. The seizures are reproducible, stable and resistant to diazepam. Brain damages are confined to the hippocampus with similar features to that found in human mesial temporal lobe epilepsy. This model reproduces the symptomatogenic and the irritative zone usually seen in human MTLE, with the additional advantage of having a clear delineation of the epileptogenic zone. However, the mechanism of actions of the penicillin as a proconvulsant agent does not replicate all of the much more complex physiological and cellular mechanisms that are involved in human epilepsy and represent a limitation of our study that one must be aware of.

Swine model for translational research of invasive intracranial monitoring

Focal cortical epilepsy is currently studied most effectively in humans. However, improvement in cortical monitoring and investigational device development is limited by lack of an animal model that mimics human acute focal cortical epileptiform activity under epilepsy surgery conditions. Therefore, we assessed the swine model for translational epilepsy research. Swine were used due to their cost-effectiveness, convoluted cortex, and comparative anatomy. The anatomy has all the same brain structures as the human, and in similar locations. Focal subcortical injection of benzyl-penicillin produced clinical seizures correlating with epileptiform activity demonstrating temporal and spatial progression. Swine were evaluated under five different anesthesia regimens. Of the five regimens, conditions similar to human intraoperative anesthesia, including continuous fentanyl with low dose isoflorane, was the most effective for eliciting complex, epileptiform activity after benzyl-penicillin injection. The most complex epileptiform activity (spikes, and high frequency activity) was then repeated reliably in nine animals, utilizing 14 swine total. There were 20.1 ± 10.8 [95% confidence interval (CI) 11.8-28.4] epileptiform events with > 3.5 Hz activity occurring per animal. Average duration of each event was 46.3 ± 15.6 (95% CI 44.0-48.6) s, ranging from 20-100 s. In conclusion, the acute swine model of focal cortical epilepsy surgery provides an animal model that mimics human surgical conditions with a large brain and gyrated cortex, and is relatively inexpensive among animal models. Therefore, we feel this model provides a valuable, reliable, and novel platform for translational studies of implantable hardware for intracranial monitoring.

Swine models in the design of more effective medical countermeasures against organophosphorus poisoning

Although the three most commonly used large mammal species in the safety assessment of drugs remain the dog, the macaque and the marmoset, swine, especially minipigs, have also been widely used over the years in many toxicological studies. Swine present a number of interesting biological and physiological characteristics. Similarities in skin properties with humans have led to extensive in vitro and in vivo studies. There is a specific interest in cardiovascular research, as well as in anaesthesiology and critical care medicine due to common features of swine and human physiology. Although knowledge of swine brain structure and functions remains incomplete, data does exist. The multiple blood sampling that is necessary in pharmacokinetic and toxicokinetic studies are possible, as well as multiparametric monitoring and interventions with equipment used in human clinical settings. Practicality (handling), scientific (stress reduction) and ethical (invasive monitoring) reasons have led research teams to incorporate anaesthesia into their paradigms which makes the analysis of data increasingly difficult. Although not substantiated by scientific data, the swine appears to have an intermediate position in the scale of public perception between non-human primates and animals commonly referred to as pets (i.e. dogs and cats) and rodents. The benefits of the swine model justify the use of these animals in the design of more effective medical countermeasures against known chemical warfare agents (nerve agents, vesicants and lung damaging agents). Exposure to organophosphorus (OP) pesticides represents a severe health issue in developing countries, while OP intoxication with the more lethal military nerve agents is not only of military concern but also a terrorist threat. Tailoring therapeutic regimens to the reality of OP poisoning is of the utmost importance when little experimental data and sparse human clinical data are available in the decision making process. We will present some of the advantages and disadvantages of the swine model in OP countermeasures elaborating on two examples. First, we will present the issues related to the use of anaesthesia during experimental OP poisoning and second we will show how results from experiments with swine can be integrated into a kinetic-based dynamic model to evaluate oxime efficacy. A better knowledge of OP poisoning in swine (comparative toxicokinetics, pharmacokinetics and biochemistry) is definitely necessary before accepting it as a first choice non-rodent model. However, there exists a large amount of data in the model on anaesthesia and different types of shock favouring their use for evaluation of complex situations such as the anaesthesia of OP poisoned patients and combined injuries.

