1. Synaptophysin is responsible for the cycling of the synaptic vesicles containing the neurotransmitter, and it can be phosphorylated. 2. This study examined whether repeated whisker stimulation alters the expression of synaptophysin mRNA in the rat barrel cortex, and found induced expression of synaptophysin mRNA in the contralateral barrel cortex compared to that in the ipsilateral hemi sphere. 3. This result suggests that synaptophysin is involved in the modulation of the synaptic plasticity.