Acupuncture inhibits the activation of spinal microglia in the acute uterine cervical distension rats

Background: Although labor pain is treated clinically by the administration of local anesthetics alone or with opioids in the epidural or spinal spaces, however, the mechanisms of labor pain mechanisms have not been fully elucidated during to the lack of animal models, and the side effects of drugs still existed. Spinal microglia can be activated or mobilized under several pain states, and we want to explore the activation of spinal microglia is involved in the acute uterine cervical distension rats or not.

Methods: (I) The electromyographic (EMG) response to uterine cervical distension (UCD) was observed. Twenty-four Sprague-Dawley rats were randomly divided into three groups: standard group, sham group, and UCD group (n=8). EMG response to UCD was recorded at 30, 60 and 120 min after distension, respectively. The activation of microglia in the spinal cord at UCD 60 min was seen. Grouping following the first part (n=4), four rats were executed perfusion after distension of 60 min, the T12 to L2 spinal cord segments were removed for immunohistochemical analysis. (II) After successfully implantation of the intrathecal catheter, 36 Sprague-Dawley rats were randomly divided into the PBS group, minocycline group and UCD group (n=12). EMG response to UCD was recorded before distension and after 30, 60, and 120 min after distension (n=8). Four rats of each group were executed perfusion at 60 min after distension, the T12 to L2 spinal cord segments were removed for immunohistochemical analysis. (III) Thirty-six Sprague-Dawley rats were randomly divided into an electrical acupuncture group, non-acupuncture group, and UCD group (n=12). EMG response to UCD was recorded at 30, 60, and 120 min after distension. Four rats of each group were executed at 60 min after distension, and the T12 to L2 spinal cord segments were removed for immunohistochemical analysis to observe the effect of Hegu and Sanyinjiao acupuncture electric stimulation in the activation of spinal microglia.

Results: (I) EMG based value of sham group, standard group, and the UCD group were no statistical significance (P>0.05). After UCD, the EMG of the UCD group were increased at 30, 60, 120 min. Compared with fundamental values (P<0.05), which the most apparent EMG change at 60 min after UCD (P<0.05). Sixty min after UCD, compared with the sham group and the standard group, the EMG of the UCD group was higher (P<0.05), but no difference was observed between standard group and sham group (P>0.05). Compared with the sham group, the number of Iba1 (microglia markers)positive cells in thoracic, lumbar spinal cord (T12 to L2) was higher at 60 min after UCD (P<0.05), the most Iba1 labeled cells expressed in IV-V layer and X layer of lumbar spinal cord dorsal horn. (II) EMG based value of UCD group, PBS group, and minocycline group had no significant difference (P>0.05). Sixty min after UCD, compared with the PBS and UCD group, the EMG of the minocycline group was decreased significantly (P<0.05), but there was no difference between the PBS group and UCD group (P>0.05). At 30 and 120 min after UCD, the difference of EMG among the UCD group, PBS group, and minocycline group was no statistical significance (P>0.05). Compared with the PBS and UCD group, the number of Iba1 positive cells at the thoracic, lumbar spinal cord in the minocycline group decreased significantly (P<0.05). But no difference was observed between the PBS group and minocycline group (P>0.05). (III) In the fourth part of the study: EMG based value of electrical acupuncture group, non-acupuncture group, and UCD group were no different (P>0.05). Sixty min after UCD, compared with non-acupuncture and UCD group, the EMG of the acupuncture group was decreased significantly (P<0.05), but no difference was observed between the UCD group and non-acupuncture group (P>0.05).

Conclusions: The activation of spinal microglia is involved in the formation of acute visceral pain induced by uterine cervical distension, Electrical acupuncturing Hegu, and Sanyinjiao alleviate pain, and the possible mechanism is inhibiting the activation of spinal microglia in the acute uterine cervical distension rats.