Acupuncture Improved Neurological Recovery after Traumatic Brain Injury by Activating BDNF/TrkB Pathway

Abstract

How to promote neural repair following traumatic brain injury (TBI) has long been an intractable problem. Although acupuncture has been demonstrated to facilitate the neurological recovery, the underlying mechanism is elusive. Brain-derived neurotrophic factor (BDNF) exerts substantial protective effects for neurological disorders. In this study, we found that the level of BDNF and tropomyosin receptor kinase B (TrkB) was elevated spontaneously after TBI and reached up to the peak at 12 h. Nevertheless, this enhancement is quickly declined to the normal at 48 h. After combined stimulation at the acupoints of Baihui, Renzhong, Hegu, and Zusanli, we found that BDNF and TrkB were still significantly elevated at 168 h. We also observed that the downstream molecular p-Akt and p-Erk1/2 were significantly increased, suggesting that acupuncture could persistently activate the BDNF/TrkB pathway. To further verify that acupuncture improved recovery through activating BDNF/TrkB pathway, K252a (specific inhibitor of TrkB) was treated by injection stereotaxically into lateral ventricle. We observed that K252a could significantly prevent the acupuncture-induced amelioration of motor, sensation, cognition, and synaptic plasticity. These data indicated that acupuncture promoted the recovery of neurological impairment after TBI by activating BDNF/TrkB signaling pathway, providing new molecular mechanism for understanding traditional therapy of acupuncture.

Figure 1

The expression of BDNF and phosphorylated TrkB had been transiently enhanced after TBI. Combined stimulation at the acupoint of Baihui, Renzhong, Hegu, and Zusanli was treated after TBI (once daily for 14 days). The level of BDNF at 0 h, 6 h, 12 h, 24 h, and 48 h after TBI was examined by ELISA kit (a). The phosphorylated TrkB at 0 h, 6 h, 12 h, and 24 h after TBI was detected by western blot (b) and immunohistochemistry (d). (c) is the quantitative analysis of (b). Scale bar, 50 m. ^∗P < 0.05 and ^∗∗P < 0.01 versus 0 h after TBI. ^##P < 0.01 versus 12 h after TBI.

Figure 2

The expression of BDNF and phosphorylated TrkB in acupuncture-treated rats had been persistently enhanced after TBI. The level of BDNF at 6 h, 12 h, 48 h, 96 h, and 168 h after TBI was examined by ELISA kit (a). The phosphorylated TrkB at 48 h, 96 h, and 168 h after TBI was detected by western blot (b) and immunohistochemistry (d). (c) is the quantitative analysis of (b). Scale bar, 50 m. Acu: acupuncture. ^∗P < 0.05 and ^∗∗P < 0.01 versus TBI group. ^#P < 0.05 versus TBI group at 6 h.

Figure 3

The phosphorylation of downstream molecular BDNF/TrkB signaling pathway was significantly increased in acupuncture-treated rats had been persistently enhanced after TBI. The phosphorylated Akt at 12 h, 48 h, 96 h, and 168 h after TBI was examined by western blot (a) and immunohistochemistry (e). (b) is the quantitative analysis of (a). The phosphorylated Erk1/2 at 12 h, 48 h, 96 h, and 168 h after TBI was examined by western blot (c) and immunohistochemistry (f). (e) is the quantitative analysis of (d). The phosphorylated PLCγ1 at 12 h, 48 h, 96 h, and 168 h after TBI was examined by western blot (g). (h) is the quantitative analysis of (g). Scale bar, 50 m. Acu: acupuncture. ^∗P < 0.05 and ^∗∗P < 0.01 versus TBI group.

Figure 4

Blocking BDNF/TrkB pathway significantly prevented acupuncture-induced amelioration of neurological deficit. K252α (specific inhibitor of TrkB phosphorylation) was injected stereotaxically into lateral ventricle. The mNSS score, BWT score, and climbing angle were assessed at 7 d and 21 d after TBI. Acu: acupuncture. ^∗P < 0.05 and ^∗∗P < 0.01 versus TBI group. ^##P < 0.01 versus TBI + Acu group.

Figure 5

Blocking BDNF/TrkB pathway significantly prevented acupuncture-induced amelioration of cognitive impairment. The rats were trained to remember the hidden platform in the maze from 14 to 19 days after TBI (a). The platform was removed at 21 days, then the time stayed in the target quadrant (b), and the number of crossing platform (c) were examined. (d–f) LTP measurements were performed at 21 days after TBI. Normalized excitatory postsynaptic potential (EPSP) slope (d) and population spike (PS) amplitude (e) were measured. ^∗P < 0.01 and ^∗∗P < 0.01 versus TBI group; ^##P < 0.01 versus TBI + Acu group.