Abstracts

Rationale: Early life stress (ELS) may be a causal factor for mesial temporal lobe epilepsy (MTLE), a common form of focal epilepsy. We showed previously in rats that ELS, in the form of maternal separation (MS), aggravates limbic epileptogenesis in adult life (Salzberg et al., 2007). As mechanisms underlying such effects have been little explored, we studied endocrine responses and hippocampal cellular changes using a similar model, hypothesising that enhanced limbic epileptogenesis in MS rats would be associated with increased corticosterone response to seizures and, in key regions of hippocampus, decreased neuronal numbers and altered neurogenesis. Methods: On postnatal days 2-14, male and female Wistar rat pups underwent either MS for 180 min/day, or brief early handling and separation for 15 min/day (EH). Rapid amygdala kindling started at 8 weeks of age. Serum corticosterone (CORT) levels were measured before kindling, immediately after the 12th and 24th stimulations and after a seizure elicited 2 weeks after reaching the fully kindled state. To measure neurogenesis, daily injections of BrdU (50mg/kg i.p.) were given for 7 days after the end of kindling. Unbiased stereological pyramidal cell counts in ipsilateral hippocampal CA3c region were performed on brains of kindled rats euthanased 3 weeks after attaining the fully kindled state. BrdU positive newborn cells in subgranular zone and granule cell layer were counted and calculated as number of cells/mm3 of dentate gyrus. Data are presented as mean±SEM. We employed repeated measures one-way ANOVA for kindling data, and for all other data 2-way ANOVA with intervention and kindling as independent variables followed by planned comparison. Results: MS rats kindled faster than EH controls (no. of stimulations: Female (F): 49.3 ± 8.5 vs. 73.1 ± 6.8, n= 8-9; Male (M): 49.6 ± 4.5 vs. 72.2 ±8.1, p<0.05 n=6-9). CORT responses post-seizure were greater in MS rats, for example the serum CORT level (ng/ml) at the fully kindled stage was: F: 742.4 ± 39.53 vs. 281.1 ± 86.9, p<0.05, n= 6-9; M: 325.3 ± 53.4 vs. 217.13 ± 31.5, n=7-9. There were fewer total CA3c pyramidal cells in female MS rats post-kindling (no. of cells/mm3, F: 37821 ± 2599 vs. 53235 ± 3275, p<0.05 n=6-9), with a non-significant trend in male MS rats (M: 46945 ±3269 vs. 56488 ± vs. 2596, n= 8-9). Increased neurogenesis was observed in all kindled groups compared to sham kindled, but in kindled females this was greater in MS compared to EH rats (no. of cells/mm3: F: 8283 ±544 vs. 5993 ± 374, n= 6-9).