Activation of cardiac
sympathetic outflow, but not vagal withdrawal, during spontaneous motor
activity in decerebrate cats
Akito Kadowaki, Kanji Matsukawa, Tomoko Nakamoto,
Department of
Physiology, Graduate School of Health Sciences,
It
is thought that acceleration of cardiac pacemaker rhythm at the start of
exercise is evoked by withdrawal of cardiac vagal nerve activity (CVNA) rather
than by activation of cardiac sympathetic nerve activity (CSNA). To examine whether this assumption is
true, we directly measured CVNA and CSNA during spontaneous motor activity in eight
decerebrate and paralyzed cats.
Heart rate and mean arterial pressure increased by 4 ± 1 beats/min (mean
± SE) and 17 ± 1 mmHg during spontaneous motor activity, which was identified
by efferent discharges of the tibial nerve. As soon as the motor activity occurred, CSNA
increased by 93 ± 14% at 1 s from the onset of motor activity. In contrast, CVNA gradually increased by
75 ± 17% during motor activity. The
increases in CSNA and CVNA were diminished by partial sinoaortic denervation. On the other hand, in response to passive
muscle stretch of the hindlimb, CSNA rapidly increased by 45 ± 12%, while CVNA
gradually decreased by 51 ± 12%. In
conclusion, central command causes an increase in cardiac sympathetic outflow (but
not a decrease in cardiac vagal outflow), which contributes to the cardiovascular
adaptation at onset of spontaneous motor activity. In contrast, a muscle mechanoreflex causes
reciprocal responses in CSNA and CVNA.
Key words: cardiac vagal nerve
activity, spontaneous motor activity, decerebrate cat