Effects of electroacupuncture at 2 and 100 Hz on rat type 2 diabetic neuropathic pain and hyperalgesia-related protein expression in the dorsal root ganglion

Abstract

Objective: To investigate the analgesic effects of electroacupuncture (EA) at 2 and 100 Hz on type 2 diabetic neuropathic pain (DNP) and on the expressions of the P2X3 receptor and calcitonin gene-related peptide (CGRP) in the dorsal root ganglion (DRG).

Methods: Rat type 2 DNP was induced by a high calorie and high sugar diet fed for 7 weeks, plus a single intraperitoneal injection of streptozotocin (STZ) after 5 weeks. EA at 2 and 100 Hz was carried out once every day after 7 weeks for 7 consecutive days. Body weight, serum fasting insulin (FINS), fasting blood glucose (FBG), insulin sensitivity index (ISI), and paw withdrawal latency (PWL) were measured. The expressions of L4-L6 DRG P2X3 receptors and CGRP were assessed by immunofluorescence.

Results: Type 2 DNP was successfully induced as shown by the increased body weight, FINS, and FBG, as well as the reduced ISI and PWL. Expressions of P2X3 receptors and CGRP in L4-L6 DRGs increased. EA at both 2 and 100 Hz relieved type 2 DNP, but the analgesic effect of EA was stronger at 2 Hz. P2X3 receptor expression decreased in L4-L6 DRGs following EA at 2 Hz and in L5 and L6 DRGs following EA at 100 Hz. EA at both 2 and 100 Hz down-regulated CGRP overexpression in L4-L6 DRGs.

Conclusions: These findings indicate that EA at 2 Hz is a good option for the management of type 2 DNP. The EA effect may be related to its down-regulation of the overexpressions of the DRG P2X3 receptors and CGRP in this condition.

Keywords: Calcitonin gene-related peptide; Dorsal root ganglion; Electroacupuncture; P2X3 receptor; Type 2 diabetic neuropathic pain.

Conflict of interest statement

Compliance with ethics guidelines: Xiao-fen HE, Jun-jun WEI, Sheng-yun SHOU, Jian-qiao FANG, and Yong-liang JIANG declare that they have no conflict of interest.

All institutional and national guidelines for the care and use of laboratory animals were followed.

Figures

Fig. 1

Changes in body weight (a), fasting insulin (b), fasting blood glucose (c), insulin sensitivity index (d), and paw withdrawal latency (e) of rats subjected to a high calorie and high sugar diet for 7 weeks and a single intraperitoneal injection of a small dose (35 mg/kg) of STZ at 5 weeks Data are presented as mean±SEM (n=8 in the normal group and n=44 in the model group). The data were analyzed using an independent-sample t-test. **P<0.01, compared with the normal group

Fig. 2

Effects of electroacupuncture (EA) at different frequencies on the paw withdrawal latency of diabetic neuropathic pain (DNP) rats Data are presented as mean±SEM (n=8 or 9 rats per group). The data were analyzed using ANOVA. **P<0.01, compared with the normal group; ##P<0.01, compared with the DNP group; ∆∆P<0.01, compared with the DNP+2 Hz EA group

Fig. 3

Effects of electroacupuncture (EA) at different frequencies on dorsal root ganglion (DRG) P2X3 receptors of diabetic neuropathic pain (DNP) rats (a) Representative bright-field micrographs showing P2X3 receptor-immunoreactive (IR) neurons in L4, L5, and L6 DRGs of rats in the normal, DNP, DNP+2 Hz EA, and DNP+100 Hz EA groups. Scale bar=100 μ m. (b) Statistical analyses of L4, L5, and L6 DRG P2X3 receptor-IR neurons. Five non-consecutive sections were analyzed to obtain the average for each rat, and three rats were analyzed for each group. Data are presented as mean±SEM. The data were analyzed using ANOVA. **P<0.01, compared with the normal group; #P<0.05, ##P<0.01, compared with the DNP group; ∆P<0.05, compared with the DNP+2 Hz EA group

Fig. 4

Effects of electroacupuncture (EA) at different frequencies on calcitonin gene-related peptide (CGRP) in dorsal root ganglion (DRG) of diabetic neuropathic pain (DNP) rats (a) Representative bright-field micrographs showing CGRP-immunoreactive (IR) neurons in L4, L5, and L6 DRGs of rats in the normal, DNP, DNP+2 Hz EA, and DNP+100 Hz EA groups. Scale bar=100 μ m. (b) Statistical analyses of L4, L5, and L6 DRG CGRP-IR neurons. Five non-consecutive sections were analyzed to obtain the average for each rat, and three rats were analyzed for each group. Data are presented as mean±SEM. The data were analyzed using ANOVA. **P<0.01, compared with the normal group; #P<0.05, ##P<0.01, compared with DNP group