Journal of Applied Physiology, Vol 50, Issue 5 994-998, Copyright © 1981 by American Physiological Society
Comparison of phrenic motoneuron activity during eupnea and gasping
W. M. St John and D. Bartlett Jr
Single-fiber phrenic nerve action potentials were recorded together with
activity of contralateral whole phrenic nerve rootlets during eupnea and
gasping in decerebrate, cerebellectomized, vagotomized, paralyzed, and
ventilated cats. Gasping was reversibly produced by cooling a fork thermode
positioned through the pontomedullary junction. In eupnea, phrenic
motoneurons were distributed into "early" and "late" populations relative
to their onset of activity during inspiration. During gasping, however,
both fiber types typically commenced activity at the beginning of the
phrenic nerve burst. Moreover, late fibers, but not early units, exhibited
an augmentation of discharge frequency with the onset of gasping. The
concentration of activity of all phrenic motoneurons at the beginning of
inspiration and the increase in late-unit discharge frequency account for
the faster rise of the gasp as compared with the eupneic breath. It is
concluded that the pattern of phrenic nerve activation during gasping
differs fundamentally from that during eupnea. These results support the
concept that mechanisms underlying the neurogenesis of gasping and eupnea
may not be identical.
