Abstracts

Rationale: The thalamic reticular nucleus (TRN) and the zona incerta form an essential part of the circuits that links the thalamus to the cerebral cortex. Both structures contain significant proportion of the inhibitory neurons. The TRN is penetrated by the fibers passing between the thalamus and cortex which give off excitatory, glutamatergic projections to the neurons of the TRN. The TRN is divided into several distinct functional sectors each related to a particular cortical area and thalamic nuclei and the reticular neurons send GABAergic fibers back to the thalamus. The zona incerta (ZI) contains a neurochemically diverse cell groups forming four distinct sectors - each having extensive afferent and efferent connections. Incertocortical projections are GABAergic and terminate in the 1st neocortical layer. In an effort to better understand the development of neuronal damage in the diencephalic structures after status epilepticus (SE) neuronal degeneration was analyzed within both structures. Methods: Experiments were carried out in Wistar pups 12,15,18, 21 and 25 days old. Lithium - pilocaprpine model of SE was used. Lithium chloride (3 mmol/kg i.p.) was injected 24 hours before pilocarpine (40 mg/kg i.p.). Only animals exhibiting convulsive SE were included in this study. The rats survived for 4,8,12,24,48 hours and 1 week after SE. The animals were perfused with PBS followed by 4% paraformaldehyde in PBS under an overdose of urethane anesthesia. Coronal sections (40 μm) were cut on cryostat and processed with cresyl violet or with a fluorescent stain Fluoro - Jade B (FJB) used for detection of degenerated neurons. Sections were examined with an epifluorescence microscope using a filter system suitable for visualizing fluorescein or FITC. Results: No degenerating neurons were observed in either structure in 12- and 15-day-old rat pups. The TRN as well as the ZI contained a moderate to large number of degenerating neurons in 18-day-old and older rats. Degenerating neurons were evident in the whole anteroposterior extent of the TRN especially in its dorsal third. The rostral sector of the ZI exhibited neuronal degeneration, number of FJB-positive neurons increased with age. The Only isolated degenerating neurons were found in ventral and dorsal sectors of the ZI. Conclusions: Lithium-pilocarpine SE in immature animals resulted in degeneration of neurons in the TRN and in the ZI. Degenerating neurons were distributed unequally: majority of them was found in the dorsal half of the TRN and the rostral sector of ZI. Supported by a Research Project LC-554.