Journal of Applied Physiology, Vol 54, Issue 4 919-925, Copyright © 1983 by American Physiological Society
Expiratory motor responses in the suckling opossum
J. P. Farber
To evaluate developmental aspects of expiratory muscle utilization,
ventilation and electromyographic (EMG) activity from abdominal muscles
were measured in unanesthetized suckling opossums. From about 20-35 days of
age, breathing against a continuous positive airway pressure (CPAP) or
inhalation of hypercapnic and asphyxiant test gases (ventilatory
chemostimulation) increased or initiated a sustained expiratory-phased
abdominal EMG discharge. Using younger animals, such responses could not be
demonstrated during test manipulations, or pattern of activation was not
typical of that observed in the older group. In another series of
experiments, vagal mechanisms underlying expiratory abdominal muscle
responses were evaluated by using lightly anesthetized animals. Unilateral
vagotomy reduced abdominal EMG levels during ventilatory chemostimulation
while minimally affecting breathing pattern; in addition, abdominal muscle
activity during CPAP was of slower onset than before vagotomy. Slow onset
of abdominal muscle activity was also seen in relatively young intact
unanesthetized animals during responses to CPAP. Thus vagal afferents
mediate expiratory motor responses during chemostimulation of breathing and
may account, in part, for maturation of expiratory responses to CPAP.
