Vol. 94, Issue 4, 1421-1430, April 2003
Short-term plasticity of descending synaptic input to phrenic
motoneurons in rats
F.
Hayashi,
C.
F. L.
Hinrichsen, and
D. R.
McCrimmon
Department of Physiology and Institute for Neuroscience,
Feinberg School of Medicine, Northwestern University, Chicago,
Illinois 60611-3008
Respiratory afferent stimulation
can elicit increases in respiratory motor output that outlast the
period of stimulation by seconds to minutes [short-term potentiation
(STP)]. This study examined the potential contribution of
spinal mechanisms to STP in anesthetized, vagotomized, paralyzed rats.
After C1 spinal cord transection, stimulus trains (100 Hz,
5-60 s) of the C1-C2 lateral funiculus
elicited STP of phrenic nerve activity that peaked several seconds
poststimulation. Intracellular recording revealed that individual
phrenic motoneurons exhibited one of three different responses to
stimulation: 1) depolarization that peaked several seconds
poststimulation, 2) depolarization during stimulation and
then exponential repolarization after stimulation, and 3)
bistable behavior in which motoneurons depolarized to a new, relatively
stable level that was maintained after stimulus termination. During the
STP, excitatory postsynaptic potentials elicited by single-stimulus
pulses were larger and longer. In conclusion, repetitive activation of
the descending inputs to phrenic motoneurons causes a short-lasting
depolarization of phrenic motoneurons, and augmentation of excitatory
postsynaptic potentials, consistent with a contribution to STP.
central control of breathing; short-term potentiation; bistability; bulbospinal pathways