Abstracts

RATIONALE: We have recently demonstrated that kainic acid (KA) induced status epilepticus (SE) results in increases in ceramide levels at 2-30 hours after KA, and that such alterations lead to apoptosis in the hippocampus. The mechanisms that lead to ceramide increases during, and after, SE have not been investigated. The three isoenzymes of sphingomyelinase (SMASE) catalyze the breakdown of sphinomyelin to form ceramide, and have been shown to be responsible for ceramide increases in other apoptosis models, but not in neurons after SE. The objective of this study is to determine sequentially the activity of those isoenzymes during, and after, SE in an attempt to understand the mechanisms that lead to ceramide increases after SE.
METHODS: Adult Sprague-Dawley rats (2-5/group) received, intraperitoneally, 15 mg/kg KA, were sacrificed at 1, 2, 3, ,4 12, 18 and 24 hours after KA, and were compared to vehicle injected matched control rats. The right hippocampus was dissected, proteins were extractred, and then assayed for the activity of Magnesium Independent Neutral SMASE (MI-NSMASE), Magnesium Dependent Neutral SMASE (MD-NSMASE), and for Acidic SMASE (ASMASE). ANOVA was used for analyzing the data.
RESULTS: As Compared to baseline, MI-NSMASE, and MD-NSMASE increased at the 4, 18, and 24 hour time points (p[lt]0.05 in each of the paired comparisons, data presented in table). Other paired comparisons were not significant. A-SMASE did not show any significant differences either (p[gt]0.05, see table for data).
CONCLUSIONS: After KA induced SE there is activation of MD-NSMASE and MI-NSMASE starting at 4 hours after KA injection. These increases explain at least some of the increases in ceramide levels previously reported to occur after SE, and thus may be contributing to the process of SE induced apoptosis.[table1]
[Supported by: DCR114170-26323]