Effects of Prestimulus Respiratory Levels on Inhibitory Respiratory Response by Nociceptive Muscular Afferents.

Morphine Inhibits Resting Respiration, but It Attenuates Reflexive Respiratory Suppression in Anesthetized Cat through .KAPPA.-Receptor.

“…The magnitude of the poststimulus suppression was attenuated by raising the prestimulus respiratory level [4]. However, when that level was near the control level, morphine markedly attenuated the magnitude of the poststimulus suppression, and this attenuation was antagonized by naloxone.…”

“…Care and experiments on all animals used in this study were carried out according to the Guiding Principles for the Care and Use of Animals approved by the Council of the Physiological Society of Japan. Details of the general procedure are described in the preceding companion paper [4]. Briefly, the animals were vagotomized, glomectomized, paralyzed, and artificially ventilated by use of an air-oxygen mixture.…”

“…To normalize data among cats, respiratory responses to inhaled CO 2 (CO 2 response) were measured by using a modified rebreathing method under artificial ventilation [4]. To examine the reproducibility of CO 2 response curves of RO, CO 2 responses were tested again 144 to 260 min after the first trials in 5 cats.…”

“…The level of the resting respiration was controlled by a changing ventilation rate without altering the stroke volume of the respirator. Since the prestimulus level of respiration influences the magnitude of the poststimulus respiratory suppression [4], ES was applied when the prestimulus level of respiration was near the control level. The magnitudes of the poststimulus suppression in the RO, PK, and RR were represented as the differences between the values during the 2 to 15 min period after stopping ES and the values for a 1-min period before the stimulus.…”

“…This suppression is reversed or greatly reduced by naloxone, suggesting the involvement of endogenous opioids. However, when the respiratory level was augmented by means of either hypercapnia, hypoxia, or naloxone administration, the magnitude of the poststimulus suppression was markedly attenuated without consistently altering the facilitatory response during the period of stimulation [4]. Although prestimulus respiratory activity is an important factor in determining the magnitude of the poststimulus suppression, a preliminary study had shown that morphine attenuated the magnitude of the poststimulus suppression when the prestimulus level of respiration was near the control level.…”