Fig. 2. VR1 mRNA is expressed by both the NGF- and GDNF-responsive small cell populations. In situhybridization for VR1 mRNA (a, c,e) combined with fluorescence histochemistry (b, d, f).a, b, trkA. Most small- to medium-sized trkA-immunoreactive cells express VR1 mRNA (thin arrows). A few small trkA cells (thick white arrows) and large-diameter cells (asterisks) have little or no detectable VR1 mRNA. c,d, IB4. As with the trkA subpopulation of small- to medium-sized cells, most IB4-labeled cells express VR1 (thin arrows). Some IB4 cells, however, do not possess levels of VR1 mRNA above background (thick white arrows). Some very small-diameter IB4-negative profiles have high levels of VR1 mRNA (thick black arrows). e,f, RET. Whereas small RET-positive cells are often labeled for VR1 mRNA (thin arrows), large RET-positive cells and other large cells do not express VR1 (asterisks). A very small-diameter RET-positive cell is shown that has very high levels of VR1 mRNA (double arrows and insert in f). Scale bars: a–f, 50 μm; inset, 10 μm.