Determination of Spinal Cord Monamines and Metabolites Using Three Micron Columns and Dual Electrochemical Detection

A model of experimental spinal cord trauma based on computer-controlled intervertebral distraction: characterization of graded injury

STUDY DESIGN

: A new model of experimental spinal cord injury is detailed based on the application of tensile (distraction) force to the vertebral column of the rat.

OBJECTIVES

: To develop an experimental model of graded spinal cord injury by application of tensile forces to the vertebral column.

SUMMARY OF BACKGROUND DATA

: Distraction is frequently an integral component of human spinal cord injury, but the acute application of tensile forces to the spinal cord has not been modeled rigorously.

METHODS

: A computer-controlled, motorized outrigger device was used to apply a longitudinal stretching force to sublaminar hooks oriented proximally at T9 and distally at T11. Distraction force was applied using a program that varied the length, speed, and duration of its distraction. A modified 14-point Tarlov score was used to establish the presence of hindlimb dysfunction. This score was correlated with acute changes in somatosensory-evoked potential amplitude, the comprehensive open-field test of locomotor function at 4 weeks, and postmortem measurements of serotonin content and metabolism in spinal cord rostral and distal to the site of injury.

RESULTS

: Of distraction parameters, only length of distraction correlated significantly with each outcome measure. For outcome measures, open-field test inventory and distal/proximal ratio of the spinal content of serotonin were correlated most closely with final Tarlov scores. Acute somatosensory-evoked potential amplitudes proved to be an excellent index of the acute injury but were poor measures of long-term outcome.

CONCLUSIONS

: Distraction-induced spinal cord injury was uniformly mild in rats with intact facet capsular ligaments, regardless of distraction parameters. Cutting the facet joint ligaments consistently generated outcome measures associated with mild, moderate, and severe spinal cord injury at 3-, 5-, and 7-mm distraction lengths, respectively.

The effect of mercury on the feeding behavior of fathead minnows (Pimephales promelas)

Fathead minnows (Pimephales promelas) were exposed to mercury (1.69, 6.79, and 13. 57 microg/L HgCl(2), 10 days exposure), and afterward their foraging ability was tested in a vegetated habitat for 7 days. Among the foraging metrics used were foraging efficiency, capture speed, and the ability to learn and retain information regarding habitat characteristics. In addition to behavioral tests, muscle tissue acetylcholinesterase activity and brain levels of several neurotransmitters were investigated. Comparisons with control fish and fish from the two highest exposure groups revealed consistent performance deficits in foraging efficiency and capture speed. However, no treatment effects on learning were detected, nor were differences in neurotransmitter levels detected. In determining the underlying proximate cause of the foraging deficits, it is believed that the greater pause time exhibited by treatment fish while foraging was the main cause of treatment differences. In the future, behavioral studies will continue to allow toxicity testing of environmentally relevant variables such as those used by behavioral ecologists.

Spinal cord injury produced by consistent mechanical displacement of the cord in rats: behavioral and histologic analysis

We examined the ability of an electromechanical device to produce consistent and incomplete thoracic (T9) spinal cord injuries in rats by brief displacement (Dspl) of the exposed dural surface. Open field walking, inclined plane, grid walking, and footprint analysis, and a determination of the percentage of tissue spared at the lesion center were used to assess chronic outcome (6 weeks postinjury). Laminectomy control animals showed no evidence of a functional deficit or histologic lesion. Complete spinal cord transections in normal rats and in a group of animals previously injured (1.1 mm Dspl) and allowed to recover resulted in complete loss of hindlimb function, demonstrating an important functional role for the remaining spared fibers at the lesion site. Consistent spinal cord displacements (0.80 mm, 0.95 mm, and 1.10 mm) resulted in behavioral groups with low outcome variability over a narrow range of incomplete recovery of neurologic function. Significant behavioral (open field walking, inclined plane, and grid walking) and histologic differences were found between the control and Dspl groups and between the 0.80 mm and 1.10 mm Dspl groups. Significant correlations were observed among the injury parameters, behavioral, and histologic scores. Open field walking and inclined plane performance were sensitive indicators of both the early and late phases of neurologic recovery. Grid walking was most useful in animals with small chronic residual deficits. The footprint analysis resulted in less significant correlations and differences between the behavioral groups than the other outcome measures. This may result from a relatively narrow range of sensitivity (open field walking scores between 3.3 and 4.0) and increased variability within the groups.

