Analysis of respiratory neuronal activity in fetal sheep.
We developed a new method to monitor fetal medullary respiratory neurons utilizing a two-stage approach. At 129-133 days of gestation, sheep were anesthetized, and a window was placed over the area of the fourth ventricle. After a recovery period of 3-5 days, the fetus was exteriorized into a saline bath under maternal spinal anesthesia, and the head was connected rigidly to a stereotaxic frame. Microelectrodes were inserted into the area of the nucleus tractus solitarius during rapid-eye-movement sleep, and extracellular recordings of 223 respiratory neurons were analyzed: 76% were inspiratory, 9% expiratory, and 15% phase spanning, as classified by visual and computer correlation to diaphragmatic activity. More detailed analysis of 100 neurons was done to assess the respiratory component (eta 2) by use of a modification of the method developed by Orem and Dick (J. Neurophysiol, 50: 1098-1107, 1983). With use of cohorts of 25 breaths, fetal respiratory neurons were found to frequently change their phase relationship to diaphragmatic activity. The eta 2 statistic of fetal respiratory neurons was not a stable characteristic but changed over time. This could be a reflection of an immature central respiratory system before birth or the lack of major sensory inputs.
Ioffe
S
S
Perinatal Physiology Laboratory, University of Manitoba, Winnipeg, Canada.
Jansen
A H
AH
Chernick
V
V
D000818:Animals; D001784:Blood Gas Analysis; D003964:Diaphragm / Q000294:innervation / Q000502:physiology; D004576:Electromyography; D005260:Female; D005333:Fetus / Q000502:physiology*; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D011247:Pregnancy; D012137:Respiratory System / Q000294:innervation*; D012756:Sheep