RELATIONSHIP BETWEEN BDNF-EXPRESSING AND TRK-EXPRESSING NEURONS IN RAT DORSAL-ROOT GANGLION - AN ANALYSIS BY IN-SITU HYBRIDIZATION

BRAIN-DERIVED neurotrophic factor (BDNF) is synthesized in sensory neu rones and suggested to operate on these same neurones by an autocrine mechanism, but it is unclear whether these neurones express the functi onal receptor (TrkB) for BDNF. We therefore examined the co-localizati on of BDNF and neurotrophin receptor mRNAs in adult rat dorsal root ga nglion (DRG) neurones by in situ hybridization histochemistry. BDNF mR NA signals were detected in about 40-50% of DRG neurones (L4-5). Almos t all the trkA mRNA-expressing neurones (95%) were positive for BDNF m RNA, while no trkB mRNA- and few trkC mRNA-expressing neurones display ed BDNF mRNA signals. These findings suggest that BDNF is mainly synth esized in the sensory neurones that are responsive to nerve growth fac tor but not to BDNF or neurotrophin-3. It is unlikely that BDNF is inv olved in an autocrine loop in sensory ganglia.