Skin-visceral divergent projection of cholecystokinin-containing dorsal root ganglion neurons: a tri-labelling study with fluorescent tracers and immunohistochemistry.

Skin-visceral divergent projections of cholecystokinin (CCK)-containing dorsal root ganglion neurons were studied by combined technique of fluorescent double-labelling and immunohistochemistry. Fast blue (FB) and nuclear yellow (NY) were injected into the coeliac ganglion and the cutaneous branches of left 9th-11th intercostal nerves, respectively. Three kinds of neurons labelled with fluorescein were observed in T9-11 dorsal root ganglia: FB-labelled neurons with blue-fluorescent cytoplasm; NY-labelled neurons with yellow-fluorescent nucleus and double-labelled neurons with blue cytoplasm and yellow nucleus. The double-labelled neurons were found to account for 2.8% of total labelled neurons. The sections containing neurons labelled with fluorescein were stained by CCK-immunohistochemical procedure. Four kinds of neurons could be identified: NY-neurons with CCK-immunoreactivity (NY+CCK); FB-neurons with CCK-immunoreactivity (FB+CCK); NY+FB neurons with CCK-immunoreactivity (NY+FB+CCK); and neurons only CCK-positive. NY+FB+CCK tri-labelled neurons accounted for approximately 11.5% of NY+FB double-labelled neurons, and for 0.4% of all CCK-positive neurons. The findings clearly indicated that the peripheral processes of some sensory dorsal root ganglion neurons divergently project to both skin and visceral structure and contain CCK.