Denervation of the rabbit hind limb studied by 31-phosphorus magnetic resonance spectroscopy

MR intensity measurements of nondenervated muscle in patients following severe forearm trauma

Fluid increases resulting in higher MRI signal intensities in T(2) -weighted and short tau inversion recovery (STIR) sequences can be used to diagnose nerve injury. By comparing the signal intensities over time, MRI may become a new method for monitoring the healing process. Muscle edema is assessed by comparing the signal intensity of affected muscle with that of nonaffected muscle. However, in severe forearm trauma, the signal of nondenervated muscle may also be increased by wound edema, thus masking the effect of denervation. Hence, the purpose of this study was to investigate the influence of wound edema on muscle signal intensity in 29 consecutive patients examined on a 1.5-T MRI scanner at 1, 3, 6, 9 and 12 months after severe forearm trauma. The long-term course of wound edema and the influence of wound distance were thus investigated using a standardized imaging, calibration and post-processing protocol. The signal intensities of nondenervated intrinsic hand muscles were measured in the affected and contralateral sides. Muscle signal intensities were increased on the trauma side at 1 and 3 months (18% and 7.4%, respectively; p < 0.001) and normalized thereafter. In the contralateral hand, no significant signal changes were seen. No relationship was found between wound distance and the severity of wound edema. This study shows that wound edema influences muscle signal intensity comparisons in patients with forearm trauma. When comparing denervated muscle with nondenervated muscle, an additional scan of the contralateral side is indicated during the first 6 months after trauma to assess the extent of wound edema. After 6 months, the ipsilateral side can be used for muscle signal intensity comparisons.

Metabolic imaging of atrophic muscle tissue using appropriate markers in 1H and 31P NMR spectroscopy

INTRODUCTION

The purpose of this feasibility study was to demonstrate non-invasive metabolic imaging of human muscular atrophy using significant changes of NMR signals that are related directly or indirectly to fiber necrosis.

METHODS

Single-voxel (1)H NMR spectroscopy and two-dimensional (31)P spectroscopic imaging on a 1.5-T whole-body scanner were used for in vivo mapping of areas of muscle damage in two cases of differently localized and pronounced atrophy. Spectral patterns affiliated with severe and intermediate stages of degeneration were compared to data of healthy control tissue to derive appropriate metabolic markers related to lipid infiltration or high-energy (31)P metabolism.

RESULTS

Reliable detection of atrophic tissue was achieved by the following parameters: (1) liposclerotic turnover is related to a drastic reduction in the water/lipid (1)H signal intensity ratio (up to a factor of 74 compared to adjacent healthy tissue); (2) the (31)P resonance of phosphocreatine (PCr) is an adequate marker for differentiation of intact myocells with high-energy metabolism from regions dominated by terminal fiber necrosis (PCr signal vanished nearly completely or intensity was reduced by a factor of 3 in affected muscles). Metabolic images based on this signal allowed accurate non-invasive localization of atrophic tissue.

CONCLUSION

The molecular information provided by NMR spectroscopy--previously only used with poor localization in atrophy studies--enables access to both the myocell-specific high-energy metabolism and the result of lipid infiltration allowing non-invasive mapping of degenerate tissue. The ability to investigate the results of these advanced levels of atrophy would also be useful for studies of more subtle degrees of denervation.

MR Imaging in the Diagnosis of Denervated and Reinnervated Skeletal Muscles: Experimental Study in Rats

PURPOSE

To describe the magnetic resonance (MR) imaging findings of denervation and reinnervation of skeletal muscles in rats.

MATERIALS AND METHODS

The posterior tibial nerve was transected in 48 rats (nerve section group) and was repaired just after transection in another 48 rats (nerve repair group). At 2, 4, 6, and 8 weeks after surgery, changes in the area and signal intensity of the gastrocnemius muscle on T1- and T2-weighted MR images in vivo (four rats in each group) and T1s and T2s were analyzed in vitro in both groups (20 rats each) and compared with electromyographic findings. Water volume content and extracellular fluid space of the muscle in vitro were also examined in both groups (24 rats each). Four rats were used as controls for in vitro analysis.

RESULTS

At T2-weighted MR imaging, the muscle showed continuously high signal intensity in the nerve section group. In the nerve repair group, the signal intensity was high until 4 weeks, when it recovered. Increases in signal intensity on T2-weighted MR images and T2s were seen in the nerve section group throughout the study period. In the nerve repair group, increased signal intensity on T2-weighted MR images was noted at 2 and 4 weeks and significantly returned to normal at 6 weeks (P <.014), just after the detection of the M wave at electromyography. T2 increased at 2 weeks, then decreased significantly at 4 weeks (P =.012). Extracellular fluid space significantly increased in the nerve section group at all measurement times and in the nerve repair group at 2 and 4 weeks, then it decreased after 6 weeks (P <.003), which is parallel to the change in signal intensity on T2-weighted MR images, although there was little change in total water volume content in either group.

