| BackgroundThe degree of spinal cord injury is based on the damage displacement and speed and force,and the increase of velocity will not only aggravate the damage of white matter and blood spinal cord barrier,but also cause the change of neuroelectrophysiology.While the increase of damage depth and force can aggravate spinal cord injury and demyelination area.Many kinds of traumatic spinal cord contusion model according to the different contusion depth and speed had ben created to simulate the process of clinical contusion,but most studies coupling of the impact velocity and displacement,instead of an independent control of mechanical parameters,will increase the degree of variability of spinal cord injury.Therefore,it is necessary to independently control the biomechanical parameters of the contusion to establish the model of spinal contusion to increase the repeatability and consistency.A variety of behavioral science evaluation methods are used to evaluate nerve function after spinal cord injury in rats,but behavior usually reflect the sensory and motor information after the processing of composite process,and cannot effectively distinguish between sensory conduction function of ascending and descending movement pathways.The combination of somatosensory evoked potentials and motor evoked potentials is thought to objectively monitor the sensory and motor conduction tracts of the spinal cord,with the latter more sensitive to spinal cord injury.Although the use of this nerve monitoring mode provides a way to identify spinal cord injury,the relative efficiency of each on assessing the gross and fine motor function after spinal cord injury remains to be fully studied.Objective1.To establish a unilateral cervical spinal cord contusion injury model in rats,and to evaluate the behavioral and histological changes with different degrees of cervical spinal cord injury.2.To study the relative efficacy of somatosensory evoked potentials and transcranial electrical stimulation motor evoked potentials in the evaluation of neurologic function after spinal cord injury in rats.Methods1.Model of cervical spinal cord hemicontusion injury in rats with displacement controlThirty-two adult and male Sprague-Dawley rats were randomly divided into 1.2-mm SCI(n=12),2.0-mm SCI(n=12)and the sham control group(n=8).Contusion injuries were produced by a servo-electromagnetic material testing machine with a modified 1.5-mm-diameter impounder to perform 1.2 mm and 2 mm contusion at 500 mm/s at the left dorsal cord of C5.The sham group exposed the spinal cord without contusion.Forelimb locomotor scores and grooming test were used to assess clinical neurological function.All outcome measures were estimated weekly prior to and up to 8 weeks following injury.Histological outcome measures were performed to all animals including spared area of gray and white matter at the lesion epicenter.2.Efficiency of evoked potentials as a functional evaluation for a rat model of unilateral cervical spinal cord contusionContusion injury of varying severity(sham,1.2mm,2mm)depending on impact depth was applied to the left dorsal cord of C5 using a 1.5-mm-diameter impounder at 500 mm/s in adult rats.Electrophysiological analysis,motor behavior scoring,and histological quantifications were performed to identify relationships among pathway conductivity,motor function,and tissue preservation.All outcome measures were estimated prior to injury and up to 12 weeks following injury.Results1.Model of cervical spinal cord hemicontusion injury in rats with displacement controlThe peak force and actual contusion displacement were(0.99±0.14)N and(1.20±0.004)mm in 1.2-mm group,and(1.53±0.22)N and(2.0±0.01)mm in 2-mm group,respectively.There was significant difference in the peak force between groups(P<0.05).Behavior outcomes showed that rats in the two experimental groups both presented neurologic dysfunction ipsilateral to the lesion.Animals subjected to 2 mm injury performed significantly worse and more durable in forelimb locomotive ability than those subjected to 1.2 mm injury.Histological analysis demonstrated that There was unilateral structural failure and cavity of cord in the treatment group at 8 weeks after injury.1.2 mm contusion caused primarily dorsal column,Spinal dorsal horn and part of dorsolateral fasciculus damage while 2 mm contusions produced additional damage to lateral and ventral tissue.Significant difference exsited between the two experimental groups on both spared area of gray and white matter at epicenter.(p<0.05)2.Efficiency of evoked potentials as a functional evaluation for a rat model of unilateral cervical spinal cord contusionSSEP latency in injury group and the control group had significant difference before injury,with prolong latency in 1.2mm and 2mm group(P<0.01).no difference extisted between groups after a month,and the latency had recovered to the level of baseline.The amplitude of SSEP in the injured group was different at all time points(P<0.001),and the moderate injury group improved obviously,but the severe injury group had only partial recovery.The change rate of SSEP amplitude strongly correlated with FLS(r=0.92,p<0.0001),grooming(r=0.8,p<0.001),rearing(r=0.92,p<0.92)and staircase(r=0.79,p<0.0001),respectively.While The variation rate of SSEP latency also showed a significant correlation with both FLS(r=-0.93,p<0.001),grooming(r=-0.91,p<0.001),rearing(r=-0.68,p<0.05)and staircase(r=-0.68,p<0.05).There was a significant difference between injury groups and the sham group in the change rate of TcMEPs latency and amplitude.TcMEP amplitude was significantly associated with FLS(r=0.87,P<0.001),grooming(r=0.88,P<0.01),rearing(r=0.67,P<0.05),and staircase(r=0.68,P<0.05),and TcMEP latency closely correlated with FLS(r=0.96,P<0.0001),grooming(r=0.90,P<0.001),rearing(r=0.79,P<0.01)and staircase(r=0.76,P<0.01).Both amplitude and latency for SSEPs and TcMEPs recorded from the forelimb contralateral to injury showed a fast and substantial recovery to preoperative levels after slight reduction postinjury.Conclusion1.This study had successfully established a different degree of unilateral cervical spinal cord contusion model in rats,which showed persistent unilateral neurological dysfunction and structural destruction of the injured spinal cord and the motor impairment,and it can be used for basic research of spinal cord injury.2.Somatosensory and motor evoked potentials can reflect mild cervical spinal cord injury in rats nerve function,and can not fully reflect the severe spinal cord injury.The recovery of fine motor function simultaneously requires significant improvement in both SSEPs and MEPs,so it is necessary to combine somatosensory and motor evoked potentials to objectively evaluate the fine motor function of rats. |
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