Synaptic mechanisms of olfactory recognition memory.

The complexity and inaccessibility of the mammalian brain prevent the localization and description of memory traces and the definition of the processes that produce memories. The model reviewed here is the olfactory recognition memory formed to male pheromones by a female mouse at mating. The memory trace has been localized to the reciprocal dendrodendritic synapse between mitral cells and granule cells in the accessory olfactory bulb. An increase in noradrenaline after mating reduces inhibitory transmission of gamma-aminobutyric acid (GABA) from the granule cells to mitral cells and induces an olfactory memory of pheromones present at mating. Recent work has shown that the activation of mGluR2, a metabotropic glutamate receptor, localized at granule cell dendrites suppresses the GABA inhibition of the mitral cells and permits the formation of a specific olfactory memory that faithfully reflects the memory formed at mating. This simple olfactory memory may provide an excellent model system with which to investigate the molecular mechanisms of the synaptic plasticity involved in learning and memory.