Abstracts

Rationale: In adult animals, convulsive status epilepticus (SE) is known to induce mesiotemporal sclerosis and epilepsy. In rats younger than 2 weeks, early and delayed effects of SE on hippocampal functions and morphology were not yet described in detail. The aim of present study was to describe both short and long time functional and morphological changes in the hippocampus of rats experiencing SE at postnatal day (P) 12. Methods: SE was induced by pilocarpine (40 mg/kg) in P12 rats pretreated with LiCl 24 h earlier. One group of animals was perfused 24 h after SE to assess acute damage using Fluoro Jade B and silver stain. To assess impairment of hippocampal functions, another group of animals was tested as adults in Morris water maze and hippocampal excitability was determined using commissural evoked potentials. Then the animals were video/EEG monitored for 5 days to detect recurrent seizures, and after the end of tests animals were perfused and the hippocampus was morphologically examined. The number of hilar neurons was stereologically estimated and the volume of the hippocampus was assessed. Results: In acute phase, degenerating neurons were detected in both the pyramidal layer of CA1 and in the hilus of the hippocampus. Damaged cells predominated in the septal end of the hippocampus. In chronic phase, functional tests revealed cognitive impairment expressed as a worsening performance in Morris water maze. Animals with SE were able to learn how to solve this task, but they never reached the level of control siblings (fully trained animals with SE needed 36% more time to reach platform compared to controls). Excitability of the hippocampus increased and more than 50% of animals developed epilepsy. Morphometric assessment revealed hippocampal atrophy, the hippocampal volume was reduced by 7% compared to controls. The density of neurons in the septal hilus was by 20% lower than in controls. Conclusions: Early SE leads to impairment of hippocampus-dependent functions, development of epilepsy and hippocampal atrophy in adulthood. Supported by projects LC554 and ME08045 of the Ministry of Education of the Czech Republic.