Doetsch G S, Stoney S D, Hauge D H
Department of Surgery, Section of Neurosurgery, Medical College of Georgia, Augusta 30912.
Exp Neurol. 1992 Feb;115(2):250-9. doi: 10.1016/0014-4886(92)90059-y.
The aim of this study was to compare the physiological properties of single neurons in the glabrous (G) and heterogeneous (H) subdivisions of primary somatosensory digit 3 cortex of adult raccoons. Extracellular recordings were obtained from 50 G neurons whose receptive fields (RFs) were confined to the glabrous skin of a digit, and 41 H neurons whose RFs were located on hairy skin, claws, or mixtures of skin types. Both electrical and mechanical stimulation of the digits were used to assess excitatory neuronal responsiveness. The two sets of neurons, which had nearly identical depth distributions, differed considerably in their input convergence: (i) the percentage of neurons (%N) responding to electrical or mechanical stimulation of each off-focus digit and (ii) the number of digits from which individual cells could be driven were significantly greater for H neurons. Those G and H cells which could be excited by off-focus inputs were examined for probability of response (P), number of spikes per response (S/R), and latency of response (L) to digit stimulation. Surprisingly, for input from any one digit, there were no significant differences in these response properties between the two sets of neurons. However, inputs from different (on-focus versus off-focus) digits varied significantly and revealed patterns of response properties that were qualitatively similar for both G and H neurons. Specifically, %N and P decreased while L increased symmetrically with distance of each off-focus digit from the central on-focus digit 3, reflecting corresponding variations in the synaptic accessibility and conduction time of off-focus excitatory inputs. In contrast, S/R values were very similar for all digits, suggesting that the synaptic strength of off-focus inputs is regulated independently of accessibility. Finally, preliminary findings indicated that denervation of the third digit caused a decrease in off-focus response latencies, while the normal latency profile across digits was retained. This suggests that the previously existing pattern of off-focus inputs to G and H neurons provides a template for denervation-induced cortical reorganization, whereby the synaptic efficacy of off-focus inputs is increased by disinhibition or facilitation.
本研究的目的是比较成年浣熊初级体感第3指皮层无毛（G）和异质（H）亚区单个神经元的生理特性。从50个感受野（RFs）局限于某一指的无毛皮肤的G神经元和41个RFs位于有毛皮肤、爪子或皮肤类型混合处的H神经元获得了细胞外记录。通过对指进行电刺激和机械刺激来评估神经元的兴奋性反应。这两组神经元的深度分布几乎相同，但在输入汇聚方面有很大差异：（i）对每个离焦指进行电刺激或机械刺激时有反应的神经元百分比（%N），以及（ii）单个细胞可被驱动的指的数量，H神经元显著更多。对那些可被离焦输入兴奋的G和H细胞，检测其对指刺激的反应概率（P）、每次反应的尖峰数量（S/R）和反应潜伏期（L）。令人惊讶的是，对于来自任何一个指的输入，两组神经元在这些反应特性上没有显著差异。然而，来自不同（聚焦与离焦）指的输入有显著差异，并揭示了G和H神经元在反应特性模式上在质量上相似。具体而言，%N和P随着每个离焦指与中央聚焦指3的距离对称地减少，而L增加，这反映了离焦兴奋性输入的突触可及性和传导时间的相应变化。相比之下，所有指的S/R值非常相似，表明离焦输入的突触强度与可及性无关，是独立调节的。最后，初步研究结果表明，第3指去神经支配导致离焦反应潜伏期缩短，同时保留了各指之间正常的潜伏期分布。这表明，先前存在的G和H神经元离焦输入模式为去神经支配诱导的皮层重组提供了一个模板，由此离焦输入的突触效能通过去抑制或易化作用而增加。
