Relationship between BDNF- and trk-expressing neurones in rat dorsal root ganglion

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Abstract
Brain-derived neurotrophic factor (BDNF) is synthesized in sensory neurones and suggested to operate on these same neurones by an autocrine mechanism, but it is unclear whether these neurones express the functional receptor (TrkB) for BDNF. We therefore examined the co-localization of BDNF and neurotrophin receptor mRNAs in adult rat dorsal root ganglion (DRG) neurones by in situ hybridization histochemistry. BDNF mRNA signals were detected in about 40-50% of DRG neurones (L4-5). Almost all the trkA mRNA-expressing neurones (95%) were positive for BDNF mRNA, while no trkB mRNA- and few trkC mRNA-expressing neurones displayed BDNF mRNA signals. These findings suggest that BDNF is mainly synthesized in the sensory neurones that are responsive to nerve growth factor but not to BDNF or neurotrophin-3. It is unlikely that BDNF is involved in an autocrine loop in sensory ganglia.