Journal of Applied Physiology, Vol 73, Issue 5 1972-1981, Copyright © 1992 by American Physiological Society
Analysis of respiratory neuronal activity in fetal sheep
S. Ioffe, A. H. Jansen and V. Chernick
Perinatal Physiology Laboratory, University of Manitoba, Winnipeg, Canada.
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.
