Gabbott P L, Stewart M G
Biology Department, Open University, Milton Keynes, U.K.
Exp Brain Res. 1987;68(1):103-14. doi: 10.1007/BF00255237.
The quantitative effects of dark-rearing and light exposure on the ultrastructural characteristics of synapses and synaptic boutons in layer 4 of the rat visual cortex (area 17) have been investigated using stereological techniques. Two experimental groups (each containing 5 animals) were investigated-i) animals dark-reared upto weaning at 21 days post natum (21DPN) and then light exposed until 52DPN (Group 21/31), and ii) littermate animals totally dark-reared until 52DPN (Group 52dD). The results indicate a significantly higher mean density of synapses in the neuropil of layer 4 in group 21/31 (3.58 X 10(8).mm-3) compared with group 52dD (2.68 X 10(8).mm-3). Although the density per unit volume of synapses with identified asymmetrical synaptic membrane specialisations was not significantly different in group 21/31 than in group 52dD (but was significantly lower than animals reared normally), the density of synapses with identified symmetrical synaptic membrane specialisations was about 200% higher in group 21/31 versus group 52dD. However, significant differences were detected in the number of asymmetrical synapses established by single synaptic boutons in group 21/31 (1.21 +/- 0.11) compared with group 52dD (1.10 +/- 0.09). On the basis of the numbers of post-synaptic targets contacted by an individual synaptic bouton, a significantly higher density of synaptic boutons was found in group 21/31 (2.32 X 10(8).mm-3) compared with group 52dD (1.82 X 10(8).mm-3). Furthermore, planar quantitative data indicated significant intergroup differences in the ultrastructure of asymmetrical and symmetrical synaptic boutons. The results of this study provide evidence indicating marked structural alterations in the synaptic connectivity of layer 4 of the rat visual cortex following the light exposure of rats dark-reared upto weaning. Indeed visual deprivation severely affected the 'inhibitory' circuitry in the major thalamorecipient territory of the visual cortex.
利用体视学技术，研究了暗饲养和光照对大鼠视皮层（17区）第4层突触和突触小体超微结构特征的定量影响。研究了两个实验组（每组5只动物）：i）出生后21天（21DPN）断奶前一直暗饲养，然后光照至52DPN的动物（21/31组），ii）同窝动物一直暗饲养至52DPN（52dD组）。结果表明，与52dD组（2.68×10⁸.mm⁻³）相比，21/31组第4层神经毡中突触的平均密度显著更高（3.58×10⁸.mm⁻³）。虽然21/31组中具有明确不对称突触膜特化的突触单位体积密度与52dD组相比无显著差异（但显著低于正常饲养的动物），但21/31组中具有明确对称突触膜特化的突触密度比52dD组高约200%。然而，与52dD组（1.10±0.09）相比，21/31组单个突触小体形成的不对称突触数量存在显著差异（1.21±0.11）。根据单个突触小体接触的突触后靶点数量，21/31组（2.32×10⁸.mm⁻³）的突触小体密度显著高于52dD组（1.82×10⁸.mm⁻³）。此外，平面定量数据表明，不对称和对称突触小体的超微结构在组间存在显著差异。本研究结果提供了证据，表明断奶前一直暗饲养的大鼠光照后，大鼠视皮层第4层的突触连接存在明显的结构改变。事实上，视觉剥夺严重影响了视皮层主要丘脑接受区的“抑制性”回路。
