MRNAS for one, two or three members of trk receptor family are expressed in single rat trigeminal ganglion neurons

We studied the expression of mRNAs of neurotrophin (NTF) receptors trkA, trkB and trkC in single rat trigeminal ganglion neurons at embryonic days 12 and 16 to determine, whether single trigeminal ganglion neurons express one trk family member or coexpress several of them. For that purpose we elaborated a sensitive technique of reverse transcriptase-polymerase chain reaction to detect all neurotrophin receptors in a single neuron. Expression of neurofilament light chain mRNA was used as a positive marker to confirm the recovery of mRNAs from single neurons. Neurofilament-positive samples were subsequently analyzed for the expression of mRNAs for catalytic trkA, trkB and trkC, and in some cases, low-affinity neurotrophin receptor (p75). We found neurons expressing one, coexpressing two, or even all three trk receptors. In many neurons analyzed, p75 mRNA was coexpressed with trks, but we also found neurons expressing only trks without p75, and a neuron expressing p75 alone. There were also neurons containing neither trk receptors nor p75. We provide here first direct evidence that single sensory neurons can simultaneously express three or even four neurotrophin receptors.