Department of Psychology, University of Washington, Seattle, Washington 98195-1525, USA.
J Comp Neurol. 2012 Apr 1;520(5):914-32. doi: 10.1002/cne.22738.
Retinal input plays an important role in the specification of topographically organized circuits and neuronal response properties, but the mechanism and timing of this effect is not known in most species. A system that shows dramatic dependence on retinal influences is the interhemispheric connection through the corpus callosum. Using ferrets, we analyzed the extent to which development of the visual callosal pattern depends on retinal influences, and explored the period during which these influences are required for normal pattern formation. We studied the mature callosal patterns in normal ferrets and in ferrets bilaterally enucleated (BE) at postnatal day 7 (P7) or P20. Callosal patterns were revealed in tangential sections from unfolded and flattened brains following multiple injections of horseradish peroxidase in the opposite hemisphere. We also estimated the effect of enucleation on the surface areas of striate and extrastriate visual cortex by using magnetic resonance imaging (MRI) data from intact brains. In BEP7 ferrets we found that the pattern of callosal connections was highly anomalous and the sizes of both striate and extrastriate visual cortex were significantly reduced. In contrast, enucleation at P20 had no significant effect on the callosal pattern, but it still caused a reduction in the size of striate and extrastriate visual cortex. Finally, retinal deafferentation had no significant effect on the number of visual callosal neurons. These results indicate that the critical period during which the eyes influence the development of callosal patterns, but not the size of visual cortex, ends by P20 in the ferret.
视网膜输入在特化拓扑组织的回路和神经元反应特性方面起着重要作用，但在大多数物种中，这种影响的机制和时间尚不清楚。一种对视网膜影响表现出明显依赖性的系统是通过胼胝体的大脑半球间连接。我们使用雪貂分析了视觉胼胝体模式的发育在多大程度上依赖于视网膜的影响，并探索了这些影响对正常模式形成所必需的时期。我们研究了正常雪貂和在出生后第 7 天（P7）或第 20 天（P20）双侧眼球摘除（BE）的雪貂的成熟胼胝体模式。在对侧半球多次注射辣根过氧化物酶后，在展开和平坦化的大脑的切线切片中显示出胼胝体模式。我们还通过使用来自完整大脑的磁共振成像（MRI）数据来估计眼球摘除对纹状和纹外视觉皮层表面积的影响。在 BEP7 雪貂中，我们发现胼胝体连接的模式非常异常，并且纹状和纹外视觉皮层的大小都显著减小。相比之下，在 P20 时眼球摘除对胼胝体模式没有显著影响，但仍导致纹状和纹外视觉皮层的大小减小。最后，视网膜去传入对视觉胼胝体神经元的数量没有显著影响。这些结果表明，眼睛影响胼胝体模式发育的关键时期，但不影响视觉皮层的大小，在雪貂中于 P20 结束。
