Attenuation of spinal cord injury-induced astroglial and microglial activation by repetitive transcranial magnetic stimulation in rats

Abstract

Spinal cord injury (SCI) causes not only loss of sensory and motor function below the level of injury but also chronic pain, which is difficult and challenging of the treatment. Repetitive transcranial magnetic stimulation (rTMS) to the motor cortex, of non-invasive therapeutic methods, has the motor and sensory consequences and modulates pain in SCI-patients. In the present study, we studied the effectiveness of rTMS and the relationship between the modulation of pain and the changes of neuroglial expression in the spinal cord using a rat SCI-induced pain model. Elevated expressions of Iba1 and GFAP, specific microglial and astrocyte markers, was respectively observed in dorsal and ventral horns at the L4 and L5 levels in SCI rats. But in SCI rats treated with 25 Hz rTMS for 8 weeks, these expressions were significantly reduced by about 30%. Our finding suggests that this attenuation of activation by rTMS is related to pain modulation after SCI. Therefore, rTMS might provide an alternative means of attenuating neuropathic pain below the level of SCI.

Keywords: Astrocytes; Microglia; Repetitive Transcranial Magnetic Stimulation; Spinal Cord Injury.

Fig. 1

Expression of Iba1 in the spinal dorsal horns. Immunofluorescent images of spinal dorsal horns from (A) the naive control, (B) the sham, and (C) rTMS groups. Numbers of Iba1 positive microglia were increased at 8 weeks after injury in sham group (B). Activated microglia with round-shaped perikaryon were observed in high power view (a, b, and c). However, activated microglia were less numerous in spinal dorsal horn in the rTMS group than in the sham group (C). Size of scale bar: 100 µm (D). Quantitative analysis of numbers of Iba1 immunoreactive cells in spinal dorsal horns. Iba1 positive areas were significantly attenuated by rTMS (P = 0.028). Results are presented as mean ± SDs.

Fig. 2

Expression of GFAP in the spinal dorsal horns. The spinal dorsal horns were from (A) naive control, (B) sham, and (C) rTMS groups. Immunoreactity for GFAP increased in the spinal dorsal horns of L4-5 segments after SCI (B). At higher magnification, reactive astrocytes with increased immunoreactivity and hypertrophy were noted (b). Reactive astrocyte numbers, GFAP expression, were lower in rTMS than in sham group (C and c). Size of scale bar: 100 µm (D). Quantitative analysis of the number of GFAP immunereactive cells in spinal dorsal horns. In quantitative analysis of numbers of GFAP, the immunoreactive positive area was significantly lower in the rTMS group, than in sham group (P = 0.009). Results are presented as mean ± SDs.