NMDA-receptor blockade by CPP impairs post-training consolidation of a rapidly acquired spatial representation in rat hippocampus

Eur J Neurosci. 2005 Sep;22(5):1201-13. doi: 10.1111/j.1460-9568.2005.04272.x.

Abstract

Recent evidence suggests that N-methyl-D-aspartate (NMDA)-receptor mediated plasticity in hippocampus has a more subtle role in memory-based behaviours than originally thought. One idea is that NMDA-based plasticity is essential for the consolidation of post-training memory but not for the initial encoding or for short-term memory. To further test this idea we used a three-phase variant of the hidden goal water maze task. In the first phase, rats were pre-trained to an initial location. Next, intense, massed training was done in a 2-h interval to teach the rats to go to a new location after either an injection of the NMDA receptor antagonist (6)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) or of vehicle. Finally, under drug-free conditions 24 h after new location training, a competition test was done between the original and new locations. We find that N-methyl-D-aspartate (NMDA)-receptor blockade has little or no effect on new location training. In contrast, when tested 24 h later, the strength of the trace for the new location learned during NMDA-receptor blockade was much weaker compared with the trace for the new location learned after saline injection. Further experiments showed similar effects when NMDA-receptors were blocked immediately after the new location training, suggesting that this is a memory consolidation effect. Our results therefore reinforce the notion that hippocampal NMDA-receptors participate in post-training memory consolidation but are not essential for the processes necessary to learn or retain navigational information in the short term.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Behavior, Animal
  • Excitatory Amino Acid Antagonists / pharmacology*
  • Hippocampus / drug effects
  • Hippocampus / physiology*
  • Maze Learning / radiation effects
  • Piperazines / pharmacology*
  • Rats
  • Reaction Time / drug effects
  • Reaction Time / physiology
  • Receptors, N-Methyl-D-Aspartate / antagonists & inhibitors
  • Receptors, N-Methyl-D-Aspartate / physiology*
  • Retention, Psychology / drug effects*
  • Retention, Psychology / physiology
  • Space Perception / drug effects*
  • Space Perception / physiology
  • Time Factors

Substances

  • Excitatory Amino Acid Antagonists
  • Piperazines
  • Receptors, N-Methyl-D-Aspartate
  • 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid