An enhanced therapeutic effect of repetitive transcranial magnetic stimulation combined with antibody treatment in a primate model of spinal cord injury

Abstract

Repetitive transcranial magnetic stimulation (rTMS) targeting the primary motor cortex (MI) is expected to provide a therapeutic impact on spinal cord injury (SCI). On the other hand, treatment with antibody against repulsive guidance molecule-a (RGMa) has been shown to ameliorate motor deficits after SCI in rodents and primates. Facilitating activity of the corticospinal tract (CST) by rTMS following rewiring of CST fibers by anti-RGMa antibody treatment may exert an enhanced effect on motor recovery in a primate model of SCI. To address this issue, we examined whether such a combined therapeutic strategy could contribute to accelerating functional restoration from SCI. In our SCI model, unilateral lesions were made between the C6 and the C7 level. Two macaque monkeys were used for each of the combined therapy and antibody treatment alone, while one monkey was for rTMS alone. The antibody treatment was continuously carried out for four weeks immediately after SCI, and rTMS trials applying a thermoplastic mask and a laser distance meter lasted ten weeks. Behavioral assessment was performed over 14 weeks after SCI to investigate the extent to which motor functions were restored with the antibody treatment and/or rTMS. While rTMS without the preceding antibody treatment produced no discernible sign for functional recovery, a combination of the antibody and rTMS exhibited a greater effect, especially at an early stage of rTMS trials, on restoration of dexterous hand movements. The present results indicate that rTMS combined with anti-RGMa antibody treatment may exert a synergistic effect on motor recovery from SCI.

Fig 1. Experimental design and extent of SCI lesions.

(A) Experimental design. According to a modified Brinkman board test, dexterous motor behavior was assessed over a total of 16 weeks (wks) before and after SCI (2 and 14 weeks, respectively). Treatment with anti-RGMa antibody (RGMa-Ab) was started concurrently with the SCI surgery and continued for four weeks. Following the antibody treatment, rTMS trials over the forelimb region of the MI were performed for a total of approximately 10 weeks. Then, BDA injections into the contralesional MI were made about eight weeks before sacrifice. (B) Extent of SCI lesions (in pink) overlaid on a template transverse section. Lesions were made unilaterally at the border between the C6 and the C7 level to involve largely the lateral sector of the cervical cord. Monkeys A and C with both the antibody treatment and rTMS (RGMa-Ab+rTMS), monkeys M and Z with the antibody treatment alone (RGMa-Ab), monkey G with rTMS alone (rTMS), and monkeys I and Y without either the antibody treatment or rTMS (Control SCI). Each percentage represents the ratio of the lesioned area to the total area of a hemi-transverse section. Note that there is no marked difference in the extent of SCI lesions (58.9–70.7%) across the seven monkeys. L, left; R, right. On the right side, photomicrographs of representative sections Nissl-stained with Cresyl violet taken from monkeys C, Z, G, and Y. Scale bars, 1 mm.

Fig 2. Setup of the newly developed rTMS system.

(A) Schematic diagram of the present system for achieving constant and effective stimulation targeting the MI of an awake monkey. (B) A thermoplastic mask shaped to fit the monkey’s head is utilized to fix the monkey’s head, secure a sufficient space for a figure-of-eight coil, and contact the coil close to the scalp. (C) The thermoplastic mask is firmly screwed to the upper part of a monkey chair for restraining any head movement. (D) Three laser distance meters are positioned to measure accurate three-dimensional coordinates of the figure-of-eight coil. For details, see “Development of rTMS system” of the Results section.

Fig 3. Results of behavioral assessment based on the modified Brinkman board test in the seven monkeys tested.

(A) Total number of pellets collected through both the vertical and the horizontal slots. (B) Number of pellets collected through the vertical slots. (C) Number of pellets collected through the horizontal slots. Note that rTMS combined with the antibody treatment appears to yield a more rapid improvement in the motor performance requiring manual dexterity, compared with the antibody treatment alone.