THE POSSIBLE ROLE OF C5 SEGMENT INSPIRATORY INTERNEURONS INVESTIGATEDBY CROSS-CORRELATION WITH PHRENIC MOTONEURONS IN DECEREBRATE CATS

We tested the role of C5 segment inspiratory interneurons in transcrib ing central respiratory drive to phrenic motoneurons and mediating int ersegmental reflexes by cross-con-elating the spontaneous activity of 26 interneurons with that of the ipsi and contralateral C5 phrenic ner ves in decerebrate cats. There were 10 interneurons that discharged on ly during inspiration (phrenic burst) and 16 that discharged tonically with increased firing during inspiration. Of the cross-correlograms f or 26 of the interneurons with the ipsilateral phrenic, 20 were flat a nd 2 had peaks centred about time zero, interpreted as a common activa tion of the interneurons and motoneurons. The cross-correlograms for 4 other interneurons had troughs centred about time zero, interpreted a s a synchronous excitation of the interneurons and inhibition of the m otoneurons. Of the cross-correlograms for 23 interneurons with the con tralateral phrenic, 22 were flat and 1 had a peak centred about time z ero, interpreted as a common activation of the interneuron and motoneu rons. Nine of ten cross-correlograms between pairs of interneurons wer e flat; one had a peak centred about time zero. We conclude that, desp ite their inspiratory modulated discharge patterns, there is no eviden ce from this study that the C5 segment inspiratory interneurons convey central respiratory drive to C5 phrenic motoneurons.