MULTIFUNCTIONAL VENTRAL RESPIRATORY GROUP - BULBOSPINAL EXPIRATORY NEURONS PLAY A ROLE IN PUDENDAL DISCHARGE DURING VOMITING

Pudendal motoneurons are activated in phasic bursts during the retchin g and expulsion phases of vomiting. The resulting contraction of the a nal and urethral sphincters serves to maintain continence during the l arge increase in abdominal pressure that occurs during vomiting. We ev aluated the contribution of bulbospinal expiratory neurons located in the portion of the ventral respiratory group (VRG) caudal to the obex (nucleus retroambigualis) to the control of pudendal motoneurons durin g fictive vomiting in decerebrate, paralyzed cats. Pudendal nerve disc harge is abolished by cutting the axons of caudal VRG expiratory neuro ns as they cross the midline between the obex and C1 before descending in the spinal cord. All caudal VRG expiratory neurons that were antid romically activated from the sacral spinal cord, where the pudendal mo tor pool (nucleus of Onuf) is located, discharged strongly during the end of the expulsion phase of vomiting. However, only a small proporti on of these neurons was active in phase with pudendal discharge during the retching phase. The apparent involvement of caudal VRG expiratory neurons in the control of pudendal motoneurons during vomiting is ano ther example of the multifunctional role that can be played by respira tory-related neurons in the mammalian nervous system.