Tomatsu Saeka, Kim Geehee, Confais Joachim, Seki Kazuhiko
Department of Neurophysiology, National Institute of Neuroscience, Tokyo, Japan; and.
Department of Neurophysiology, National Institute of Neuroscience, Tokyo, Japan; and
J Neurophysiol. 2017 Feb 1;117(2):796-807. doi: 10.1152/jn.00874.2016. Epub 2016 Dec 14.
Presynaptic inhibition of the sensory input from the periphery to the spinal cord can be evaluated directly by intra-axonal recording of primary afferent depolarization (PAD) or indirectly by intraspinal microstimulation (excitability testing). Excitability testing is superior for use in normal behaving animals, because this methodology bypasses the technically challenging intra-axonal recording. However, use of excitability testing on the muscle or joint afferent in intact animals presents its own technical challenges. Because these afferents, in many cases, are mixed with motor axons in the peripheral nervous system, it is crucial to dissociate antidromic volleys in the primary afferents from orthodromic volleys in the motor axon, both of which are evoked by intraspinal microstimulation. We have demonstrated in rats that application of a paired stimulation protocol with a short interstimulus interval (ISI) successfully dissociated the antidromic volley in the nerve innervating the medial gastrocnemius muscle. By using a 2-ms ISI, the amplitude of the volleys evoked by the second stimulation was decreased in dorsal root-sectioned rats, but the amplitude did not change or was slightly increased in ventral root-sectioned rats. Excitability testing in rats with intact spinal roots indicated that the putative antidromic volleys exhibited dominant primary afferent depolarization, which was reasonably induced from the more dorsal side of the spinal cord. We concluded that excitability testing with a paired-pulse protocol can be used for studying presynaptic inhibition of somatosensory afferents in animals with intact spinal roots. Excitability testing of primary afferents has been used to evaluate presynaptic modulation of synaptic transmission in experiments conducted in vivo. However, to apply this method to muscle afferents of animals with intact spinal roots, it is crucial to dissociate antidromic and orthodromic volleys induced by spinal microstimulation. We propose a new method to make this dissociation possible without cutting spinal roots and demonstrate that it facilitates excitability testing of muscle afferents.
从外周到脊髓的感觉输入的突触前抑制可以通过初级传入去极化（PAD）的轴内记录直接评估，也可以通过脊髓内微刺激（兴奋性测试）间接评估。兴奋性测试在正常行为动物中使用更具优势，因为这种方法绕过了技术上具有挑战性的轴内记录。然而，在完整动物身上对肌肉或关节传入神经进行兴奋性测试也有其自身的技术挑战。因为在许多情况下，这些传入神经与外周神经系统中的运动轴突混合在一起，所以将初级传入神经中的逆向冲动与运动轴突中的顺向冲动区分开来至关重要，这两种冲动都是由脊髓内微刺激诱发的。我们已经在大鼠中证明，应用具有短刺激间隔（ISI）的配对刺激方案成功地分离了支配内侧腓肠肌的神经中的逆向冲动。通过使用2毫秒的ISI，在背根切断的大鼠中，第二次刺激诱发的冲动幅度降低，但在腹根切断的大鼠中，幅度没有变化或略有增加。对脊髓根完整的大鼠进行的兴奋性测试表明，假定的逆向冲动表现出主要的初级传入去极化，这是从脊髓更靠背侧合理诱发出来的。我们得出结论，使用配对脉冲方案的兴奋性测试可用于研究脊髓根完整的动物中躯体感觉传入神经的突触前抑制。在体内实验中，初级传入神经的兴奋性测试已被用于评估突触传递的突触前调制。然而，要将这种方法应用于脊髓根完整的动物的肌肉传入神经，区分脊髓微刺激诱发的逆向和顺向冲动至关重要。我们提出了一种新方法，无需切断脊髓根就能实现这种区分，并证明它有助于肌肉传入神经的兴奋性测试。
