Abstracts

RATIONALE: We have previously demonstrated that lithium-pilocarpine status epilepticus (LiPC-SE) results in age specific patterns of neuronal injury. Rat pups at PND14, an age at which CA1 cells are particularly vulnerable to LiPC induced damage, were studied to determine the temporal evolution of injury in the immature rat hippocampus. METHODS: 2-wk old Wistar rat pups were given LiCl(3mEq, i.p.) followed 16-20h later by pilocarpine hydrochloride (60mg/kg, s.c.). Animals were killed at 2,6,12,18,24,72h and 5,7 and 14d after the onset of SE (n=6 per time point). Brains were processed for light microscopic examination of neuronal damage using hematoxylin and eosin (H&E) and TUNEL labeling. A 450 M long region in both dorsal hippocampi were used for analyses. Additionally, some adjacent sections were stained with cresyl violet (CV) or hematoxylin with lighter concentrations of eosin viewed with fluorescent light to compare the efficacy of these two common histological stains. RESULTS: Some CA1 injury was visible as early as 6h after the onset of SE and became maximal after 24h at which 30% (45 b6 of 150 b23 counted neurons) exhibited acidophilic cytoplasm with pyknotic nuclei. TUNEL labeling did not appear until 24h, remained strong after 3d and was evident as late as 7d after recovery. In addition, fluorescent microscopy aided in detecting cells with acidophilic cytoplasm when damaged cells were not readily discernible with CV. CONCLUSIONS: Our data suggest that LiPC induced CA1 damage in the developing rat brain can be detected within a short period and peaks at 1d after the onset of SE. While light microscopy alone can not distinguish the type of cell injury, DNA fragmentation seen with TUNEL staining and prior studies of biochemical and ultrastructural features in the 2-wk old hippocampus at 24h suggest that some cells in this region undergo apoptosis. Finally, in regions lacking widespread neuronal injury, H&E staining viewed with fluorescence may be a sensitive tool for detecting damaged cells. [Supported by grants NS01792, NS13515 from NIH and the VA Research Service.]