Le Bon-Jego Morgane, Cattaert Daniel
Laboratoire de Neurobiologie des Réseaux, United Mixte de Recherche 5816, Centre National de la Recherche Scientifique, Université Bordeaux 1, Biologie Animale, Bât B2, 33405 Talence Cedex, France.
J Neurophysiol. 2002 Nov;88(5):2575-88. doi: 10.1152/jn.00178.2002.
The aim of this study was to investigate the inhibitory components of a resistance reflex in the walking system of the crayfish. This study was performed using an in vitro preparation of several thoracic ganglia including motor nerves and the proprioceptor that codes movements of the second joint (coxo-basipodite chordotonal organ-CBCO). Sinusoidal movements were imposed on the CBCO, and intracellular responses were recorded from levator (Lev) and depressor (Dep) motoneurons (MNs). We found that in MNs that oppose the imposed movements (e.g., the Lev MNs during the imposed downward movement), the response consists in a depolarization resulting from the summation of excitatory postsynaptic potentials (EPSPs). A movement in the opposite direction resulted in hyperpolarization during which inhibitory postsynaptic potentials (IPSPs) summated. The inhibitory pathway to each MN is oligosynaptic (i.e., composed of a small number of neurons in series) and involves spiking interneurons because it was blocked in the presence of a high-divalent cation solution. The IPSPs were mediated by a chloride conductance because their amplitude was sensitive to the chloride concentration of the bathing solution and because they were blocked by the chloride channel blocker, picrotoxin. Resistance reflex IPSPs related to single CBCO neurons could be identified. These unitary IPSPs were blocked in the presence of 3-mercapto-propionic acid, an inhibitor of gamma-amino-butyric acid (GABA) synthesis, indicating that they are mediated by GABA. In addition to this GABAergic pathway, electrical stimulation of the CBCO sensory nerve induced compound IPSPs that were blocked by glutamate pyruvate transaminase (GPT), indicating the presence of glutamatergic inhibitory pathways. These glutamatergic interneurons do not appear to be involved in the resistance reflex, however, as GPT did not block the unitary IPSPs. Functionally, the resistance reflex is mainly supported by movement-coding CBCO sensory neurons. We demonstrate that such movement-coding CBCO neurons produce both monosynaptic EPSPs in the MNs opposing imposed movements and oligosynaptic IPSPs in the antagonistic motoneurons. These results highlight the similarities between the inhibitory pathways in resistance reflex of the crayfish and in the stretch reflex of vertebrates mediated by Ia inhibitory interneurons.
本研究旨在探究小龙虾行走系统中抵抗反射的抑制成分。本研究采用体外制备的几个胸神经节进行，包括运动神经和编码第二关节运动的本体感受器（coxo - basipodite弦音器器官 - CBCO）。对CBCO施加正弦运动，并记录提肌（Lev）和降肌（Dep）运动神经元（MNs）的细胞内反应。我们发现，在对抗施加运动的MNs中（例如，在施加向下运动时的Lev MNs），反应表现为兴奋性突触后电位（EPSPs）总和导致的去极化。相反方向的运动则导致超极化，在此期间抑制性突触后电位（IPSPs）总和。每条MN的抑制性通路是寡突触的（即由少量串联的神经元组成），并且涉及发放中间神经元，因为在高双价阳离子溶液存在时该通路被阻断。IPSPs由氯离子电导介导，因为它们的幅度对浸泡溶液的氯离子浓度敏感，并且因为它们被氯离子通道阻滞剂印防己毒素阻断。与单个CBCO神经元相关的抵抗反射IPSPs可以被识别。这些单一的IPSPs在γ - 氨基丁酸（GABA）合成抑制剂3 - 巯基丙酸存在时被阻断，表明它们由GABA介导。除了这条GABA能通路外，对CBCO感觉神经的电刺激诱导出被谷氨酸丙酮酸转氨酶（GPT）阻断的复合IPSPs，表明存在谷氨酸能抑制通路。然而，这些谷氨酸能中间神经元似乎不参与抵抗反射，因为GPT并未阻断单一的IPSPs。在功能上，抵抗反射主要由编码运动的CBCO感觉神经元支持。我们证明，这种编码运动的CBCO神经元在对抗施加运动的MNs中产生单突触EPSPs，在拮抗运动神经元中产生寡突触IPSPs。这些结果突出了小龙虾抵抗反射中的抑制通路与脊椎动物由Ia抑制性中间神经元介导的牵张反射中的抑制通路之间的相似性。
