Strain differences in seizure-induced cell death following pilocarpine-induced status epilepticus

Abstract

Mouse strains differ from one another in their susceptibility to seizure-induced excitotoxic cell death. Previously, we have demonstrated that mature inbred strains of mice show remarkable genetic differences in susceptibility to the neuropathological consequences of seizures in the kainate model of status epilepticus. At present, while the cellular mechanisms underlying strain-dependent differences in susceptibility remain unclear, some of this variation is assumed to have a genetic basis. However, it remains unclear whether strain differences in susceptibility to seizure-induced cell death observed following kainate administration are observed following systemic administration of other chemoconvulsants. In rodents, the cholinomimetic convulsant pilocarpine is widely used to induce status epilepticus (SE), followed by hippocampal damage and spontaneous recurrent seizures, resembling temporal lobe epilepsy. This model has initially been described in rats, but is increasingly used in mice. We characterized neuronal pathologies after pilocarpine-induced status epilepticus (SE) in eight inbred strains of mice focusing on the hippocampus. A ramping-up dose protocol for pilocarpine was used and behavior was monitored for 4-5 h. While we did not observe any significant differences in seizure latency or duration to pilocarpine among the inbred strains, we did observe a significant difference in susceptibility to the neuropathological consequences of pilocarpine-induced SE. Of the eight genetically diverse mouse strains screened for pilocarpine-induced status, BALB/cJ and BALB/cByJ were the only two strains that were resistant to the neuropathological consequences of seizure-induced cell death. Additional studies of these murine strains may be useful for investigating genetic influences on pilocarpine-induced status epilepticus.

Fig. 1

Strain differences in susceptibility to pilocarpine-induced cell loss and degeneration among two representative inbred strains of mice, as compared to a sham control mouse of the C57BL/6J strain. Low magnification cresyl violet staining of horizontal sections through the hippocampus and high-magnification cresyl violet and Gallyas silver staining of the dentate hilus and area CA3, seven days following systemic administration of pilocarpine. Note that significant pilocarpine-induced cell loss and degeneration is observed in the DBA/2J strain within the dentate hilus and area CA3. In contrast, no significant cell loss or degeneration was observed after systemic pilocarpine administration to BALB/cByJ mice. CA1 and CA3 denote the hippocampal subfields; H, dentate hilus. Scale bars = 750 µm (A, E,I); 100 µm (a–l).

Fig. 2

Quantitative analysis of neuronal density in the dentate hilus following systemic administration of pilocarpine to eight inbred strains of young adult mice. Viable surviving neurons were estimated by cresyl violet staining. Bars denote the percentage of surviving neurons (as compared with saline-injected sham control C57BL/6J mice) in the dentate hilus. Differences in the extent of cell loss were observed 7 days following pilocarpine administration and were dependent on the mouse strains examined. Data represent the mean ± SEM of at least 5 mice/strain. Asterisk denotes a significant difference as compared to vehicle-injected sham control mice (P<0.05).

Fig. 3

Quantitative analysis of neuronal density in area CA3 following pilocarpine administration to eight inbred mouse strains. Viable surviving neurons were estimated by cresyl violet staining. Bars denote the percentage of surviving neurons (as compared with saline-injected sham control C57BL/6J mice) in area CA3. A strain-dependent difference in cell loss in area CA3 was observed at 7 days following pilocarpine administration. Data represent the mean ± SEM of at least 5 mice/strain. Asterisk denotes a significant difference as compared to vehicle-injected sham control mice (P<0.05).