Adult CD-1 male mice were injected intravenously with 2.5 mu g/g of hi
ghly purified murine NGF and then assessed for hot plate responding (5
2 degrees C) at 15, 30, 60, 180, and 360 min (repeated test) or at 30,
60, or 360 min (single test, i.e., exposure to hot plate only once).
Control animals received cytochrome c (2.5 mu g/g). In the repeated te
st, NGF produced hyperalgesia, increasing the number of jumps (particu
larly at 30 and 60 min postinjection), while in the single test the pa
in reaction of NGF-treated animals remained unaffected. Sensitization
of C-fibers in the periphery or release of bioactive mediators from ma
st cells may account for NGF-induced changes in nociception.