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two objectives were pursued during this acute experiment - 1 ) validate a new animal model able to constitute a trade - off between small animal species and human for spinal cord stimulation purposes and 2 ) assess direct spinal stimulation impact on animal bladder and bowel functions  accordingly , the implemented experimental protocol was preceded by a substantial literature study to identify a large animal model and define an anesthetic procedure preserving spinal cord excitability while minimizing animal suffering .
finally , experiment was facilitated by an innovative stimulation device developed within the team ( camin inria team , former demar team , montpellier , france . beyond its wide availability
, the porcine model  especially for young individuals ( 3 to 4 months old ) - presents both urinary and spinal structures close to human ones . presenting a bladder capacity of approximately 600ml and an urethra of 8 cm long for 6 mm wide , 50 kg female individuals possess humanlike urinary characteristics . unlike in males , where urethra presents many convolutions ,
females urinary tract is straight and joins the vaginal wall to half the distance of the cervix making transurethral catheterization possible . from a neuro - anatomical point of view
although stopping at s2 vertebra , pigs spinal cord possesses similarities with human structures ( assumptions confirmed during surgery ) ; similarities concerning both support and neural frameworks ( vertebrae , meninges ) . due to these peculiarities ,
studies dedicated to visceral centers identification within pig spinal grey matter have already been performed ( mainly in minipigs ) . by highlighting cell bodies from ( low ) l6 to ( up ) s2 ,
horseradish peroxidase injection indicated arrival of parasympathetic and somatic axons from bladder and external urethral sphincter ( striated ) to the lower portion of the spine .
the combination of these points seem to justify the use of this animal species in studies dedicated to spinal cord stimulation , particularly regarding bladder and bowel functions restoration . while regularly use in experimental context , the elaboration of an anesthetic protocol compatible with both pig model and spinal stimulation was challenging . given the identified constraints - 1 ) adapted to porcine model , 2 ) long term efficiency ( surgery + stimulation sessions ) , 3 ) spinal excitability conservation , 4 ) urinary and bowel functions preservation .
a combination of propofol and morphine ( at relatively low doses ) was retained to provide sufficient anesthesia acute experiment was performed on one landras female pig ( 50 kg , 4 months old ) according to european ethical rules concerning animal experiments ( a2260 approval number ) .
after premedication ( intramuscular injection of ketamine and calmivet ) , the animal was placed under mechanical ventilation and an intravenous route was inserted at the ear vein for propofol and morphine delivery . to ensure animal welfare ,
after anesthesia induction , a transurethral catheter made of a silicon double - lumen bladder catheter was positioned and used to record lower urinary tract pressure ( i.e. bladder response ) .
similarly , a rectal probe was placed to monitor changes in rectal pressure . both pressures ( bladder and rectal )
were acquired using an acquisition system - developed within the team - triggered by stimulation .
lumbar and sacral vertebrae were highlighted and an incision was performed in order to reveal l6 to s5 vertebral spinous process .
a laminectomy was , then , performed and meninges were opened to expose the spinal cord . for stimulation purposes , a matrix electrode ( axonic , france ) was used to test different spatial configuration
. constituted by 8 contacts arranged in 4 rows of 2 poles , this array allowed test of several bipolar configurations ( fig .
once the spinal cord exposed , the electrode was inserted between spinal tissue and s1 vertebral body - segment involved in urinary and bowel function management according to literature  and bipolar stimulation were performed .
unfortunately , although intra - operative stimulation of the s1 right spinal root ( s1 ) did not elicit any bladder or rectal responses , proximity between this root and spinal tissue induced mechanical constraints , thereby necessitating its section for electrode placement at the s2 ventral level .
in addition to bladder and rectal pressures , a pair of needle electrode were inserted in the anal sphincter to monitor stimulation - induced emg responses .
