Recordings from arterial pressure-sensitive units in the awake dog

Recordings were made from units in or near nucleus ambiguus (NA) in the awake, drug-free dog while arterial pressure (AP) was increased and decreased nonpharmacologically by inflating occlusion cuffs that had been placed around the descending aorta and inferior vena cava, respectively. Units were recorded differentially through floating fine-wire electrodes that extended from vertically movable cannulas in a chronically implanted microdrive. Fifty-three percent of units recorded in or near NA were excited by increased AP, but were unresponsive to decreased AP. The remaining units were unresponsive to increased or decreased AP. About 25% of AP-sensitive units had activity patterns related to the cardiac cycle. AP-sensitive, cardiac cycle related units located in NA displayed several of the properties previously demonstrated for antidromically identified preganglionic parasympathetic cardiac motoneurons involved in baroreflex control of heart rate and rhythm. Recording from such neurons in the awake, neurologically intact, drug-free dog permits the fullest and most natural expression of neuro-cardiologic interactions and will allow the investigation of behavioral influences on autonomic and cardiovascular function.