Abstracts

Rationale: Temporal Lobe Epilepsy (TLE) is the most common epileptic syndrome in humans. Status Epilepticus (SE), one of the primary events leading to TLE, induces neuronal loss, one of the major hallmarks in TLE patients. In this study, we (1) built a comparative map of neurodegenerating areas 24 h after SE induced by systemic pilocarpine (S-PILO) and intrahippocampal pilocarpine (H-PILO) in rats and (2) evaluated the neurodegeneration pattern 12, 24 and 168 h after SE only in the group induced by H-PILO. Methods: Adult Wistar rats (240-340 g) were submitted to H-PILO(n=4; 2,4 mg/µl; 1 µl) and S-PILO (n=4; 320 mg/kg). After 90 minutes of SE, all animals received diazepam injection (5 mg/kg, i.p.). Neurodegeneration was evaluated with Fluoro-Jade B histochemistry (FJ). All areas presenting FJ-positive (FJ+) cells, in at least one animal in the group, were included in Table 1. This was followed by characterization of FJ neurodegeneration 24 h after SE in both S-PILO and H-PILO groups. Other H-PILO groups were perfused 12 (n=9), 24 (n=8) and 168 h (n=12) after SE. FJ+ cells were counted with a computer-based imaging system (Olympus BX60 microscope; NIH-Image J). All procedures were approved by the Ribeirão Preto School of Medicine Commission on Ethics on Animal Experimentation (CETEA; protocol 195/2005). Results: We identified a differential distribution of neurodegenerating areas between S-PILO and H-PILO groups. Thirty-seven regions presented FJ+ cells, among which 3 were seen exclusively in the H-PILO group, 12 were exclusive for S-PILO group and 22 were seen in both groups (see Table 1). In the time-course evaluation of neurodegeneration in H-PILO groups, animals from the 12 h group presented higher neurodegeneration in the hilus of the dentate gyrus (DG) than the 168 h group (64.00±0.4 vs. 45.70±3.62). Animals of the 24 h group had higher neurodegeneration in CA3 than the 12 h group (35.30±4.70 vs. 11.82±4.41). Finally, animals from the 168 h group showed higher neurodegeneration in CA1 than the other two groups (12h and 24h; 37.00±3.40 vs. 27.93 ± 5.93 vs. 23.77 ± 3.84, respectively). All results are expressed as mean ± SEM (ANOVA Kruskal-Wallis One Way with post hoc Dunn's; p<0,01). Conclusions: One of the main highlights of the H-PILO model is the region selectivity, in contrast with the S-PILO model, in which we observed more widespread neurodegeneration. In the particular case of H-PILO FJ+ cells were observed in all temporal windows after SE in DG (hilus), CA1 and CA3 (pyramidal cells), but the number of stained cells differed throughout time among regions. We observed neurodegeneration early in the DG (hilus), followed by CA3 and finally in CA1, thus the pattern of FJ+ neurodegeneration in animals submitted to SE is region and time dependent. The FJ method was a reliable tool to characterize neurodegeneration kinetics in the new H-PILO model. Financial support: FAPESP, Cinapce-FAPESP, PRONEX, PROEX-CAPES, CNPq and FAEPA.