The experimental contusion injury of the spinal cord in sheep

The Translational Benefits of Sheep as Large Animal Models of Human Neurological Disorders

The past two decades have seen a considerable rise in the use of sheep to model human neurological disorders. While each animal model has its merits, sheep have many advantages over small animal models when it comes to studies on the brain. In particular, sheep have brains more comparable in size and structure to the human brain. They also have much longer life spans and are docile animals, making them useful for a wide range of in vivo studies. Sheep are amenable to regular blood and cerebrospinal fluid sampling which aids in biomarker discovery and monitoring of treatment efficacy. Several neurological diseases have been found to occur naturally in sheep, however sheep can also be genetically engineered or experimentally manipulated to recapitulate disease or injury. Many of these types of sheep models are currently being used for pre-clinical therapeutic trials, particularly gene therapy, with studies from several models culminating in potential treatments moving into clinical trials. This review will provide an overview of the benefits of using sheep to model neurological conditions, and highlight naturally occurring and experimentally induced sheep models that have demonstrated translational validity.

An ovine model of spinal cord injury

OBJECTIVE

To develop a large animal model of spinal cord injury (SCI), for use in translational studies of spinal cord stimulation (SCS) in the treatment of spasticity. We seek to establish thresholds for the SCS parameters associated with reduction of post-SCI spasticity in the pelvic limbs, with implications for patients.

STUDY DESIGN

The weight-drop method was used to create a moderate SCI in adult sheep, leading to mild spasticity in the pelvic limbs. Electrodes for electromyography (EMG) and an epidural spinal cord stimulator were then implanted. Behavioral and electrophysiological data were taken during treadmill ambulation in six animals, and in one animal with and without SCS at 0.1, 0.3, 0.5, and 0.9 V.

SETTING

All surgical procedures were carried out at the University of Iowa. The gait measurements were made at Iowa State University.

MATERIAL AND METHODS

Nine adult female sheep were used in these institutionally approved protocols. Six of them were trained in treadmill ambulation prior to SCI surgeries, and underwent gait analysis pre- and post-SCI. Stretch reflex and H-reflex measurements were also made in conscious animals.

RESULTS

Gait analysis revealed repeatable quantitative differences in 20% of the key kinematic parameters of the sheep, pre- and post-SCI. Hock joint angular velocity increased toward the normal pre-injury baseline in the animal with SCS at 0.9 V.

CONCLUSION

The ovine model is workable as a large animal surrogate suitable for translational studies of novel SCS therapies aimed at relieving spasticity in patients with SCI.

A computerized system for the application of Basso, Beattie and Bresnahan scale in Wistar rats

OBJECTIVES

To develop and test a computer program to assist researchers in assigning scores in the application of the Basso, Beattie and Bresnahan (BBB) scale and to compare these scores when doing so in free, targeted and automated computer-assisted modes.

METHOD

To test the program, the participants used the Impactor methodology recommended by the New York University (USA), in which 12 Wistar rats submitted to spinal cord injury were filmed on the 28(th) day after the injury. Eight researchers from the Laboratory of Medical Investigation, Faculdade de Medicina da Universidade de São Paulo, SP, Brazil took part in the study. The two heads of the laboratory, with 15 years of experience in the application of the scale, were considered the gold standard.

RESULTS

The results of the scale application were not significantly different in relation to the gold standard, considering the mean of the evaluators in each method: free, targeted and automated form (with the help of the computer).

CONCLUSIONS

The application of the BBB scale in the automated mode, using the computer program, did not present any difference in relation to the gold standard for all the evaluators. Level of Evidence II, Diagnostic Studies.

The pressure distribution of cerebrospinal fluid responds to residual compression and decompression in an animal model of acute spinal cord injury

STUDY DESIGN

In vivo large animal (pig) model study of cerebrospinal fluid (CSF) pressures after acute experimental spinal cord injury (SCI).

OBJECTIVE

To determine how the CSF pressure (CSFP) and CSF pulse pressure amplitude (CSFPPA) cranial and caudal to the injury site change after an acute SCI with subsequent thecal occlusion and decompression.

SUMMARY OF BACKGROUND DATA

Lowering intrathecal pressure via CSF drainage is currently instituted to prevent ischemia-induced SCI during thoracoabdominal aortic aneurysm surgery and was recently investigated as a potential intervention for acute traumatic SCI. However, in SCI patients, persistent extradural compression commonly occludes the subarachnoid space. This may generate a CSFP differential across the injury site, which cannot be appreciated with lumbar catheter pressure measurements.

