Analysis of neuronal death in the central nervous system using a new apoptosis model

To examine in detail neural apoptosis in the central nervous system (CNS) for the establishment of new therapies, we have developed an experimental in vitro model of neuronal death and analyzed the mechanism of apoptosis. Septal nuclei were dissected from embryonic brains (E16) of Wistar rats and cultured in chemically defined medium. Highly enriched neurons were obtained from the cultures at 4 days. Exposure to heat shock (43.0 degrees C, 60 min) between 24 and 36 h later, resulted in the death of approximately 70% of cells. Morphologically, dying neurons showed disruption of neurites, nuclear condensation, multiple nuclear fragments, condensation of cytoplasm and multiple cellular fragmentation. Agarose electrophoresis of chromosomal DNA revealed a typical ladder-pattern of fragmentation. Following heat treatment, incubation at 37 degrees C was necessary to detect DNA fragmentation. Quantitative analysis by in situ terminal deoxynucleotidyl transferase assay, revealed that the percentage of apoptotic cells markedly increased 8 h after heat treatment, and continued to gradually increase up until 30 h. Neuronal death and DNA fragmentation were prevented by inhibiting RNA and protein synthesis. Cell death and the DNA cleavage were also inhibited by cultivation in calcium-free medium. The addition of homogenous basic fibroblast growth factor to the medium markedly enhanced cell survival under these pathogenic conditions. These results suggest that neural cell death after mild heat treatment has apoptotic characteristics and may be useful for analyzing the mechanism of apoptosis. The clinical application of drugs acting against molecular components and as well as neurotrophic factors, may in the future prevent apoptosis in neural disease.