Expression and regulation of NMDA receptor subunit R1 and neuronal nitric oxide synthase in cortical neuronal cultures: Correlation with cytochrome oxidase

Our previous studies showed a differential distribution of the glutamatergi c terminals in cytochrome oxidase-rich and -poor regions of the visual cort ex. The NMDA type of glutamate receptors have been proposed to be involved in the activation of nitric oxide synthase to produce nitric oxide, the neu rotransmitter. In the present study, we hypothesized that the expressions o f glutamate receptor, NMDA receptors (NMDAR1) and neuronal nitric oxide syn thase (nNOS) were colocalized and were also correlated with that of cytochr ome oxidase (CO) in a subset of neurons. We used primary cultures of postna tal rat visual cortical neurons as a model system, so that we could examine both the somatic and dendritic expressions of these neurochemicals in indi vidual neurons. We found a difference in the sequence of developmental expr essions of NMDAR1, nNOS, CO, and Na+/K+ ATPase. Triple labeling showed that all nNOS-positive neurons were immunoreactive for NMDAR1, and a subpopulat ion of them had high CO activity. The expression of NMDAR1 was positively c orrelated with CO activity. This is consistent with our previous finding th at CO activity is strongly governed by excitatory glutamatergic synapses. A fter 40 hours of depolarizing potassium chloride treatment, CO activity was increased, and NMDAR1and nNOS levels were up-regulated in parallel. One we ek of tetrodotoxin significantly decreased the expression of NMDAR1, nNOS, and CO activity. Our results demonstrate that NMDA receptors and nNOS do co -exist in a subset of neurons that have high CO activity and their expressi ons are under the control of neuronal activity.