Kossut M, Juliano S L
Department of Neurophysiology, Nencki Institute of Experimental Biology, Warsaw, Poland.
Neuroscience. 1999;92(3):807-17. doi: 10.1016/s0306-4522(98)00722-2.
We examined the potential for changes in cortical connectivity to accompany long-term plastic changes in functional cortical representations of mystacial vibrissae. Plasticity in the barrel cortex of young adult mice was evoked by vibrissectomy that spared row C of whiskers. We found that 2-deoxyglucose brain mapping causes a progressive expansion of cortical representation of the spared vibrissae. Two months after vibrissectomy, when the width of the cortical map of the spared row of vibrissae doubled, living cortical slices of the barrel cortex were injected with fluorescent dextrans. The injections were centered on spared, deprived and control vibrissal columns. The injections labeled three intracortical projection systems: (i) local connections from one vibrissal column to neighboring columns; (ii) long-range projections running in the septa and walls of the barrels and spanning several barrels; and (iii) very-long-range fibers running horizontally in the lower part of layer V. The local, short-range projection system was analysed following small injections into the centers of columns in layers III and IV. We found that injections into spared barrels labeled axons extending for significantly greater distances in all layers (except layer V), and labeled cell bodies situated significantly further, than after injections into deprived or control barrels. Also, the total axonal density labeled by injections into the spared barrel was higher by 70% than for the deprived or control barrels. Alterations of topographical maps in adult somatosensory cortex may occur immediately after functional denervation, but may also increase with time, as in the case of our experimental situation. Our results indicate that persistent, long-term plastic change can remodel connectivity in the barrel cortex.
我们研究了在触须功能皮层表征发生长期可塑性变化时，皮层连接性改变的可能性。通过切除触须但保留C排触须的手术，诱发了成年幼鼠桶状皮层的可塑性。我们发现，2-脱氧葡萄糖脑图谱显示，保留触须的皮层表征会逐渐扩展。触须切除术后两个月，当保留触须排的皮层图谱宽度翻倍时，向桶状皮层的活体切片注射荧光葡聚糖。注射集中在保留、剥夺和对照触须柱上。这些注射标记了三个皮层内投射系统：(i) 从一个触须柱到相邻柱的局部连接；(ii) 在桶隔和桶壁中运行并跨越几个桶的长距离投射；(iii) 在V层下部水平运行的极长距离纤维。在向III层和IV层柱中心进行小剂量注射后，对局部短距离投射系统进行了分析。我们发现，与向剥夺或对照桶注射相比，向保留桶注射标记的轴突在所有层（V层除外）延伸的距离明显更长，标记的细胞体位置也明显更远。此外，向保留桶注射标记的总轴突密度比剥夺或对照桶高70%。成年体感皮层地形图的改变可能在功能去神经支配后立即发生，但也可能随时间增加，就像我们实验中的情况一样。我们的结果表明，持续的长期可塑性变化可以重塑桶状皮层的连接性。
