Abstracts

Rationale: Amygdaloid complex (AmyC) electrical stimulation leads to self-sustained Status Epilepticus (SSSE) in adult rats. Animals presenting SSSE can be divided according to their behavior. This division correlates to decreased Neu-N expression in selected areas of the brain. Our aim is to investigate circuitry activation and neurodegeneration and their possible relationship with the behavior and anatomical patterns observed in this model. Methods: Adult male Wistar rats (240-320g) were implanted under anesthesia (ketamine, 0.7 mg/kg, xylazine 1.0 mg/kg) with electrodes in the left AmyC and hippocampal formation (HF). Video-EEG was recorded. AmyC was electrically stimulated with biphasic square waves, 300 µA, 60 Hz, 100 ms, each half a second, for 30 min. Control animals were implanted but were not stimulated. Animals developed SSSE for 1.5 h, after what they received 5 mg/kg diazepam. They were perfused under deep anesthesia after 3 h (n = 7 stimulated, 4 controls) and 24 h (n = 6 stimulated, 3 controls). Brain slices were stained for Fos (3 h group) and Fluoro-Jade C (FJ; 24 h group). All slices were analyzed under light or fluorescence microscopy (Olympus BX-60). Analyzed areas were neocortex, entorhinal cortex, pyriform cortex, AmyC and HF. Each area was classified according to the relative number of stained cells, as (-) no, (+) weak, (++) intermediate and (+++) strong staining (see Table 1). This qualitative, arbitrary scale was validated by three observers blinded to the animal’s group. All experiments were conducted observing international standards in Ethics on Animal Experimentation. Results: The rats were divided based on the behavioral pattern during SSSE: type I (3 h, n = 5; 24 h, n = 3) with the most severe behavior (limb myoclonus, rearing, falling, running and jumping) and type II (3 h, n = 3; 24 h, n = 3) with the less severe SE (facial automatisms and neck myoclonus, with rare progression to forelimb myoclonus). Epileptiform EEG was recorded in AmyC and HF. None of the control rats presented behavior or EEG alterations. There was a stronger Fos staining in the SE type I in neocortex (p<0.05) and amygdala (p<0.0001). There was strong neurodegeneration in all analyzed areas, and FJ staining was significantly higher in HF of SE type I than in SE type II (p<0.05). SE type II presented mostly unilateral neurodegeneration in all analyzed areas (p<0.0001). Table 1 presents Fos and FJ regional mapping. Conclusions: This study shows that behavioral expression of SE is associated to specific circuitry activation (Fos) and neurodegeneration (FJ) patterns. Widespread activation and neurodegeneration are seen in SE type I and are more restrict in SE type II. These results are in agreement with our previous study, where lack of Neu-N staining was found in the areas here shown as strongly stained with FJ. Additional investigations must be conducted to verify the relationship between the severity of SE and associated plasticity in the underlying circuitry. [Supported by FAPESP, Cinapce-FAPESP, PROEX-CAPES, CNPq and FAEPA]