Analysis of respiratory mechanics by impulse oscillometry in non-sedated and diazepam-sedated swine

Analysis of respiratory mechanics using impulse oscillometry is applicable to sedated, or non-sedated (trained) pigs when they are fixed in a sling. In this study, the influence of the following sources of variability on measurement results was examined: (i) sedation with diazepam; (ii) body weight of animals (ranging in age: 40 to 102 days); and (iii) time of the measurement (circadian influences). The following parameters were examined: respiratory rate (RR), tidal volume (v(t)), spectral resistance, reactance and coherence, each at 5, 10, 15 and 20 Hz (R5,...R20, X5,...X20, CO5...CO20, respectively), distal respiratory resistance (Rdist), and proximal airway resistance (Rprox). After sedation (using 1.5 mg diazepam per kg body weight), RR and v(t) decreased significantly. There was a significant improvement of CO5, CO10 and CO15. Increase in body weight was strongly correlated to v(t), furthermore to spectral resistance parameters. Impulse oscillometry system (IOS) parameters showed only slight non-significant alterations in dependency on the time of day. In consequence, different sources of variability must be taken into account when performing IOS measurements in swine.

Central apnea and acute cardiac ischemia in a sheep model of epileptic sudden death

The etiology of sudden death in patients with epilepsy remains unclear. Previous studies in a well-established sheep model of status epilepticus showed that more than one-third of the unsedated animals died within 5 minutes of seizure onset due to hypoventilation. The relative contributions of airway obstruction and central hypoventilation could not be determined because airway flow and respiratory effort were not monitored. In this study, status epilepticus was induced in unsedated sheep with tracheostomies monitored by electrocardiography, electroencephalography, arterial line, serial blood gases, and airway flowmeter. All 8 animals demonstrated central apnea and hypoventilation, which resulted in the death of 1 and contributed to the death of another. A third animal died of acute heart failure within 2 minutes of seizure onset, accompanied by a large septal myocardial hemorrhage, contraction bands, and signs of global cardiac ischemia. More subtle contraction bands, subendocardial hemorrhage, and signs of acute myocardial ischemia were seen in other animals as well, none of which died of cardiac causes. Malignant arrhythmia was not seen in any of the sheep. Central hypoventilation and apnea accompany generalized status epilepticus and may be an important cause of sudden death in epileptics. Acute cardiac failure may also be a cause of epileptic sudden death.

Noninvasive capnometry monitoring for respiratory status during pediatric seizures

OBJECTIVE

To determine the reliability and clinical value of end-tidal CO2 by oral/nasal capnometry for monitoring pediatric patients presenting post ictal or with active seizures.

DESIGN

Clinical, prospective, observational study.

SETTING

University affiliated children's hospital.

INTERVENTIONS

One hundred sixty-six patients (105 patients with active seizures, 61 post ictal patients) had end-tidal CO2 obtained by oral/nasal sidestream capnometry, and respiratory rates, oxygen saturation, and pulse rates recorded every 5 mins until 60 mins had elapsed. End-tidal CO2 values were compared with a capillary PCO2 and clinical observation.

MEASUREMENTS AND MAIN RESULTS

The mean end-tidal CO2 reading was 43.0 +/- 11.8 torr [5.7 +/- 1.6 kPa] and the mean capillary PCO2 reading was 43.4 +/- 11.7 torr [5.7 +/- 1.6 kPa]. The correlation between end-tidal CO2 and capillary PCO2 was significant (r2 = .97; p < .0001). A relative average bias of 0.33 torr (0.04 kPa) with end-tidal CO2 lower than capillary PCO2 was established with 95% limits of agreement +/-4.2 torr (+/-0.6 kPa). Variability of difference scores was not related to range of mean scores (r2 = .00003), age (r2 = .0004), or respiratory rates (r2 = .0009). End-tidal CO2 (r2 = .22; p < .001) correlated better with respiratory rate changes when compared with oxygen saturation (r2 = .02; p = .01).

CONCLUSIONS

Dependable end-tidal CO2 values can be obtained in pediatric seizure patients using an oral/nasal cannula capnometry circuit. Continuous end-tidal CO2 monitoring provides the clinician with a reliable assessment of pulmonary status that can assist with decisions to provide ventilatory support.

General anesthetic techniques in swine

General anesthesia techniques for swine can be challenging due to the animal's temperament, anatomic traits, physical condition, and the environment in which the clinician may be working. Taking these factors into consideration, this article provides specific information on preanesthetic considerations, venous catheterization, drug selection, monitoring, perioperative complications and therapy, recovery, and analgesia.

