Abstract: Selective activation of cannabinoid receptor 1 (CB₁ R) has been shown to suppress neuropathic pain symptoms in rodents. However, there is relatively little known about changes in CB₁R and its endogenous ligands during development or maintenance of neuropathic pain. Using immunohistochemistry, Western blot, real-time reverse transcription polymerase chain reaction, as well as liquid chromatography/mass spectrometry, we studied the changes in CB₁Rs and endocannabinoids N-arachidonyl ethanolamine/anandamide (AEA) and 2-arachidonyl glycerol (2-AG) in rat lumbar (L4 and L5) dorsal root ganglia (DRG) after neuropathic pain induction (L5 spinal nerve ligation: SNL). Immunohistochemistry revealed that in control rats, CB₁R was expressed in the majority (76–83%) of nociceptive neurons as indicated by co-labeling with isolectin B4 (IB4) or antibodies recognizing transient receptor potential vanilloid (TRPV1), calcitonin gene related peptide (CGRP), and the NR2C/2D subunits of the N-methyl D-aspartate receptor. After L5 SNL, CB₁R mRNA and protein increased in the ipsilateral uninjured L4 DRG whereas the percentages of CB₁R immunoreactive (CB₁R-ir) neurons remained unchanged in L4 and L5 DRG. However, for these CB₁R-ir neurons, we observed significant increases in % of TRPV1-ir cells in ipsilateral L4 DRG, and decreases in % of IB4- and CGRP-co-labeled cells in ipsilateral L5 DRG. Levels of both AEA and 2-AG were significantly increased only in the ipsilateral L5 DRG. In addition, we also examined lumbar spinal cord dorsal horn where the central terminals of the primary afferents terminate. At L4 level, IB4-positive superficial dorsal horn area showed a significant increase of CB₁R-ir. This finding was also confirmed by Western Blot. These results are consistent with the preserved analgesic effects of cannabinoids in neuropathic pain and provide a rational framework for the development of endocannabinoid-based therapeutic interventions for neuropathic pain.