Abstracts

RATIONALE: To describe detailed topography and time course of status epilepticus-induced neuronal degeneration in the piriform cortex and the deep piriform region (including the ventral endopiriform nucleus (VEn), the dorsal endopiriform nucleus (DEn) and claustrum (CLD)) in developing rats and to find out if there is a relationship to the age when status epilepticus (SE) was elicited. Above mentioned structures have been identified as an area involved in the generation of epileptic seizures and they are heavily damaged after SE in adult animals.
METHODS: Experiments were carried out in rat pups (Wistar albino) 12, 15, 18, 21, and 25 days old. Lithium-pilocarpine model of SE was used. Lithium chloride (3 mmol/kg i.p.) was injected 24 hours prior to injection of pilocarpine (40 mg/kg i.p.). Only animals exhibiting clear-cut motor SE were included into this study. The rats survived for 4, 8, 12, 24, 48 hours and/or 1 week after SE. Under an overdose of urethane anesthesia the animals were perfused with PBS followed by 4% paraformaldehyde in PBS. Coronal sections (40 um thick) were cut on a cryostat, mounted onto gelatin coated slides and processed with cresyl violet or with a novel fluorescent stain (Fluoro-Jade B, FJB) used for detection of degenerating neurons. Sections were examined with an epifluorescence microscope using a filter system suitable for visualizing fluorescein or FITC.
RESULTS: There was no change in the CLD of 12-day-old rat pups at any survival interval. Isolated FJB-positive neurons were scattered in the whole DEn at all survival intervals with a prevalence in medial and basal parts fo DEn. Degenerated neurons were rarely seen in CLD of 15-day-old rats. They prevailed in the medial part of the nucleus. DEn exhibited slightly more FJB-positive neurons dispersed in its whole extent. Both subdivisions of the claustrum contained moderat to large number of FJB-positive neurons in 18-, 21-, and 25-day-old animals/ Positive neurons prevailed along the medial margin of the CLD. In the DEn degenerating neurons were scattered in the whole nucleus with a prevalence in its medial part. Animals 18 and more days old exhibited a peak in the number of degenerating neurons in both subdivisions of claustrum 24 and 48 hours after SE.
CONCLUSIONS: Lithium pilocarpine model of status epilepticus resulted in degeneration of neurons in the deep piriform region in all age groups studied (rat pups 12, 15, 18, 21, and 25 days old). Fluoro Jade B-positive neurons were not numerous in the two youngest groups; they were detected in the dorsal claustrum as well as in the dorsal endopiriform nucleus. In 18-day-old and older animals number of degenerting neurons increased in both subdivisions of claustrum. They were mainly localized in the medial and dorsal parts of the dorsal claustrum. Degenerating neurons were found mainly in marginal parts of the rostral half of the dorsal endopiriform nucleus whereas medial margin represents the dominant localization in the caudal half of DEn. Localization of neuronal loss in both dorsal and ventral claustrum are age-dependent with a marked change between postnatal days 15 and 18 in rats.
[Supported by: the Grant Agency of the Czech Republic - grants No. 304/99/0193 and 309/00/1644.]; (Disclosure: Honoraria - Pavel Mares - speaker for Glaxo Wellcome, Janssen Cilag, Sanofi, Desitin at local meetings)