Effects of prestimulus respiratory levels on inhibitory respiratory response by nociceptive muscular afferents

Abstract

We have previously shown that the inhibitory respiratory response, which we call post-stimulus suppression, is induced by nociceptive muscular afferents. This phenomenon is thought to be caused by a negative feedback induced by excessive afferent inputs. In the present study, we investigated whether augmented levels of prestimulus respiration would influence the magnitude of poststimulus suppression by recording the phrenic nerve discharges in chloralose-urethane anesthetized, vagotomized, paralyzed and artificially ventilated cats. The respiratory level was augmented by means of either hypercapnia, hypoxia or naloxone administration, all of which markedly facilitated the peak amplitude (PK) of integrated phrenic discharges, neural tidal volume. When the electrical stimulation of thin-fiber muscular afferents was performed at these augmented PK levels, the magnitude of poststimulus suppression in the PK was markedly attenuated without consistently altering the facilitatory response during the stimulation period. It seems that the facilitatory component of the augmented level of resting respiration may reduce the inhibitory component of poststimulus suppression. The results indicate that prestimulus respiratory activity is an important factor in determining the magnitude of poststimulus suppression.