In situ detection of DNA damage in the mouse hippocampus following status epilepticus induced by kainic acid

This study examined the dynamic progression of DNA damage following status epilepticus (SE) using three complementary in situ techniques-PANT, Klenow, and TUNEL-combined with Fluoro-Jade B (FJB) staining in the susceptible hippocampal neurons. SE was induced by intracerebroventricular injection of kainic acid, which triggered early oxidative DNA lesions characterized by single-strand breaks (ssDNA) detectable by PANT and Klenow as early as 6 h post-insult. A transient decline in ssDNA labeling at 16 h suggested the possible activation of DNA repair mechanisms during the latent phase preceding irreversible degeneration. From day 1 onward, DNA damage intensified, with PANT and Klenow signals resurging and temporally coinciding with increased neuronal death. TUNEL, which detects double-strand DNA (dsDNA) breaks, consistently exhibited lower signal intensity than PANT/Klenow but followed a similar temporal pattern. Quantitatively, PANT demonstrated higher sensitivity for early ssDNA lesions (6-16 h), while PANT and Klenow showed comparable sensitivity at later stages (1-7 d), indicating progression toward complex DNA fragmentation. The convergence of DNA damage signals with FJB staining from day 3 post-SE highlighted the transition from reversible DNA lesions to irreversible neurodegeneration. Notably, TUNEL's limited specificity-due to its detection of non-apoptotic 3'-OH ends-was evident in its lower yield compared to ssDNA-specific methods. These findings reveal SE-induced DNA damage as a dynamic continuum-from early ssDNA breaks to delayed dsDNA fragmentation-that drives delayed neuronal loss, providing morphological insights into the neurodegenerative mechanisms following epileptic insults.