Journal of Applied Physiology, Vol 58, Issue 4 1285-1290, Copyright © 1985 by American Physiological Society
Effects of early hypoxia on breathing pattern in rabbit pups before and after vagotomy
T. Trippenbach, G. Kelly and R. Affleck
We examined the influence of vagal pulmonary receptors exerted on the
breathing pattern and inspiratory activities of phrenic nerve and
intercostal electromyograms (EMG) during hypoxia in rabbit pups. Animals in
their second week of life were anaesthetized with ketamine (50 mg/kg) and
acepromazine (3 mg/kg) and tracheostomized. While they breathed
spontaneously, we recorded tidal volume (VT), integrated phrenic activity
(PHR), integrated external intercostal EMG (INT), and blood pressure (BP).
To prevent secondary ventilatory depression, animals were exposed to 12% O2
(balanced with N2) for no longer than 5 min before and after vagotomy. All
measurements were taken from 1 min following the onset of hypoxic exposure
until the end of the run. During hypoxia, VT, PHR, and INT increased in
intact rabbit pups. There was an almost immediate decrease in BP that was
maintained during the total period of hypoxia exposure. Hypoxia resulted in
inconsistent changes in inspiratory (TI) and expiratory (TE) time in intact
animals. Following vagotomy, PHR, INT, VT, BP, and TE responses were the
same as in intact animals. However, TI significantly decreased in all
animals. In response to hypoxia with and without vagal feedback, INT
increased less than PHR in most cases. Qualitatively similar effects of
hypoxia were observed in an adult rabbit. The results reveal that the
increase in VT and the shortening of TI in response to hypoxia do not
depend on vagal feedback in rabbits during the early postnatal period. In
fact TI shortening was significant only without vagal feedback.
