A New Rat Model of Epileptic Spasms Based on Methylazoxymethanol-Induced Malformations of Cortical Development

Abstract

Malformations of cortical development (MCDs) can cause medically intractable epilepsies and cognitive disabilities in children. We developed a new model of MCD-associated epileptic spasms by treating rats prenatally with methylazoxymethanol acetate (MAM) to induce cortical malformations and postnatally with N-methyl-d-aspartate (NMDA) to induce spasms. To produce cortical malformations to infant rats, two dosages of MAM (15 mg/kg, intraperitoneally) were injected to pregnant rats at gestational day 15. In prenatally MAM-exposed rats and the controls, spasms were triggered by single (6 mg/kg on postnatal day 12 (P12) or 10 mg/kg on P13 or 15 mg/kg on P15) or multiple doses (P12, P13, and P15) of NMDA. In prenatally MAM-exposed rats with single NMDA-provoked spasms at P15, we obtain the intracranial electroencephalography and examine the pretreatment response to adrenocorticotropic hormone (ACTH) or vigabatrin. Rat pups prenatally exposed to MAM exhibited a significantly greater number of spasms in response to single and multiple postnatal NMDA doses than vehicle-exposed controls. Vigabatrin treatment prior to a single NMDA dose on P15 significantly suppressed spasms in MAM group rats (p < 0.05), while ACTH did not. The MAM group also showed significantly higher fast oscillation (25–100 Hz) power during NMDA-induced spasms than controls (p = 0.047). This new model of MCD-based epileptic spasms with corresponding features of human spasms will be valuable for future research of the developmental epilepsy.

In vivo MRI Successfully Reveals the Malformation of Cortical Development in Infant Rats

“…On the basis of these pathological findings, we also tested whether the MCDs in infancy can be diagnosed through in vivo imaging techniques in clinical settings. We observed a quantifiable reduction in RSC length and whole-brain length, as previously shown in this model (Kim et al, 2017), which are potential biomarkers of FCD in clinical settings (Figures 5A-C). A new imaging technique involving glutamate measurement, GluCEST imaging, also revealed significantly decreased glutamate in the RSC, and 1H-MRS analysis supported this finding by showing a significant reduction in glutamate and glutamate-plus-glutamine in the RSC (Figures 2B, 5D,E).…”

“…Various animal models of MCDs have been used for translational research (Kuzniecky, 2015;Luhmann, 2016), and the methylazoxymethanol (MAM) model is one of them. The offspring of MAM-treated rats are affected by developmental brain abnormalities similar to those observed in patients with MCDs (Chevassus-Au-Louis et al, 1999;Colacitti et al, 1999;Luhmann, 2016;Kim et al, 2017). Previously, our group reported in vivo anatomical disruption as well as increased spasm susceptibility, cognitive impairment, and abnormal cortical electrical activities in this MAM-induced MCD rat model (Kim et al, 2017).…”

“…Although neocortical structures in the early developmental period have not been extensively investigated in this rat model, the altered firing properties of their neuronal subpopulations at 3-7 weeks of age and abnormal neocortical electrical activities at P15 have been reported (Chevassus-Au-Louis et al, 1998;Kim et al, 2017). To demonstrate the abnormal neocortical neuronal migration at early stages, we selected the RSC for pathological investigation in this study.…”

“…In particular, MCDs are the most common cause of pediatric intractable epilepsy (Barkovich et al, 2015;Iffland and Crino, 2017;Kim et al, 2017), and epilepsy surgery is the only curative treatment option because of the poor response to anticonvulsant drugs (Colciaghi et al, 2011;Barkovich et al, 2015). However, in clinical settings, localization of MCDs for epilepsy surgery is not always possible with current imaging techniques, especially in infants or in individuals with small focal cortical dysplasia (FCD).…”

In Vivo Multimodal Magnetic Resonance Imaging Changes After N-Methyl-d-Aspartate-Triggered Spasms in Infant Rats

“…Tone conditioning was conducted on P27. Modified from a previous report ( 22 ), the conditioning consisted of a 3-min baseline habituation in the experimental chambers, followed by exposure to five pairings of a tone (conditioned stimulus; 30 s, 85 dB, 2,000 Hz) with white-light illumination, each ending with a final footshock (unconditioned stimulus; 0.8 mA, 2.0 s) followed by a 20-s silent interval. Response to the context was monitored on P28 (24 h after the conditioning trial).…”