METHODS

Anesthetized pigs were subjected to an acute contusive SCI at T11 and 8 hours of sustained compression (n = 12), or sham surgery (n = 2). CSFP was measured cranial and caudal to the injury site, using miniature pressure transducers, during compression and for 6 hours after decompression.

RESULTS

The cranial-caudal CSFP differential increased (mean, 0.39 mm Hg/h), predominantly due to increased cranial pressure. On decompression, cranial CSFP decreased (mean, -1.16 mm Hg) and caudal CSFP increased (mean, 0.65 mm Hg). The CSFP differential did not change significantly after decompression. Cranial CSFPPA was greater than caudal CSFPPA, but this differential did not change during compression. On decompression, the caudal CSFPPA increased in some but not all animals.

CONCLUSION

Although extradural compression exists at the site of injury, lumbar CSFP may not accurately indicate CSFP cranial to the injury. Decompression may provide immediate, though perhaps partial, resolution of the pressure differential. CSFPPA was not a consistent indicator of decompression in this animal model. These findings may have implications for the design of future clinical protocols in which CSFP is monitored after acute SCI.

Development of a large-animal model to measure dynamic cerebrospinal fluid pressure during spinal cord injury

Object

Spinal cord injury (SCI) often results in considerable permanent neurological impairment, and unfortunately, the successful translation of effective treatments from laboratory models to human patients is lacking. This may be partially attributed to differences in anatomy, physiology, and scale between humans and rodent models. One potentially important difference between the rodent and human spinal cord is the presence of a significant CSF volume within the intrathecal space around the human cord. While the CSF may “cushion” the spinal cord, pressure waves within the CSF at the time of injury may contribute to the extent and severity of the primary injury. The objective of this study was to develop a model of contusion SCI in a miniature pig and establish the feasibility of measuring spinal CSF pressure during injury.

Methods

A custom weight-drop device was used to apply thoracic contusion SCI to 17 Yucatan miniature pigs. Impact load and velocity were measured. Using fiber optic pressure transducers implanted in the thecal sac, CSF pressures resulting from 2 injury severities (caused by 50-g and 100-g weights released from a 50-cm height) were measured.

Results

The median peak impact loads were 54 N and 132 N for the 50-g and 100-g injuries, respectively. At a nominal 100 mm from the injury epicenter, the authors observed a small negative pressure peak (median −4.6 mm Hg [cranial] and −5.8 mm Hg [caudal] for 50 g; −27.6 mm Hg [cranial] and −27.2 mm Hg [caudal] for 100 g) followed by a larger positive pressure peak (median 110.5 mm Hg [cranial] and 77.1 mm Hg [caudal] for 50 g; 88.4 mm Hg [cranial] and 67.2 mm Hg [caudal] for 100 g) relative to the preinjury pressure. There were no significant differences in peak pressure between the 2 injury severities or the caudal and cranial transducer locations.

Conclusions

A new model of contusion SCI was developed to measure spinal CSF pressures during the SCI event. The results suggest that the Yucatan miniature pig is an appropriate model for studying CSF, spinal cord, and dura interactions during injury. With further development and characterization it may be an appropriate in vivo largeanimal model of SCI to answer questions regarding pathological changes, therapeutic safety, or treatment efficacy, particularly where humanlike dimensions and physiology are important.

Experimental animal models of neurogenic bladder dysfunction

Neurogenic bladder is related to various types of neurogenic disease and injury, including cerebrovascular accident, brain tumor, spinal cord injury, and Parkinson's disease. The results of urodynamic study show different types of detrusor and sphincter function. According to these urodynamic results, the physician decides on a treatment plan, such as anticholinergics or alpha-blockers. In the development of a new medication, it is necessary to test the medication's efficacy and toxicity by using a laboratory animal. The proper laboratory animal should have several characteristics. These are biological similarity to humans, a short generation period, and an environment that is easy to control. We describe the development of laboratory animals for the study of neurogenic bladder by decerebration, stroke, and spinal cord injury.

Animal models used in spinal cord regeneration research

STUDY DESIGN

A literature review was conducted.

OBJECTIVES

To review animal models and injury paradigms used in the neurobiologic study of spinal cord regeneration, and to assist the spinal clinician in interpreting the many encouraging reports of potential therapies emerging from basic science laboratories.

SUMMARY OF BACKGROUND DATA

An enormous amount of interest in spinal cord regeneration research has been generated within the past 20 years with the hope that experimental therapies will become available for individuals with spinal cord injuries. The use of various animal models in the laboratory setting has been critical to the development of such experimental therapies.

METHODS

A literature review was conducted.

