The Exacerbation of Hippocampal Excitotoxicity by Glucocorticoids Is Not Mediated by Apoptosis

Abstract

Both endogenous and exogenous glucocorticoids (GCs) are known to cause apoptosis in a number of peripheral tissues and in some cases in the CNS. Additionally, GCs can exacerbate the neuron loss associated with such acute neurological insults as hypoxia-ischemia, excitotoxicity, and metabolic disruption. This exacerbation is accompanied by increased accumulation of glutamate in the synapse, excessive cytosolic calcium, and increased oxygen radical activity, markers usually attributed to pathways of necrotic cell death. It is also known that acute insults can involve apoptotic mediators. In this context, one outstanding question that has received little attention is whether the exacerbation of insult-mediated cell death in neurons is apoptotic in mechanism. In this study we investigate whether the GC-mediated exacerbation of hippocampal excitotoxicity in culture involves apoptosis. Specifically, we show that while the magnitude of hippocampal neuron death caused by the excitotoxin kainic acid is indeed worsened in the presence of GCs, there is no evidence of increased markers of apoptosis. Specifically, we show that neither kainic acid nor GCs alone, or in combination, cause activation of caspase 3, a critical executor of insult-induced apoptosis. Furthermore, while kainic acid causes a significant incidence of apoptotic nuclear condensation, the incidence of this morphological indicator of apoptosis is not worsened by GCs. Thus, GCs appear to augment excitotoxic death in hippocampal neurons without augmenting the occurrence of apoptosis. We suggest that this finding is to be expected, given some energetic features of GC action and the energetic demands of apoptosis.