The primate striate cortex is parceled into functional modules and streams revealed partly by the distribution of the enzyme cytochrome oxidase (CO). CO is a sensitive indicator of neuronal functional integrity, not only under normal conditions but also in response to visual deprivation. Deprived cortical neurons do not response alike to the same functional insult; the metabolically most active ones are most vulnerable. Despite the wide use of CO, little is known about the molecular mechanism of its regulation, which is critical for understanding how visual cortical neurons regulate their activity-dependent energy metabolism. CO, a bigenomic enzyme, requires precise coordination between the nuclear and the mitochondrial genomes to form a functional holoenzyme. Two transcription factors, nuclear respiratory factors 1 and 2 (NRF-1 & NRF-2) may play a coordinating role. They are known to activate genes for some of the nuclear-encoded CO subunits, and a gene that indirectly regulates the production of mitochondrial-encoded CO subunits. The goal of the PI is to probe these transcription factors at the protein and mRNA levels in the visual cortex of normal and visual deprived monkeys. The distribution of these proteins will be compared to CO activity, and the density of the NRF-2 subunits, (and (, will be compared to the density of CO in distinct metabolic cell types within cortical puffs. If NRF-1 and NRF-2 are molecularly linked to CO expression in vivo, then their distributions should closely correlate with that of CO. Monocular deprivation will determine if the regulation of NRF-1 and NRF-2 is activity-dependent and whether this occurs by translational or transcriptional control. An in vitro model of primary cultures of rat visual cortical neurons will reveal how NRF-1 responds to depolarizing stimulation, and if the time course of the response is upstream of CO gene expression in the two genomes. The gene for a glutamate receptor, GluR2, was recently reported to be activated by NRF-1 in vitro. As glutamate is a major excitatory transmitter in visual neurons, the co-expression of GluR2 and NRF-1 may provide another link between neuronal activity and energy metabolism. NRF-1 knockout mice will be studied to see if visual cortical neurons are adversely affected, if levels of CO & GluR2 are reduced, and if NRF-2 is up regulated in compensation. Results from these studies are expected to provide insight into the molecular basis of metabolic responses of visual cortical neurons to changing functional demands.
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