Abstracts

Rationale: Neonatal status epilepticus in humans increases the risk for subsequent neurodevelopmental dysfunction and epilepsy. Three episodes of kainic acid-induced status epilepticus (3KA-SE) or of maternal separation at postnatal days (PN) 4-6 have sex- and age-specific effects upon GABAA related function. Here, we investigate the effects of 3KA-SE and maternal separation at PN4-6 on (a) visuospatial learning and memory at PN16-19 and (b) the anticonvulsant effects of phenobarbital in the flurothyl seizure model at PN32, as a function of sex and treatment. To determine if the age at seizure or stress induction influences their effects on flurothyl seizures, we also studied rats exposed to 3KA-SE or maternal separation at PN14-16. Methods: 3KA-SE were induced in male and female Sprague Dawley rats at PN4-6 (KA456) or at PN14-16 [KA(14-16)]. Stress controls included vehicle-injected rats separated from the dam for 6h/day between PN4-6 (SS456) or PN14-16 [(SS(14-16)]. Na ve controls were vehicle-injected but kept with their dam. Visuospatial learning and memory were evaluated at PN16-19 in KA456, SS456, and control groups using the Barnes maze (n=7-13 rats/group). At PN32, 20 or 40 mg/kg phenobarbital or equal volume of saline were given intraperitoneally 30 minutes before flurothyl exposure (n=8-40 rats/group). Flurothyl seizure thresholds for the first clonic or the first tonic seizure were determined as the amount of flurothyl administered till the occurrence of each of these seizure types. The threshold for seizure propagation was the difference between the tonic and clonic thresholds.Results: 1) Transient learning delay was noted in male KA456 and SS456 rats compared to controls, but not in females. 2) Early life 3KA-SE or stress did not change the flurothyl thresholds. 3) Pre-treatment with phenobarbital increased the flurothyl thresholds for clonic, tonic seizures, and seizure propagation in a dose-dependent manner. 4) The anticonvulsant effect of phenobarbital was enhanced in: (a) male SS(14-16) compared to KA(14-16) or controls (clonic threshold; 40mg/kg phenobarbital only); (b) female KA456 compared to female SS456 or controls (tonic and propagation threshold) and male KA456 (tonic threshold) (20mg/kg phenobarbital only). Conclusions: Male rats are more vulnerable than females to learning delays following neonatal 3KA-SE or maternal separation. In contrast, early life 3KA-SE or maternal separation had no overall impact on the threshold to flurothyl seizures or their responsiveness to phenobarbital at PN32. Only the male SS(14-16) and female KA456 groups appeared to be more responsive to phenobarbital showing greater delay in the onset of clonic or tonic seizures respectively. The mechanisms, therefore, underlying the long-term effects of early life 3KA-SE or maternal separation upon learning are sex-specific and distinct from those involved in flurothyl seizure susceptibility. This study supported by grants from NINDS (R21NS078333, R01NS020253), CURE, Autism Speaks, Heffer Family and Siegel Family Foundations.