CONCLUSION

Changes in signal intensity on T2-weighted MR images that are related to denervation may result from an increase of extracellular fluid space. MR imaging clearly demonstrates that changes in rat skeletal muscle are reversed when the nerve heals and reinnervation proceeds.

Investigation of skeletal muscle denervation and reinnervation using magnetic resonance spectroscopy

OBJECTIVE

To determine changes in skeletal muscle metabolism after nerve transection and repair and to correlate metabolic changes with functional recovery.

STUDY DESIGN AND SETTING

Male Wistar rats were divided into 6 experimental groups plus a control group. The posterior tibial nerve was transected and reapproximated. At varying times after surgery (1, 2, 4, 6, or 8 weeks) animals were sacrificed, the gastrocnemius muscle was harvested, and proton nuclear magnetic resonance (NMR) spectroscopy was performed. Functional recovery was measured using the sciatic function index.

RESULTS

Animals undergoing nerve repair all showed functional recovery whereas the nonrepaired nerve group did not. Concentration of glucose and lactate increased after denervation and then returned toward normal. Choline concentration decreased and then returned toward normal. In animals not undergoing nerve repair, the metabolic abnormalities persisted and showed no sign of recovery over the 8-week observation period.

CONCLUSIONS

1H NMR spectroscopy is a potentially useful tool to study changes in skeletal muscle metabolism after motor nerve injury.

SIGNIFICANCE

NMR spectroscopy is rapidly developing into a clinically useful tool. High-field magnets have improved resolution and data acquisition. Basic experiments, such as those described here, will help guide the use of NMR spectroscopy in clinical medicine and will also lead to a better understanding of basic mechanisms of nerve injury and repair.

Functional and histologic effects of a free nonvascularised muscle graft implanted into a reinnervated muscle after prolonged denervation

Striated muscle atrophy and degeneration, which increase with the delay of denervation, represent two of the main causes for poor recovery following delayed nerve repair. The present study, using a rat model, tests the hypothesis that an adjunction of small, free, nonvascularised muscle grafts of contralateral healthy triceps into a chronically denervated triceps improves muscle regeneration and recovery following sciatic nerve repair delayed for 3 months. Our experiments seem to show a relative increase in mechanical properties in animals in which free muscle graft into the triceps was performed 3 weeks following nerve repair. The improvement of the regenerative process of muscles which have suffered a long period of denervation should be considered as an additional therapeutic procedure in the case of late nerve repair.

Effects of denervation on energy metabolism of rat hindlimb muscles: application of (31)P-MRS and (19)F-MRS

We studied the effects of denervation on the energy metabolism and peripheral circulation dynamics of rat hindlimb muscles during and after exercise. The sciatic nerves of male Wistar rats were cut to produce denervation. Energy metabolism was assessed by phosphorus-31 magnetic resonance spectroscopy (MRS), and circulation by fluorine-19 MRS. Exercise of rat hindlimb muscles was induced by electrical stimulation at 40 Hz. The inorganic phosphate (Pi) / ¿Pi + phosphocreatine (PCr)¿ ratio, an indicator of the energy level, was 0.795 immediately after denervation. The ratios 4 and 8 weeks after denervation were 0.870 and 0.853, respectively. The intracellular pH during the 4 min after initiation of stimulation was significantly reduced 4 and 8 weeks after denervation compared with the value immediately after denervation. The signal strength of the research perfluoro-carbon (FC-43; perfluorotributylamine) a measure of circulation dynamics, increased to 167% in controls during exercise, but an increase of only 134% was seen in rats 8 weeks after denervation. These results showed that the energy supply and circulation dynamics in denervated atrophic muscles decreased during exercise compared with findings in control muscles.

Succinylcholine-induced fasciculations in denervated rat muscles as measured using 31P-NMR spectroscopy: the effect of pretreatment with dantrolene or vecuronium

BACKGROUND

We have previously demonstrated by 31P nuclear magnetic resonance (NMR) that succinylcholine (SCh) induces metabolic changes in denervated muscle. To specify those changes, we attempted to inhibit them using two different kinds of drugs, dantrolene and vecuronium.

METHODS

Three weeks after unilateral sciatic nerve section, 75 male Wistar rats were randomly assigned to one of the following 5 groups: (1) non-pretreated normal muscle group; (2) non-pretreated denervated muscle group; (3) denervated muscle group pretreated with a low dose of vecuronium (0.02 mg.kg(-1)); (4) denervated muscle group pretreated with a high dose of vecuronium (0.2 mg.kg(-1)); (5) denervated muscle group pretreated with dantrolene (2 mg.kg(-1)). The change of the inorganic phosphate/phosphocreatine (Pi/PCr) ratio of each muscle was measured by 31P-NMR before and after SCh (1 mg.kg(-1)) administration and the corresponding peak amplitude of the electromyograms (EMG) was determined.

