Animal Models Of Disorders Of Cortical Development And The Expressions Of GABA In Cortex

Objective: We developed two animal models of disorders of cortical development ( DCDs )which can mimic human to study the mechanisms underling epileptogenesis with DCDs and understand the relationship between DCDs and intractable epilepsy(IE). Both above may provide a theory base for prevention DCDs and IE .Methods: Animal models of DCDs were made in two ways. ⑴ The first method was that pregnant Wistar rats were exposed toγ-ray using a single dose of 2.0 Gy on embryonic day 15 (E15) for 210 seconds. The brain of their offsprings might receive lesions through this method. ⑵ The other way was that we used a 2-mm-diameter copper cylinder cooled with liquid nitrogen that temperature below -50℃ to injure the cortical plate of neonatal rats (postnatal days 2, P2 ). The experimental little rats were divided into model groups and normal control groups. We observed the following aspects to confirm the success ratio and the credibility in the animal models of DCDs : ① On postnatal days 22 , the freeze- lesion-rats and the offsprings of irrated-pregnat-rats were killed to be used to histomorphology and histopathologic studies. Neuronal changes in hippocampus and cerebral cortex were detected by Nissl stain. Through this way we can confirm the seizures ratio and styles of the DCDs. ② Before EEG recordings, rats were observed daily activities which included consciousness, living ability , attack behavior as well as spontaneous seizures. ③Rats were induced seizures by warm-water- immersion (45℃). ④ The memory capacity was tested by using a Morris-water-maze method. ⑤ The expressions of GABA in cortex were observed by immuno- hisochemistry.Results: ① The weight of the brains in model groups rats were lighter than the control groups (P﹤0.05 ). All of the irrated-pregnat-rats′ offsprings ( 100% ) were caused brain lesions resulting in neuronal migration disorders. All of the neonatal little rats ( 100% ) received liquid nitrogen freeze lesions had cortical malformation mimics human microgyria. Model rat shows a thin cortical plate and distinct clusters of neuronal elements that represent heterotopias. In the control rat cortex, the typical six-layered lamination pattern is apparent, whereas the model rat cortex shows laminar disorganization and thinning. In addition, there are clusters of large neurons in both superficial and deep layers in the model rat cortex. Nissl stains showed the presence of multiple cortical areas of neuronal clustering and a focal four-layered cortex, moreover pyramidal cell dispersion was seen in the hippocampal formations. ② Animal model groups have less activities than the normal control groups. We did not observed the spontaneous seizures. ③ The latent period that warm- water- immerse induced the seizures was significantly shorter than the control (P﹤0.05). ④ The searching platform latency of model rats was significantly longer than that of the normal controls (P﹤0.05) . ⑤ The GABA positive cells in the cortex of model rats could be detectived loss by immuno- hisochemistry.Conclusions: 1. we can succeed in developing the animal models of DCDs , The first method was that pregnant rats were exposed toγ-ray on embryonic day 15 (E15) , The other method was that we used a copper cylinder cooled with liquid nitrogen that temperature below -50℃ to injure the cortical plate of neonatal rats (postnatal days 2, P2 ). 2. The weight of the brain and body in model groups rats were lighter than those of the control groups. DCDs was a handicap to the development of the body and brain. 3. All of the irrated-pregnat-rats′offsprings ( 100% ) were caused brain lesions resulting in cortical dysplasia and neuronal migration disorders which similar to human neuronal heterotopia malformation.4. All of the neonatal rats ( 100% ) received liquid nitrogen freeze lesions had cortical malformation mimics human microgyria.5. Opposite to the control groups, models rats have decreasing seizure threshold and increased seizure susceptibility as well as cognitive handicap...