Bosco G, Rankin A, Poppele R E
Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Neurophysiol. 2003 Nov;90(5):3361-71. doi: 10.1152/jn.00203.2003.
Spinocerebellar neurons (DSCT) receive converging sensory information from various sensory receptors in the hindlimbs and lower trunk. Previous studies have shown that sensory processing by DSCT neurons results in a representation of global hindlimb kinematic parameters such as the length and the orientation of the limb axis. In addition to the sensory input, the DSCT circuitry also receives a descending input from the raphe nuclei in the brain stem. Recent studies have demonstrated that the raphe serotonergic terminals synapse directly on DSCT neurons and exert a differential modulatory influence on their sensory inputs. We examined the role of serotonergic modulation on the DSCT representation of hindlimb kinematic parameters by recording DSCT activity during passive hindlimb movements before and after perturbing serotonergic transmission. We used two types of perturbation: electrical stimulation of the raphe areas in the brain stem to release serotonin in the spinal cord (42 neurons) and intravenous administration of serotonergic agonists or antagonists, mostly the 5HTP2 antagonist ketanserin (30 neurons). We found that movement responses were altered in approximately 70% of the DSCT units studied with each protocol. Changes could include shifts in mean firing rate, increases or decreases in response amplitude, and changes in response waveform. We used a principal component analysis (PCA) to examine waveform components and to determine how they contributed to the response waveform changes caused by serotonin perturbation. Such changes could be explained by new or different response components that might indicate a modification in the data processing or by a different weighting of existing components that might indicate a modification of synaptic weighting. The results were consistent with the second alternative. We found that the same underlying response components could account for both control responses and those altered by serotonin perturbations. The observed changes in waveform could be entirely accounted for by a re-weighting of response components. In particular, the changes observed after raphe stimulation could be accounted for by selective changes in the weighting of the first principal component (PC) with only minor changes of the weighting of the second PC. Because these response components were shown previously to correlate with the limb axis orientation and length trajectories respectively, the finding is consistent with the idea that limb axis length and orientation information are processed separately within the spinal circuitry.
脊髓小脑神经元（DSCT）从后肢和下躯干的各种感觉受体接收汇聚的感觉信息。先前的研究表明，DSCT神经元的感觉处理会产生后肢整体运动学参数的表征，例如肢体轴的长度和方向。除了感觉输入外，DSCT神经回路还接收来自脑干中缝核的下行输入。最近的研究表明，中缝5-羟色胺能终末直接与DSCT神经元形成突触，并对其感觉输入施加差异性调节影响。我们通过记录在干扰5-羟色胺能传递前后被动后肢运动期间的DSCT活动，研究了5-羟色胺能调节对后肢运动学参数DSCT表征的作用。我们使用了两种类型的干扰：电刺激脑干中的中缝区域以在脊髓中释放5-羟色胺（42个神经元），以及静脉内给予5-羟色胺能激动剂或拮抗剂，主要是5-HTP2拮抗剂酮色林（30个神经元）。我们发现，在每种实验方案研究的DSCT单位中，约70%的运动反应发生了改变。变化可能包括平均放电率的改变、反应幅度的增加或减少以及反应波形的改变。我们使用主成分分析（PCA）来检查波形成分，并确定它们如何导致由5-羟色胺扰动引起的反应波形变化。这种变化可以通过可能表明数据处理发生改变的新的或不同的反应成分来解释，或者通过可能表明突触权重改变的现有成分的不同加权来解释。结果与第二种可能性一致。我们发现相同的潜在反应成分可以解释对照反应和由5-羟色胺扰动改变的反应。观察到的波形变化可以完全由反应成分的重新加权来解释。特别是，中缝刺激后观察到的变化可以通过第一主成分（PC）权重的选择性变化来解释，而第二PC的权重仅有微小变化。因为这些反应成分先前已分别显示与肢体轴方向和长度轨迹相关，所以该发现与肢体轴长度和方向信息在脊髓神经回路中分别处理的观点一致。
