Zhao F Y, Roberts A
School of Biological Sciences, University of Bristol, UK.
J Comp Physiol A. 1998 Dec;183(6):753-8. doi: 10.1007/s003590050298.
This paper investigates the proposal that the frequency of the swimming central pattern generator in young Xenopus tadpoles is partly determined by the population of glutamatergic premotor interneurons active on each cycle. During fictive swimming spinal neurons also receive cholinergic and electrotonic excitation from motoneurons. As frequency changes during swimming we make two predictions: first, since most motoneurons fire very reliably at all frequencies, the electrotonic and nicotinic drive from motoneurons should remain constant, and second, when swimming frequency decreases, the glutamatergic drive should decrease as the number of active premotor excitatory interneurons decreases. We have tested these predictions by measuring the excitatory synaptic drive to motoneurons as frequency changes during fictive swimming. The components of synaptic drive were revealed by the local microperfusion of strychnine together with different excitatory antagonists. After blocking the nicotinic acetylcholine receptor, the mainly glutamatergic excitatory synaptic drive still changed with frequency. However, when glutamate receptors or all chemical transmission was blocked, excitation did not change with frequency. Our predictions are confirmed, suggesting that premotor excitatory interneurons are a major factor in frequency control in the tadpole central pattern generator and that motoneurons provide a stable background excitation.
本文研究了一种观点，即非洲爪蟾幼体中游泳中枢模式发生器的频率部分由每个周期中活跃的谷氨酸能运动前中间神经元群体决定。在模拟游泳过程中，脊髓神经元还会从运动神经元接收胆碱能和电紧张性兴奋。由于游泳过程中频率会发生变化，我们做出了两个预测：第一，由于大多数运动神经元在所有频率下都能非常可靠地放电，运动神经元的电紧张性和烟碱样驱动应该保持恒定；第二，当游泳频率降低时，随着活跃的运动前兴奋性中间神经元数量减少，谷氨酸能驱动也应该降低。我们通过在模拟游泳过程中测量频率变化时运动神经元的兴奋性突触驱动来检验这些预测。通过局部微量灌注士的宁和不同的兴奋性拮抗剂来揭示突触驱动的成分。阻断烟碱型乙酰胆碱受体后，主要的谷氨酸能兴奋性突触驱动仍随频率变化。然而，当谷氨酸受体或所有化学传递被阻断时，兴奋不再随频率变化。我们的预测得到了证实，这表明运动前兴奋性中间神经元是蝌蚪中枢模式发生器频率控制的主要因素，而运动神经元提供了稳定的背景兴奋。
