the spinal cord injury ( sci ) often leads to serious neurological sequelae and various complications such as neurogenic bladder , lower extremities muscle atrophy , etc .
electrostimulation on sacral nerve roots is currently being tried with some promising results as a treatment for a wide spectrum of voiding dysfunctions .
besides , several investigators reported additional effects of the sacral nerve stimulation such as change of spasticity and spasm , increased motility of intestinal tract and defecation , and improvement of locomotor function in experimental and clinical studies3,6,11,12,14 ) .
furthermore , there is a case report about additional improvement of lower extremity motor6 ) .
they reported that one patient with a long history of progressive spinal multiple sclerosis was able to stand and transfer , but not walk , before the sacral nerve stimulation6).another paraplegic patient was showed improvement of motor power slowly , and after 2 years the patient could stand as confident as before6 ) .
the purpose of this study is ( 1 ) to establish a rat thoracic spinal cord stimulation model and ( 2 ) to compare effects of thoracic cord neuromodulation to that of sacral nerve neuromodulation on locomotor function , bladder and lower extremities muscles .
twenty sprague dawley rats of 6 months old female , weighing 200 to 250 gm , were randomly divided into 4 groups : a normal control group ( n=5 ) , sci with sham stimulation group ( sci , n=5 ) , and sci with electrical stimulation at thoracic spinal cord ( sci+tes , n=5 ) , and sci with electrical stimulation at sacral nerve ( sci + ses , n=5 ) .
the sci group included rats that were injured with electrodes implanted but did not receive stimulation .
the sci+tes and sci+ses group included rats that received epidural electrical stimulation at the thoracic spinal cord or s2/s3 nerve root using needle electrode , respectively .
rats in the each group were kept in separate cages under the same living conditions for a week before receiving sci .
the animals were anesthetized with an intramuscular injection of zoletil 15 mg and xylazine 3 mg . under general anesthesia , rats were placed in a prone position . after routine disinfection , a surgical incision was made through the skin , subcutaneous tissue , and the t8 - 12 vertebral lamina to the spinal canal .
the scis were induced in rats using an nyu - mascis ( new york university - multicenter animal spinal cord injury study ) impactor .
the impact height of 25 mm was considered for severe cord injury based on a prior investigation1 ) . for sacral neuromodulation , a surgical incision at the s1 - 3 level was made through the skin , subcutaneous tissue , and the s2 - 3 vertebral lamina ( fig .
needle electrodes ( 0.527 g ) were implanted at bilateral s2 or s3 neural foramina .
wounds were cleaned and sutured with wires inserted through the subcutaneous tissue extruding from the neck . for thoracic spinal cord stimulation ,
we put the needle electrode on the thoracic epidural space through the laminectomy site ( fig .
the sci+tes and sci+ses groups received electrical stimulation 7 days after sci with the following protocol : stimulation time 30 minutes ; pulse duration , 0.1 ms ; and frequency , 20hz . epidural low frequency electric stimulation was applied 30 minutes per day for 4 weeks .
post - injury motor behavior is assessed by the basso , beattie , and bresnahan ( bbb ) locomotor scale method4,5 ) .
the scale ( 0 - 21 ) represents sequential recovery stages and categorizes combinations of rat joint movement , hindlimb movements , stepping , forelimb and hindlimb coordination , trunk position and stability , paw placement , and tail position . to evaluate the bladder contracting function , urodynamic study using cystometrogram was performed with a serial fashion .
all rats were sacrificed at 4 weeks after sci . under general anesthesia , the gastrocnemius muscle was harvested , weighed , and stained with hematoxylin and eosin ( h&e ) to identify the muscle fiber cross - sectional area ( csa ) .
the animals were anesthetized with an intramuscular injection of zoletil 15 mg and xylazine 3 mg . under general anesthesia
after routine disinfection , a surgical incision was made through the skin , subcutaneous tissue , and the t8 - 12 vertebral lamina to the spinal canal .
the scis were induced in rats using an nyu - mascis ( new york university - multicenter animal spinal cord injury study ) impactor .
the impact height of 25 mm was considered for severe cord injury based on a prior investigation1 ) . for sacral neuromodulation , a surgical incision at the s1 - 3 level was made through the skin , subcutaneous tissue , and the s2 - 3 vertebral lamina ( fig .
needle electrodes ( 0.527 g ) were implanted at bilateral s2 or s3 neural foramina .
wounds were cleaned and sutured with wires inserted through the subcutaneous tissue extruding from the neck . for thoracic spinal cord stimulation
, we put the needle electrode on the thoracic epidural space through the laminectomy site ( fig .
the sci+tes and sci+ses groups received electrical stimulation 7 days after sci with the following protocol : stimulation time 30 minutes ; pulse duration , 0.1 ms ; and frequency , 20hz . epidural low frequency electric stimulation was applied 30 minutes per day for 4 weeks .
post - injury motor behavior is assessed by the basso , beattie , and bresnahan ( bbb ) locomotor scale method4,5 ) .
the scale ( 0 - 21 ) represents sequential recovery stages and categorizes combinations of rat joint movement , hindlimb movements , stepping , forelimb and hindlimb coordination , trunk position and stability , paw placement , and tail position . to evaluate the bladder contracting function ,
the gastrocnemius muscle was harvested , weighed , and stained with hematoxylin and eosin ( h&e ) to identify the muscle fiber cross - sectional area ( csa ) .
three of the five suddenly died after the first stimulation on the thoracic spinal cord .
