GDNF and neuropathic pain: Similar to neurotrophins, in adult rodents, peripherally injected I125 labeled GDNF family ligands are internalized and retrogradely transported to the DRG and accumulate in neurons that express the appropriate receptors [14], and several studies have shown that exogenously-supplied GDNF both normalizes gene expression in injured DRG neurons and exerts analgesic effects in models of neuropathic pain in rodents [15], [16].