The serotonin antagonist mianserin improves functional recovery following experimental spinal trauma

The ability of the serotonin antagonist mianserin to improve neurological recovery after graded impact trauma to the thoracic region of the spinal cord was compared to that of cyproheptadine and ketanserin in pentobarbital-anesthetized rats. Spinal cord injury was produced at T-10 by the weight-drop method and confirmed by the disappearance of the somatosensory-evoked response during the subsequent 15 minutes. In all experiments, drug or vehicle treatments were randomly administered as a single intravenous bolus 15 minutes after injury. Functional outcome was blindly assessed for 2 weeks after injury using a modified Tarlov scale, and in some cases, the Rivlin-Tator angleboard test. The survival of descending raphe-spinal axons was determined by the measurement of serotonin in postmortem spinal tissues located above and below the site of injury. In separate acute experiments, the physiological and hemodynamic correlates of a 50 gm cm injury and either mianserin or vehicle injection were examined, as were the effects on serotonin content and metabolism in spinal tissues harvested 30 minutes after injury. All doses of mianserin were associated with some index of improved recovery following a 50 gm cm injury, with a 1-mg/kg dose being clearly superior. Both ketanserin (0.1 mg/kg) and cyproheptadine (2 mg/kg) displayed marginal therapeutic actions for 50 gm cm injuries. In acute studies, mianserin at 1 mg/kg was associated with the preservation of posttraumatic spinal cord blood flow at T-12 as well as a pronounced alteration in postmortem spinal serotonin content and metabolism, in contrast to vehicle control treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of a serotonin antagonist, opioid antagonist, and TRH analog for the acute treatment of experimental spinal trauma

The therapeutic efficacies of a serotonin antagonist (mianserin), an opioid antagonist (nalmefene), and a TRH analog (YM-14673) were compared in a well-characterized model of experimental spinal trauma in the rat. Injury was produced by the weight-drop method at T10 and confirmed by the disappearance of the somatosensory evoked response during the subsequent 15 minutes. Drug or vehicle treatments were administered randomly as a single intravenous bolus 15 minutes after injury. Functional outcome was blindly assessed for 2 weeks postinjury using a modified Tarlov scale and the Rivlin-Tator angleboard test. The survival of descending raphe-spinal axons was determined by measurement of serotonin in postmortem spinal tissues located above and below the injury, and histopathologic studies were carried out at the site of injury. All agents displayed similar and significant efficacies with respect to Tarlov and Rivlin-Tator measures of motor recovery and preservation of raphe-spinal fibers below the lesion site. In contrast, none of the agents were effective for preserving the central gray matter or myelin staining in the white matter in slices of tissue from the site of injury. Results are discussed in terms of the early treatment of spinal cord injury and future clinical trials.

Safety versus efficacy of spinal cord stimulation for the generation of motor-evoked potentials in the rat

The relative safety and efficacy of direct versus indirect methods of spinal cord stimulation for the production of descending motor-evoked responses was studied in pentobarbital-anesthetized rats (n = 39). Electrical stimuli were delivered for 1 h, either directly to the cord dorsum using silver ball electrodes or indirectly through jeweler's screws implanted in the intact laminae. Compound muscle action potentials (CMAPs) were recorded differentially in the quadriceps and evaluated for their morphology and reproducibility. The traumatic effects of stimulation were assessed using intraoperative somatosensory-evoked potentials, blinded neurological examinations for 2 weeks postoperatively, and histopathological and neurochemical analyses in postmortem spinal tissues. In separate experiments, the neural substrates of the muscle-evoked response to indirect cord stimulation were examined. Direct, epidural stimulation of the spinal cord at intensities sufficient to elicit reproducible CMAPs consistently resulted in mild behavioral deficits (13 of 18 animals) that were accompanied by postmortem changes in spinal histology and chemistry. Some of these behavioral deficits (5 of 13 animals) were resolved at 2 weeks. There was rarely an early sign of motor or sensory conduction derangement in these animals. In 2 animals with severe behavioral dysfunction, the somatosensory-evoked response was abolished immediately after spinal stimulation. However, CMAP responses were unaltered. Examination of the strength-duration relationship for the production of threshold responses to translaminar constant current stimulation, as well as experiments using selective transection of the dorsal columns, revealed the CMAP responses to be neurally mediated and conducted through the cord independent of the ascending sensory tracts that mediate the rat's somatosensory-evoked response. Data are discussed in terms of the potential experimental usefulness of CAMPs elicited by indirect dorsal spinal stimulation.

Serotonergic response to spinal distraction trauma in experimental scoliosis

The effects of distraction injury to the spinal cord on serotonin (5HT) content and metabolism in a rat model of scoliosis were studied. Previous studies in this laboratory (Salzman et al., 1987a) have identified the 5HT response as a major component of the posttraumatic progression of spinal injury after impact trauma in the rabbit. The present study was designed to determine the universality of this response by examining a different model of injury in a different species. The results demonstrate that distraction trauma in the rat, like impact injury in the rabbit, is associated with a rapid and robust increase in the local spinal cord content and metabolism of 5HT and a long-term depletion of 5HT below the site of injury. The roles of the blood platelet and the raphe-spinal tract in the acute response and the disruption of axoplasmic transport during the chronic phase of injury are discussed.

