Abstracts

Rationale: Inheritance patterns between mouse strains suggest that a robust genetic influence determines individual susceptibility to pilocarpine-induced hippocampal cell death. DBA/J (DBA) and BALB/cJ (BALB) mice exhibit differential susceptibility to pilocarpine-induced cell death, with DBA being relatively sensitive and BALB mice relatively resistant. In the present study, we used inbred mice to investigate the genetic determinants of susceptibility to pilocarpine-induced cell death. Resistant and susceptible strains of mice were crossed to produce F1 hybrids. F2 intercross mice were also produced to indicate the number of genes that may control the cell death resistant phenotype.Methods: To determine the inheritance pattern of cell death susceptibility, we analyzed F1 progeny 5 days following systemic pilocarpine (PILO) administration. Following PILO, mice were monitored continuously for 4 h and scored for seizures. Brains from animals in each cross were processed for histopathologic evaluation five days following PILO administration to evaluate the severity of seizure-induced brain damage. To examine the genetic loci that confer resistance to seizure-induced cell death, F2 intercross mice were assessed for phenotyping differences in susceptibility. Microsatellite mapping techniques were then used and 83 markers typed in the F2 population were examined for associations with susceptibility or resistance to PILO-induced cell death. Quantitative trait loci (QTL) mapping methods were used to identify regions of the genome that contribute to variation in susceptibility.Results: Irrespective of mouse strain or cross, no significant effects were found with regard to qualitative differences in seizure intensity or duration and there was no clear relationship between seizure sensitivity and susceptibility to seizure-induced cell death. Nearly half of the F1 mice were susceptible to cell death following pilocarpine, while nearly half were resistant, suggesting that resistance is inherited in a semi-dominant manner. Among F2 mice, 30% showed resistance, 68% showed susceptibility to seizure-induced cell death, and 2% were of an intermediate phenotype, suggesting that multiple genetic variants are responsible for the expression of the trait. Results of a whole genome analysis for F2 mice with a simple interval mapping approach show that the locus of greatest effect was found on Chr 16 (LOD=4.02, P=0.06).Conclusions: Our findings demonstrate that susceptibility to PILO-induced cell death can be modulated by the presence of strain-specific gene products in mice. Furthermore, data suggest that seizure susceptibility to PILO-induced status is genetically separate from seizure-induced cell death in F1 and F2 crosses of BALB and DBA mice. The identification of a putative QTL for PILO-induced cell death on Chr 16 may ultimately lead to the identification of genes influencing individual differences in PILO-induced cell death threshold in mice and aid in the discovery of novel neuroprotective agents.