RESULTS

Experimental interventions in animal models of spinal cord injury were evaluated both anatomically and functionally. Anatomic assessments use various histologic techniques and frequently include the use of anterograde and retrograde axonal tracers. Functional assessments can be performed neurophysiologically or by the observation of motor and sensory performance on a number of different tests. Sharp spinal cord injury paradigms in which the cord is completely or partially transected are useful for assessing axonal regeneration anatomically. In contrast, blunt injury models in which the cord is compressed or contused more accurately mimic the typical human injury and provide a good setting for the study of secondary pathophysiologic processes immediately after injury.

CONCLUSIONS

Animal models will continue to play a critical role in the development of experimental therapies for spinal cord injuries. Both sharp and blunt spinal cord injury paradigms have unique characteristics that make them useful in addressing slightly different neurobiologic problems.

Traumatic spinal cord injury produced by controlled contusion in mouse

Previous work from this laboratory has described a rat spinal cord injury (SCI) model in which the mid-thoracic spinal cord is subjected to a single rapid and calibrated displacement at the site of a dorsal laminectomy. Injury is initiated at the tip of a vertical shaft driven by an electromagnetic shaker. Transducers arranged in series with the shaft record the patterns of displacement and force during the impact sequence. In the present study, this device and the relevant surgical procedures were adapted to produce a spinal contusion injury model in laboratory mice. The signal generator for the injury device has also been converted to a computer-controlled interface to permit extension of the model to other laboratories. Mice were subjected to SCI across a range of severities by varying the amplitude of displacement and the magnitude of measured preload force on the dural surface. A moderate injury produced by displacement of 0.5 mm over 25 msec resulted in initial paralysis and recovery of locomotion with chronic deficits in hindlimb function. The magnitude of the peak force, impulse, power, and energy generated at impact were correlated with behavioral outcome at 1 day postinjury, while peak displacement and impulse were the best predictors of behavioral outcome at 28 days postinjury. The shape of the force recording proved to be a highly sensitive measure of subtle variations in the spinal compartment that were otherwise difficult to detect in this small species. The results demonstrate that the electromagnetic spinal cord injury device (ESCID) can be used to produce a well-controlled contusion injury in mice. The unique features of controlled displacement and monitoring of the biomechanical parameters at the time of impact provide advantages of this model for reducing outcome variability. Use of this model in mice with naturally occurring and genetically engineered mutations will facilitate understanding of the molecular mechanisms of pathophysiology following traumatic spinal cord injury.

A sheep model for continuous intrathecal infusion of test substances

Pharmaceutical research and new drug development rely extensively on animal research. The development of novel agents for intrathecal administration requires preclinical studies of toxic effects in an animal model. We have developed a nonrodent animal model for this purpose. Our sheep model: 1 Is an animal whose neural axis is similar to the human 2 Allows for the percutaneous placement of intrathecal catheters 3 Has minimal possibilities of infection because the infusion system is totally implanted 4 Provides continuous infusion of the test agent 5 Generates behavioral, motor, neurological and histopathological information so that safety guidelines can be established prior to preclinical studies.

A mouse model of graded contusive spinal cord injury

A mouse model of spinal cord injury (SCI) could further increase our basic understanding of the mechanisms involved in injury and recovery by taking advantage of naturally-occurring and genetically engineered mutations available in mice. We have, therefore, investigated whether methods used to produce and evaluate graded experimental contusive SCI in the rat could be modified to produce a mouse model of traumatic SCI. C57BL6 mice were anesthetized with 2,2,2-tribromoethanol and a restricted laminectomy performed at the T8 vertebral level. The spinal column was stabilized and a weight drop technique used to produce contusive injury. Experimental groups were distinguished by the amount of weight or the height from which the weight was dropped onto an impounder resting on the dura (1 g x 2.5 cm, 2 g x 2.5 cm, 3 g x 2.5 cm, and 3 g x 5.0 cm). Functional deficits over time were examined up to 28 days after SCI by testing hindlimb reflex responses and coordinated motor function. Chronic lesion histopathology was evaluated by light microscopy and analyzed with morphometric techniques. All groups demonstrated profound functional deficits after injury followed by gradual recovery. Recovery correlated with the weight dropped and percent of white matter spared that was 41.3+/-6.0% (mean +/- SEM) in the 2 g x 2.5 cm group and 24.3+/-5.0% in the 3 g x 2.5 cm group. A replicate experiment confirmed reproducibility of the injury. This new mouse model of contusive SCI could pave the way for in vivo studies of the effect of genetic modifications produced by specific mutations on injury and recovery processes after spinal cord trauma.