RESULTS

The high dose of vecuronium totally inhibited SCh-induced fasciculation on EMG (100%-->2%). In this group, though the Pi/PCr ratio significantly increased 10 min after SCh, the peak after 5 min disappeared. The inhibition with dantrolene was about the same order of magnitude as with the low dose of vecuronium (35%:21%). However, the increase in the Pi/PCr only lasted about 10 min, in contrast to the other drugs.

CONCLUSION

Our findings indicate that the Pi/PCr increases 5 and 10 min after SCh, respectively, as a result of two different processes. The first peak is caused by an excessive energy consumption in response to excessive muscle contraction. This in turn triggers the second peak, caused by breakdown of glycogen, initiated by an increased Ca2+ concentration.

Time course of recovery from nerve injury in skeletal muscle: energy state and local circulation

This study examined the time course of recovery from nerve injury on energy state assessed by phosphorus-31 magnetic resonance spectroscopy and local circulation dynamics by fluorine-19 magnetic resonance spectroscopy in skeletal muscles of rats. The hindlimb muscles that had undergone unilateral sciatic nerve compression for 2 wk (CN) were compared with sham-operated (SO) muscles and with muscles that had the compression removed after 2 wk and were allowed to recover for 4 wk (R4) or for 6 wk (R6). The energy state and local circulation dynamics of CN muscles were less than those of SO muscles (P < 0.01). The energy state of R4 muscles remained at levels similar to CN muscles, whereas the local circulation dynamics improved but not back to SO values. In R6 muscles, both parameters returned to SO values. These results showed that the recovery processes of circulation precede those of energy state in skeletal muscles.

The effect of succinylcholine on energy metabolism studied by 31P-NMR spectroscopy in rat denervated skeletal muscle

BACKGROUND

The goals of this study were: (1) to demonstrate the differences of metabolic changes induced by succinylcholine (SCh) administration between normal and denervated muscle by 31P-NMR spectroscopy: (2) to determine whether three kinds of drugs (vecuronium, midazolam and magnesium sulfate) could prevent these metabolic changes.

METHODS

Following unilateral sciatic nerve section, 20 male Wistar rats were studied at three-week intervals. After SCh 1 mg.kg-1 was administered intravenously, the changes of the inorganic phosphate/phosphocreatine (Pi/PCr) ratio, the beta ATP/(PCr+Pi) ratio, and intracellular pH were measured by 31P-NMR both in normal and denervated hind limb muscles of 5 rats. The other 15 rats were allocated to the pretreatment groups by the following drugs: vecuronium 0.02 mg.kg-1, midazolam 0.1 mg.kg-1 and magnesium sulfate 60 mg.kg-1. After pretreatment 3 min before SCh administration, we measured the same parameters by 31P-NMR.

RESULTS

SCh administration did not change the Pi/PCr ratio in normal muscle, but significantly increased that in denervated muscle (P < 0.05). This increase of the Pi/PCr ratio was also observed in all pretreated groups but was minimal as compared with that in non-pretreatment denervated muscle.

CONCLUSION

These data suggested that SCh administration decreased the level of "energy reserve" in denervated muscle, and that this metabolic change was not totally inhibited by vecuronium, midazolam, or magnesium sulfate.

31P-magnetic resonance spectroscopy of the rabbit masseter muscle

Dynamic biochemical changes in the masseter muscle were studied in 14 New Zealand adult male rabbits by 31P-nuclear magnetic resonance (NMR) spectroscopy. NMR spectra were obtained during rest and electrical stimulation of the muscle in the anaesthetized animal at 33 recording sessions. Electrical stimulation was applied by a pair of copper wires placed separately with hypodermic needles into the muscle. NMR spectra were acquired with a 2 x 3 cm, double-turn, copper transmit/receive coil. Sixteen spectra were averaged over 30 s to obtain averaged spectra continuously during a 30-min recording. The spectra were processed automatically using a non-linear 'least-squares' fitting program on the spectrometer. A Lorentzian line shape was assumed for the peaks, and values of peak height, area and chemical shifts were generated. Each averaged spectrum consisted of five peaks: inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to ATP. Data were analysed as to absolute changes in Pi and PCr, in the ratio of Pi/PCr, and the shift of Pi to PCr to estimate pH. Several protocols were used in which ranges of frequency, intensity and duration of electrical stimulation were tested. The protocol for detailed studies involved stimulating the muscle twice at 5 Hz for 3 min separated by a 3-min rest period, then stimulating twice at 50 Hz for 3 min separated by a rest period. During contraction of the muscle, there was a significant increase in the Pi/PCr ratio (p < 0.05) as compared to the resting level. The ratio reached a plateau over a 3-min contraction using 5-Hz stimulation, then increased significantly more with the 50-Hz stimulation but decayed during the 3 min. Sustained stimulation with 50 Hz for 15-45 min evoked an initial sharp change in Pi/PCr, which then reached a steady plateau that remained over the entire stimulation. These findings indicate that the rabbit masseter muscle is relatively fatigue resistant in maintaining a steady-state equilibrium in the relation of Pi to PCr.