Papers of the Week

It is becoming increasingly clear that robust sex differences exist in the processing of acute and chronic pain in both rodents and humans. However, the underlying mechanism has not been well characterized. The dorsal horn of the lumbar spinal cord is the fundamental building block of ascending and descending pain pathways. It has been shown that numerous neurotransmitter and neuromodulator systems in the spinal cord, including the endocannabinoid system and its main receptor, the cannabinoid 1 receptor (CB R), play vital roles in processing nociceptive information. Our previous findings have shown that CB R mRNA is widely expressed in the brain in sex-dependent patterns. However, the sex-, lamina-, and cell-type-specific characteristics of CB R expression in the spinal cord have not been fully described. In this study, the CB R-iCre-EGFP mouse strain was generated to label and identify CB R-positive (CB R ) cells. We reported no sex difference in CB R expression in the lumbar dorsal horn of the spinal cord, but a dynamic distribution within superficial laminae II and III in female mice between estrus and nonestrus phases. Furthermore, the cell-type-specific CB R expression pattern in the dorsal horn was similar in both sexes. Over 50% of CB R cells were GABAergic neurons, and approximately 25% were glycinergic and 20-30% were glutamatergic neurons. The CB R-expressing cells also represented a subset of spinal projection neurons. Overall, our work indicates a highly consistent distribution pattern of CB R cells in the dorsal horn of lumbar spinal cord in males and females.