Distribution of trigeminothalamic and spinothalamic-tract neurons showing substance P receptor-like immunoreactivity in the rat.

Trigeminothalamic and spinothalamic-tract neurons provided with substance P receptor (SPR) were examined in the rat by SPR immunofluorescence histochemistry combined with Fluoro-Gold (FG) fluorescent retrograde labeling. After FG injection in the thalamic regions, FG-labeled cells with SPR-like immunoreactivity were seen mainly in laminae I and III of the medullary and spinal dorsal horns and lateral spinal nucleus. In these regions, about one-fourth to one-third of FG-labeled cells showed SPR-like immunoreactivity.