Activity of in vivo canine ventricular neurons

The spontaneous activity of 113 neurons located in the ganglionated plexus in the epicardial fat overlying the cranial portion of the ventral intraventricular groove and the origin of the circumflex coronary artery was recorded in ten anesthetized dogs. Ganglia that contained varying numbers of neurons, some with two or more nucleoli, were subsequently identified anatomically in the vicinity of the recording sites. Spontaneous activity was correlated with the cardiac cycle in 81% and with the respiratory cycle in 17% of the identified neurons. The spontaneous cardiovascular-related activity occurred in relation to specific phases of the cardiac cycle when arterial pressure was between approximately 80 and 175 mmHg. When systolic pressures fell below approximately 80 mmHg or increased above approximately 175 mmHg, neurons displaying cardiovascular-related activity were inactive. The activity of 62% of all identified neurons was altered when discrete regions of the heart or pulmonary tissue were mechanically distorted by gentle touch. In many instances mechanical distortions of tissues were still able to alter neuronal activity following acute decentralization. Single stimuli or trains of stimuli delivered to the vagosympathetic complexes, stellate ganglia, or cardiopulmonary nerves generated bursts of activity in ganglionic neurons. Spontaneous activity occurred whether the ganglia were connected to the central nervous system or acutely decentralized. It is concluded that some neurons located on the canine ventricle display spontaneous activity that is related to cardiovascular or respiratory dynamics. The results also demonstrate that ventricular neurons can be influenced by sympathetic or parasympathetic efferent axons as well as cardiac mechanoreceptors.