The respiratory response to stimulation of juxta-pulmonary capillary receptors in the non-anesthetized cat

To avoid the modifying influence of general anesthesia on vagal control of respiration, we investigated the effect of phenyldiguanide (PDG), a drug known to stimulate juxta-pulmonary capillary ("J") receptors, in the non-anesthetized, unrestrained cat and recorded EEG, eye movements, neck muscle EMG, EKG and respiratory movements. The response to bolus injection of PDG into the right atrium was qualitatively similar to the one seen in cats under anesthesia, consisting of bradycardia and apnea followed by rapid shallow breathing (RSB). The injection-response latencies ranged from 1.5 to 3 s, indicating that the effect originated on the venous side of the cardiopulmonary region. Vagal block with lidocaine, which was applied via external tubings feeding into implanted vagal "sleeves", abolished the responses to PDG, demonstrating their dependence on vagal mediation. Atropine blocked the bradycardia but did not affect the apnea. All doses of PDG which affected respiration uniformly produced initial apnea, whose duration, in any given animal and trial session, exhibited a consistent dose-response relationship. Slow injections also produced apnea. RSB following the apnea was variable in frequency and amplitude of excursions and in its overall duration, and failed to reveal a dose-response relationship. Apnea lasted significantly longer when injections were made during slow wave sleep or REM sleep as compared to injections given during wakefulness or drowsiness. Arousal from all states of sleep occurred simultaneously with the onset of apnea and bradycardia and was also dependent on the vagi. Spontaneous awakening from sleep, by contrast, was always associated with an increase in breathing.(ABSTRACT TRUNCATED AT 250 WORDS)