Rudomin P, Hernández E, Lomelí J
Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y Estudios Avanzados, Av.Instituto Politécnico Nacional 2508, 07360, Mexico, DF, Mexico.
Exp Brain Res. 2007 Jan;176(1):98-118. doi: 10.1007/s00221-006-0600-x. Epub 2006 Aug 1.
The aim of this study was to examine the functional organization of the spinal neuronal networks activated by myelinated afferent fibers in the posterior articular nerve (PAN) of the anesthetized cat. Particular attention was given to the tonic and phasic GABAa inhibitory modulation of these networks. Changes in the synaptic effectiveness of the joint afferents were inferred from changes in the intraspinal focal potentials produced by electrical stimulation of the PAN. We found that conditioning stimulation of cutaneous nerves (sural, superficial peroneus and saphenous) and of the nucleus raphe magnus often inhibited, in a differential manner, the early and late components of the intraspinal focal potentials produced by stimulation of low and high threshold myelinated PAN afferents, respectively. The degree of the inhibition depended on the strength of both the conditioning and test stimuli and on the segmental level of recording. Conditioning stimulation of group I muscle afferents was less effective, but marked depression of the early and late focal potentials was produced by stimuli exceeding 5 xT. The i.v. injection of 1-2.5 mg/kg of picrotoxin, a GABAa blocker, had relatively minor effects on the early components of the PAN focal potentials, but was able to induce a significant increase of the late components. It also reduced the inhibitory effects of cutaneous and joint nerve conditioning on PAN focal responses. Conditioning autogenetic stimulation with high-frequency trains depressed the PAN focal potentials. The late components of the PAN responses remained depressed several minutes after discontinuing the conditioning train, even after picrotoxin administration. The present observations indicate that the neuronal networks activated by the low threshold PAN afferents show a relatively small post-activation depression and appear to be subjected to a minor tonic inhibitory GABAa control. In contrast, the pathways activated by stimulation of high threshold myelinated afferents have a strong post-activation depression and are subjected to a significant tonic GABAergic modulation. These contrasting features, together with the phasic differential GABAergic inhibition of the responses produced by stimulation of the different populations of joint afferents, may contribute to the preservation of the original information on joint position transmitted by large diameter joint afferents, in contrast with the tonic presynaptic inhibition exerted on the fine myelinated joint afferents, which may be involved in the adjustment of compensatory reactions to inflammation.
本研究的目的是检测麻醉猫后关节神经（PAN）中有髓传入纤维激活的脊髓神经元网络的功能组织。特别关注这些网络的强直性和阶段性GABAa抑制调节。通过电刺激PAN产生的脊髓内局部电位变化推断关节传入纤维突触效能的变化。我们发现，对皮神经（腓肠神经、腓浅神经和隐神经）和中缝大核的条件刺激通常分别以不同方式抑制低阈值和高阈值有髓PAN传入纤维刺激产生的脊髓内局部电位的早期和晚期成分。抑制程度取决于条件刺激和测试刺激的强度以及记录的节段水平。对I组肌肉传入纤维的条件刺激效果较差，但超过5×T的刺激会使早期和晚期局部电位明显降低。静脉注射1 - 2.5 mg/kg的荷包牡丹碱（一种GABAa阻滞剂）对PAN局部电位的早期成分影响相对较小，但能使晚期成分显著增加。它还减少了皮肤和关节神经条件刺激对PAN局部反应的抑制作用。高频串刺激的自身条件刺激使PAN局部电位降低。即使在给予荷包牡丹碱后，停止条件刺激串几分钟后，PAN反应的晚期成分仍处于抑制状态。目前的观察结果表明，低阈值PAN传入纤维激活的神经元网络激活后抑郁相对较小，似乎受到较小的强直性GABAa抑制控制。相比之下，高阈值有髓传入纤维刺激激活的通路具有强烈的激活后抑郁，并受到显著的强直性GABA能调节。这些对比特征，连同对不同群体关节传入纤维刺激产生的反应的阶段性差异GABA能抑制，可能有助于保留由大直径关节传入纤维传递的关于关节位置的原始信息，这与对细有髓关节传入纤维施加的强直性突触前抑制形成对比，后者可能参与炎症代偿反应的调节。
