Bonnot A, Morin D
Laboratoire des Neurosciences de la Motricité, Université de Bordeaux 1, UMR-CNRS 5807, Avenue des Facultés, 33405 Talence Cedex, France.
Brain Res. 1998 May 18;793(1-2):136-48. doi: 10.1016/s0006-8993(98)00153-x.
In vitro isolated spinal cord preparations of newborn mice were used to examine the localisation of neuronal network(s) involved in the centrally-driven command of motor activities. Transections of reduced spinal cord preparations were performed under different extracellular bathing conditions, to obtain the smallest piece of cord capable of generating spinal motor rhythm. Under normal bathing medium, the whole lumbosacral cord from 0 to 2-day-old mice (P0-2 group) must be maintained to generate spontaneous motor bursts on lumbar ventral roots. In the P3-5 group, however, a three segment long section from the sacral part of the cord was still able to produce spontaneous episodes of rhythmic activity. Using a Mg2+-free medium to activate quiescent motor neuronal networks, transection procedures revealed that a double lumbar segment and a single segment (at both lumbar and sacral levels) of the cord continued to exhibit rhythmic locomotor-like discharges in P0-2 and P3-5 groups, respectively. In some experiments in which isolated reduced preparations did not generate any rhythmic activity in ventral roots, central inhibitory influences were blocked by addition of bicuculline (20-30 microM) or strychnine (20 microM) to the superperfusate. Under these conditions, a slow and synchronous rhythmic activity was typically recorded from lumbar and sacral outputs in both P0-2 and P3-5 groups. Finally, transection experiments showed that lumbar and sacral hemisegments of the cord retained the ability to generate a bicuculline- or strychnine-induced motor rhythm. These results suggest that (1) intersegmental connections appear to be stronger in P0-2 than in P3-5 group, since under both normal or Mg2+-free bathing medium, spinal rhythmic activity was more affected by transection procedures in preparations from the younger animals, and (2) neuronal networks producing rhythmic motor activities in mouse may be segmentally organised, each hemisegment being able to generate its own spinal motor rhythm.
利用新生小鼠的体外分离脊髓制备物来检查参与运动活动中枢驱动指令的神经网络的定位。在不同的细胞外浴液条件下对简化的脊髓制备物进行横切，以获得能够产生脊髓运动节律的最小脊髓片段。在正常浴液中，必须保留0至2日龄小鼠的整个腰骶段脊髓（P0 - 2组）才能在腰腹根产生自发运动爆发。然而，在P3 - 5组中，来自脊髓骶部的三段长切片仍能产生有节律活动的自发发作。使用无镁培养基激活静止的运动神经元网络，横切程序显示，在P0 - 2组和P3 - 5组中，脊髓的双腰段和单段（腰段和骶段）分别继续表现出节律性的类似运动的放电。在一些实验中，分离的简化制备物在腹根未产生任何节律性活动，通过向灌流液中添加荷包牡丹碱（20 - 30微摩尔）或士的宁（20微摩尔）来阻断中枢抑制性影响。在这些条件下，通常在P0 - 2组和P3 - 5组的腰段和骶段输出中记录到缓慢且同步的节律性活动。最后，横切实验表明，脊髓的腰段和骶段半节段保留了产生荷包牡丹碱或士的宁诱导的运动节律的能力。这些结果表明：（1）P0 - 2组的节段间连接似乎比P3 - 5组更强，因为在正常或无镁浴液中，年轻动物制备物中的脊髓节律性活动受横切程序的影响更大；（2）小鼠中产生节律性运动活动的神经网络可能是按节段组织的，每个半节段都能够产生自身的脊髓运动节律。
