Université de Bordeaux, Centre National de la Recherche Scientifique, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Biologie Animale, Talence Cedex, France.
J Neurophysiol. 2013 Jun;109(11):2793-802. doi: 10.1152/jn.01063.2012. Epub 2013 Mar 13.
Altering neuronal membrane properties, including input resistance, is a key modulatory mechanism for changing neural activity patterns. The effect of membrane currents generated by either synaptic or voltage-dependent channels directly depends on neuron input resistance. We found that local application of serotonin to different regions of identified motoneurons (MNs) of the postural/walking network of isolated crayfish produced different changes in input resistance. Puff-applied 5-HT in the periphery of the initial segment produced exclusively inhibitory responses. In contrast, when 5-HT was puff-applied on the central arbor of the same depressor (Dep) MN, exclusively depolarizing responses were obtained. Both inhibitory and excitatory responses were direct because they persisted in low-calcium saline. We found numerous close appositions between 5-HT-immunoreactive processes and the initial segment of dextran-rhodamine-filled Dep MNs. In contrast, almost no close apposition sites were found in Dep MN arbor. It seems that the 5-HT controls the level of excitability of postural network MNs by two mechanisms acting at two different sites: inhibitory responses (consistent with an action involving opening of K(+) channels) occur in the initial segment region and may involve classic synaptic transmission, whereas depolarizing responses (consistent with an action involving closing of K(+) channels) occur on MN branches via apparent paracrine effects.
改变神经元膜的性质，包括输入电阻，是改变神经活动模式的关键调节机制。由突触或电压依赖性通道产生的膜电流的作用直接取决于神经元的输入电阻。我们发现，局部应用 5-羟色胺到已鉴定的运动神经元（MN）的不同区域（姿势/行走网络的孤立螯虾）会导致输入电阻发生不同的变化。在起始段的外围局部应用 5-HT 只会产生抑制性反应。相比之下，当 5-HT 在同一降压（Dep）MN 的中央树突上局部应用时，只会产生去极化反应。这两种反应都是直接的，因为它们在低钙盐水中持续存在。我们发现，在 5-HT 免疫反应性过程和 dextran-rhodamine 填充的 Dep MN 的起始段之间有许多紧密的贴合。相比之下，在 Dep MN 树突中几乎找不到紧密贴合的位点。似乎 5-HT 通过两种作用于两个不同部位的机制来控制姿势网络 MN 的兴奋性水平：抑制性反应（与涉及打开 K(+) 通道的作用一致）发生在起始段区域，可能涉及经典的突触传递，而去极化反应（与涉及关闭 K(+) 通道的作用一致）通过明显的旁分泌作用发生在 MN 分支上。
