Berkowitz Ari
Department of Zoology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA.
J Neurophysiol. 2008 Jun;99(6):2887-901. doi: 10.1152/jn.90235.2008. Epub 2008 Apr 2.
Distinct types of rhythmic movements that use the same muscles are typically generated largely by shared multifunctional neurons in invertebrates, but less is known for vertebrates. Evidence suggests that locomotion and scratching are produced partly by shared spinal cord interneuronal circuity, although direct evidence with intracellular recording has been lacking. Here, spinal interneurons were recorded intracellularly during fictive swimming and fictive scratching in vivo and filled with Neurobiotin. Some interneurons that were rhythmically activated during both swimming and scratching had axon terminal arborizations in the ventral horn of the hindlimb enlargement, indicating their likely contribution to hindlimb motor outputs during both behaviors. We previously described a morphological group of spinal interneurons ("transverse interneurons" or T neurons) that were rhythmically activated during all forms of fictive scratching at higher peak firing rates and with larger membrane potential oscillations than scratch-activated spinal interneurons with different dendritic orientations. The current study demonstrates that T neurons are activated during both swimming and scratching and thus are components of the shared circuitry. Many spinal interneurons activated during fictive scratching are also activated during fictive swimming (scratch/swim neurons), but others are suppressed during swimming (scratch-specialized neurons). The current study demonstrates that some scratch-specialized neurons receive strong and long-lasting hyperpolarizing inhibition during fictive swimming and are also morphologically distinct from T neurons. Thus this study indicates that locomotion and scratching are produced by a combination of shared and dedicated interneurons whose physiological and morphological properties are beginning to be revealed.
在无脊椎动物中，使用相同肌肉的不同类型节律性运动通常在很大程度上由共享的多功能神经元产生，但脊椎动物的情况则了解较少。有证据表明，尽管缺乏细胞内记录的直接证据，但运动和抓挠部分是由脊髓中间神经元回路共同产生的。在这里，在体内的虚拟游泳和虚拟抓挠过程中对脊髓中间神经元进行了细胞内记录，并注入了神经生物素。一些在游泳和抓挠过程中均有节律性激活的中间神经元在后肢膨大的腹角有轴突终末分支，表明它们在两种行为中可能对后肢运动输出有贡献。我们之前描述过一组脊髓中间神经元（“横向中间神经元”或T神经元），它们在所有形式的虚拟抓挠过程中均有节律性激活，与具有不同树突方向的抓挠激活脊髓中间神经元相比，其峰值放电频率更高，膜电位振荡更大。当前研究表明，T神经元在游泳和抓挠过程中均被激活，因此是共享回路的组成部分。许多在虚拟抓挠过程中被激活的脊髓中间神经元在虚拟游泳过程中也被激活（抓挠/游泳神经元），但其他一些在游泳过程中被抑制（抓挠特化神经元）。当前研究表明，一些抓挠特化神经元在虚拟游泳过程中受到强烈且持久的超极化抑制，并且在形态上也与T神经元不同。因此，这项研究表明，运动和抓挠是由共享和专用中间神经元共同产生的，其生理和形态特性正开始被揭示。