these electrodes were connected to a differential emg amplifier system ( biopac system , usa ) and all signals ( both pressure and emg ) were acquired using a data acquisition card ( ni usb-6218 , national instrument , usa ) connected to a personal computer equipped with labview signal express software ( national instrument , usa ) for data display and recording . to focus current on target tissue and avoid excessive dissipation
, no pigs direct spinal stimulation was mentioned in literature , thus , particular attention was paid to bladder and bowel activation threshold determination .
the 12 current controlled channels stimulator - stimnd stimulation device developed within the team in cooperation with axonic company ( france ) - used during the experiment enables modulation of the delivered current in real time ( senis manager software , camin inria team , former demar team , montpellier , france ) .
this allowed a graduate increase in stimulation intensity ( 20a minimum steps ) and thus an identification of activation thresholds for all selected poles configurations ( fig .
4 ) . given the slow contraction dynamics of both bladder and rectum muscles , increases in intensity were performed in successive stimulation increments .
beyond its wide availability , the porcine model  especially for young individuals ( 3 to 4 months old ) - presents both urinary and spinal structures close to human ones . presenting a bladder capacity of approximately 600ml and an urethra of 8 cm long for 6 mm wide , 50 kg female individuals possess humanlike urinary characteristics . unlike in males , where urethra presents many convolutions ,
females urinary tract is straight and joins the vaginal wall to half the distance of the cervix making transurethral catheterization possible . from a neuro - anatomical point of view
although stopping at s2 vertebra , pigs spinal cord possesses similarities with human structures ( assumptions confirmed during surgery ) ; similarities concerning both support and neural frameworks ( vertebrae , meninges ) . due to these peculiarities , studies dedicated to visceral centers identification within pig spinal grey matter
have already been performed ( mainly in minipigs ) . by highlighting cell bodies from ( low ) l6 to ( up ) s2 ,
horseradish peroxidase injection indicated arrival of parasympathetic and somatic axons from bladder and external urethral sphincter ( striated ) to the lower portion of the spine .
the combination of these points seem to justify the use of this animal species in studies dedicated to spinal cord stimulation , particularly regarding bladder and bowel functions restoration . while regularly use in experimental context , the elaboration of an anesthetic protocol compatible with both pig model and spinal stimulation was challenging . given the identified constraints - 1 ) adapted to porcine model , 2 ) long term efficiency ( surgery + stimulation sessions ) , 3 ) spinal excitability conservation , 4 ) urinary and bowel functions preservation .
a combination of propofol and morphine ( at relatively low doses ) was retained to provide sufficient anesthesia
acute experiment was performed on one landras female pig ( 50 kg , 4 months old ) according to european ethical rules concerning animal experiments ( a2260 approval number ) .
after premedication ( intramuscular injection of ketamine and calmivet ) , the animal was placed under mechanical ventilation and an intravenous route was inserted at the ear vein for propofol and morphine delivery . to ensure animal welfare ,
after anesthesia induction , a transurethral catheter made of a silicon double - lumen bladder catheter was positioned and used to record lower urinary tract pressure ( i.e. bladder response ) .
similarly , a rectal probe was placed to monitor changes in rectal pressure . both pressures ( bladder and rectal )
were acquired using an acquisition system - developed within the team - triggered by stimulation .
lumbar and sacral vertebrae were highlighted and an incision was performed in order to reveal l6 to s5 vertebral spinous process .
a laminectomy was , then , performed and meninges were opened to expose the spinal cord .
for stimulation purposes , a matrix electrode ( axonic , france ) was used to test different spatial configuration . constituted by 8 contacts arranged in 4 rows of 2 poles , this array allowed test of several bipolar configurations ( fig .
once the spinal cord exposed , the electrode was inserted between spinal tissue and s1 vertebral body - segment involved in urinary and bowel function management according to literature  and bipolar stimulation were performed .
unfortunately , although intra - operative stimulation of the s1 right spinal root ( s1 ) did not elicit any bladder or rectal responses , proximity between this root and spinal tissue induced mechanical constraints , thereby necessitating its section for electrode placement at the s2 ventral level .
