Christie Kimberly J, Whelan Patrick J
Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.
J Neurophysiol. 2005 Aug;94(2):1554-64. doi: 10.1152/jn.00299.2005. Epub 2005 Apr 13.
Bath application of monoamines is a potent method for evoking locomotor activity in neonatal rats and mice. Monoamines also promote functional recovery in adult animals with spinal cord injuries by activating spinal cord networks. However, the mechanisms of their actions on spinal networks are largely unknown. In this study, we tested the hypothesis that monoamines establish rostrocaudal gradients of rhythmicity in the thoracolumbar spinal cord. Isolated neonatal mouse spinal cord preparations (P0-P2) were used. To assay excitability of networks by monoamines, we evoked a disinhibited rhythm by bath application of picrotoxin and strychnine and recorded neurograms from several thoracolumbar ventral roots. We first established that rostral and caudal segments of the thoracolumbar spinal cord had equal excitability by completely transecting preparations at the L3 segmental level and recording the frequency of the disinhibited rhythm from both segments. Next we established that a majority of ventral interneurons retrogradely labeled by calcium green dextran were active during network activity. We then bath applied combinations of monoaminergic agonists [5-HT and dopamine (DA)] known to elicit locomotor activity. Our results show that monoamines establish rostrocaudal gradients of rhythmicity in the thoracolumbar spinal cord. This may be one mechanism by which combinations of monoaminergic compounds normally stably activate locomotor networks.
在新生大鼠和小鼠中，将单胺注入浴槽是诱发运动活动的有效方法。单胺还可通过激活脊髓网络促进成年脊髓损伤动物的功能恢复。然而，它们对脊髓网络的作用机制在很大程度上尚不清楚。在本研究中，我们检验了以下假设：单胺在胸腰段脊髓中建立了头尾方向的节律梯度。使用了新生小鼠离体脊髓标本（P0 - P2）。为了检测单胺对网络兴奋性的影响，我们通过在浴槽中加入印防己毒素和士的宁诱发去抑制节律，并记录多个胸腰段腹根的神经电图。我们首先通过在L3节段水平完全横断标本并记录两个节段去抑制节律的频率，确定胸腰段脊髓的头端和尾端节段具有相同的兴奋性。接下来我们确定，大多数被钙绿葡聚糖逆行标记的腹侧中间神经元在网络活动期间是活跃的。然后我们在浴槽中加入已知可诱发运动活动的单胺能激动剂组合[5 - 羟色胺和多巴胺（DA）]。我们的结果表明，单胺在胸腰段脊髓中建立了头尾方向的节律梯度。这可能是单胺能化合物组合通常稳定激活运动网络的一种机制。
