Fine structure of the human fetal cervical ganglia

Cervical sympathetic ganglia from nine human fetuses in the second trimester were studied by light-, fluorescence- and electronmicroscopy. Within ganglia granule-containing cells, corresponding to the small intensely fluorescent (SIF) cells, were sparsely distributed along capillaries. Satellite cells were interspersed among neuronal cell types. All stages of the developing sympathetic ganglion cells were present. Primitive sympathetic ganglion cells (PSC) had dark nuclei and scanty cytoplasm in which the rough endoplasmic reticulum (RER) was not organized. These cells often contacted each other vs the more mature pattern of satellite cell support. Neuroblasts had more voluminous cytoplasm, RER was more apparent than in the PSCs and dense-cored vesicles and mitochondria were more frequently seen. Their diameter was between 5 and 20 μm. The most mature neuronal cell type, the young sympathetic ganglion cell, was often covered by satellite cells, but synaptic contacts often appeared on the somata. Maturity of the cells was underscored by an abundant RER and ribosomes organized as Nissl bodies. Indeed all the organelles typical of an adult ganglion cell were present and fully developed, although in smaller amounts. However, the diameter (20-30 μm) of the cells was smaller than in adult ganglia. All ganglia examined possessed mature axodendritic and axosomatic synapses. Large dense-cored vesicles were found in some neuroblasts and in young sympathetic ganglion cells. However, neither cytoplasmic nor synaptic small dense-cored vesicles were seen. These morphological results correlate with pharmacological and immunohistochemical data on human fetal tissue which show that both cholinergic and adrenergic receptors, catecholamine-synthesizing enzymes and enkephalin are developed by the end of the first trimester.