Cardiac Sensory Neurons

Abstract

Abstract The nervous system intrinsic to the heart contains all of the components necessary for information processing. That parasympathetic efferent postganglionic neurons are associated with the intrinsic cardiac nervous sys­ tem has been known for some time.22,63 Recently, afferent neurons,2,10,29A4 sympathetic efferent postganglionic neurons,25,86 and interconnecting local circuit neurons13,i4,37 have been identified within the intrinsic cardiac nervous system. As a matter of fact, it was the functional identification of the somata of afferent neurons within this system2 that permitted the development of the thesis that there is a little brain on the heart that modulates regional cardiodynamics on a beat-to-beat basis.10,63 Cardiac sensory nerve terminals (neurites) are associated with somata in ganglia located relatively distant from the heart, those in nodose and dorsal root ganglia.64,84 These neurons, plus those associated with sensory neurites in intrathoracic and cervical vessels, transduce the cardiac and intrathoracic vascular milieu to medullary (Chapter 6) and spinal cord (Chapter 5) neurons, respectively. Recent evidence indicates that afferent neuronal somata located in intrathoracic extracardiac ganglia are associated with sensory neurites in cardiac tissues and the adventitia of intrathoracic vessels.8,23 The latter population of afferent neurons transduces the cardiovascular milieu to cardiac postganglionic motor neurons in intrathoracic ganglia, doing so primarily via intrathoracic local circuit neurons.10 Each cardiac afferent neuron displays unique transduction capabilities so that the information they provide to second-order processing neurons within different levels of the cardiac neuronal axis varies. These in turn influence cardiac efferent neurons, some of which also receive indirect inputs via central neurons from afferent neurons with sen­sory neurites in extrathoracic tissues. The latter include the carotid arteries1,12 and skin of the extremities.