Electroacupuncture at “Zusanli” (ST36) suppresses food intake in high-fat diet-fed mice by improving vagal afferent desensitization

To investigate the mechanism by which electroacupuncture (EA) at “Zusanli” (ST36) ameliorates the impairment of feeding behavior and gastric vagal afferent signaling induced by short-term high-fat diet (HFD) exposure.

The study comprised two parts. In part 1, 42 SPF male C57BL/6J mice were randomly divided into a normal diet (ND) group (n=14) and an HFD group (n=28). After 4 weeks, HFD-fed mice were subdivided into an HFD group and an EA group (n=14 each). The EA group received EA at bilateral “Zusanli” (ST36). Stimulation parameters were: 2 mA, 2 Hz/15 Hz, 20 min/session, once daily, 6 sessions/week for 2 consecutive weeks. Body weight was recorded weekly. After the intervention, 24 h food intake was measured. Liver wet weight, inguinal white adipose tissue (iWAT) wet weight, and epididymal white adipose tissue (eWAT) wet weight were recorded. Gastric emptying rate was assessed using the phenol red meal test. Serum cholecystokinin (CCK) content was measured by ELISA. Protein expressions of protein gene product 9.5(PGP9.5) and calcitonin gene-related peptide (CGRP) in the gastric antrum were evaluated by Western blot. The co-expression density index of PGP9.5 and CGRP in the gastric antrum and c-Fos expression levels in the nodose ganglion (NG) were detected by immunofluorescence staining. In part 2, another 32 SPF male C57BL/6J mice were fed an HFD for 4 weeks and then randomly divided into 4 groups (n=8 each): sham operation group, sham + EA group, vagotomy (resection of the gastric vagal branches) group, and vagotomy + EA group. The acupoint and intervention parameters were the same as above. Body weight, 24 h food intake, liver wet weight, iWAT wet weight, eWAT wet weight, the co-expression of PGP9.5 and CGRP in the gastric antrum, and the number of c-Fos positive neurons in the NG were measured.

Compared to the ND group, 4-week HFD feeding increased body weight, liver wet weight, and adipose tissue (iWAT and eWAT) wet weights, while decreased gastric emptying rate and serum CCK levels (P<0.05). The relative protein expressions of both PGP9.5 and CGRP in the gastric antrum were down-regulated (P<0.05). Meanwhile, the co-expression density index of PGP9.5 and CGRP in the gastric antrum was reduced (P<0.05). The number of c-Fos positive neurons in the NG decreased in HFD-fed mice (P<0.05). Compared to the HFD group, EA treatment reduced body weight, 24 h food intake, liver wet weight, and adipose tissue (iWAT and eWAT) wet weights (P<0.05). EA also increased gastric emptying rate and serum CCK levels (P<0.05). Moreover, EA up-regulated the relative protein expressions of PGP9.5 and CGRP as well as their co-expression density index in the gastric antrum (P<0.05). Finally, EA increased the number of c-Fos positive neurons in the NG (P<0.05). In the vagotomy experiment, compared with the sham operation group, the sham + EA group showed a significant decrease in body weight, food intake, liver wet weight, adipose tissue wet weight (P<0.05). After gastric branch vagotomy, however, the regulatory effects of EA on body weight, food intake, liver wet weight, and other indicators were weakened. Similarly, after surgery EA did not exert a significant modulatory effect on the co-expression level of PGP9.5 and CGRP in the gastric antrum or on the expression of c-Fos-positive neurons in the NG.

Short-term HFD leads to desensitization of gastric vagal afferent signaling, manifested as impairment of local gastric vagal sensory nerves and a decrease in the number of activated neurons in the NG. EA can suppress food intake by repairing gastric vagal afferent signaling.