Abstracts

RATIONALE: Flurothyl is a volatile convulsant widely used to induce experimental seizures in animals. However, very little is known about its mechanism of action and which brain region(s) is(are) involved in seizure genesis. Recent work has implicated the locus coeruleus (LC), and we have shown previously that the neocortex of mature mice may be more sensitive than the hippocampus to this convulsant. In the present study, we asked whether there are age-dependent differences in regional c-fos mRNA expression to varying durations of exposure to flurothyl. METHODS: Male C3H mice (aged P17 or P55-60) were either sham-treated or exposed to flurothyl (20 l/min) for varying durations until either a myoclonic jerk [MJ], a single generalized [SG] seizure, or two generalized [2G] seizures were elicited. One hour after treatment, each mouse was sacrificed, the brain frozen, tissue sections prepared for c-fos in situ hybridization with a 33P-c-fos probe, and optical densities measured using standard methods. RESULTS: In mature mice, c-fos mRNA expression increased significantly in the neocortex after either a SG or 2G seizures (0.138 0.004, 0.160 0.014, respectively, p<0.05; control, 0.037 0.002), in the hippocampus (CA1, CA3, dentate gyrus) only after 2G seizures (p<0.01), and in the LC after all three timepoints (0.042 0.003, 0.114 0.016, and 0.185 0.028, respectively, p < 0.01; control, 0.03 0.006). In immature mice, c-fos mRNA expression was not significantly elevated in either neocortex or hippocampus at any of the seizure endpoints tested; however, c-fos mRNA expression in the LC was significantly elevated only after 2G seizures (0.045 0.012 and 0.097 0.001 for control and 2G seizures, respectively, p < 0.01). CONCLUSIONS: Using c-fos mRNA expression as a marker of neuronal activation, we found that the neocortex and LC of adult mice are more sensitive to flurothyl than the hippocampus. In immature mice, c-fos was not an accurate measure of seizure activity; other immediate early genes (e.g., c-jun) may prove to be more reliable indicators in this regard than c-fos. [This work was supported by VAMC (PS), and NIH research grant K08 NS 01974 (JMR)].