Abstracts

Pilocarpine induced status epilepticus (SE) in adult and immature animals results in neurodegenerative changes in many thalamic nuclei In the group of midline thalamic nuclei massive neuronal degeneration was found in immature animals in the reuniens nucleus. The nucleus reuniens (RE) is the largest of the midline nuclei and major source of projections to the hippocampus. Afferent projections originate mainly from limbic structures. Immunocytochemical studies have revealed calretinin (CR) and calbindin (CB) immunoreactive neurons in the RE and 70 % of CR-immunoreactive cells also showed CB-immunoreactivity. The present study was focused on distribution and dynamics of neuronal degeneration in the RE and on changes in CR-immunoreactivity within this nucleus in immature rats surviving up to one week after lithium-pilocarpine SE., Experiments were performed in Wistar rats 12, 15, 18, 21 and 25 days old. Lithium-pilocarpine model of SE was used. Only animals exhibiting convulsive SE were included in this study. Rats of all age groups were sacrificed 4, 8, 12, 24, 48 hours and 1 week after SE. Animals were deeply anesthetized with urethane (2.5 g/kg i.p) and perfused with 0.01 PBS (pH 7.4) followed by 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4). The brains were postfixed and cryoprotected. Blocks of the brain were sectioned in a coronal plane (50 [mu]m), mounted on gelatin-coated slides and processed for FluoroJade B (FJB) histochemistry. Another group of 25-day-old animals surviving 1 week after SE was processed for localization of CR. To determine the CR-expressing cells the standard immunocytochemical techniques were used. Sections were observed under an epifluorescence microscope Olympus Provis AX 70 using FITC filter set., Since P15 massive neuronal degeneration was evident in the RE. Damage was found in all age groups (P15, 18, 21, 25) and number of degenerated (FJB positive) neurons[uml]increased with age of SE elicitation and with survival interval. Neuronal degeneration was evident in all parts of nucleus, but the majority of FJB-positive cells was in the rostral half of the RE. A significant decrease in number of CR-positive neurons was apparent in animals surviving 1 week. CR-reactive neurons were absent in the lateral portions of the RE, while the medial part of the nucleus exhibited a few of CR-positive cells., The reuniens nucleus belong among thalamic nuclei where massive neuronal degeneration was evident since P15. The number of degenerated neurons increased with age and survival time after SE. Significant decrease in number of CR-immunoreactive neurons indicate that calretinin has no neuroprotective effect within the reuniens nucleus., (Supported by a grant No.304/04/0464 of the Grant Agency of the Czech Republic.)