The sensory innervation of the tooth pulp is considered to be chiefly or solely nociceptive although many pulpal afferents have cytochemical and morphological properties that are generally associated with low-threshold mechanoreceptors. Most of the trigeminal ganglion neurons that project to the tooth pulp have cytochemical features of the class of nociceptors that are NGF responsive (express TrkA and p75), but very few (about 2%) bind the plant lectin IB4, a widely used marker for non-peptidergic nociceptors that respond to the GDNF family of neurotrophic factors. There is, however, a report that GDNF is transported from tooth pulp to the trigeminal ganglion (Nosrat et al., 1997, SFN Abstract 875.17). In the present study, expression of GDNF receptors by pulpal afferents was tested by immunostaining for GFRalpha-1 in cell bodies of pulpal afferents identified by retrograde labeling. Fluoro-gold was applied to maxillary molars of young adult female Sprague-Dawly rats, and the animals were perfusion fixed w...