Introduction

Traumatic spinal cord injury (SCI) occurs in 3.6 to 195.4 patients per million worldwide (Jazayeri et al., 2015). Many cases of SCI result in tetraplegia and although this complication leads to tremendous personal loss and societal costs, treatments for SCI are not standardized and are highly variable.

The pathophysiology of SCI involves the primary injury and the subsequent secondary injury, which results from a progressive local cascade of tissue destruction, including the change in the microenvironment of the injured spinal cord(ischemia of the microcirculation, edema, inflammation,glutamatergic excitotoxicity) and apoptosis. The change in the microenvironment is the pathological basis of the functional deficits after SCI. The increased concentration of platelet-activating factor in the blood and tissue is an important factor that promotes the changes in the microenvironment (Faden et al., 1992; Wang et al., 2016). The longterm neurological deficits after SCI may be due in part to widespread apoptosis of the neurons and oligodendroglia in distant regions (Crowe et al., 1997; Emery et al., 1998).Many studies have shown that an important apoptotic pathway that mediates apoptosis after SCI is the family of caspases, including caspase-3 and caspase-9 (Springer et al.,1999; Nakagawa et al., 2000; Dong et al., 2015).

Decompression has been proven to be effective (Rabinowitz et al., 2008; Fehlings et al., 2012; Jones et al., 2012; Wilson et al., 2012). The focus of debate is on outlining the optimal timing of decompression for patients with acute SCI. Many scholars agree that early decompression (＜ 24 hours) leads to a clinical improvement in neurological status, but delayed decompression (＞ 24 hours) for acute SCI has not resulted in optimal outcomes in neurological status (Wilson et al.,2012; Dahdaleh et al., 2013). SCI cannot be cured by decompression, so performing decompression along with effective adjunctive therapies is an appropriate approach to enhance the treatment of acute SCI.

Adjunctive therapies are a key factor in continuously promoting optimal treatment of acute SCI. The adjunctive therapies, such as corticosteroids (Fehlings et al., 2014; Schroeder et al., 2014) and neuroprotectant agents (Wilson et al., 2013;Grossman et al., 2014), have some protective effect on the spinal cord and nerve roots, but the overall effects are not ideal.

Regarding traditional Chinese medicine, the spine has a close relationship with the Governor Vessels. SCI is regarded as a stasis in the meridian of the Governor Vessels. The cardiovascular complications and the change in hemorheology after SCI are evidence of the relationship between SCI and stasis in the Governor Vessel (Berlly et al., 2007; Furlan et al., 2008). Also, Governor Vessel electroacupuncture(EA) has been proven to prevent secondary damage and to improve neuroprotective effects after SCI (Liu et al., 2011;Juarez Becerril et al., 2015; Wei et al., 2017). A recent meta-analysis showed that combining acupuncture with other therapies had a higher cure rate and effectiveness than acupuncture alone (Deng et al., 2017). Thus, Governor Vessel EA may be an effective adjunctive therapy for SCI.

The upper cervical spine is adjacent to the medulla oblongata, so when the cervical spine is injured, it can affect breathing and be life-threatening. So far, no mature upper cervical SCI animal model has been developed. Thus, there have been fewer studies of upper cervical SCI (Sharifalhoseini et al., 2017).

To identify effective treatment strategies for acute upper SCI, we attempted to combine decompression with EA to treat acute upper SCI. Given the different effects of early and delayed decompression, we investigated the effect of EA combined with early or delayed decompression in rats with acute upper cervical SCI.

Materials and Methods

Animals

A total of 42 female Wistar rats aged 6 months and weighing 280 ± 20 g were obtained from the Laboratory Animal Center of the Academy of Military Medical Sciences in Beijing of China (animal license No. SCXK (Jun) 2017-0004). The rats were housed in individual cages at 23 ± 2°C, and allowed free access to food and water. The rats (n= 42) were equally and randomly divided into seven groups (n= 6 per group): sham, 12-hour SCI, 12-hour EA (SCI + EA), 12-hour methylprednisolone(MP) (SCI + MP), 48-hour SCI, 48-hour EA (SCI + EA), and 48-hour MP (SCI + MP). All experiments were approved by the Institutional Animal Care and Use Committee of the China-Japan Friendship Hospital of China (No. ).

Establishment of SCI models

The establishment of an acute upper cervical SCI animal model was based on a previous study of ours (Tan et al.,2016). All rats were anesthetized with pentobarbital (Sigma-Aldrich, St. Louis, MO, USA). The external occipital protuberance was cut longitudinally to expose the atlanto-axial space and the atlanto-occipital space on the right side (Figure 1A). After removal of soft tissue and ligaments above the atlanto-axial space and the atlanto-occipital space, a balloon catheter (SPLX, 2.5 mm × 12.0 mm;Medtronic, Inc., Minneapolis, MN, USA) was inserted into the atlanto-occipital space, and the top of a balloon catheter was pulled out from the atlanto-occipital space (Figure 1B)by a balloon catheter compression system (Figure 1C). Finally, the balloon catheter was fi xed on the back and head of the rats (Figure 1D). When the rat models were successfully generated 24 hours later, the sham group was non-pressurized; in the other groups, the end of the balloon catheters was connected with manumotive force-pumps (30 atm,Medtronic, Inc.). Iohexol (General Electric Pharmaceutical Co., Ltd., Shanghai, China) was injected into the balloon catheter continuously until the pressure reached 3 bar (1 bar = 100 kPa). Half of the rats maintained the compression for 48 hours and the other half maintained the compression for 12 hours. The balloon catheters were then decompressed and removed. During the model development, all rats were kept in separate cages with free access to food and water at 25 ± 3°C. The standard of model evaluation was spasmodic oscillation of the tail, unilateral limb and body retraction,and unilateral or bilateral paralysis. If there were rat deaths or serious complications during the experiment, we would fi ll in the rats and make sure that each group had six rats.