The somato-visceral divergent projections of peripheral processes of substance P-containing spinal ganglionic neurons--tri-labeling study of combining fluorescein tracing with immunocytochemistry.

The chemical nature of the spinal ganglionic neuron with peripheral processes projecting divergently to the somatic and visceral areas, has been identified by means of tri-labeling method of combining fluorescein tracing with immunocytochemistry. 10 rats were used. First, 2 microliters of 2% fast blue(FB) were injected into the left coeliac ganglion. Two days later, 2% nuclear yellow (NY) was injected into left 9-11 intercostal nerves, 1 microliter for each. On the 4th day, the animal was perfused with 10% formalin in 0.1 mol phosphate buffer. The left T9-11 spinal ganglia were removed and cut into sections by cryostat. The sections were observed under fluorescence microscope and photographed. The results showed that there were three kinds of neurons in the spinal ganglia: 1) single FB labeled cells with blue fluorescent cytoplasm accounted for 38.8% of total cells; 2) single NY labeled cells with yellow fluorescent nuclei accounted for 52.7%; 3) FB and NY double-labeled cells, mostly small or medium in size, accounted for 8.5%. Then, the sections containing double-labeled cells were further processed by substance P-demonstrating PAP immunocytochemical staining. The photographs with immunostaining and fluorescein labelings in the same section were compared. We found that the labeling ratio of SP/NY was 1.4%, SP/FB was 7%, and SP/NY + FB was 28.8%. The present study detected not only the convergence of somato-visceral sensation in the spinal ganglia but also the chemical nature of these neurons containing substance P (SP) for the first time. In addition, these results may provide a morphological basis for the mechanisms of referred pain and somato-visceral reflection.