Cervical dorsal root ganglion cells with collaterals to both shoulder skin and the diaphragm. A fluorescent double labelling study in the rat. A model for referred pain?

Rat cervical spinal ganglion cells were retrogradely double-labelled with fluorescence dyes following injection of one dye into a cutaneous shoulder nerve and the other into the diaphragm. We suggest that the peripheral dichotomization of these ganglion cells could form the structural basis for the referred 'phrenic' pain in the shoulder region that can follow irritation of the diaphragm.