FLUORIDE-RESISTANT ACID-PHOSPHATASE (FRAP)-POSITIVE PRIMARY AFFERENT CENTRAL TERMINALS IN THE MOUSE SUBSTANTIA-GELATINOSA

The ultrastructure of the central terminals of nociceptive primary aff erent (CI terminals) neurons in the mouse substantia gelatinosa was st udied by the cytochemical method using fluoride-resistant acid phospha tase (FRAP). Small roundish, slender, sinuous and large scalloped term inals showed FRAP reactivity. The FRAP reaction was seen as electron d ense granular deposits between spherical synaptic vesicles and around the membrane of the synaptic vesicles. Especially, dark, small sinuous and large scalloped terminals showed intense FRAP reactivity. From th e previous studies, these terminals were in accord with the capsaicin- sensitive CI terminals. Furthermore,larger, roundish terminals with le ss packed spherical synaptic vesicles, many mitochondria and a few den se cored synaptic vesicles showed FRAP reactivity. Our recent results that CII terminals are also sensitive to capsaicin support the FRAP ac tivity of the CII terminals in the present study. Thus, various types of FRAP-positive CI terminals and some CII terminals are considered to be central endings of the capsaicin-sensitive nociceptive primary aff erents.