Methylprednisolone or naloxone treatment after acute spinal cord injury: 1-year follow-up data. Results of the second National Acute Spinal Cord Injury Study

The 1-year follow-up data of a multicenter randomized controlled trial of methylprednisolone (30 mg/kg bolus and 5.4 mg/kg/hr for 23 hours) or naloxone (5.4 mg/kg bolus and 4.0 mg/kg/hr for 23 hours) treatment for acute spinal cord injury are reported and compared with placebo results. In patients treated with methylprednisolone within 8 hours of injury, increased recovery of neurological function was seen at 6 weeks and at 6 months and continued to be observed 1 year after injury. For motor function, this difference was statistically significant (p = 0.030), and was found in patients with total sensory and motor loss in the emergency room (p = 0.019) and in those with some preservation of motor and sensory function (p = 0.024). Naloxone-treated patients did not show significantly greater recovery. Patients treated after 8 hours of injury recovered less motor function if receiving methylprednisolone (p = 0.08) or naloxone (p = 0.10) as compared with those given placebo. Complication and mortality rates were similar in either group of treated patients as compared with the placebo group. The authors conclude that treatment with the study dose of methylprednisolone is indicated for acute spinal cord trauma, but only if it can be started within 8 hours of injury.

The use of hyperbaric oxygen to modify the effects of recent contusion injury to the spinal cord

Studies on the experimental spinal contusion injury in animals confirm that posttraumatic ischemia contributes to central cystic necrosis or fibrosis occurring at the level of the spinal cord lesion. Hyperbaric oxygen (HBO) modifies the degree and extent of the pathology in the spinal cord of the experimental animals. HBO has been used for 45 patients with recent spinal cord injuries. The extent of recovery in 27 patients with upper motor neuron lesions treated with adequate HBO is reported. Fifteen of the 27 patients had useful functional recovery.

Therapeutic effects of disulfiram in spinal cord contusion of rabbits

The purpose of the present investigation was to evaluate methods to prevent the development of the immediate and delayed tissue damage in the injured spinal cord by early drug (disulfiram) interference with the molecular mechanism of tissue injury. The edematous inflammation as well as change in the levels and distribution of metallic ions like calcium following spinal cord contusion is known to contribute to the destructive process. A contusion model was applied in the spinal cord of rabbits using a pneumatic impactor. The effect of the systemically administered drug, disulfiram, in the traumatized spinal cord was determined by assaying the tissue water and Ca2+ contents at different locations of the spinal cord. A significant increase in the levels of the assayed parameters at the injured site of the spinal cord is markedly reduced by the pretreatment with disulfiram.

Methylprednisolone and neurological function 1 year after spinal cord injury. Results of the National Acute Spinal Cord Injury Study

A multi-center double-blind randomized clinical trial was conducted by the National Acute Spinal Cord Injury Study Group to examine the efficacy of high-dose methylprednisolone (1000-mg bolus and 1000 mg daily thereafter for 10 days) compared with that of a standard dose (100-mg bolus and 100 mg daily for 10 days). No significant difference was observed in neurological recovery of motor function, pinprick response, or touch sensation 1 year after injury between the two treatment groups, after adjustment for other potentially confounding factors. Analyses that specifically took into account the patients' total steroid dose and relative weight confirmed the lack of a steroid treatment effect. The case fatality rate was 10.7% during the 1st year after injury, and this was not associated with the steroid treatment protocol or the patient's gender. Deaths did occur significantly more frequently among patients who were completely (15.3%) and partially (8.6%) plegic than among those who were paretic (2.5%, p = 0.0005), and among patients aged 50 years or older (38.6%, p = 0.0001).

Monoamine and tissue fluid levels in contused spinal cord of sheep

Methods are described for the determination of sheep spinal cord tissue fluid content and norepinephrine, serotonin, and dopamine concentrations after experimental injury. The amount of tissue fluid varied in different regions of sheep spinal cord following injury. Norepinephrine and serotonin wet weight concentrations were corrected for this variation in tissue fluid. Corrected norepinephrine wet weight cord concentrations did not change up to 3 hr after injury. Levels of serotonin at 60 min after injury were similar to controls. Dopamine was not detected in sheep spinal cord. alpha-Methyl tyrosine significantly reduced fluid in the spinal cord at 75 min after injury.

A study of the effects of hyperbaric oxygen on the experimental spinal cord injury

The degree of motor recovery in sheep with a controlled contusion to the thoracic spinal cord is compared with the recovery in sheep treated with hyperbaric oxygen and confirms the results of a preliminary series previously reported. The degree of central cord cystic necrosis and degeneration in the surrounding white matter is compared in the control and treated animals. The improvement in motor recovery and in the degree of cord degeneration after treatment with hyperbaric oxygen suggests that ischaemia plays a significant role in the experimental animal with a contusion injury to the spinal cord.