Immunohistochemical evidence of axonal regrowth across polyethylene glycol-fused cervical cords in mice

Immunohistochemical evidence of axonal regrowth across polyethylene glycol-fused cervical cords in mice

It is generally accepted that a severed spinal cord is asso‐ciated with permanent paralysis. Recently, a spinal cord fusion protocol (GEMINI) has been proposed, whereby an acutely controlled, sharp, operative transection of the spinal cord is carried out.is scenario is not comparable (even in principle) to the clinical situation of a traumatic spinal cord injury, in which major tissue disruption (mechanical, hemorrhagic, scar‐ and cyst‐associated) occurs (Canavero, 2015). During 1950s—1960s, neurosurgeon Dr. Freeman made extensive observations of what happens when a spi‐nal cord is sharply transected. He reported slow recovery of behavioral motor function in several animals over months (reviewed in Canavero et al., 2016), with clear signs of electrophysiological conduction. Most importantly, silver stained histologic sections showed numerous growing ax‐ons connecting the divided ends (Freeman, 1963).is re‐covery can be accelerated by treating the severed cord with a fusogen (e.g., polyethylene glycol) (see for full discussion and rationale from Canavero, 2013; Kim, 2016). Here, we clearly prove that axonal regrowth is possible across the severance interface using immunohistochemistry and elec‐tron microscopy.

Figure 1 Schematic view and image analysis of spinal cervical cord.

This report focuses on the ventral compartment of the cord where the motor system is located. Histologically, clear signs of axonal sprouting were detected across the gap at both low and high magnifications in longitudinal sections (Figure 1B). As expected, given the sharp severance, cyst formation normally observed in spinal cord injury was ab‐sent, and the gap between cuts was fi lled by the DAPI stained migrated cells. In line with another study showing regener‐ation of rat spinal cord fi bers across the gap using graphene nano‐ribbons in a hemi‐transection model (Palejwala et al., 2016), our data provide further histological evidence that cervical spinal cord regeneration is possible. In transverse sections, a large amount of sprouting axons are shown in the reconnected area (Figure 1C), in a region especially rich in propriospinal neurons (Figure 1A). Ultrastructurally, both myelinated axons with the axoplasm containing intact mi‐tochondria, adjacent astrocytes (Figure 1D), disorganized splitting myelination (Figure 1E) and non‐myelinating ax‐ons (Figure 1E) were observed.

Contrary to neurological dogma, the true engine of mo‐tor function in mammals, including man, is the so‐called cortico‐trunco‐reticulo‐propriospinal pathway (Canavero and Ren, 2016; Canavero et al., 2016), a network of propri‐ospinal neurons that spans the whole length of the spinal cord and channels impulses from the brainstem reticular formation to the motor neurons. For instance, primates can perform arm and hand movements (including the dexterous movements of the fingers and precision grip) without a pyramidal tract because of the neural circuits of the propriospinal system alone (Canavero and Ren, 2016). After sharp severance, it is the sprouting of the proprio‐spinal neurons across the gap that sustains motor recovery (Canavero and Ren, 2016). Recent data proved that pro‐priospinal neurons, unlike supraspinal axons, are capable of extending axons through a spinal lesion, which is rich in neuroactive substances that inhibit growth,i.e., can penetrate the “hostile” micro‐environment of a traumatic injury as in patients with spinal cord injury (Fenrich and Rose, 2009), but no correlative behavioral study was done, making that fi nding clinically dubious.

We previously showed that a fusogen‐assisted sharp sec‐tion of the cervical (Kim et al., 2016) and dorsal (Ye et al., 2016) cord is followed by behaviorally relevant motor recov‐ery in experimental animals. Here, we correlate the recovery to evidence of sprouting across the polyethylene glycol‐treat‐ed plane of fusion. Sprouting neurons were especially located in lamina VIII, where propriospinal neurons are particularly concentrated in the mouse cervical cord.

The work was partially supported by the National Research Foundation of Korea (NRF), No. 2015R1C1A1A02037047.

C-Yoon Kim＊, Hanseul Oh, Xiaoping Ren, Sergio Canavero

Department of Stem Cell Biology, School of Medicine, Konkuk University, Seoul, Korea (Kim CY)

Department of Laboratory Animal Medicine, College of Veter‐inary Medicine, Seoul National University, Seoul, Korea (Kim CY, Oh H)

Hand and Microsurgical Center, the Second A ffiliated Hospital of Harbin Medical University; State‐Province Key Laboratories of Biomedicine‐Pharmaceutics, Harbin Medical University, Harbin, Heilongjiang Province, China (Ren X)

Turin Advanced Neuromodulation Group, Turin, Italy (Canavero S)

Heaven/Gemini International Collaborative Group, Turin, Italy (Kim CY, Oh H, Ren X, Canavero S)

＊Correspondence to: C-Yoon Kim, D.V.M., Ph.D., vivavets@gmail.com.

Accepted:2016-12-26

orcid: 0000-0003-1199-8024 (C-Yoon Kim)

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10.4103/1673-5374.199014

How to cite this article:Kim CY, Oh H, Ren X, Canavero S (2017) Immunohistochemical evidence of axonal regrowth across polyethylene glycol-fused cervical cords in mice. Neural Regen Res 12(1):149-150.

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