Prime L, Pichon Y
Equipe Canaux et Récepteurs Membranaires, UMR CNRS 6026, Université de Rennes 1, Bâtiment 13, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Cedex Rennes, France.
Eur Biophys J. 2004 May;33(3):265-73. doi: 10.1007/s00249-003-0379-7. Epub 2004 Jan 15.
The swimming behaviour of lower vertebrates has been used as a model to study the function of simple neuronal circuits. Good examples are the lamprey and the Xenopus tadpole. In these two cases, glutamate-activated NMDA receptors are involved, and the relative importance of the NMDA and non-NMDA receptors as well as the involvement of other ion channels has been studied using a combination of electrophysiological recordings and modelling experiments, but little attention had been paid to their evolution during development. In the present experiments, which have been performed on Xenopus embryos from stages 31 to 42, we have probed the relative importance of the two categories of receptors using selective blockers [respectively dl-2-amino-5-phosphonovaleric acid (APV) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)]. The sensitivity of the swimming behaviour to APV was found to increase during development and that to CNQX to decrease. Furthermore, it has been observed that the spike activity recorded from the ventral roots is more complex in late embryonic stages that in early embryos. These modifications are associated with changes of the neuronal circuit, some of which correspond to a lengthening of the axon and an increased complexity of the dendritic tree of the motoneurons. We have incorporated these modifications in a simplified model of the central pattern generator built with Neuron software. The results indicate that at least part of the observed changes can be associated with changes in the length of the dendrites and axons.
低等脊椎动物的游泳行为已被用作研究简单神经回路功能的模型。七鳃鳗和非洲爪蟾蝌蚪就是很好的例子。在这两种情况下，谷氨酸激活的NMDA受体都参与其中，并且已经结合电生理记录和建模实验研究了NMDA受体和非NMDA受体的相对重要性以及其他离子通道的参与情况，但很少有人关注它们在发育过程中的进化。在目前对处于31至42阶段的非洲爪蟾胚胎进行的实验中，我们使用选择性阻滞剂[分别为dl-2-氨基-5-磷酸戊酸（APV）和6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）]探究了这两类受体的相对重要性。发现游泳行为对APV的敏感性在发育过程中增加，而对CNQX的敏感性降低。此外，还观察到从腹根记录到的锋电位活动在胚胎后期比早期胚胎更为复杂。这些变化与神经回路的改变有关，其中一些变化对应于运动神经元轴突的延长和树突树复杂性的增加。我们已将这些变化纳入用Neuron软件构建的中央模式发生器的简化模型中。结果表明，观察到的变化中至少有一部分可能与树突和轴突长度的变化有关。
