Abstracts

Rationale: Systemic pilocarpine injection in rodents is a widely accepted method for pharmacological induction of status epilepticus (SE) in rodents and involves the development of spontaneous seizures and sprouting of mossy fibers into the inner molecular layer of the dentate gyrus. The sprouting seen in pilocarpine-treated mice and rats is often far more robust than that seen in humans with temporal lobe epilepsy (TLE). The FVB/N mouse strain has not yet been characterized as a model for TLE after pilocarpine-induced SE, although important transgenic strains are produced on this background. Here, we induced SE in FVB/N mice and characterized the model through electrophysiological and histological analysis. Methods: Pilocarpine (283-293mg/kg) was injected intraperitoneally to induce SE in CD-1 and FVB/N mice. Seizure activity was observed for 2h following injection and characterized based on Racine’s scale. Whole-cell patch-clamp recordings were made from dentate gyrus granule cells in transverse hippocampal sections. Photolysis of caged glutamate was performed in some sections to activate recurrent excitatory circuits while monitoring glutamatergic EPSCs. Sections were perfused with nominally Mg2+-free ACSF containing bicuculline methiodide to enhance excitation. Histological analysis was performed post hoc at >3 weeks post-injection on Timm stained dentate gyri by an investigator blind to the study.Results: Behavioral seizure activity and mossy fiber sprouting in the dentate gyrus was observed in CD-1 and FVB/N mice following pilocarpine-induced SE. The strains were found to have similar number of seizures during SE. Spontaneous epileptiform activity and photolysis-induced EPSCs indicative of recurrent excitation of dentate granule cells was evident in slices from FVB/N mice which underwent SE. This activity was not observed in untreated mice or those which did not undergo SE. Three to six weeks after pilocarpine treatment and SE, CD-1 mice had a significantly higher Timm score than did FVB/N mice (2.74 ± 0.15 versus 1.82 ± 0.16; p<0.05). Conclusions: After pilocarpine-induced SE, both CD-1 and FVB/N mouse strains had spontaneous seizures and mossy fiber sprouting. The FVB/N mouse had significantly less sprouting than CD-1, but synaptic responses in the dentate gyrus nonetheless indicated the presence of a robust recurrent excitatory circuit. The FVB/N mouse provides a useful model for studying spontaneous seizure development while exhibiting a degree of mossy fiber sprouting that may more closely resemble that observed in many TLE patients. (Funding source NIH/NINDS NS052302).