Silver M A, Stryker M P
W.M. Keck Center for Integrative Neuroscience, Department of Physiology, University of California, San Francisco, California 94143-0444, USA.
J Neurosci. 1999 Dec 15;19(24):10829-42. doi: 10.1523/JNEUROSCI.19-24-10829.1999.
Monocular eyelid closure in cats during a critical period in development produces both physiological plasticity, as indicated by a loss of responsiveness of primary visual cortical neurons to deprived eye stimulation, and morphological plasticity, as demonstrated by a decrease in the total length of individual geniculocortical arbors representing the deprived eye. Although the physiological plasticity appears maximal after 2 d of monocular deprivation (MD), the shrinkage of deprived-eye geniculocortical arbors is less than half-maximal at 4 d and is not maximal until 7 d of deprivation, at which time the deprived arbors are approximately half their previous size. To study this form of plasticity at the level of individual thalamocortical synapses rather than arbors, we developed a new double-label colocalization technique. First, geniculocortical afferent arbors serving either the deprived or nondeprived eye were labeled by injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin into lamina A of the lateral geniculate nucleus. Then, using antibodies to synaptic vesicle proteins, we identified presynaptic terminals within the labeled arbors in layer IV of the primary visual cortex. Analysis of serial optical sections obtained using confocal microscopy allowed measurement of the numerical density of presynaptic sites and the relative amounts of synaptic vesicle protein in geniculocortical afferents after both 2 and 7 d of MD. We found that the density of synapses in geniculocortical axons was similar for deprived and nondeprived afferents, suggesting that this feature of the afferents is conserved even during periods in which synapse number is reduced by half in deprived-eye arbors. These results are not consistent with the hypothesis that a rapid loss of deprived-eye geniculocortical presynaptic sites is responsible for the prompt physiological effects of MD.
在发育的关键时期，猫的单眼眼睑闭合会产生生理可塑性，这表现为初级视皮层神经元对被剥夺眼刺激的反应性丧失；同时也会产生形态可塑性，这表现为代表被剥夺眼的单个膝状体皮质树突总长度的减少。虽然单眼剥夺（MD）2天后生理可塑性似乎达到最大，但被剥夺眼的膝状体皮质树突在4天时收缩不到最大程度的一半，直到剥夺7天时才达到最大程度，此时被剥夺的树突约为之前大小的一半。为了在单个丘脑皮质突触而非树突层面研究这种可塑性形式，我们开发了一种新的双标记共定位技术。首先，通过将顺行示踪剂菜豆白细胞凝集素注射到外侧膝状体核的A层，标记服务于被剥夺或未被剥夺眼的膝状体皮质传入纤维。然后，使用针对突触囊泡蛋白的抗体，我们在初级视皮层IV层的标记纤维中识别出突触前终末。使用共聚焦显微镜对连续光学切片进行分析，使得我们能够测量MD 2天和7天后膝状体皮质传入纤维中突触前位点的数量密度以及突触囊泡蛋白的相对含量。我们发现，被剥夺和未被剥夺的传入纤维在膝状体皮质轴突中的突触密度相似，这表明即使在被剥夺眼的树突中突触数量减少一半的时期，传入纤维的这一特征仍得以保留。这些结果与以下假设不一致，即被剥夺眼的膝状体皮质突触前位点的快速丧失是MD迅速产生生理效应的原因。
