Substance P-immunoreactive nerve fibers in tracheobronchial lymph nodes of the guinea pig: origin, ultrastructure and coexistence with other peptides.

Double-labeling immunofluorescence of guinea pig tracheobronchial lymph nodes revealed complete coincidence of SP and CGRP immunoreactivities in perivascular nerves and axons of the medullary lymphatic tissue. Additional dynorphin A or cholecystokinin immunoreactivity was seen only in some of the medullary fibers. Ultrastructurally, all SP-immunoreactive axons were unmyelinated and displayed vesicle-containing varicosities. Retrograde neuronal tracing combined with immunohistochemistry revealed a sensory origin from dorsal root ganglia of SP/CGRP-immunoreactive fibers ramifying within paratracheal lymph nodes, and an additional neuronal population being devoid of SP/CGRP immunoreactivity. The findings provide evidence for several types of sensory nerve fibers innervating lymph nodes.