Modifications of the firing rate of bulbar reticular units (nucleus gigantocellularis) after intra-arterial injection of bradykinin into the limbs

Abstract To define the role of the nucleus gigantocellularis (NGC) of the bulbar reticular formation in the pain process, modifications of the firing rate of NGC cells were studied after nociceptive stimulation induced by intra-arterial injection of bradykinin into the limbs of cats. Eighty-two per cent of NGC cells were affected. Sixty-five per cent were excited; the mean increase in firing rate was 415%, the mean latency 14.5 sec and the mean duration 17 sec. Twelve per cent were inhibited and one-half of these cells were also inhibited by natural stimulation. Five per cent had a mixed response. Modifications of firing rate were reproducible in any given cell. The observed modifications of firing rate appeared to be independent of arousal mechanisms. The possible functional significance of these results is discussed.