RESPIRATORY INTERNEURONS OF THE LOWER CERVICAL (C4-C5) CORD - MEMBRANE-POTENTIAL CHANGES DURING FICTIVE COUGHING, VOMITING, AND SWALLOWING IN THE DECEREBRATE CAT

The possible roles of interneurons in the C4-C5 cervical spinal cord i n conveying central drives to phrenic motoneurons during different beh aviour patterns were investigated using intracellular recordings in de cerebrate, paralysed, artificially ventilated cats. Eleven cells were tentatively classified as respiratory interneurons since they: (i) cou ld not be antidromically activated from the ipsilateral whole intratho racic phrenic nerve, and (ii) exhibited large membrane potential chang es during eupnea (7.3 mV +/- 3.6, range 2-13.5 mV) or non-respiratory behaviour patterns. Six neurons depolarized in phase with phrenic disc harge; four others depolarized during the expiratory phase; one neuron exhibited depolarization during the end of both expiration and inspir ation. A variety of responses was observed during fictive coughing, vo miting, and swallowing. The results are consistent with C4-C5 expirato ry interneurons conveying inhibition to phrenic motoneurons during dif ferent behaviour patterns. The responses of inspiratory and multiphasi c neurons suggest that the roles of these interneurons are mode comple x than simply relaying central excitatory or inhibitory drive to phren ic motoneurons.