Mammalian Cardiac Ganglia as Local Integration Centers: Histochemical and Electrophysiological Evidence

Abstract

The mammalian parasympathetic cardiac ganglia form a complex intrinsic cardiac nervous system composed of parasympathetic postganglionic projection neurons, local interneurons and possibly afferent neurons with central projections. In addition to the preganglionic parasympathetic cholinergic excitatory innervation, the cardiac ganglia are innervated by sympathetic postganglionic fibers and afferent fibers derived from both the spinal dorsal root ganglia and the vagal sensory ganglia. Thus, multiple neurotransmitters can potentially modulate activity of the cardiac neurons. Results discussed here identify the neurochemically-coded fiber inputs and summarize the neuronal response to some of these transmitters in a model system, the guinea pig cardiac ganglia. The diverse functional and neurochemical properties of cardiac neurons and their strategic location position them to mediate local reflex mechanisms initiated by changes in cardiac performance or by changes in the local environment within the myocardium. Thus, it is critical to better understand the integrative mechanisms within the cardiac ganglia.