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Axonal sprouting is recognized to be an important mean of repair after neurologic injury. Some characteristic aftermaths of pilocarpine-induced status epilepticus (SE) in the immature rat are nerve cell loss and rearrangement of neuronal fibers. SE induced cell degeneration exclusively in the hippocampal CA1 subfield. Development of neuronal death becomes evident within hours after SE, following a delayed time course ranging from 6 to 48 h post-SE. An incidental finding is that pilocarpine induces within 48 h an aberrant growth of hippocampal mossy fibers in the hippocampus, especially in the infrapyramidal region of the CA3-subfield. We found a strong infrapyramidal band of mossy fibers along the entire stratum oriens of the CA3-region. No mossy fibers sprouting into the inner molecular layer of the dentate gyrus, or CA1 sprouting into the stratum moleculare of CA1 were noted. Signs of aberrant connectivity were found in six of the 10 pilocarpine-treated animals. This study provides the demonstration that pilocarpine within 48 h consistently results in the formation of ectopic hippocampal mossy fibers in a 2-week-old pup. This indicates a high degree of axonal reorganization in the hippocampus. It remains controversial whether such reorganization is the cause or consequence of chronic seizures. We assume that these additional infrapyramidal mossy fibers may influence the way in which granule cells drive pyramidal cells in CA3. [ABSTRACT FROM AUTHOR]

We found a dramatic upregulation in the expression of LC3 in the hippocampus of rats upon status epilepticus (SE). However, the enhancement in LC3 expression might be caused by a reduction in lysosomal activity or by alterations in autophagosome-lysosome fusion leading to a cytosolic vesicular retention. In order to dissect this aspect, we monitored the spatial and temporal expression of LC3 and LAMP1 in the hippocampus of rats with SE. The Western blot analysis showed that the expression of LAMP1 was slightly increased in hippocampal cells at 6, 24, and 48 h post-SE. However, immunofluorescence analysis showed dramatic spatial changes in LAMP1 distribution within the hippocampus. LAMP1 in controls was localised only in cytosol as dot like staining, however at 24 h post-SE LAMP1 was not only highly expressed, but accumulated in mossy fibers of dentate gyrus. In parallel, we found few scattered LC3-positive-dots in neurites of dentate gyrus which co-localise with LAMP1-positive structures. We conclude that SE not only increased autophagosomal abundance, but also lysosomal activities and a massive accumulation of LAMP1 in axons of dentate gyrus. This could support the hypothesis that the marked increased autophagosomal abundance in cytosol reflects an increase in the autophagic activity more than an inhibition of autophagosomal clearance. Although LAMP1 may have contributed to cell damage in the selective vulnerable hippocampal CA1-subfield, it is also possible that lysosomal/autophagic mechanisms in mossy fibers were compensatory and reflected an attempt to survive the epileptic insult by breaking down non-essential components. [ABSTRACT FROM AUTHOR]

HS1-associated protein X1 (HAX-1) is a mitochondrial protein which interacts with a diverse group of molecules such as inflammatory cytokines; interleukin-1, hematopoietic lineage specific protein-1 and vimentin. It has been reported that HAX-1 may act as antiapoptotic protein in HeLa- and Jurkat cells after Fas-treatment, irradiation or serum deprivation. This underlines the evidence that HAX-1 might be involved in both receptor- and mitochondria-mediated apoptosis pathways. However, the role of HAX-1 in neuronal death induced by status epilepticus in the immature brain has not been reported. In this study, we performed a status epilepticus in rats and investigated the dynamic changes of HAX-1 expression, HtrA2 distribution and caspase-3 activation in the hippocampus. Western blot and immunohistochemistry analysis revealed that HAX-1 was expressed at very low levels in the hippocampus. Status epilepticus in the immature brain significantly induced increased cytosolic accumulation of HAX-1 in a biphasic manner, induced an upregulation of HtrA2 and enhanced caspase-3 activity in the selectively vulnerable hippocampal CA1-subfield. Taken together, these results suggested that HAX-1 is probably involved in the pathophysiology of cell death induced by epilepsy. [ABSTRACT FROM AUTHOR]

Omi/HtrA2 is a pro-apoptotic mitochondrial serine protease involved in caspase-dependent as well as caspase-independent cell death upon various brain injuries. However, the role of Omi/HtrA2 in neuronal death induced by status epilepticus (SE) in the immature brain has not been reported. In this study, we analyzed the contribution of serine protease Omi/HtrA2, its substrate X-linked inhibitor of apoptosis protein (XIAP) and the caspase-3 activation to damage of hippocamplal CA1 cells following lithium-pilocarpine SE in P14 rat pups. Status epilepticus in the immature brain significantly induced translocation of Omi/HtrA2 from mitochondria into the cytosol, increased cytosolic accumulation of Omi/HtrA2, induced appearance of XIAP-breakdown products and enhanced caspase-3 activity in the selectively vulnerable hippocampal CA1-subfield. Taken together, these results demonstrate for the first time that SE in the immature brain results in Omi/HtrA2 accumulation in the cytosol, where it probably promotes neuronal death by neutralizing and cleaving XIAP, one of the most potent endogenous inhibitors of apoptosis. [ABSTRACT FROM AUTHOR]