Abnormal Rat Cortical Development Induced by Ventricular Injection of rHMGB1 Mimicked the Pathophysiology of Human Cortical Dysplasia

Abstract

Background Cortical dysplasia (CD) is a common cause of drug-resistant epilepsy. Increasingly, innate immunity is involved in CD with epilepsy. However, it is unclear whether innate immune factors contribute to induce epileptogenic CD. Here, we injected recombinant human HMGB1 (rHMGB1) into the embryonic rat ventricle to determine whether rHMGB1 can induce epileptogenic CD with pathophysiological characteristics similar to those of human CD.Methods At gestational day 14.5, rHMGB1 was injected into the ventricles of Sprague Dawley (SD) rat embryos. At 2 months postnatal, the effects of rHMGB1 on cortex construction were examined by Nissl staining; the alterations of nerve tissue were detected using immunostaining. At 3 months postnatal, the susceptibility and severity of pilocarpine-induced seizures and the spontaneous epileptic discharges were evaluated by EEG. Open-field tests, novel object recognition tests, and Morris water maze tests were performed to observe the behavior of rHMGB1-treated rats.Results The results showed cortical organization was severely disrupted in the rHMGB1-treated rats, and microgyria and heterotopia also emerged; additionally, disoriented neurons, dysmorphic neurons, and dysplastic neurons were found in the cortical lesions and heterotopias. Subcortical heterotopia also appeared in the white matter and the gray-white junction of the rHMGB1-treated rats. Moreover, the numbers of neurons and astrocytes were increased in the cortical lesions; the neuronal dendrites were thickened, randomly oriented, and frequently crossed each other. Moreover, the immunoreactivity of NR2A, NR2B, NR1, GAD65/67, EAAT1 and EAAT2 indicated that the excitation of cortical lesions and heterotopia were significantly increased. Furthermore, EEG showed more susceptibility and severity of seizures in rHMGB1-treatment rats compared with the control rats. Intriguingly, spontaneous nonepileptic seizure discharges were also detected in the rHMGB1-treated rats after 5 months of age, and spike-wave discharges of approximately 8 Hz were the most significantly increased synchronously propagated waves throughout the general brain cortex.Conclusions These results indicated that rHMGB1 exposure during pregnancy can modify the cerebral structure of offspring, which results in increased susceptibility to seizures and mimics the pathophysiological characteristics of human CD. Those results suggested that HMGB1 upregulation resulting from various insults could contribute to the development of epileptogenic CD during pregnancy.