CENTRAL TERMINALS OF CAPSAICIN-SENSITIVE PRIMARY AFFERENT MAKE SYNAPTIC CONTACTS WITH NEURONAL SOMA IN THE MOUSE SUBSTANTIA-GELATINOSA

Degeneration of primary afferent central terminals (C-terminals) that contact neuronal soma in the substantia gelatinosa of the spinal dorsa l horn was examined by electron microscopy 2h after s.c. injection of capsaicin into newborn and adult mice. The C-terminals were small, dar k, sinuous or slender terminals with clear synaptic vesicles in the ea rly postnatal period. They are thought to develop into scalloped CI-te rminals, surrounded by dendrites and a few axonal endings, forming syn aptic glomeruli. The same type of nonglomerular terminals making presy naptic contacts with neuronal soma showed degeneration in both the new born and adult animals, and were identified as capsaicin-sensitive CI- terminals. This finding suggests that capsaicin-sensitive C-fibers hav e a modulatory role on their own nociceptive input besides functioning in nociceptive transmission in the substantia gelatinosa.