Chronic seizures and collateral sprouting of dentate mossy fibers after kainic acid treatment in rats.

Kainic acid (KA) injections destroy hippocampal pyramidal cells, induce recurrent collateral sprouting of the hilar mossy fibers (MFs), and lead to chronic seizures. In the present study, rats were injected systemically with KA (14 mg/kg) to determine whether the subsequent occurrence of seizures was correlated with MF sprouting, as indicated by Timm's staining of proximal dendrites. At 4 weeks, 56% of the KA-treated rats had MF sprouting in the temporal (ventral) hippocampus, and 52% had shown seizures between 10 and 28 days. Both seizures and sprouting were seen in 32% of the treated animals. While Timm's staining of MFs in the inner molecular layer was not directly correlated with seizure scores, animals which exhibited chronic seizures had significantly more sprouting than animals which did not have seizures.