The use of fluorescent tracers in the peripheral sensory nervous system.

We have developed an injection technique which simplifies the use of fluorescent tracers in investigating the projections of peripheral nerves both in rats and pigeons, and avoids the difficulties experienced with the cut nerve technique. The tracers are injected into the peripheral nerve and transported to cell bodies in the dorsal root ganglia (DRG). By a careful choice of tracer it is possible to investigate the projections of two or more nerves in the same preparation. We have used two combinations of tracer which can be viewed simultaneously in the cell at the same excitation wavelength (405 nm): (1) propidium iodide (PI) and bisbenzimide (Bb) which produce an orange cytoplasmic fluorescence and blue nuclear fluorescence respectively; and (2) Fast blue (FB) and Nuclear yellow (NY) which label the cytoplasm blue and the nucleus yellow. This distribution of tracers is similar to that reported in central neurones but differs from that reported in the efferent peripheral nervous system. Using these tracers we have observed double-labelled neurones in the DRG of both rats and pigeons, which is an indication for the dichotomizing of peripheral fibres. The existence of two tracers in double-labelled cells has been confirmed microspectrophotometrically.