What neurobiological mechanisms in hippocampus support rapid spatial learning with familiar information in the Morris Water Task?

Long-term potentiation (LTP) is proposed as a molecular mechanism for learning and memory. N-methyl-D-aspartate receptors (NMDARs) are implicated during LTP and new learning. However, if rats are pre-trained prior to new learning NMDARs are not needed. Rather the activation of voltage gated calcium channels (VGCCs) and associated calcium influx might be responsible for LTP independent of NMDARs, and new learning with familiar information. The hypothesis was that to impair new learning with familiar information both NMDARs and VGCCs would need to be blocked. Rats were trained in a version of the Morris water task, consisting of a pre-training, mass-training, and a probe test. Before mass-training NMDARs and VGCCs were blocked in the hippocampus using AP5 and Verapamil, which are receptor antagonists. All rats were able to learn regardless of their experimental condition, which means that activation of NMDARs and VGCCs is not crucial for new spatial learning with familiar information.