Fluoride-Resistant Acid Phosphatase (FRAP)-Positive Primary Afferent Central Terminals in the Mouse Substantia Gelatinosa.

Abstract

The ultrastructure of the central terminals of nociceptive primary afferent (Cl terminals) neurons in the mouse substantia gelatinosa was studied by the cytochemical method using fluoride-resistant acid phosphatase (FRAP). Small roundish, slender, sinuous and large scalloped terminals showed FRAP reactivity. The FRAP reaction was seen as electron dense 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 the previous studies, these terminals were in accord with the capsaicin-sensitive Cl terminals. Furthermore, larger, roundish terminals with less packed spherical synaptic vesicles, many mitochondria and a few dense cored synaptic vesicles showed FRAP reactivity. Our recent results that Cll terminals are also sensitive to capsaicin support the FRAP activity of the Cll terminals in the present study. Thus, various types of FRAP-positive Cl terminals and some Cll terminals are considered to be central endings of the capsaicin-sensitive nociceptive primary afferents.