Ultrastructural Study on the Development of the Small Granule-Containing Cells in Superior Cervical Ganglion of Human Fetus

인태아 상경신경절내 소형의 과립함유세포에 관한 전자현미경적 연구

The development of small granule-containing cell in the superior cervical ganglion was studied by electron microscopic method in human fetuses ranging from 40 mm to 260 mm crown rump length (10 to 30 weeks of gestational age). At 40 mm fetus, the superior cervical ganglion was composed of clusters of undifferentiated cells, primitive neuroblasts, and unmyelinated nerve fibers together with blood vessels. At 90 mm fetus, the superior cervical ganglion consisted of neuroblasts, satellite cell, small granule-containing cells, and unmyelinated nerve fibers. Two morphological types of the small granule-containing cells in the superior cervical ganglion were first indentified at 90 mm fetus, but were rare. Type I granule-containing cell occurred in solitary and had long processes, whereas type II cells tend to appeared in clusters near the blood capillaries. The granule-containing cells were characterized by the presence of dense-cored vesicles ranging from $150{\sim}300nm$ in diameter in both the cell bodies and processes. Other organelles included abundant mitochondria, rough endoplasmic reticulum, neurotubules, and widely distributed ribosomes. The granule-containing cells had long processes similar to those found in principal ganglionic cells. They could be identified by their content in dense-cored vesicles. The small granule-containing cells increased somewhat in size and number with increase of fetal age. Synaptic contacts were first found on the solitary granule-containing cell at 150 mm fetus. Synaptic contacts between the soma and processes of type I granule-containing cells and preganglionic axon terminals were observed. In addition, synaptic junctions between the processes of granule-containing cells and presumed dendrite of postganglionic neuron were also observed from 150 mm onward. On the basis of these features type I granule-containing cells could be considered as interneurons. The clusters of type II granule-containing cells were located in the interstitial or subcapsular portions of the ganglion, and had short processes which ended in close relation to fenestrated capillaries. Therefore it may be infer that clusters of type II granule-containing cells have an endocrine function.