RESUMO
We investigated the pathophysiological mechanisms of glutamate-induced delayed neuronal damage in rat hippocampal slice cultures [Stoppini et al. (1991) J. Neurosci. Methods 37, 173-182], with propidium iodide as a marker of cell death. Exposure of the cultures to growth medium containing 10 mM glutamate for 30 min resulted in a slowly developing degeneration of hippocampal principal cells, starting from the medial end of the CA1 region and reaching the dentate gyrus by 48 h. By 24 h, most pyramidal cells in CA1 were damaged. An acute phase of degeneration preceded the delayed damage at 2-6 h, affecting cells in a spatially diffuse manner. When tetrodotoxin (0.5 microM) was present during the glutamate insult, a marked protection (mean 57%, P<0.001) of the CA1 damage was observed. Rather strikingly, when tetrodotoxin was applied immediately following or even with a delay of 30 min after the insult, a similar amount of protection was achieved. In field recordings carried out after the insult, the glutamate-treated slices exhibited spontaneously occurring negative shifts with a duration of 1-10 s and an amplitude of up to 400 microV in the CA3 region, whereas the control slices were always quiescent. Taken together, the results suggest that post-insult neuronal network activity, rather than the direct action of exogenous glutamate, is a major cause of delayed CA1 pyramidal cell death in the organotypic slices. These observations may have implications in the design of neuroprotective strategies for the treatment of brain traumas which are accompanied by delayed and/or distal neuronal damage.
Assuntos
Lesões Encefálicas/metabolismo , Morte Celular/fisiologia , Ácido Glutâmico/toxicidade , Hipocampo/efeitos dos fármacos , Degeneração Neural/metabolismo , Neurotoxinas/toxicidade , Células Piramidais/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Lesões Encefálicas/patologia , Lesões Encefálicas/fisiopatologia , Isquemia Encefálica/metabolismo , Isquemia Encefálica/patologia , Isquemia Encefálica/fisiopatologia , Morte Celular/efeitos dos fármacos , Epilepsia/metabolismo , Epilepsia/patologia , Epilepsia/fisiopatologia , Ácido Glutâmico/metabolismo , Hipocampo/metabolismo , Hipocampo/fisiopatologia , Degeneração Neural/induzido quimicamente , Degeneração Neural/fisiopatologia , Rede Nervosa/efeitos dos fármacos , Rede Nervosa/metabolismo , Rede Nervosa/fisiopatologia , Neurotoxinas/metabolismo , Técnicas de Cultura de Órgãos , Células Piramidais/metabolismo , Ratos , Tetrodotoxina/farmacologia , Fatores de TempoRESUMO
Synaptically evoked transmembrane movements of Ca2+ in the adult CNS have almost exclusively been attributed to activation of glutamate receptor channels and the consequent triggering of voltage-gated calcium channels (VGCCs). Using microelectrodes for measuring free extracellular Ca2+ ([Ca2+]o) and extracellular space (ECS) volume, we show here for the first time that synaptic stimulation of gamma-aminobutyric acid-A (GABAA) receptors can result in a decrease in [Ca2+]o in adult rat hippocampal slices. High-frequency stimulation (100-200 Hz, 0.4-0.5 s) applied in stratum radiatum close (
