Rudomin P, Lomelí J
Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y de Estudios Avanzados, Av. Instituto Politécnico Nacional 2508, Mexico, DF, 07360, Mexico.
Exp Brain Res. 2007 Jan;176(1):119-31. doi: 10.1007/s00221-006-0601-9. Epub 2006 Aug 1.
We have examined in the anesthetized cat the threshold changes produced by sensory and supraspinal stimuli on intraspinal collaterals of single afferents from the posterior articular nerve (PAN). Forty-eight fibers were tested in the L3 segment, in or close to Clarke's column, and 70 fibers in the L6-L7 segments within the intermediate zone. Of these, 15 pairs of L3 and L6-L7 collaterals were from the same afferent. Antidromically activated fibers had conduction velocities between 23 and 74 m/s and peripheral thresholds between 1.1 and 4.7 times the threshold of the most excitable fibers (xT), most of them below 3 xT. PAN afferents were strongly depolarized by stimulation of muscle afferents and by cutaneous afferents, as well as by stimulation of the bulbar reticular formation and the midline raphe nuclei. Stimulation of muscle nerves (posterior biceps and semitendinosus, quadriceps) produced a larger PAD (primary afferent depolarization) in the L6-L7 than in the L3 terminations. Group II were more effective than group I muscle afferents. As with group I muscle afferents, the PAD elicited in PAN afferents by stimulation of muscle nerves could be inhibited by conditioning stimulation of cutaneous afferents. Stimulation of the cutaneous sural and superficial peroneal nerves increased the threshold of few terminations (i.e., produced primary afferent hyperpolarization, PAH) and reduced the threshold of many others, particularly of those tested in the L6-L7 segments. Yet, there was a substantial number of terminals where these conditioning stimuli had minor or no effects. Autogenetic stimulation of the PAN with trains of pulses increased the intraspinal threshold in 46% and reduced the threshold in 26% of fibers tested in the L6-L7 segments (no tests were made with trains of pulses on fibers ending in L3). These observations indicate that PAN afferents have a rather small autogenetic PAD, particularly if this is compared with the effects of heterogenetic stimulation. Therefore, the depression of the PAN intraspinal fields produced by autogenetic stimulation described by Rudomin et al. (Exp Brain Res DOI 10.1007/s00221-006-0600-x, 2006) may be ascribed to other mechanisms besides a GABAa PAD. It is suggested that the small or no autogenetic PAD displayed by the examined joint afferents prevents presynaptic filtering of their synaptic actions and preserves the original information generated in the periphery. This could be important for proper adjustment of limb position.
我们在麻醉猫身上研究了感觉刺激和脊髓上刺激对来自后关节神经（PAN）的单根传入纤维脊髓内侧支产生的阈值变化。在L3节段，于克拉克柱内或其附近对48根纤维进行了测试，在中间带的L6 - L7节段对70根纤维进行了测试。其中，15对L3和L6 - L7侧支来自同一传入纤维。逆向激活的纤维传导速度在23至74米/秒之间，外周阈值为最易兴奋纤维阈值（xT）的1.1至4.7倍，其中大多数低于3xT。刺激肌肉传入纤维、皮肤传入纤维以及延髓网状结构和中线缝际核，均可使PAN传入纤维发生强烈去极化。刺激肌肉神经（肱二头肌和半腱肌、股四头肌）在L6 - L7节段产生的初级传入纤维去极化（PAD）比在L3节段的终末更大。II类肌肉传入纤维比I类更有效。与I类肌肉传入纤维一样，刺激肌肉神经在PAN传入纤维中引发的PAD可被皮肤传入纤维的条件刺激所抑制。刺激腓肠皮神经和腓浅神经会使少数终末的阈值升高（即产生初级传入纤维超极化，PAH），并降低许多其他终末的阈值，尤其是在L6 - L7节段测试的那些终末。然而，有相当数量的终末，这些条件刺激对其影响较小或无影响。用脉冲串对PAN进行自身刺激，在L6 - L7节段测试的纤维中，有46%的纤维脊髓内阈值升高，有26%的纤维阈值降低（未对终止于L3的纤维进行脉冲串测试）。这些观察结果表明，PAN传入纤维的自身PAD相当小，尤其是与异源刺激的作用相比。因此，Rudomin等人（《实验脑研究》DOI 10.1007/s00221 - 006 - 0600 - x，2006）所描述的自身刺激引起的PAN脊髓内场的抑制，可能归因于除GABAa PAD之外的其他机制。有人提出，所检测的关节传入纤维显示出的自身PAD较小或无，可防止其突触作用的突触前滤波，并保留在外周产生的原始信息。这对于肢体位置的适当调整可能很重要。
