Translation of NMDA receptor subunits GluN1 and GluN2A increases after LTP induction in adult rats

AGUIRRE AI; BAEZ MV; CERCATO MC; OBERHOLZER MV; JERUSALINSKY DA

Barcelona

Congreso; 8th FENS Forum of Neuroscience; 2012

Federation of European Neuroscience Societies (FENS)

NMDA receptors (NMDAR) are tetramers containing two GluN1 and two variable regulatory subunits, which determines some NMDAR functional properties. In rat hippocampus major GluN2 subunits are GluN2A and GluN2B, being GluN2A predominat at mature synapses. Belloni and Nicoll (2007) reported that LTP induction in hippocampal pyramidal cells of P2 or P9 rats, produced immediate kinetic changes in voltage clamp recordings and modified the sensitivity to a GluN2B selective antagonist. This was interpreted as a rapid decrease in GluN2B-containing NMDAR –attributed to endocytosis- and as an increase in GluN2A-containing NMDAR at the cell surface -attributed to an increased delivery of GluN2A-containing receptors to the synaptic membrane. Little is known about expression -transcription-translation- of GluN2 subunits longer after LTP induction. Hence, to evaluate NMDAR subunits, field potentials were recorded from hippocampal fresh slices of young adult rats (P42-60). LTP was induced by a theta burst stimulation protocol. The slices were analyzed by Westernblot in order to determine GluN1, GluN2A and GluN2B levels. Preliminary results showed a slight, though non-significant increase in GluN1 and GluN2B 30 min after LTP induction. At 70 min there were conspicuous increases in GluN1 and GluN2A levels (about 6 and 5 fold respectively). Preincubation of slices with the translation blocker cycloheximide seemed to prevent those changes. Immunofluorescence assays of cultured hippocampal neurons treated with high KCl pulses (considered an LTP-like inducing protocol), showed that the increase in NMDAR subunits predominantly occurred at dendritic level. Therefore, our findings show that GluN2A expression is highly modified during LTP establishment long after induction, strongly supporting the hypothesis for a direct involvement of postsynaptic NMDARs in LTP establishment and maintenance, with a translation-dependent component. This also suggest that NMDAR subunits could be among the main plasticity proteins. Further assays are being performed to determine whether this change is transcription-dependent. Support: ECOS-A08S04, LIA-DEVENIR(CONICET/CNRS).