in addition to bladder and rectal pressures , a pair of needle electrode were inserted in the anal sphincter to monitor stimulation - induced emg responses .
these electrodes were connected to a differential emg amplifier system ( biopac system , usa ) and all signals ( both pressure and emg ) were acquired using a data acquisition card ( ni usb-6218 , national instrument , usa ) connected to a personal computer equipped with labview signal express software ( national instrument , usa ) for data display and recording .
to focus current on target tissue and avoid excessive dissipation an intradural approach was privileged . according to our knowledge
, no pigs direct spinal stimulation was mentioned in literature , thus , particular attention was paid to bladder and bowel activation threshold determination .
the 12 current controlled channels stimulator - stimnd stimulation device developed within the team in cooperation with axonic company ( france ) - used during the experiment enables modulation of the delivered current in real time ( senis manager software , camin inria team , former demar team , montpellier , france ) .
this allowed a graduate increase in stimulation intensity ( 20a minimum steps ) and thus an identification of activation thresholds for all selected poles configurations ( fig .
4 ) . given the slow contraction dynamics of both bladder and rectum muscles , increases in intensity were performed in successive stimulation increments .
a total of 9 stimulation sessions were performed for two different electrode positioning ( see fig . 3 and table 1 for details ) .
for each matrix placement , 4 monophasic stimulation sessions were devoted to study 2 distinct pairs of contacts , successively configured as anode / cathode and cathode / anode .
these pairs of poles were chosen because of their close contact with the ventral spinal cord . although still in process , raw data show , as desired , the possible induction of bladder ( see fig
. 5 for data corresponding to the 8th stimulation session ) and rectal ( fig . 6 , also recorded during the 8th stimulation ) high responses - up to trigger stool evacuation ( per - operating statement)- and suggest an interesting mapping implication of the cathode - anode distinction analysis .
the observed spinal structures and pressure dynamics ( a few tenth of cmh2o ) seemed in agreement with those observed in human intraoperatively , thus positioning pig model as a perfect trade - off between rodent and human and confirming , at least partially , porcine model validity .
even if data processing is , at present time , not finalized , the preliminary results confirmed , at least partially , the implemented methodology . although performed on young  presenting doubtlessly a partially immature nervous system- and nonspinalized individuals ( to avoid bias linked to this immaturity ) , the porcine model validity seems not have to be questioned .
similarly , the section of the s1 right spinal root can induce interrogation but its intraoperative monitoring seemed to exclude its involvement in lower visceral processes . from a technological point of view
, matrix electrode design constitutes the limiting point for further selectivity studies . nevertheless , the use of a powerful stimulation device enabling real time modulation of stimulation parameters allowed flexibility in threshold determination methodology .
the observation of significant visceral responses tends to confirm the potential of spinal cord stimulation on urinary and intestinal functions .
experiments whose data processing is expected for the next few weeks and results , we hope , ready for being presented and discussed during the ifess conference .
spinal cord injuries ( sci ) result in the loss of movement and sensory feedback as well as organs dysfunctions . 
 for example , nearly all sci subjects loose their bladder control and are prone to kidney failure if they do not proceed to intermittent ( self- ) catheterization . 
 electrical stimulation of the sacral spinal roots with an implantable neuroprosthesis is a promising approach , with commercialized products , to restore continence and control micturition . 
 however , many persons do not ask for this intervention since a surgical deafferentation is needed and the loss of sensory functions and reflexes become serious side effects of this procedure . 
 recent results renewed interest in spinal cord stimulation . 
 stimulation of existing pre - cabled neural networks involved in physiological processes regulation is suspected to enable synergic recruitment of spinal fibers . 
 the development of direct spinal stimulation strategies aiming at bladder and bowel functions restoration would therefore appear as a credible alternative to existent solutions . 
 however , a lack of suitable large animal model complicates these kinds of studies . in this article 
 , we propose a new animal model of spinal stimulation -pig- and will briefly introduce results from one first acute experimental validation session .