Antidepressant effect of electroacupuncture regulates signal targeting in the brain and increases brain-derived neurotrophic factor levels

Abstract

Electroacupuncture improves depressive behavior faster and with fewer adverse effects than antidepressant medication. However, the antidepressant mechanism of electroacupuncture remains poorly understood. Here, we established a rat model of chronic unpredicted mild stress, and then treated these rats with electroacupuncture at Yintang (EX-HN3) and Baihui (DU20) with sparse waves at 2 Hz and 0.6 mA for 30 minutes, once a day. We found increased horizontal and vertical activity, and decreased immobility time, at 2 and 4 weeks after treatment. Moreover, levels of neurotransmitters (5-hydroxytryptamine, glutamate, and γ-aminobutyric acid) and protein levels of brain-derived neurotrophic factor and brain-derived neurotrophic factor-related proteins (TrkB, protein kinase A, and phosphorylation of cyclic adenosine monophosphate response element binding protein) were increased in the hippocampus. Similarly, protein kinase A and TrkB mRNA levels were increased, and calcium-calmodulin-dependent protein kinase II levels decreased. These findings suggest that electroacupuncture increases phosphorylation of cyclic adenosine monophosphate response element binding protein and brain-derived neurotrophic factor levels by regulating multiple targets in the cyclic adenosine monophosphate response element binding protein signaling pathway, thereby promoting nerve regeneration, and exerting an antidepressive effect.

Keywords: TrKB; brain-derived neurotrophic factor; chronic unexpected mild stress; cyclic adenosine monophosphate response element binding protein signal pathway; depression; electroacupuncture; fluoxetine; nerve regeneration; neural regeneration; neurotransmitter; protein kinase A.

Figure 1

Effect of EA and Flu on behavior and body weight in CUMS rats. (A) Horizontal activity (crossing activity: frequency of crossing the square) in the open field test; (B) vertical activity (rearing activity: frequency of rearing) in the open field test; (C) immobility time (5 minutes) in the forced swimming test; and (D) body weight. Data are presented as the mean ± SD. One-way analysis of variance and Tukey's post hoc test were used to examine differences among groups. #P < 0.05, ##P < 0.01, vs. control group; *P < 0.05, **P < 0.01, vs. CUMS group. CON: Control; CUMS: chronic unexpected mild stress; EA: electroacupuncture; Flu: fluoxetine.

Figure 2

Effect of EA and Flu on neurotransmitters in the hippocampus of CUMS rats (detected by high performance liquid chromatography). (A) 5-HT in blood; (B) NE in blood; (C) Glu in the hippocampus; and (D) GABA in the hippocampus. Data are presented as the mean ± SD. Experiments were performed five times. One-way analysis of variance and Tukey's post hoc test were used to examine differences among groups. #P < 0.05, ##P < 0.01, vs. control group; *P < 0.05, **P < 0.01, vs. CUMS group. CON: Control; CUMS: chronic unexpected mild stress; EA: electroacupuncture; Flu: fluoxetine; 5-HT: 5-hydroxytryptamine; NE: norepinephrine; Glu: glutamate; GABA: γ-aminobutyric acid.

Figure 3

Effect of EA and Flu on protein levels in the hippocampus of CUMS rats (western blot assay). Immunoreactivity of TrkB (A), BDNF (B), pCREB (C), CREB (D), PKA (E), CaMKII (F), and Akt (G) in the hippocampus. Protein bands of BNDF and BDNF-related factors in the hippocampus (H). Data are presented as the mean ± SD. Experiments were performed four times. One-way analysis of variance and Tukey's post hoc test were used to examine differences among groups. #P < 0.05, ##P < 0.01, vs. control group; *P < 0.05, **P < 0.01, vs. CUMS group. CON: Control; CUMS: chronic unexpected mild stress; EA: electroacupuncture; Flu: fluoxetine; BDNF: brain-derived neurotrophic factor; pCREB: phosphorylated-CREB; CREB: cyclic adenosine monophosphate response element binding protein; PKA: protein kinase A; CaMKII: calcium-calmodulin-dependent protein kinase.

Figure 4

Effect of EA and Flu on mRNA levels of BDNF- and CREB-related genes in the hippocampus of CUMS rats (real-time PCR). mRNA levels of (A) TrkB, (B) BDNF, (C) CREB, (D) PKA, (E) CaMKII, and (F) Akt in the hippocampus. Data are presented as the mean ± SD. Experiments were performed five times. One-way analysis of variance and Tukey's post hoc test were used to examine differences among groups. #P < 0.05, ##P < 0.01, vs. control group; *P < 0.05, **P < 0.01, vs. CUMS group. CON: Control; CUMS: chronic unexpected mild stress; EA: electroacupuncture; Flu: fluoxetine; BDNF: brain-derived neurotrophic factor; CREB: cyclic adenosine monophosphate response element binding protein; PKA: protein kinase A.