Status Epilepticus Enhances Depotentiation after Fully Established LTP in an NMDAR-Dependent but GluN2B-Independent Manner

Neural Plast. 2016:2016:6592038. doi: 10.1155/2016/6592038. Epub 2016 Jan 3.

Abstract

N-Methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) can be reversed by low-frequency stimulation (LFS) referred to as depotentiation (DP). We previously found GluN2B upregulated in CA1 neurons from post-status epilepticus (post-SE) tissue associated with an enhanced LTP. Here, we tested whether LFS-induced DP is also altered in pathological GluN2B upregulation. Although LTP was enhanced in post-SE tissue, LTP was significantly reversed in this tissue, but not in controls. We next tested the effect of the GluN2B subunit-specific blocker Ro 25-6981 (1 μM) on LFS-DP. As expected, LFS had no effect on synaptic strength in the presence of the GluN2B blocker in control tissue. In marked contrast, LFS-DP was also attained in post-SE tissue indicating that GluN2B was obviously not involved in depotentiation. To test for NMDA receptor-dependence, we applied the NMDA receptor antagonist D-AP5 (50 μM) prior to LFS and observed that DP was abolished in both control and post-SE tissue confirming NMDA receptor involvement. These results indicate that control Schaffer collateral-CA1 synapses cannot be depotentiated after fully established LTP, but LFS was able to reverse LTP significantly in post-SE tissue. However, while LFS-DP clearly required NMDA receptor activation, GluN2B-containing NMDA receptors were not involved in this form of depotentiation.

MeSH terms

  • Animals
  • Electric Stimulation
  • Excitatory Postsynaptic Potentials / drug effects
  • Hippocampus / drug effects
  • Hippocampus / physiopathology*
  • Long-Term Potentiation*
  • Long-Term Synaptic Depression*
  • Male
  • Phenols / administration & dosage
  • Pilocarpine
  • Piperidines / administration & dosage
  • Rats, Wistar
  • Receptors, N-Methyl-D-Aspartate / antagonists & inhibitors
  • Receptors, N-Methyl-D-Aspartate / physiology*
  • Status Epilepticus / chemically induced
  • Status Epilepticus / physiopathology*
  • Up-Regulation

Substances

  • NR2B NMDA receptor
  • Phenols
  • Piperidines
  • Receptors, N-Methyl-D-Aspartate
  • Ro 25-6981
  • Pilocarpine