Discharge Patterns of Bulbar Respiratory Neurons during Retching and Vomiting in Decerebrate Dogs.

Abstract

To determine whether bulbar respiratory neurons are active in a manner similar to respiratory motor nerves, in which diverse activity patterns have been observed in dogs, the discharge of 112 bulbospinal and 155 propriobulbar respiratory neurons was observed during retching and vomiting evoked by stimulation of the vagal nerve in decerebrate, paralyzed dogs. During retching, the respiratory activities of all respiratory neurons changed. The discharge patterns during retching were classified into seven types in accordance with the discharge phase in the retching cycle and the discharge frequency. Inspiratory bullbospinal neurons (39) in the ventral respiratory group (VRG) exhibited discharge synchronous with retches at higher (14/39) or lower (4/39) frequencies than those of their respiratory discharge, discharge between retches at higher (3/39) or lower (14/39) frequencies and discharge depressed throughout the retching period (4/39). Inspiratory bulbospinal neurons (30) in the dorsal respiratory group (DRG) and expiratory bulbospinal neurons (23) in the VRG also fired with some of the seven types of discharge. No significant difference was recognized between the ratio of the numbers of inspiratory bulbospinal neurons firing with the seven types of discharge and that of expiratory bulbospinal neurons. On the other hand, the respiratory propriobulbar neurons (73) in the VRG and those (45) in the DRG seemed to be differently activated; that is, 44% of the propriobulbar neurons in the VRG fired synchronously with retches at a higher frequency than their frequency during breathing, while only 22% of those in the DRG fired at such a high frequency with retches. However, the ratio of whole inspiratory neurons (174) exhibiting the seven types of discharge was almost the same as that of whole expiratory neurons (93). During vomiting (fictive expulsion), three of five expiratory neurons fired, but most (14/16) of inspiratory neurons did not. In conclusion, all of the activity patterns which have been observed during retching in motor fibers innervating respiratory muscles are found in both bulbospinal and propriobulbar respiratory neurons in dogs. Furthermore, since the firing patterns of inspiratory bulbospinal neurons during retching in the dogs in this study are apparently different from those in cats (Miller et al., 1990), inspiratory neurons and muscles seem to be differently organized during retching in cats and dogs.