Changes in suhcellular distribution and phosphorylation of GluR1 in lesioned striatum of 6-hydroxydopamine-lesioned and L-dopa-treated rats

Recent evidence has linked striatal amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor function to the adverse effects of long-term dopaminergic treatment in Parkinson's disease. The phosphorylation of AMPA subunit, GluR1, reflects AMPA receptor activity. To determine whether serine phosphorylation of GluR1 subunit by activation of Ca2+/calmodulin-dependent protein kinase 11 (CaMKII) contributes to the process, we examined the effects of unilateral nigrostriatal depletion with 6-hydroxydopamine and subsequent L-dopa treatment on motor responses and phosphorylation states. Three weeks of L-dopa administration to rats shortened the duration of the rotational response. We found a significant reduction in the abundance of both phosphorylated GluR1 at serine-831 site (pGluR1S831) and GluR1 in the cell plasma membrane of lesioned striatum. Chronic treatment of lesioned rats with L-dopa markedly upregulated a concomitant normalization of the plasma membrane GluR1 abundance, which lasted at least 1 day after withdrawal of chrome L-dopa treatment. Our immunostaining data showed that these changes were confined to parvalbumin-positive neurons where GluR1 subunits are exclusively expressed. Both the altered motor response duration and the degree of pGluR1S831 were attenuated by the intrastriatal administration of CaMKII inhibitor KN-93. These findings suggest that activation of CaMKII contributes to both development and maintenance of motor response duration alterations, through a mechanism that involves an increase in pGluR1S831 within parvalbumin-positive neurons.