Dynamics of olfactory learning-induced up-regulation of L1 in the piriform cortex and hippocampus.

L1 is a cell adhesion molecule implicated in the formation of neural circuits and synaptic plasticity. We have examined the sequence and time-frame in which modifications in the synaptic expression of L1 occur in the piriform cortex and hippocampus in the course of rule learning of an olfactory discrimination task. Rats were trained to choose the correct odour in a pair to be rewarded with drinking water. Such training requires 6-8 days on average before rats reach maximal performance. We observed a learning-induced L1 up-regulation that occurred at an early training stage in the piriform cortex but only after rule-learning establishment in the hippocampus. We suggest that the dynamics of L1 up-regulation may reflect the functional role of these brain regions in olfactory rule learning.