Glucocorticoid Receptor Deficient Neuronal Model And Involvement Of Glucocorticoid's Nongenomic Action In Excitotoxicity

Using immunobloting, immunofluorescence staining and RT-PCR techniques, our study revealed an interesting example of culture condition and embryonic stage dependent silence of glucocorticoid receptor (GR) expression in hippocampal neuron: in serum free cultural condition, hippocampal neurons from E16 and E18 showed silence of GR expression, but those from E20 and P0 did not. These GR deficient neurons can serve as a novel model for studying nongenomic effects of glucocorticoid (GC) in neural system. Using this model, we found that GC could enhance the NMDA neurotoxicity. Interestingly, the NMDA neurotoxicity itself is mediated by NR2B-containing NMDARs, whereas the enhancement effect of GC was mediated by NR2A-containing NMDARs. It is also found that GC rapidly potentiated NMDA induced p38 activation but inhibited ERK activation, and also intensified the NMDA induced increment of [Ca2+]i , which may underlie the nongenomic actions of the enhancing effect of GC on NMDA neurotoxicity. Moreover, the study also figured out a scenario of developmental dependent increasing of susceptibility to NMDA neurotoxicity in hippocampal neurons both in vivo and in vitro. Studies on NMDA induced calcium response and p38 activation suggested that NMDARs may link to different intracellular signaling pathways as a function of development, although the detail mechanism remains to be elucidated.