Somato-visceral convergence in cat dorsal root ganglion neurones demonstrated by double-labelling with fluorescent tracers.

We have investigated the possibility of somato-visceral convergence in thoracic sensory dorsal root ganglia (DRG) of cats, using the technique of double-labelling with fluorescent tracers. Combinations of propidium iodide (PI) and Fast Blue (FB) or bisbenzimide (Bb) were found to be the most appropriate. FB or Bb were injected into the splanchnic nerve, and PI into the intercostal nerves. The 9th-11th thoracic cord segments and ganglia were removed after perfusal and frozen sections cut. Single- and double-labelled neurones were observed in the DRG and single-labelled neurones only in the ventral horn (PI) and lateral horn (FB, Bb) of the thoracic spinal cord. The double-labelled neurones accounted for approximately 1% of all labelled neurones, although this may be an underestimate due to the techniques used to prevent migration of the tracer from labelled cells. The double-labelled neurones provide evidence for somato-visceral convergence and indicate that the pre-spinal convergence hypothesis could explain the phenomenon of referred pain.