Effects of Electroacupuncture with Dominant Frequency at SP 6 and ST 36 Based on Meridian Theory on Pain-Depression Dyad in Rats

Abstract

Epidemic investigations reveal an intimate interrelationship between pain and depression. The effect of electroacupuncture (EA) on pain or depression has been demonstrated individually, but its effect on pain-depression dyad is unknown. Our study aimed to screen a dominant EA frequency on pain-depression dyad and determine the validity of acupoint selection based on meridian theory. The pain-depression dyad rat model was induced by reserpine and treated using EA with different frequencies at identical acupoints to extract a dominant frequency and then administrated dominant-frequency EA at different acupoints in the above models. Paw withdrawal latency (PWL), emotional behavior of elevated zero maze (EZM) test, and open field (OF) test were conducted. We found that 100 Hz EA at Zusanli (ST 36) and Sanyinjiao (SP 6) (classical acupoints for spleen-deficiency syndrome) were the most effective in improving PWL, travelling distance in the EZM, and maximum velocity in OF compared to EA with other frequencies; ST 36 and SP 6 were proved more effective than other acupoints beyond the meridian theory and nonacupoints under the same administration of EA. Therefore, we concluded that 100 Hz is the dominant frequency for treating the pain-depression dyad with EA, and acupoints on spleen and stomach meridians are preferable choices.

Figure 1

Experimental procedure. Right after the baseline pain threshold was tested, animals in the experimental groups and the normal group were administered reserpine injection or vehicle (0.2 mL/kg, subcutaneously), respectively, for three consecutive days. On the fourth day, PWL tests to examine mechanical allodynia were performed before and after the EA treatment, respectively. On the fifth day, another EA treatment was performed, followed by PWL test, EZM test, and OF test.

Figure 2

Effect of EA with different frequencies on paw withdrawal latency in rats with pain-depression dyad. The PWL was measured with an electronic von Frey apparatus (Bioseb, EVF3.0). Graphs represent the mean ± SEM (n = 10) in each group. ^* P < 0.05, compared to the normal group. ^# P < 0.05, compared to the model group.

Figure 3

Effect of EA on the pain-depression dyad in elevated zero maze test. Columns represent the mean ± SEM of all 10 animals in each group. ^* P < 0.05, compared to normal group. ^# P < 0.05, compared to model group. (a)–(f) Three-dimensional activity of one rat in the open field from the normal group, model group, 2 Hz group, 15 Hz group, 100 Hz group, and 2/100 Hz group, respectively; (g) travel distance in the close arms in each group; (h) the mean speed in the entire maze for each group.

Figure 4

Effects of EA at different frequencies on the pain-depression dyad in open field test. ^* P < 0.05, compared to normal group. ^# P < 0.05, compared to model group. (a)–(f) Representative trajectories in the open field of the normal group, model group, 2 Hz group, 15 Hz group, 100 Hz group, and 2/100 Hz group, respectively; (g) time mobile in each group; (h) the maximum locomotor speed in the normal group and five experimental groups.

Figure 5

Effects of EA at different locations (100 Hz) on paw withdrawal latency in the pain-depression dyad model. The PWL was measured with an electronic von Frey apparatus (Bioseb, EVF3.0). Graphs represent the mean ± SEM of all 8 animals in each group. ^* P < 0.05 compared to normal group. ^# P < 0.05, compared to model group. ^& P < 0.05, compared to ST 36 + SP 6 group.

Figure 6

Effects of 100 Hz EA on elevated zero maze test in the pain-depression dyad model rats. Columns represent the mean ± SEM of all 8 rats in each group. ^* P < 0.05, compared to normal group (P < 0.05). ^# P < 0.05, compared to model group. ^& P < 0.05, compared to the ST 36 + SP 6 group. (a)–(e) Three-dimensional activity of one rat in the open field from the normal group, model group, ST 36 + SP 6 group, LI 11 + TE 5 group, and nonacupoint group, respectively; (f) distance travelled in the close arms; (g) the mean locomotor speed in the entire maze in each group.

Figure 7

Effect of 100 Hz EA treatment on open field test in the pain-depression dyad model rats. Graphs represent the mean ± SEM of all 8 animals in each group. ^* P < 0.05, compared to normal group. ^# P < 0.05, compared to model group. ^& P < 0.05, compared to ST 36 + SP 6 group. (a)–(e) Examples of trajectory in the open field among the normal group, model group, ST 36 + SP 6 group, LI 11 + TE 5 group, and nonacupoint group, respectively; (f) average time mobile of each group; (g) the maximum locomotor speeds in each group.