Figure 1.

BDNF expression in the DRG of the BDNF-LacZ knock-in reporter mouse. A, β-Gal expression was found in a heterogeneous population of primary afferent neurons. Levels of expression varied, with some cells completely filled by β-Gal (high expression), others with punctate nuclear and cytoplasmic staining (medium expression), and some with only punctate cytoplasmic staining (low expression). B, The number of β-Gal-positive DRG cells did not differ in male and female mice. C, By counterstaining with a panel of markers of subpopulations of DRG neurons, we determined that ∼67% of BDNF-expressing neurons express NF200 (D), a marker of myelinated fibers. Only ∼12% of BDNF cells expressed peripherin (E), a marker of most small-diameter afferents. Similarly, only ∼14% of BDNF-positive afferent expressed TRPV1 (F) and ∼20% expressed CGRP (G), markers of small-diameter, peptidergic nociceptors. H, IB4, a lectin that binds small, non-peptidergic nociceptors, was only found in ∼10% of BDNF neurons. Finally, there was virtually no overlap (∼0.5%) with TH (I), a marker of small-diameter, low-threshold, mechanosensory afferents. Data are mean ± SEM. Statistical significance was determined by Student’s t test. Arrows indicate cells with overlap of β-Gal with other markers. Numbers of animals are indicated in B, C. Scale bars = 100 μm.