Substance P increases the polymorphism of the synaptic vesicles in the temporal isocortex cultured in vitro

Rat's temporal cortex was cultured in vitro in a feeding medium enriched with substance P. Normal controls were used for correlation. The ultrastructural study of the explant exposed to substance P revealed a marked increase of the polymorphism of the synaptic vesicles in the presynaptic terminals. Large numbers of the synaptic vesicles were large, of a mean diameter of 142.5 A, dark-looking like the catecholaminergic vesicles. Coated vesicles were seen in the presynaptic terminals as well as in the postsynaptic ones. Large elongated vesicles and S-like vesicles were seen in the axonic terminals mainly in axosomatic synapses and in axodendritic synapses with large dendritic profiles. In most of the synapses, a remarkable thickness of the postsynaptic membrane was noticed. In a large number of postsynaptic terminals, the cisternae of the smooth endoplasmic reticulum were dilated and intermixed with dilated vesicles and fragmented microtubules. Some of the presynaptic terminals demonstrated marked thickness of the presynaptic membrane. Glycogen granules were frequently seen in the postsynaptic terminals. In conclusion, substance P administered in vitro, increases the polymorphism of the synaptic vesicles in the presynaptic terminals of neurons derived from the temporal isocortex.