all rats but the sci+tes group survived through the entire 4 weeks . before the injury , all rats showed normal function on the bbb score .
all injured rats exhibited a severe bbb score at 1 day after sci . at day 1 of sci ,
the bbb scores of the sci and the sci+ses group were 2.80.7 and 2.70.8 , respectively .
the difference between two groups was not significant . during subsequent scoring periods , bbb scores increased and plateaued around 14 days after sci .
the locomotor function improved significantly at days 3 , 7 , and 14 after sci ( 3 days : 7.31.2 and 7.31.5 , 7 days : 13.10.9 and 13.21.1 , and 14 days : 14.60.8 and 14.70.6 ) .
the all survived rats improved over time but there was no significant difference at any point in time between sci and sci + ses groups .
all rats experienced urinary retention after the injury and recovered self - voiding after 3 - 9 days .
voiding contraction interval was 25.57.5 minutes in the sci group , 16.55.3 minutes in the sci+ses group , and 12.54.2 minutes in the control ( fig .
the recovery of voiding contraction interval was significant in the sci+ses group comparing to the sci group ( p<0.05 ) .  
the gastrocnemious muscle weight decreased after the sci , whereas the weight increased by 7.9% after sacral neuromodulation .
the csa of the muscle was slightly greater in the sci+ses than in the sci group , however , the difference was not significant . cross - sectional shape of the muscle fiber was markedly turned into round by sci .
after sacral neuromodulation , the shape was turned into angled again ( fig . 3 and 4 ) .
this study was designed to establish a rat thoracic spinal cord stimulation model and to compare effects of thoracic cord neuromodulation to that of sacral nerve neuromodulation on locomotor function , bladder and lower extremities muscles .
however , we failed to accomplish the comparative analysis , because all five rats of the sci+tes group expired within 3 days after the injury . three of the five suddenly died after the first stimulation on the thoracic spinal cord .
we suggest that the cause of death is associated with epidural spinal cord stimulation in the thoracic spine which is located near the heart .
nevertheless , the present study showed that sacral neuromodulation has a therapeutic potential to improve neurogenic bladder and muscle atrophy .
the urodynamic study using cystometrogram revealed that the recovery of voiding contraction interval was significant in the sci+ses group comparing to the sci group .
furthermore , lower extremities muscle such as the gastrocnemious muscle was relatively better preserved after sacral neuromodulation .
electrical stimulation has been reported to cause neurobiological effects , such as relieving pain in the area of head and face and restoring movement and function in individuals with spinal cord injury6,8 ) .
it has also been indicated that electrical stimulation can directly influence on regenerating neural tissues observed under a well - controlled experimental environment8 ) .
several investigators have reported that a low - frequency electrical stimulation is a promising approach to accelerate nerve regeneration after injury2,10 ) .
there are a few studies on neuroprotective effects of sacral nerve stimulation in the sci patients2,3,6,9,12,14 ) .
the additional effect of sacral neuromodulation was improvement of neurogenic bladder , intestinal motility , penile erection , pain discrimination , and motor power of leg6 ) .
however , the current study showed that sacral neuromodulation to rat injured thoracic spinal cord did not improve the locomotor function .
several investigators have reported that a low - frequency electrical stimulation could accelerate nerve regeneration after injury2,10 ) . however , a high frequency of electrical stimulation may increase failure rate of nerve regeneration13 ) .
hence , these results can not exclude potential beneficial effects of sacral nerve stimulation in other models of sci with different treatment protocols , the disappointing outcomes in this study should be limited by the treatment protocol .
in a rat thoracic spinal cord contusional model , we failed to establish a rat spinal cord stimulation model .
however , sacral neuromodulation has a therapeutic potential to improve neurogenic bladder and muscle atrophy .
further experimental studies are needed to establish a rat spinal cord stimulation model and to determine the most effective protocol of stimulation .
 objectivethe purpose of this study is to compare a neuroprotective effect of thoracic cord neuromodulation to that of sacral nerve neuromodulation in rat thoracic spinal cord injury ( sci ) model.methodstwenty female sprague dawley rats were randomly divided into 4 groups : the normal control group ( n=5 ) , sci with sham stimulation group ( sci , n=5 ) , sci with electrical stimulation at thoracic spinal cord ( sci + tes , n=5 ) , and sci with electrical stimulation at sacral nerve ( sci + ses , n=5 ) . 
 spinal cord was injured by an impactor which dropped from 25 mm height . 
 electrical stimulation was performed by the following protocol : pulse duration , 0.1ms ; frequency , 20 hz ; stimulation time , 30 minutes ; and stimulation duration at thoracic epidural space and s2 or 3 neural foramina for 4 weeks . 
 locomotor function , urodynamic study , muscle weights , and fiber cross sectional area ( csa ) were investigated.resultsall rats of the sci + tes group expired within 3 days after the injury . 
 the locomotor function of all survived rats improved over time but there was no significant difference between the sci and the sci + ses group . 
 all rats experienced urinary retention after the injury and recovered self - voiding after 3 - 9 days . 
 voiding contraction interval was 25.57.5 minutes in the sci group , 16.55.3 minutes in the sci+ses group , and 12.54.2 minutes in the control group . 
 the recovery of voiding contraction interval was significant in the sci + ses group comparing to the sci group ( p<0.05 ) . 
 muscle weight and csa were slightly greater in the sci + ses than in the sci group , but the difference was not significant.conclusionwe failed to establish a rat spinal cord stimulation model . 
 however , sacral neuromodulation have a therapeutic potential to improve neurogenic bladder and muscle atrophy . 