Neuropathogical features of a rat model for perinatal hypoxic‐ischemic encephalopathy with associated epilepsy

Abstract

Hypoxic-ischemic (HI) encephalopathy is an important neurological problem of the perinatal period. Little is known of the long-term progression of HI insults or the maladaptive changes that lead to epilepsy. Using rats with unilateral carotid occlusion followed by hypoxia at postnatal day 7, this study provides an initial analysis of the epilepsy caused by a perinatal HI insult with chronic and continuous behavioral monitoring. The histopathology was investigated at postnatal day 30 and later at ≥6 months of age using cresyl violet, Timm, and rapid Golgi staining and immunocytochemistry. The resultant epilepsy showed an increase in seizure frequency over time, with a preponderance for seizure clusters and behavioral features of an ipsilateral cerebral syndrome. In addition to parasagittal infarcts and porencephalic cysts in severe lesions, columnar neuronal death was found with cytomegaly in isolated groups of dysmorphic cortical neurons. Cortical dysgenesis was seen in the form of deep laminar cell loss, microgyri, white matter hypercellularity, and blurring of the white and gray matter junction. Mossy fiber sprouting was not only detected in the atrophied ipsilateral dorsal hippocampus of HI rats with chronic epilepsy, but was also found in comparable grades in spared ipsi-and contralateral ventral hippocampi. The cortical lesions in this animal model show histological similarities with those found in humans after perinatal HI. The occurrence of cortical abnormalities that are associated with epilepsy in humans correlates with the consequent detection of spontaneous recurrent seizures. Indexing termsanimal model; seizure clustering; cortical dysplasia; microgyri; porencephaly; dual pathology Hypoxic-ischemic (HI)-induced perinatal encephalopathies are the major cause of acute mortality and chronic neurologic morbidity, such as in epilepsy (Bergamasco et al., 1984;Aso et al., 1990;Lanska et al., 1991;Volpe, 2001;Ramaswamy et al., 2004). The multifactorial causative factors range from prematurity, low birth weight, traumatic/ prolonged labor, asphyxia, coagulation abnormalities, severe systemic cardiovascular hypotension, respiratory disorders, and maternal and fetal infections in the perinatal period HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript (Courville, 1959;Golomb et al., 2001;Scher et al., 2002;Cowan et al., 2003;Nelson and Lynch, 2004). Refractory epilepsy is a common sequela (≈30%) in children who survive such insults (Marin-Padilla, 2000a). Autopsy and surgically resected neocortical tissues have revealed dysplasias and abnormal neuronal morphologies, which are thought to underlie the abnormal electrophysiological properties recorded during intraoperative and in vitro slice studies (Palmini et al., 1994;Avoli et al., 1999;Burneo et al., 2004;Najm et al., 2004;Calcagnotto et al., 2005;Matsumoto et al., 2005). A strong association has been found between disorders of cortical development and medically refractory epilepsy in children (Mischel et al., 1995...

Effects of neonatal hypoxic-ischemic episodes on late seizure outcomes in C57 black mice

“…The ipsilateral brain infarctions that we observed from C57 black mice are in keeping with the previous studies in the rat model (Kadam and Dudek, 2007;Kadam et al, 2010), but post-HI seizure activities are infrequent in our model. Specifically, evident motor seizures corresponding to the stages 4-5 of the Racine scale were detected in only 2 post-HI mice with ipsilateral infarctions.…”

“…In our experiments, continuous video monitoring was performed only for 10 days and in post-HI mice at ages of 10 months; whereas in the study by Kadam et al (2010) post-HI rats were monitored for a minimum of 33 days. Our monitoring protocol was based on the assumption that middle-aged post-HI mice may exhibit frequent seizures as previously demonstrated in the post-HI rats of similar ages (Kadam and Dudek, 2007;Kadam et al, 2010). While the 10-day video monitoring may have detected potential frequent seizures, with a mean incidence of 0.7 seizures per day in post-HI rats (Kadam et al, 2010), this protocol may be insufficient in detecting seizures that occur at more advanced ages and/or have long inter-seizure intervals of several days (Kadam et al, 2010).…”

“…Exposure of neonatal rodents to hypoxic-ischemic episodes (HI) is a widely used model for exploring the mechanisms and treatments of HIE-related brain injury and comorbidities (Patel et al, 2014). In particular, the neonatal HI episode applied to the rat model induces progressive epileptic seizures in adulthood and these seizures develop exclusively in animals with histologically identified brain injury (Kadam and Dudek, 2007;Kadam et al, 2010). These findings inspire further investigations of HIE-related epileptogenesis using the neonatal HI model.…”

Models of hypoxia and ischemia-induced seizures

“…Moreover it is best if such recording can be carried our continuously for long periods to eliminate the chances of missing events of interest. Seizures are well known to occur in clusters and thus recordings of short epochs can easily mislead an investigator about the overall seizure frequency of a given animal (Goffin et al, 2007;Grabenstatter et al, 2005;Kadam and Dudek, 2007;Kadam et al, 2010). In a study of recurrent seizures in HI treated rats, Kadam et al (2010) employed continuous video/EEG recordings using telemetry for data transmission between the rats and the recording system.…”

Current Concepts of Enzyme Histochemistry in Modern Pathology

“…Timm reaction and acid phosphatase reactions are performed in consecutive serial sections. The Timm reaction was developed to visualize structures like axons and is currently applied in experimental pathology research [82] . The Timm reaction shows that senile plaques are associated with a dropout of specific neuronal structures in the area of plaque formation.…”