Roberts A, Tunstall M J
School of Biological Sciences, University of Bristol, United Kingdom.
Eur J Morphol. 1994 Aug;32(2-4):176-84.
We consider the hypothesis that the normal rostrocaudal spread of motor activity during swimming in Xenopus embryos depends on a longitudinal, rostrocaudal gradient in synaptic drive received by the pattern generating neurons in the spinal cord. Anatomical evidence shows that there is a rostrocaudal gradient in excitatory and inhibitory premotor interneuron numbers. Intracellular recordings were therefore made from neurons at different longitudinal positions to seek direct evidence for a gradient in synaptic drive. The main finding was that during fictive swimming the amplitude of the tonic excitatory synaptic input and the mid-cycle inhibition declined in a rostrocaudal direction and caudal to the twelfth postotic segment inhibition was absent altogether. Experimental manipulation of the gradients by the caudal application of pharmacological agents lead to changes or even reversal of the normal direction of spread of motor activity. To test whether a gradient in synaptic drive could organize a rostrocaudal spread of activity we have used a 48 neuron, 12 segment model of the spinal pattern generating network. This has shown that the gradient hypothesis can provide a sufficient explanation for much of the embryo's motor coordination. A gradient in synaptic drive provides a flexible mechanism to control sequences of motor activity.
非洲爪蟾胚胎游泳时运动活动正常的头尾扩散取决于脊髓中模式生成神经元所接收的突触驱动的纵向头尾梯度。解剖学证据表明，兴奋性和抑制性运动前中间神经元的数量存在头尾梯度。因此，我们从不同纵向位置的神经元进行细胞内记录，以寻找突触驱动梯度的直接证据。主要发现是，在模拟游泳期间，强直性兴奋性突触输入的幅度和周期中期抑制在头尾方向上下降，并且在第十二耳后节段的尾侧完全没有抑制。通过在尾部应用药物制剂对梯度进行实验性操作，导致运动活动正常扩散方向的改变甚至逆转。为了测试突触驱动梯度是否能够组织活动的头尾扩散，我们使用了一个由48个神经元、12个节段组成的脊髓模式生成网络模型。这表明梯度假说能够为胚胎的大部分运动协调提供充分的解释。突触驱动梯度提供了一种灵活的机制来控制运动活动的序列。
