Possible role of brain stem respiratory neurons in mediating vomiting during space motion sickness

Vomiting is produced primarily by the coordinated action of the respiratory muscles. The object of this study was to determine if brain stem expiratory neurons control abdominal muscle activity during vomiting. We recorded the activity of 27 ventral respiratory group (VRG) expiratory neurons, which are known to be of primary importance for control of abdominal muscle activity during respiration. During fictive vomiting produced by emetic stimulants in decerebrate, paralyzed cats, only one-third of these neurons had the appropriate firing pattern to contribute to abdominal muscle activity during vomiting. In a second series of experiments, we recorded abdominal muscle activity in five cats before and after cutting the axons of VRG expiratory neurons. Abdominal activity remained at 60-100% of prelesion values in three animals. Thus, abdominal muscle activity during vomiting must be controlled not only by some brain stem expiratory neurons but also by other input(s).