Journal of Applied Physiology, Vol 66, Issue 4 1606-1612, Copyright © 1989 by American Physiological Society
Medullary expiratory activity during opossum development
J. P. Farber
Department of Physiology and Biophysics, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
Medullary expiration-phased action potentials were obtained from
5-sec-butyl-5-ethyl-2-thiobarbituric acid- (Inactin) anesthetized suckling
opossums from approximately 30 days of age to near weaning (80-90 days of
age). The medulla was explored for expiratory neuronal action potentials
during positive pressure breathing (PPB) (approximately 3 cmH2O) because
many expiratory cells had little or no discharge during spontaneous
breathing off load. After finding an expiratory unit, the response of the
cell to removal (30-60 s) and reinstatement of PPB was measured.
Projections to the spinal cord were also examined, and position of the cell
was assessed. Results were compared with those obtained from rostral and
caudal medullary expiratory neurons in adult opossums. Mean discharge rate
of expiratory cells during PPB increased as a function of age. Discharge
started with a delay after the cessation of inspiration; this delay
decreased as a function of age. Cells averaged 7.5 spikes/breath during PPB
and 2.2 spikes/breath off load. Forty-four percent of cells discharged less
than once per breath when PPB was removed. Of cells becoming completely
silent off load, 73% lost their discharge within the first two unloaded
breaths. Only 5% of caudal and 15% of rostral medullary expiratory cells in
adult opossums became silent after the end-expiratory transpulmonary
pressure was reduced to normal. Neurons in sucklings were most often
bulbospinal as were caudal medullary cells in adults; neurons were found in
the region of the nucleus ambiguus.(ABSTRACT TRUNCATED AT 250 WORDS)