Anesthesia influences the outcome from experimental spinal cord injury

The effect of anesthesia upon the functional outcome after experimental spinal cord injury (SCI) was studied in 221 rats subjected to graded weight drop contusion in the thoracic cord. Neurologic function was assessed in a blinded fashion for one week after injury using a modification of the method of Tarlov. The post-mortem concentrations of serotonin and its metabolite were measured in injured and surrounding spinal tissues in a subset of animals in order to estimate the survival of descending long-tract axons. In initial studies using non-ventilated animals where body temperature was not controlled (n = 130), halothane anesthesia was associated with significantly better neurologic scores at all levels of injury (50, 100 and 250 g.cm) in comparison to pentobarbital. In a second experiment under these conditions (n = 53) the effect of halothane was observed after a 50 g.cm injury in comparison to both pentobarbital and nitrous oxide. Improved neurologic recovery was accompanied by the preservation of normal serotonin and metabolite concentrations in spinal tissue caudal to the site of injury. These values did not differ from those measured in sham-operated animals. Separate experiments (n = 12) revealed halothane's preservation of somatosensory-evoked responses during the early postinjury period in animals showing improved neurologic recovery. Subsequent experiments (n = 12) were performed to assess the effect of oxygen supplementation and the control of rectal temperature and a separate series of acute experiments (n = 14) examined arterial blood pressure responses to injury in halothane- and pentobarbital-anesthetized animals.(ABSTRACT TRUNCATED AT 250 WORDS)

A rapid and simple HPLC microassay for biogenic amines in discrete brain regions

A rapid microassay is described for the measurement of biogenic amines using an isocratic HPLC system with electrochemical detection. Catecholamines, indoleamines and their major metabolites were extracted with 150 microliters of perchloric acid from brain tissue punches (less than 250 micrograms) using a simple one-step sample preparation method. These compounds were separated on a short (80 mm) column with 3 microns particle size packing, and electrochemically detected within a total run time of less than 6 minutes. Detection limit sensitivity was approximately 2-5 pg. This method, detailed in an easy-to-follow description, reduces assay time, minimizes the possibility for errors, maximizes efficiency, and requires only standard HPLC equipment and supplies.

The somatosensory evoked potential predicts neurologic deficits and serotonergic pathochemistry after spinal distraction injury in experimental scoliosis

The validity of the somatosensory evoked potential as an intraoperative spinal cord monitor was evaluated in an experimental model of scoliosis in the rat and a Harrington distraction model of injury. Under these conditions, it was found that any change in latency or amplitude of the major negative wave above a certain level was a significant predictor of an adverse neurologic outcome. Changes in latency of 4% or greater and changes in amplitude of 50% or greater were unequivocal indicators of spinal cord injury. Postmortem analyses of the spinal neurotransmitter serotonin revealed that apparent false-positive results of the SEP were, in fact, true-positive results.

A simultaneous analytical method for catecholamines, indoleamines, and related compounds in 11 rat brain regions

A simple high-performance liquid chromatographic method that allows the determination of 10 biogenic amines and related compounds for crude brain extracts has been developed. The compounds that can be quantified comprise norepinephrine, epinephrine, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylglycol, dopamine, 5-hydroxyindole-3-acetic acid, homovanillic acid, 3-methoxytyramine, 5-hydroxytryptamine and tryptophan. The detection system involves a three electrode-coulometric determination followed by fluorometric determination. This method is highly selective and sensitive, and in the present study, the usefulness of this methodology was confirmed by applying it to the determination of the levels of these various substances in 11 rat brain regions.

Monoaminergic responses to spinal trauma. Participation of serotonin in posttraumatic progression of neural damage

The monoamines norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and their major metabolites were measured in the spinal cord of rabbits following laminectomy or impact injury to the thoracic cord. Samples were taken 30 minutes, 60 minutes, 4 hours, and 6 weeks after injury. Utilization ratios (metabolite/transmitter) were calculated from the data. Turnover rates for NE and DA were also calculated at 30 minutes using the alpha-methylparatyrosine method. Trauma resulted in rapid and sustained elevations in 5-HT concentration at and around the injury site. The catecholamines were depleted slightly at the injury site. Levels of 5-hydroxyindole-3-acetic acid were elevated at 30 minutes but fell to baseline by 4 hours, resulting in a decrease in the 5-HT utilization ratio. The utilization and turnover of NE was increased at the injury site, while DA function was not affected. The large short-term increase in 5-HT levels may have been due to extravasation of platelet 5-HT stores into spinal tissue, rather than due to changes in neuronal 5-HT metabolism. At 6 weeks after injury, each monoamine and metabolite appeared to accumulate in spinal cord tissue proximal to the insult. Distal to the injury, depleted amine stores displayed augmented utilization. The data are discussed in terms of a serotonergic hypothesis of the progression of neural damage after trauma, with the interaction of 5-HT with raphe-spinal nerve terminals as a principal event.

A semiautomated analysis method for catecholamines, indoleamines, and some prominent metabolites in microdissected regions of the nervous system: an isocratic HPLC technique employing coulometric detection and minimal sample preparation

The application of a commercially available coulometric electrochemical detector to the automated HPLC analysis of some monoamines and their metabolites in microdissected areas of the rat nervous system is described. Apart from the stability and high sensitivity of the system, other appealing features of the technique are the facile sample preparation and long-term sample storage characteristics which show minimal analyte degradation. Basal values of some regional monoamine and metabolite concentration are listed together with a brief appendix that serves as a user's guide to the operation and maintenance of the detection system.