Neuronal activity regulates protein and gene expressions of GluR2 in postnatal rat visual cortical neurons in culture

Ionotropic glutamate receptors, the principal excitatory neurotransmitter receptors in the CNS, are classified into NMDA and non-NMDA subtypes. Previously, we found a direct relationship between neuronal activity and NMDA receptor subunit 1 in rat primary neuronal cultures and monkey visual cortex. The present study focused on the relationship between neuronal activity and subunit 2 of AMPA glutamate receptor, GluR2. GluR2 controls Ca2+ permeability of AMPA receptors, and the transcription of its gene is activated by nuclear respiratory factor 1, which also activates the transcription of a few subunit genes of cytochrome oxidase ( CO). Primary neuronal cultures of postnatal rat visual cortex were subjected to impulse blockade with tetrodotoxin (TTX) for 6 days, or 20 mM KCl depolarizing treatment for 1, 2, 5, 10, 20, 30, and 40 hrs. After 20 hrs of KCl treatment, GluR2 immunoreactivity and CO activity were significantly increased above controls ( P < 0.01), and both remained high at 30 and 40 hrs of treatment. However, GluR2 mRNA level as shown by in situ hybridization was already up-regulated above controls after 10 hrs of KCl treatment ( P < 0.01) and remained elevated with longer periods of depolarization. TTX blockade, on the other hand, induced a significant down-regulation of GluR2 immunoreactivity, GluR2 gene expression as well as CO activity ( P < 0.01 for all). Our results indicate that both protein and mRNA expressions of GluR2 in cultured visual cortical neurons are tightly controlled by neuronal activity.