Synapsins as a family of presynaptic terminal phosphoprotein participates in 
neuronal development, but their role in the synaptic plasticity of visual cortex 
is unclear. In this study, the impact of monocular deprivation (MD) on dynamic 
changes of isoform-specific protein expression and site 1 phosphorylation of 
synapsins in visual cortex of the postnatal mice were observed by using the 
technique of Western blot analysis. The results showed that the total (T-) 
protein levels of synapsins including the isoform of Ia/b, IIa/b and IIIa were 
about 21-26% of adult level in visual cortex of mice at postnatal 7 days (P7), 
and then the T-synapsin Ia/b and IIb could quickly reach adult level at P35. 
However, the T-synapsin IIa and IIIa increased more slowly (71-74% at P35), and 
then kept increasing in the visual cortex of mice at P60. Unlike to the changes 
of T-synapsins, the level of phosphorylated (P-) synapsin Ia/b (not IIa/b and 
IIIa) at site 1 increased with development to the highest level at P21, and then 
decreased rapidly to a low level in visual cortex of mice at P35-60. In 
addition, we found that the levels of P-synapsin Ia/b increased significantly in 
left visual cortex of P28 and P35 (not P21 and P42) mice with 1-week MD of right 
eye; and no significant changes of T-synapsins were observed in both left and 
right sides of visual cortex in P21-42 mice with MD treatment. These results 
suggested that the isoform-specific protein expression and site-1 
phosphorylation of synapsins might play a different role in the synaptic 
plasticity of visual cortex, and MD delays the dynamic changes of phosphorylated 
synapsin Ia/b at site-1 in contralateral visual cortex of juvenile mice.