We have previously shown that mitochondrial membrane potential disruption is 
involved in mechanisms underlying differential vulnerabilities to the 
excitotoxicity mediated by N-methyl-d-aspartate (NMDA) receptors between primary 
cultured neurons prepared from rat cortex and hippocampus. To further elucidate 
the role of mitochondria in the excitotoxicity after activation of NMDA 
receptors, neurons were loaded with the fluorescent dye calcein diffusible in 
the cytoplasm and organelles for determination of the activity of mitochondrial 
permeability transition pore (mPTP) responsible for the leakage of different 
mitochondrial molecules. The addition of CoCl(2) similarly quenched the 
intracellular fluorescence except mitochondria in both cultured neurons, while 
further addition of NMDA led to a leakage of the dye into the cytoplasm in 
hippocampal neurons only. An mPTP inhibitor prevented the NMDA-induced loss of 
viability in hippocampal neurons, while an activator of mPTP induced a similarly 
potent loss of viability in cortical and hippocampal neurons. Although NMDA was 
more effective in increasing rhodamine-2 fluorescence as a mitochondrial calcium 
indicator in hippocampal than cortical neurons, a mitochondrial calcium 
uniporter inhibitor significantly prevented the NMDA-induced loss of viability 
in hippocampal neurons. Expression of mRNA was significantly higher for the 
putative uniporter uncoupling protein-2 in hippocampal than cortical neurons. 
These results suggest that mitochondrial calcium uniporter would be at least in 
part responsible for the NMDA neurotoxicity through a mechanism relevant to 
promotion of mPTP orchestration in hippocampal neurons.