Capsaicin causes selective damage to type I synaptic glomeruli in rat substantia gelatinosa.

Most type I synaptic glomeruli were lacking in adult rats given capsaicin neonatally, while topical cord applications of the drug caused dense degeneration of numerous CI- and very few CIIa-terminals. These data give support to the presumable origin of CI-terminals from unmyelinated primary afferents and suggest that CIIa-terminals may belong to small myelinated afferents.