The cardiac ganglia: cellular and molecular aspects.

The cardiac ganglia are distributed in different regions of the atria of a number of mammalian species, surrounding the SA node, around the roots of the venae cava and pulmonary veins, interatrial septum, in the proximity of the AV node and in the auricular appendages. A typical cardiac ganglion consists of neurons, satellite cells and SIF cells. The mammalian cardiac ganglia contain unipolar, bipolar and multipolar neurons with differing dimensions and shapes. The neurons and satellite cells of the cardiac ganglia originate from neural crest cells that migrate to the heart. Upon arriving in the outflow tract the cells segregate into parasympathetic neurons and supporting cells to form the cardiac ganglia. The sympathetic innervation of the heart arises from the cervicothoracic sympathetic chains and is derived from the trunk neural crest. The ultrastructural development of the cardiac ganglia in the chicken can be divided into three phases: (1) migration and aggregation of neuroblasts on days 3.5-5; (2) differentiating ganglia, days 5-10; (3) maturing ganglia, days 11 to hatching. The development of cholinergic mechanisms precedes that of adrenergic mechanisms. As a consequence the parasympathetic-cholinergic control becomes functional and plays a role in cardiac function earlier than the sympathetic-adrenal neural control. The genes that may control the development of certain components of the cardiac ganglia are described.