An Ultrastructural Study on the Structural Development of the Cardiac Ganglion in the Human Fetuses

ABSTRACT

The development of the cardiac ganglion was studied by electron microscopy in human fetuses ranging from 30mm to 270mm crown rump length. At 40mm fetus, the cardiac ganglia were observed in the adventitia of both the aorta and pulmonary artery, superior aspect of the left and right atrium, and interatrial septum. The cardiac ganglia were comprised of clusters of undifferentiated cells, neuroblasts, and unmyelinated nerve fibers. The ganglia were small and uncapsulated until 70mm fetus. At 70mm fetus, the cardic ganglia consisted of neuroblasts, satellite cells, and unmyelinated nerve fibers. Each ganglion was ensheathed in a connective tissue capsule. The cytoplasm of neuroblast contained Nissl bodies, mitochondria, coated vesicles, extensive Golgicomplex, and rough endoplasmic reticulum. Synaptic contacts between the cholinergic preganglionic axon and dendrites of postganglionic neuron were first observed. At 100mm fetus, the cardiac ganglia consisted of small clusters of ganglion cells and dendrites, together with supporting elements and blood vessels. During next prenatal stage from 170mm fetus, the ganglion cells were large and each contained a large nucleus with one or more nucleoli. The cytoplasm of ganglion cells contained much rough endoplasmic reticulum and extensive Golgi complex. Cholinergic preganglionic axons were numerous and interposed between the satellite cells. Adrenergic axons were rarely observed. A great number of synaptic junctions between the cholinergic preganglionic axon terminals and the dendrites of postganglinic neuron were found, and a few axosomatic synapses were also observed. Adrenergic nerve terminals did not seem to be involved in the synaptic transmission. The cardiac ganglion cells of the human fetal heart were innervated only by cholinergic nerve.