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

点击翻译按钮获取中文摘要

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