RESUMEN
Nonglomerular synapses in the neuropil of the substantia gelatinosa of adult ratspinal trigeminal nucleus were subjected to electron microscopic examination. Nonglomerular synapses in the substantia gelatinosa were associated with four main types of axonal terminals. On the basis of vesicle shapes, these were classified as round vesicle, elongate vesicle, pleomorphie vesicle, and dense cored vesicle terminals. The category of round vesicle terminals could be subdivided into large round vesicle terminals and small round vesicle terminals according to their different size of synaptic vesicles. Nonglomerular synapses included four types, i. e. axodendritic, axo-axonic, dendro-dendritic and dendro-axonic synapses. Of these, the majority of synapses were axodendritie. The functional significance of the classification of these synapses and their axonal terminals had been discussed.