[Ultrastructure of the sympathetic paravertebral ganglia in rat embryogenesis. I. Cytogenesis and cell differentiation].

The development of sympathetic paravertebral ganglia was studied in rat embryos by electron microscopy. The main attention was paid to the initial stages of ganglion formation. The first aggregations of presumptive ganglionic cells were observed in 12 day-old embryos. Single preganglionic terminals appeared in contact with cell bodies sometime later. The appearance of large granular vesicles in the cytoplasm is the first ultrastructural feature of the beginning of neural differentiation of cells. Small granulated cells observed from the 12th day of gestation and neuroblasts differentiate earlier than glial cells. In the ganglia of late fetuses nerve cells varied in the electron density of the cytoplasm, in the degree of distention of rough endoplasmic reticulum and in vacuolization of mitochondria.