Electroacupuncture Increases CB2 Receptor Expression on Keratinocytes and Infiltrating Inflammatory Cells in Inflamed Skin Tissues of Rats

Endogenous cannabinoids and peripheral cannabinoid CB2 receptors (CB2Rs) are involved in the antinociceptive effect of electroacupuncture (EA) on inflammatory pain However, it remains unclear about how EA affects the expression and distribution patterns of peripheral CB2R5 in inflamed skin tissues To study this, inflammatory pain was induced by local injection of complete Freund's adjuvant into the hindpaw of rats The mRNA and protein levels of CB2Rs were quantified by using RTPCR and Western blotting respectively The distribution of CB2Rs on keratinocytes and immune cells recruited to the inflamed skin tissues was determined by using double-immunofluorescence labeling Induction of tissue inflammation significantly increased the mRNA and protein levels of CB2Rs in the skin tissue Also, both 2 Hz and 100 Hz EA, applied to GB30 and GB34, significantly increased the mRNA and protein levels of CB2Rs in inflamed tissues compared to the sham EA group CB2Rimmunoreactivities were mainly distributed in keratinocytes, macrophages, and T-lymphocytes in the epidermis and dermis of the inflamed skin tissue Inflammation caused a significant increase in the number of CB2R-immunoreactive keratinocytes, macrophages, and T-lymphocytes Furthermore, compared to the sham EA group EA at 2 or 100 Hz significantly increased the number of keratinocytes, macrophages, and T-lymphocytes with CB2R-immunoreactivity in the inflamed skin tissue Therefore, our findings suggest that EA is associated with upregulation of local CB2Rs in the inflamed skin tissue EA primarily potentiates the expression of CB2Rs on keratinocytes and infiltrating inflammatory cells at the site of inflammation Perspective This study shows that electroacupuncture increases the CB2 receptor expression on keratinocytes and infiltrating inflammatory cells in inflammatory skin tissues This finding provides new evidence showing the potential role of CB2 receptors in the analgesic effect of acupuncture on inflammatory pain (c) 2010 by the American Pain Society