Activity- and development-dependent down-regulation of TARPγ8 and GluA1 in cultured rat hippocampal neurons

Aim: Transmembrane AMPA receptor regulatory proteins (TARPs) regulate the trafficking and expression of AMPA receptors that are essential for the fast excitatory synaptic transmission and plasticity in the brain. This study aimed to investigate the activity-dependent regulation of TARP gamma 8 in cultured rat hippocampal neurons. Methods: Rat hippocampal neurons cultured for 7-8 DIV or 17-18 DIV were exposed to the AMPA receptor agonist AMPA at a non-toxic concentration (100 mu mol/L) for 4 h. The protein levels of TARP gamma 8 and AMPA receptor subunits (GluA1 and GluA2) were measured using Western blotting analysis. AMPA-induced currents were recorded in the neurons using a whole-cell recording method. Results: Four-hour exposure to AMPA significantly decreased the protein levels of TARP gamma 8 and GluA1 in the neurons at 17-18 DIV, but did not change the protein level of TARP gamma 8 in the neurons cultured at 7-8 DIV. AMPA-induced down-regulation of TARP gamma 8 and GluA1 was largely blocked by the calpain inhibitor calpeptin (50 mu mol/L), but not affected by the caspase inhibitor zVAD (50 mu mol/L). Four-hour exposure to AMPA significantly decreased AMPA-induced currents in the neurons at 17-18 DIV, which was blocked by co-exposure to calpeptin (50 mu mol/L). Conclusion: The down-regulation of TARP gamma 8 and GluA1 protein levels and AMPA-induced currents in cultured rat hippocampal neurons is activity-and development-dependent, and mediated by endogenous calpain.