Fig. 10.

Pie chart summarizing the relationship between BDNF and trk expression in neurochemically defined DRG subclasses. DRG neurons can be divided broadly into large-diameter cells, which innervate low-threshold mechanoreceptors, and small-diameter cells, which innervate mainly nociceptors. BDNF mRNA is expressed by the subpopulation of small cells that contain the neuropeptide CGRP and the NGF receptor trkA. Small cells that do not express any trk receptor, and that can be labeled using the lectin Griffonia simplicifolia IB4 or the monoclonal antibody LA4, mainly do not express BDNF. With the exception of those trkC cells that coexpress trkA, BDNF mRNA is also largely not expressed by trkB or trkC cells. TrkC and trkB are present mainly in large-diameter cells, which can be identified using the neurofilament antisera N52 or RT97. BDNF is constitutively expressed in the cell types illustrated, but expression in trkA cells is increased further by NGF treatment.