Behavior of inhibitory and excitatory propriobulbar respiratory neurons during fictive vomiting.

The behavior of propriobulbar respiratory neurons was studied during fictive vomiting in decerebrate, paralyzed, artificially ventilated cats. Fictive vomiting was identified by a characteristic series of synchronous phrenic and abdominal nerve bursts, induced by electrical stimulation of abdominal vagal afferents and/or i.v. infusion of emetic drugs. Data were obtained from inspiratory neurons having decrementing (I-DEC) or constant (I-CON) discharge patterns and expiratory decrementing (E-DEC) neurons located in the Bötzinger complex and adjacent rostral ventral respiratory group. These neurons are known to make excitatory (I-CON) and inhibitory (I-DEC, E-DEC) connections with a variety of medullary respiratory neurons. During fictive vomiting: 8 of 14 I-DEC neurons fired in phase with synchronous bursts of phrenic and abdominal nerve discharge; the other 6 were silent. Of 12 I-CON neurons, 5 fired in phase with phrenic and abdominal bursts; 7 were silent. All (6) E-DEC neurons were either silent or fired weakly between bursts of phrenic and abdominal discharges. The possible roles of I-DEC and I-CON neurons in actively reorganizing the behavior of other respiratory neurons during fictive vomiting are discussed. In particular, the firing of many I-DEC neurons was found to be appropriate to inhibit inspiratory, and two types of expiratory, bulbospinal neurons during fictive vomiting.