Respiratory drive during status epilepticus and its treatment: comparison of diazepam and lorazepam

In order to examine the respiratory effects of tonic-clonic seizures and their treatment with i.v. diazepam or lorazepam, we utilized a spontaneously breathing piglet seizure model. A tracheostomy, arterial catheter, and epidural electrodes were inserted and pigs were maintained under ketamine anesthesia. After baseline recordings, seizures were induced with a pentylenetetrazol (PTZ) bolus and a 20 min infusion (5-6 mg/kg/min). After 10 min of PTZ infusion, randomly assigned animals received diazepam (D; N = 7; 0.5 mg/kg), lorazepam (L; N = 7; 0.2 mg/kg), or 0.9% saline (C; N = 7; controls) by rapid peripheral vein injection. Minute ventilation (Ve), Pa(CO2), and the pressure change in response to airway occlusion at end-expiration (P0.1) were measured at standard intervals. All groups had comparable increases in respiratory drive during untreated seizures. Changes in Ve and P0.1 were reduced to at or below baseline values in groups D and L, but not C, from 2 to 45 min after treatment (P < 0.05). No significant changes were observed in Pa(CO2) after either intervention. Following anticonvulsants, the cumulative duration of seizures was significantly reduced in L and D groups, compared to C (P < 0.05). We conclude that increases in respiratory drive occur during tonic-clonic seizures induced with PTZ. Amelioration of seizure activity with lorazepam or diazepam results in a reduction in respiratory drive, but not respiratory failure, in this tracheostomized model.

Effects of bicuculline on inspiratory activities in piglets

Antagonism of the alpha receptor sub-type at gamma-aminobutyric acid (GABA) recognition sites in developing pigs was evaluated using the GABAA receptor antagonist bicuculline. The effect of bicuculline infusions was to produce an increase of phrenic and hypoglossal discharge amplitudes. This bicuculline-induced effect on discharge amplitude was manifested in autopower spectra as an increase in the power of peaks located in the medium-frequency (10-50 Hz) band. More importantly, coherence estimates were increased by bicuculline administration demonstrating GABA-mediated influences on a central pattern generator with output in the 10-50 Hz band.

A piglet model of status epilepticus: comparison of cardiorespiratory and metabolic changes with two methods of pentylenetetrazol administration

STUDY OBJECTIVE

Impaired cardiac and respiratory responses during active tonic-clonic convulsions (ictal periods) may contribute to complications during seizures. This study characterized physiologic parameters in two pentylenetetrazol (PTZ)-induced seizure models.

PARTICIPANTS

Twelve spontaneously breathing piglets.

INTERVENTIONS

Under ketamine anesthesia, a tracheostomy was performed, and an arterial catheter and epidural electrodes were inserted. Piglets received a PTZ bolus (100 mg/kg), with (six; 5 mg/kg/min) or without (six) an infusion of PTZ for 20 minutes.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases, mean arterial pressure, heart rate, tidal volume, and EEG waveforms were measured. Ictal periods had high-amplitude, synchronized EEG activity; interictal periods had EEG suppression. Seizure duration (24 +/- 3.5 versus 11 +/- 3.8 minutes; mean +/- SD) was significantly increased in the infusion group (P < .05). Significant increases in heart rate, minute ventilation, and base deficit plus decreases in pH occurred in both groups during seizures compared with baseline (P < .05). The duration and severity of metabolic acidosis were greater in the infusion group. During the first ten minutes of seizures, ten-second epochs were compared: beginning of ictal period, end of same ictal period, beginning of accompanying interictal period, and end of same interictal period. Respiratory rate decreased during initial interictal (65 +/- 40) more than latter ictal more than latter interictal period, compared with initial ictal period (194 +/- 65; P < .001). Tidal volume increased during latter ictal more than latter interictal more than initial ictal period (33 +/- 11), but the greatest increases occurred during initial interictal period (140 +/- 55; P < .001).

CONCLUSION

This model demonstrates significant increases in the duration and various measures of seizure severity in piglets given a PTZ infusion compared with those receiving a bolus alone. Systematic alterations in respiratory but not cardiac responses occur during ictal-interictal cycling of PTZ-induced seizures.