Abstracts

Rationale: Intractable epilepsy in children is mainly caused by malformations of cortical development. Perinatal brain injury, such as hemorrhagic stroke, can lead to Focal Cortical Dysplasia (FCD). In response to such events, inflammation (INF) is believed to be one of the major contributors for long term lesions and epileptogenesis. In the animal model of FCD, induced by perinatal cortical freeze lesion, the participation of INF as a critical process in the establishment of brain lesions, has not been yet investigated. We propose to evaluate the glial markers GFAP and IBA-1, usually associated with INF. Methods: Neonatal (P0) albino rats were submitted to a modification of the protocol of cryogenic cortical lesion as proposed by Dvoràk and Feit (Acta Neuropathol. 1977;38(3):203-12). Briefly, after cold-induced anesthesia, animals received 10 s of contact of a metallic probe cooled in liquid N₂ over the neocortex. Animals were killed 24 h (Group A, n=8 controls; n=6 exp) or 7 days (Group B, n=8 controls; n=8 exp) after the initial insult, 14 μm paraffin-embedded slices were processed for Nissl staining, GFAP and IBA-1 DAB immunostaining. Results: Ten out of fourteen cryo-lesioned animals developed cortical lesion (4/6, 24 h; 6/8, 7 days). No alterations were detected in the control groups. It is observable a reduction in Nissl staining intensity in the area of lesion 24 h after the insult, indicating tissue disarrangement. One week later we noted a microgyric lesion as described elsewhere, resembling what is observed in human cases of polimicrogyria. When tested for IBA-1 we identified in A a group of positive cells in the perilesional region, close to white matter, and a clear indication that those cells are actually migrating upwards from the white matter and the subventricular zone to the lesion site. In B we found positive cells surrounding the microgyrus, however differently from A, in B we noted positive cells in other cortical regions. Perilesional positive cells in both groups showed amoeboid shape with virtually no processes, indicative of microglia activation. On the other hand, in B, outside the lesion site, cells with the typical morphology of resting microglia are detected. The GFAP immunostaining revealed different expression patterns of reactive gliosis between the groups. In A the staining comprises wide and dispersed cells pattern nearby the lesion site without clear delimitation of the affected area; in B we observed GFAP+ staining in a microgyric shape fashion. Positive cells inside the microgyrus migrate from the invaginating layer I, and outside the microgyrus migrate upwards from the white matter in a U-shape structure under the bottom of the lesion. Conclusions: Our findings allow us to suggest that the initial insult leads to an INF response, indirectly detected by the observed reactive astrogliosis and microglial activation, culminating in the formation of a microgyrus. The role of INF in this model is not yet clear and future studies using anti-INF drugs in the postnatal period will help understanding this issue. Financial Support: CNPq, CINAPCE-FAPESP, PROEX-CAPES, FAEPA