Silent synapses and experience-dependent development in visual cortex

视觉反应特性在出生后视觉皮层发育过程中以经验依赖的方式得到完善。未成熟的中枢兴奋性突触通常有NMDA受体，但没有功能性AMPA受体。这种被称为沉默突触的突触被转化为具有AMPA受体的功能性突触。为了研究视觉皮层沉默突触的年龄和经验依赖性变化，我们在小鼠视觉皮层切片中记录了2/3层锥体神经元的兴奋性突触电流。沉默突触在睁眼前大量存在于2/3层锥体细胞中，在正常视觉环境下，沉默突触随着发育而减少。这种变化是通过剥夺小鼠出生后在黑暗的房间里饲养的视觉输入来阻止的，即使成年，沉默的突触仍然相当大。这项研究首次表明，如果感觉输入从出生起就被剥夺，锥体细胞皮质内突触的沉默突触会持续到成年。从沉默突触到功能突触转换的年龄和经验依赖性与视觉皮质细胞视觉反应的可修饰性相似。这表明，沉默突触向功能突触的转变是经验依赖的视觉皮层回路和功能细化的突触机制之一。

Visual response properties are refined in an experience-dependent manner during postnatal development in visual cortex. Immature central excitatory synapses often have NMDA receptors but not functional AMPA receptors. Such synapses, called silent synapses, are converted into functional synapses with AMPA receptors. To examine age and experience-dependent changes in silent synapses of visual cortex, we recorded excitatory synaptic currents from layer 2/3 pyramidal neurons in mouse visual cortial slices. Silent synapses are abundantly present in layer 2/3 pyramidal cells before eye opening period and they decreases with development in normal visual environment. This change was prevented by deprivation of visual inputs by rearing mice in dark room from birth and silent synapses remains considerably even until adulthood. This study shows for the first time that silent synapses persist at intracortical synapses in pyramidal cells until adulthood if sensory inputs are deprived from birth. Age and experience dependence of conversion from silent synapses to functional ones is similar to that in modifiability of visual responsiveness of visual cortical cells. It suggests that the transition of silent to functional synapses is one of the synaptic mechanisms underlying experience dependent refinement visual cortical circuit and function.