Convergence of serotonin-, enkephalin- and substance P-like immunoreactive afferent fibers onto cat medullary dorsal horn projection neurons: a triple immunocytochemical staining technique combined with the retrograde HRP-tracing method.

Convergence of serotonin (5-HT)-, enkephalin (ENK)-, and substance P (SP)-like immunoreactive (LI) afferent fibers onto cat medullary dorsal horn projection neurons was examined by retrogradely labeling trigeminothalamic neurons and immunocytochemically labeling 5-HT, ENK and SP fibers in the same tissue section using distinct chromogens. Convergence of 5-HT-, ENK- and SP-LI fibers upon single projection neurons was often observed in laminae I and V.