Use of cord dorsum potentials to study the effects of hypoxia on spinal cord functions in neonatal rabbits

胎儿的身体和呼吸运动在缺氧时停止。胎儿呼吸运动的抑制被认为是通过上脑桥介导的，因为在这一水平的脑干横断消除了缺氧对胎儿呼吸运动的影响。因此，似乎是一个下行抑制过程来抑制胎儿缺氧时的呼吸。然而，胎儿身体运动因缺氧而被取消的机制尚不清楚。我们假设缺氧也会导致脊髓功能的下降抑制。脊髓背电位是由周围神经刺激引起的一种缓慢的、可重复的电位，最早由Gasser和Tredway（1933）描述，用于评估神经系统的功能状态。这是从脊髓背角表面记录的，是对周围神经电刺激后皮肤传入信号的反应。它由一个传入齐射、一个或多个负(N)波和一个正(P)波组成。这反映了背角中间神经元对外周刺激的兴奋反应。研究表明，有下行抑制通路聚集在这些中间神经元上，被认为可以指导特定反射通路的选择性激活，从而调节运动输出（Lundberg & Vyklicky, 1963）。在本研究中，我们试图探讨这些通路在新生儿缺氧时对脊髓功能的可能作用。选用新西兰大白兔（年龄21-28日龄，体重650-900g）。分离、切开坐骨神经，将其中央端置于双极刺激电极上。行椎板切除术，暴露脊髓的上颈椎部分（T1/T2）和下腰椎部分（L6/L7）。将Ag-AgCI球记录电极置于其上记录诱发电位。15分钟的常氧刺激后开始。然后将动物暴露于轻度缺氧，刺激和记录在氧气状态发生任何变化后15分钟。然后再次暴露颈椎板切除术，并在T1/T2处使用细刀切断脊髓，然后重复该方案。正常新生儿缺氧时N波振幅无明显变化，而中度缺氧时N波潜伏期较对照组长。两组间P波潜伏期和振幅无明显变化。脊髓切片新生儿缺氧时N波振幅有降低的趋势，但缺氧时N波潜伏期无明显变化。缺氧时P波振幅和潜伏期明显减小。总之，缺氧不会改变新生兔脊髓背电位，除非脊髓被横断。这表明在缺氧时，一些下行影响维持了脊髓中间神经元的功能。少

Fetal body and breathing movements cease in hypoxia. The inhibition of fetal breathing movements is thought to be mediated via the upper pons, since brainstem transection at this level abolishes the effect of hypoxia on fetal breathing movements. It thus appears that a descending inhibitory process operates to depress breathing in hypoxia in the fetus. However, the mechanism by which fetal body movements are abolished by hypoxia is still unknown. We hypothesized that hypoxia also causes descending inhibition of the spinal cord function.Cord dorsum potential ia a slow, reproducible potential evoked by peripheral nerve stimulation, first described by Gasser and Tredway (1933) and used to assess the functional state of the nervous system. It is recorded from the surface of the dorsal horn of the spinal cord in response to a volley in cutaneous afferents following electrical stimulation of a peripheral nerve. It consists of an afferent volley, one or more negative (N) waves and a positive … More (P) wave. These reflect the excitation of interneurons in the dorsal horn in response to peripheral stimulation. It has been shown that there are descending inhibitory pathways converging on these interneurons thought to direct the selective activation of particular reflex pathways, thereby regulating motor output (Lundberg & Vyklicky, 1963). In this study we have attempted to investigate the possible roles of theses pathways during hypoxia on the spinal cord function of the neonate.New Zealand White rabbits (age=21-28 days ; weight=650-900g) were used. The sciatic nerve was isolated, sectioned and the central end placed on bipolar stimulating electrodes. A laminectomy was performed exposing the upper cervical portions (T1/T2) and the lower lumber portions (L6/L7) of the spinal cord. A Ag-AgCI ball recording electrode was lowered onto this for the recording of evoked potentials. After a 15 min period of normoxia stimulation began. The animal was then exposed to mild hypoxia, stimulation and recording occurring 15 minutes after any change in oxygen status. The cervical laminectomy was then re-exposed and the cord severed at T1/T2 using a fine scalpel and the protocol was then repeated.In intact neonates, amplitude of N wave did not show any significant changes in hypoxia, whereas latency of N wave was longer in moderate hypoxia than in control. There were no significant changes between any of the experiments in latency and amplitude of P waves. Amplitude of N tended to decrease in hypoxia in spinal cord sectioned neonates, alhtough latency of N wave did not show any significant changes in hypoxia. P wave showed a significant decrease in amplitude and latency in hypoxia. In conclusion, hypoxia did not alter the cord dorsum potentials in neonatal rabbits unless the spinal cord had been transected. This suggests that during hypoxia some descending influence maintains the function of the interneurons in the spinal cord. Less