ACTIVITY OF DORSAL RESPIRATORY GROUP INSPIRATORY NEURONS DURING LARYNGEAL-INDUCED FICTIVE COUGHING AND SWALLOWING IN DECEREBRATE CATS

Membrane potential changes and/or discharges from 36 inspiratory neuro ns were recorded intracellularly in the dorsal respiratory group (DRG; i.e., the ventrolateral subdivision of the nucleus tractus solitarii) in decerebrate, paralyzed, and ventilated cats. Electrical activities were recorded from both somata (n=10) and axons (n=26). Activities du ring quiet breathing were compared with those observed during fictive coughing and swallowing evoked by repetitive electrical stimulation of afferent fibers of the superior laryngeal nerve (SLN). These, nonresp iratory behaviors were evident in paralyzed animals as characteristic discharge patterns of the phrenic, abdominal, and hypoglossal nerves. Twenty-six neurons exhibiting antidromic action potentials in response to electrical stimuli applied to the cervical (C3-5) spinal cord were classified as inspiratory bulbospinal neurons (IBSNs). These neurons were considered as premotoneurons. The remaining 10 inspiratory neuron s (I-NAA) were not antidromically activated by electrical stimuli appl ied to either cervical spinal cord or ipsilateral cervical vagus. Thes e neurons are thought to be propriobulbar neurons. We recorded the act ivity of 31 DRG inspiratory neurons (24 IBSNs and 7 I-NAA) during coug hing. All but one (a late-recruited IBSN) discharged a burst of action potentials during the coughing-related phrenic nerve activity. Typica lly, ramp-like membrane depolarization trajectories and discharge freq uencies during coughing were similar to those observed during inspirat ion. We recorded the activity of 33 DRG inspiratory neurons (23 IBSNs and 10 I-NAA) during swallowing. Most (28/33) neurons were briefly act ivated, i.e., discharged a burst of action potentials during swallowin g, but peak discharge frequency decreased compared with that measured during inspiration. The membrane potentials of nine somata exhibited a brief bell-shaped depolarization during swallowing, the amplitude of which was similar to that observed during inspiration. These results s uggest that some inspiratory premotoneurons and propriobulbar neurons of the DRG might be involved in nonrespiratory motor activities, even if clearly antagonistic to breathing (e.g., swallowing). We postulate the existence in the medulla oblongata of adult mammals of neurons exh ibiting a ''functional flexibility''.