Acupuncture therapy is effective in relieving
postoperative pain of neck surgery, but its underlying mechanisms remain largely unknown. This study, in the incisional
neck pain rat model, was designed to explore whether the
endocannabinoid receptor 1 (CB1) in the cervical spinal cord is involved in the
analgesic effect of
electroacupuncture (EA) or not.The incisional
neck pain model was established by making a longitudinal incision and applied EA treatment of Futu (LI18), Hegu-Neiguan (LI4-PC6), or Zusanli-Yanglingquan (ST36-GB34) for
pain relief. The results showed that EA LI18 and EA LI4-PC6 effectively relieve
allodynia caused by neck incision, which was obviously better than EA ST34-GB34 (P < 0.05). After EA, the expression levels of CB1
mRNA at 4h in the EALI18 group, and 24 and 48h in both EALI18 and EALI4-PC6 groups, and those of CB1
protein at 4, 24, and 48h in the EALI18 group, and the immunoactivity of CB1 in both EALI18 and EALI4-PC6 groups at 4h were significantly upregulated in contrast to those of the model group (P < 0.05). EA of either
acupoint group had no effect on the expression of CB2
protein (P > 0.05). Moreover, the antinociceptive effect of EA was reversed by
AM251 (CB1 antagonist). Immunofluorescence dual staining showed that CB1 expressed in astrocytes in the superficial layer (laminae I and II) of dorsal horns of the cervical spinal cord. Therefore, the findings of this study revealed that upregulation of CB1 expression in the cervical spinal cord contributes to the
analgesic effect of EA in incisional
neck pain rats. The
CB1 receptor expresses on astrocytes.