McKenna J E, Prusky G T, Whishaw I Q
Department of Psychology and Neuroscience, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada.
J Comp Neurol. 2000 Apr 10;419(3):286-96. doi: 10.1002/(sici)1096-9861(20000410)419:3<286::aid-cne2>3.0.co;2-3.
Behavioral evidence reveals that the laboratory rat and other rodent species display skilled paw and digit use in handling food during eating and skilled limb use in reaching for food in formal laboratory skilled reaching tests that is comparable to that described in carnivores and primates. Because less is known about the central control of skilled movements in rodents than in carnivores or primates, the purpose of the current study was to examine the relation between the rat's spinal motoneurons and the individual forelimb muscles that they innervate. In two experiments, 14 forelimb muscles (in the shoulder and the upper and lower arm segments) were injected with carbocyanine dye tracers. The topography of spinal motoneurons was reconstructed by using fluorescence microscopy. Motor neurons were found to be organized in columns throughout the length of the cervical and upper thoracic area, with 1) extensor motoneurons located more laterally than flexor motoneurons, 2) rostral motoneurons innervating more proximal muscles than caudal motoneurons, and 3) more dorsally located motoneurons innervating more distal muscles. These results reveal that the topography of rodent cervical spinal cord motoneurons is very similar to that of carnivores and of primates, which also are characterized by well-developed, skilled movements. In addition, the proximal-distal organization of motoneuron columns parallels the proximal-to-distal pattern of forelimb movement used by the rat when reaching. The data from this study enable the development of predictions about the specific movements that would be compromised by experimental transections or other injuries at different levels of the spinal cord in rat models of spinal injury.
行为学证据表明，在进食过程中，实验大鼠和其他啮齿动物在处理食物时展现出熟练的爪子和指部运用能力；在正式的实验室熟练抓握测试中，它们在抓取食物时也展现出熟练的肢体运用能力，这与食肉动物和灵长类动物中所描述的情况相当。由于相较于食肉动物或灵长类动物，人们对啮齿动物熟练运动的中枢控制了解较少，因此本研究的目的是探究大鼠脊髓运动神经元与其所支配的单个前肢肌肉之间的关系。在两项实验中，向14块前肢肌肉（位于肩部以及上臂和下臂部分）注射了羰花青染料示踪剂。通过荧光显微镜重建了脊髓运动神经元的拓扑结构。结果发现，运动神经元在颈段和上胸段全长范围内呈柱状排列，具体表现为：1）伸肌运动神经元比屈肌运动神经元更靠外侧；2）支配近端肌肉的嘴侧运动神经元比尾侧运动神经元更多；3）位置更靠背侧的运动神经元支配更远端的肌肉。这些结果表明，啮齿动物颈脊髓运动神经元的拓扑结构与食肉动物和灵长类动物非常相似，而后两者也具有发达的熟练运动能力。此外，运动神经元柱的近端 - 远端组织与大鼠抓握时前肢运动的近端到远端模式平行。本研究的数据有助于预测在大鼠脊髓损伤模型中，脊髓不同水平的实验横断或其他损伤会损害哪些特定运动。
