Department of Zoology and Cellular & Behavioral Neurobiology Graduate Program, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA.
Integr Comp Biol. 2011 Dec;51(6):890-902. doi: 10.1093/icb/icr041. Epub 2011 Jun 22.
Animals produce a variety of behaviors using a limited number of muscles and motor neurons. Rhythmic behaviors are often generated in basic form by networks of neurons within the central nervous system, or central pattern generators (CPGs). It is known from several invertebrates that different rhythmic behaviors involving the same muscles and motor neurons can be generated by a single CPG, multiple separate CPGs, or partly overlapping CPGs. Much less is known about how vertebrates generate multiple, rhythmic behaviors involving the same muscles. The spinal cord of limbed vertebrates contains CPGs for locomotion and multiple forms of scratching. We investigated the extent of sharing of CPGs for hind limb locomotion and for scratching. We used the spinal cord of adult red-eared turtles. Animals were immobilized to remove movement-related sensory feedback and were spinally transected to remove input from the brain. We took two approaches. First, we monitored individual spinal cord interneurons (i.e., neurons that are in between sensory neurons and motor neurons) during generation of each kind of rhythmic output of motor neurons (i.e., each motor pattern). Many spinal cord interneurons were rhythmically activated during the motor patterns for forward swimming and all three forms of scratching. Some of these scratch/swim interneurons had physiological and morphological properties consistent with their playing a role in the generation of motor patterns for all of these rhythmic behaviors. Other spinal cord interneurons, however, were rhythmically activated during scratching motor patterns but inhibited during swimming motor patterns. Thus, locomotion and scratching may be generated by partly shared spinal cord CPGs. Second, we delivered swim-evoking and scratch-evoking stimuli simultaneously and monitored the resulting motor patterns. Simultaneous stimulation could cause interactions of scratch inputs with subthreshold swim inputs to produce normal swimming, acceleration of the swimming rhythm, scratch-swim hybrid cycles, or complete cessation of the rhythm. The type of effect obtained depended on the level of swim-evoking stimulation. These effects suggest that swim-evoking and scratch-evoking inputs can interact strongly in the spinal cord to modify the rhythm and pattern of motor output. Collectively, the single-neuron recordings and the results of simultaneous stimulation suggest that important elements of the generation of rhythms and patterns are shared between locomotion and scratching in limbed vertebrates.
动物使用有限数量的肌肉和运动神经元来产生各种行为。节律性行为通常由中枢神经系统（或中枢模式发生器，CPG）内的神经元网络产生基本形式。从几种无脊椎动物中可知，涉及相同肌肉和运动神经元的不同节律性行为可以由单个 CPG、多个独立的 CPG 或部分重叠的 CPG 产生。关于脊椎动物如何产生涉及相同肌肉的多种节律性行为，人们知之甚少。有附肢的脊椎动物的脊髓包含用于运动和多种形式抓挠的 CPG。我们研究了用于后肢运动和抓挠的 CPG 共享的程度。我们使用了成年红耳龟的脊髓。动物被固定以去除与运动相关的感觉反馈，并进行脊髓横切以去除来自大脑的输入。我们采用了两种方法。首先，我们在产生运动神经元的每种节律性输出（即每种运动模式）时监测单个脊髓中间神经元（即位于感觉神经元和运动神经元之间的神经元）。许多脊髓中间神经元在向前游泳和所有三种形式的抓挠的运动模式中呈节律性激活。其中一些抓挠/游泳中间神经元具有生理和形态特征，表明它们在所有这些节律性行为的运动模式产生中发挥作用。然而，其他脊髓中间神经元在抓挠运动模式中呈节律性激活，而在游泳运动模式中被抑制。因此，运动和抓挠可能由部分共享的脊髓 CPG 产生。其次，我们同时传递游泳诱发刺激和抓挠诱发刺激，并监测由此产生的运动模式。同时刺激可能导致抓挠输入与亚阈值游泳输入相互作用，从而产生正常游泳、游泳节律加速、抓挠-游泳混合周期或完全停止节律。获得的效果类型取决于游泳诱发刺激的水平。这些效应表明，游泳诱发和抓挠诱发的输入可以在脊髓中强烈相互作用，以改变运动输出的节律和模式。总的来说，单细胞记录和同时刺激的结果表明，四肢脊椎动物运动和抓挠的节律和模式产生的重要元素是共享的。
