| Abstract: | Electron microscopy was used to study synapse development in the cardiac ganglia of human fetuses ranging from 8 to 27 weeks of ovulation time. Staining with ethanolic phosphotungstic acid was used for analysis of synaptic active zones. Specialization of interneuronal links begins with the appearance of electron dense material on plasmalemmas of nerve cells in the places of simple contacts. First synapses with single synaptic vesicles and short osmiophilic zones were found in cardiac ganglia in 8-week-old fetuses. Large granular vesicles and mitochondria vesicles are formed from cisternae of agranular endoplasmic reticulum in the preterminal parts of axons and moved by axoplasmic transport to the osmiophilic zones of future synapses. Axodendritic synapses appeared earlier in the cardiac ganglia than axosomatic ones, the latter were observed from the middle of gestation. Transient neuroglial synapse-like contacts were found in the cardiac ganglia. Staining with phosphotungstic acid made it possible to distinguish the degree of synapse maturation according to active synaptic zones. The peculiarities of synaptic development in cardiac ganglia in comparison with that in the central nervous system may be accounted for by different origins of the neural tube and of neural crest and by the level of their phylogenic development. |
