Analyses of activity generated by neurons in middle cervical or stellate ganglia versus intrinsic cardiac ganglia were performed to determine how neurons in different intrathoracic ganglia, which are involved in cardiac regulation, interact. Discharges of 19% of intrathoracic extracardiac neurons and 32% of intrinsic cardiac neurons were related to cardiodynamics. Epicardial touch increased the activity generated by ∼80% of intrinsic cardiac neurons and ∼60% of extracardiac neurons. Both populations responded similarly to epicardial chemical stimuli. Activity generated by neurons in intrinsic cardiac ganglia demonstrated no consistent short-term relationships to neurons in extracardiac ganglia. Myocardial ischemia influenced extracardiac and intrinsic cardiac neurons similarly. Carotid artery baroreceptors influenced neurons in ipsilateral extracardiac ganglia. After decentralization from the central nervous system, intrinsic cardiac neurons received afferent inputs primarily from cardiac chemosensitive neurites, whereas middle cervical ganglion neurons received afferent inputs primarily from cardiac mechanosensory neurites. It is concluded that the populations of neurons in different intrathoracic ganglia can display differential reflex control of cardiac function. Their redundancy in function and noncoupled behavior minimizes cardiac dependency on a single population of intrathoracic neurons.

The consequences of myocardial ischemia are examined from the standpoint of the neural control system of the heart, a hierarchy of three neuronal centers residing in central command, intrathoracic ganglia, and intrinsic cardiac ganglia. The basis of the investigation is the premise that while this hierarchical control system has evolved to deal with "normal" physiological circumstances, its response in the event of myocardial ischemia is unpredictable because the singular circumstances of this event are as yet not part of its evolutionary repertoire. The results indicate that the harmonious relationship between the three levels of control breaks down, because of a conflict between the priorities that they have evolved to deal with. Essentially, while the main priority in central command is blood demand, the priority at the intrathoracic and cardiac levels is heart rate. As a result of this breakdown, heart rate becomes less predictable and therefore less reliable as a diagnostic guide as to the traumatic state of the heart, which it is commonly used as such following an ischemic event. On the basis of these results it is proposed that under the singular conditions of myocardial ischemia a determination of neural control indexes in addition to cardiovascular indexes has the potential of enhancing clinical outcome.

To determine the activity characteristics displayed by different subpopulations of neurons in a single intrinsic cardiac ganglionated plexus, the behaviour and co‐ordination of activity generated by neurons in two loci of the right atrial ganglionated plexus (RAGP) were evaluated in 16 anaesthetized dogs during basal states as well as in response to increasing inputs from ventricular sensory neurites. These sub‐populations of right atrial neurons received afferent inputs from sensory neurites in both ventricles that were responsive to local mechanical stimuli and the nitric oxide donor nitroprusside. Neurons in at least one RAGP locus were activated by epicardial application of veratridine, bradykinin, the β1‐adrenoceptor agonist prenaterol or glutamate. Epicardial application of angiotensin II, the selective β2‐adrenoceptor agonist terbutaline and selective α‐adrenoceptor agonists elicited inconsistent neuronal responses. The activity generated by both populations of atrial neurons studied over 5 min periods during basal states displayed periodic coupled behaviour (cross‐correlation coefficients of activities that reached, on average, 0·88 ± 0·03; range 0·71–1) for 15–30 s periods of time. These periods of coupled activity occurred every 30–50 s during basal states, as well as when neuronal activity was enhanced by chemical activation of their ventricular sensory inputs. These results indicate that neurons throughout one intrinsic cardiac ganglionated plexus receive inputs from mechano‐ and chemosensory neurites located in both ventricles. That such neurons respond to multiple chemical stimuli, including those liberated from adjacent adrenergic efferent nerve terminals, indicates the complexity of the integrative processing of information that occurs within the intrinsic cardiac nervous system. It is proposed that the interdependent activity displayed by populations of neurons in different regions of one intrinsic cardiac ganglionated plexus, responding as they do to multiple cardiac sensory inputs, forms the basis for integrated regional cardiac control.

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