NR2A-containing NMDA receptors are required for L-LTP induction and depotentiation in CA1 region of hippocampal slices

Long-term potentiation (LTP) is a well-characterized form of synaptic plasticity that fulfills many of the criteria for the neural correlate of memory. LTP reversal (or depotentiation, DP) is thought to correlate with prevention or elimination of memory storage. LTP during and immediately after induction can be easily reversed by afferent stimulation, when applied within the optimal time window. The aim of the present study was to determine whether later-phase LTP (L-LTP) could be reversed by special patterned stimulation applied at 2 h after LTP induction, as well as to characterize the receptor mechanisms underlying this reversal. Field excitatory postsynaptic potentials evoked by Schaffer collateral stimulation were recorded from the CA1 subfield of adult rat hippocampal slices. Results demonstrated that stable LTP, which was induced by six theta-burst stimulations, was mediated by NR2A-containing N-methyl-d-aspartate receptors (NMDARs). This L-LTP was partially reversed by high-intensity paired-pulse low-frequency stimulation (HI-PP-LFS) and was inhibited by Zn2+ (30 nm), a voltage-independent NR2A-NMDAR antagonist. However, NR2B-NMDAR antagonists (Ro 25-6981, 1 mu m) displayed no effect on L-LTP reversal. L-LTP partial reversal was also induced by HI-PP-LFS, when the protein synthesis inhibitors anisomycin (25 mu m) and cycloheximide (60 mu m) were applied following LTP induction. These results suggested that NR2A-containing NMDARs are required for L-LTP induction and DP in the hippocampal CA1 area of adult rats. Moreover, HI-PP-LFS was an effective stimulation pattern to induce DP.