Activity of canine in situ left atrial ganglion neurons

The responses of 135 spontaneously active neurons were recorded from ganglionated plexi located in the three epicardial fat pads on the ventral surface of the left atrium of ten dogs. Ganglia, some of which were adjacent to the recording sites, containing varying numbers of neurons were identified throughout these fat pads. Spontaneous activity in 50% of the identified neurons was correlated with specific phases of the cardiac cycle when arterial systolic pressure was between approximately 70 and 180 mmHg and in 28% it was correlated with the respiratory cycle. More neurons displaying cardiovascular-related activity were recorded when systolic pressure was increased after administration of positive inotropic agents or aortic occlusion. However, when systolic pressure increased above approximately 150 mmHg the number of active neurons decreased, and when pressure reached approximately 180 mmHg no activity was recorded. The activity of 36% of identified neurons was altered when discrete regions of the heart, great thoracic vessels, lungs, neck, upper limb, chest wall, or abdominal wall were mechanically distorted by gentle touch. After acute decentralization of the intrathoracic nervous system some neurons still displayed spontaneous cardiovascular- or respiratory-related activity. Single stimuli or trains of stimuli delivered to the vagosympathetic complexes, stellate ganglia, or cardiopulmonary nerves activated neurons in intact or acutely decentralized preparations. It is concluded that ventral left atrial ganglionated plexi neurons display activity related to cardiovascular or respiratory dynamics, and that these neurons are influenced by sympathetic and parasympathetic efferent axons, as well as by cardiac and other mechanoreceptors.