We examined protein kinase C gamma-like immunoreactivity (PKCγ-LI) of trigeminothalamic neurons in the rat medullary dorsal horn (MDH) after injecting a retrograde tracer, Fluoro-Gold (FG), into the thalamus. Over 90% of FG-labeled neurons in the marginal layer (lamina I) and a few FG-labeled neurons in the superficial part of the magnocellular layer (lamina III) showed PKCγ-LI. No PKCγ-neurons in the substantia gelatinosa (lamina II) were labeled with FG. PKCγ-mediated regulation of trigeminothalamic neurons may contribute to the changes in MDH activity during persistent pain.