Abstracts

RATIONALE: Compared to the adult brain, the immature brain appears to have an increased susceptibility to seizures. But the immature brain is more resistant to seizure-induced neuronal damage than the mature brain. Immediate early genes such as c-jun play a critical role in neuronal damage. Therefore, we hypothesized that constitutive c-jun expression in immature culture is lower than in mature culture. METHODS: Seven and 14 DIV (days in vitro) hippocampal explant cultures derived from 8-day-old rat pups were used. Proteins extracted from individual cultures were analyzed by Western blot. Extracellular field recording was done in cultures perfused with aCSF (in mM; NaCl 120, KCl 3.5, NaH2PO4 1.23, NaHCO3 25, CaCl2 2.0, MgSO4 1.0 and Glucose 10), bubbled with 95/5 O2/CO2. A 1-sec stimulus train (60 Hz, 0.1 msec rectangular pulses) was applied to the Schaffer collaterals, and the afterdischarge (AD) was recorded in CA1 pyramidal layer. Cultures were returned to the incubator and observed serially. Intensity of propidium iodide fluorescence indicative of neuronal damage was quantitated as percent of total neuronal damage induced by 2 mM NMDA. RESULTS: c-Jun protein expression at 7 DIV was higher than that at 14 DIV (Optical Density; 0.58?0.04 vs 0.41?0.03[SEM], n=24 each; p=0.029, Mann-Whitney U). Neuronal damage in the hippocampus at 7 DIV (n=19) was significantly lower than at 14 DIV (n=14): In CA1 (7 vs 14 DIV), 1.67?0.72% vs 13.56?5.79%[SEM] at 24 hrs, p=0.008; 1.28?0.75% vs 21.54?6.55% at 48 hrs, p<0.001; 1.65?0.80% vs 18.20?5.88% at 72 hrs, p=0.001. In CA3, 0.41?0.15% vs 5.52?3.15% at 24 hrs, p=0.01; 0.37?0.17% vs 8.83?3.96% at 48 hrs, p<0.001; 0.71?0.32% vs 7.94?2.80% at 72 hrs, p<0.001, Mann-Whitney U). There were no significant differences in AD induction rate and AD duration. CONCLUSIONS: The results show reduced neuronal damage from seizures in more immature hippocampal culture. However, constitutive expression of c-Jun protein was higher in younger cultures. Thus higher constitutive expression in younger neurons may inhibit further induction of c-jun from seizures and thus result in less severe neuronal damage.