Rasmusson D D, Webster H H, Dykes R W
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Somatosens Mot Res. 1992;9(4):279-89. doi: 10.3109/08990229209144777.
Multiple penetrations in the somatosensory cortex of three anesthetized raccoons 1 week following amputation of the fourth digit provided detailed information about somatotopy and neuronal responsiveness in the deafferented cortex. Recordings in a total of 601 penetrations (292 in deafferented cortex and 309 in the surrounding cortex) were compared with those from intact control animals described previously (Rasmusson et al., 1991). The level of spontaneous activity increased within the deafferented cortex, with 42% of the sites having high or moderate levels of spontaneous activity, in comparison with 18% in control animals. There was also an increase in the incidence of inhibitory responses to stimulation of adjacent digits (26% of the penetrations vs. 10% in control animals), confirming previous findings. These two variables, increased spontaneous activity and the presence of strong lateral inhibition, were highly correlated in individual penetrations. An unexpected finding was that the cortex representing the intact parts of forepaw was also disrupted with respect to these two measures, suggesting that amputation had an effect outside the deafferented region. In contrast, response properties that are more clearly a reflection of information processing in the dorsal column-medial lemniscal pathway (adaptation and threshold) were altered only within the deafferented region. The deafferented region was not homogeneous immediately after amputation, but consisted of a radically affected core region and a slightly affected fringe adjacent to the intact representations. This inhomogeneity had also been apparent with partial digit deafferentation, reported previously. The fringe, approximately 1 mm in width, may reflect overlapping projections from adjacent digits at one or more levels of the somatosensory pathway. Since the size of the fringe is similar to the maximum extent of reorganization found in other models of reorganization, the mechanisms of plasticity within this region may involve an unmasking of pre-existing synapses with slight modification in synaptic strength. However, the plasticity within the core region of the raccoon seen in these experiments, which may be 5 mm from nondeafferented cortex, requires more extensive changes, perhaps via polysynaptic pathways.
在三只麻醉浣熊第四指截肢1周后，对其体感皮层进行多次穿刺，提供了有关去传入皮层中躯体定位和神经元反应性的详细信息。将总共601次穿刺（292次在去传入皮层，309次在周围皮层）的记录与先前描述的完整对照动物的记录进行了比较（拉斯穆森等人，1991年）。去传入皮层内的自发活动水平增加，42%的位点具有高或中等水平的自发活动，而对照动物中这一比例为18%。对相邻手指刺激的抑制反应发生率也有所增加（26%的穿刺与对照动物中的10%），证实了先前的发现。在个体穿刺中，这两个变量，即自发活动增加和强烈的侧向抑制的存在，高度相关。一个意外的发现是，代表前爪完整部分的皮层在这两项指标上也受到了干扰，这表明截肢对去传入区域之外也有影响。相比之下，更清楚地反映背柱-内侧丘系通路中信息处理的反应特性（适应性和阈值）仅在去传入区域内发生改变。截肢后，去传入区域并非立即均匀一致，而是由一个受影响严重的核心区域和一个与完整表征相邻的受影响轻微的边缘区域组成。先前报道的部分手指去传入情况中，这种不均匀性也很明显。边缘区域宽约1毫米，可能反映了在体感通路的一个或多个水平上来自相邻手指的重叠投射。由于边缘区域的大小与在其他重组模型中发现的重组最大范围相似，该区域内可塑性的机制可能涉及对预先存在的突触进行轻微的突触强度修饰后使其暴露。然而，在这些实验中，浣熊核心区域内的可塑性，该区域可能距离未去传入皮层5毫米，需要更广泛的变化，可能通过多突触通路实现。
