Consequences of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor blockade during status epilepticus in the developing brain.

To investigate if AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activation contributes to acute manifestations and long term consequences of status epilepticus (SE), we administered the AMPA receptor antagonist NBQX to P35 rats undergoing kainic acid (KA)-induced SE. NBQX (30 mg/kg/dose) given intraperitoneally (i.p.) at 30, 60 and 90 min after i.p. KA injection (12 mg/kg) reduced severity of SE. When tested as adults, rats that had received KA and NBQX were similar to controls with no long term impairment in visuospatial memory (assessed by the water maze test), or histologic damage in the CA1 or CA3 hippocampal subfields. However, both P35 groups, those receiving KA alone and those receiving KA and NBQX, had similar rates of spontaneous recurrent seizures (SRS). In P15 rats, NBQX resulted in increased acute mortality from KA associated SE. These results indicate that the effects of NBQX on KA-induced SE are age dependent, and that non-NMDA receptor activation contributes to the acute manifestations and to the long term sequelae seen after KA-induced SE in the prepubescent rat brain.

p53-dependent ceramide response to genotoxic stress.

Both p53 and ceramide have been implicated in the regulation of growth suppression. p53 has been proposed as the "guardian of the genome" and ceramide has been suggested as a "tumor suppressor lipid. " Both molecules appear to regulate cell cycle arrest, senescence, and apoptosis. In this study, we investigated the relationship between p53 and ceramide. We found that treatment of Molt-4 cells with low concentrations of actinomycin D or gamma-irradiation, which activate p53-dependent apoptosis, induces apoptosis only in cells expressing normal levels of p53. In these cells, p53 activation was followed by a dose- and time-dependent increase in endogenous ceramide levels which was not seen in cells lacking functional p53 and treated similarly. Similar results were seen in irradiated L929 cells whereby the p53-deficient clone was significantly more resistant to irradiation and exhibited no ceramide response. However, in p53-independent systems, such as growth suppression induced by TNF-alpha or serum deprivation, ceramide accumulated irrespective of the upregulation of p53, indicating that p53 regulates ceramide accumulation in only a subset of growth-suppressive pathways. Finally, ceramide did not increase p53 levels when used at growth-suppressive concentrations. Also, when cells lacking functional p53, either due to mutation or the expression of the E6 protein of human papilloma virus, were treated with exogenous ceramide, there was equal growth suppression, cell cycle arrest, and apoptosis as compared with cells expressing normal p53. These results indicate that p53 is unlikely to function "downstream" of ceramide. Instead, they suggest that, in situations where p53 performs a critical regulatory role, such as the response to genotoxic stress, it functions "upstream" of ceramide. These studies begin to define a relationship between these two pathways of growth inhibition.