Long-term potentiation and glutamate release in the dentate gyrus: links to spatial learning.

Long-term potentiation (LTP) in the dentate gyrus of the anaesthetized rat is associated with a persistent increase in the concentration of glutamate in the extracellular compartment. At the in vitro level, this is mirrored by an increase in the ability of slices or synaptosomes from potentiated tissue to release glutamate in response to a depolarizing stimulus. In both cases, the activity-induced enhancement of glutamate release is dependent on the activation of the NMDA receptor. A similar increase in glutamate release in vitro is observed in the dentate gyrus prepared from rats trained in a variety of learning tasks, including classical conditioning and the Morris water maze. These results are consistent with the hypothesis that similar presynaptic mechanisms are engaged in LTP and learning.