Remodeling of reciprocal synapses associated with persistence of long-term memory.

We investigated a model of long-term memory in which the female mouse establishes pheromonal memory of its partner at mating. We examined the reciprocal synapses of the accessory olfactory bulb and found that pheromonal memory was associated with morphological changes in excitatory synapses in the early phase of memory acquisition and by changes in inhibitory synapses in the late phases of memory persistence. After extinction of pheromonal memory, these morphological changes were no longer present. These findings suggest that the persistence of pheromonal memory is associated with continuous and dynamic changes in the morphological plasticity of reciprocal synapses in the accessory olfactory bulb.