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Broad opioid antagonism amplifies disruption of locomotor function following therapy-like hindlimb stretching in spinal cord injured rats
Study design Preclinical pilot study. Objectives To test the hypothesis that spinal opioidergic circuitry contributes to muscle stretch-induced locomotor deficits. Setting Kentucky Spinal Cord Injury Research Center, Louisville, KY, USA. Methods A pilot study with eight female Sprague-Dawley rats th...
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Published in: | Spinal cord 2022-04, Vol.60 (4), p.312-319 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Study design
Preclinical pilot study.
Objectives
To test the hypothesis that spinal opioidergic circuitry contributes to muscle stretch-induced locomotor deficits.
Setting
Kentucky Spinal Cord Injury Research Center, Louisville, KY, USA.
Methods
A pilot study with eight female Sprague-Dawley rats that received 25 g-cm T10 contusion injuries and recovered for 5 weeks. Rats were divided into two groups with one group receiving subcutaneous injections of naltrexone dissolved in saline (15 mg/kg) or an equal volume of saline. Each group received a daily 24-minute stretching protocol during weeks 6, 8, and 11 post-injury. Locomotor function was assessed throughout using the BBB Open Field Locomotor Scale.
Results
Consistent with previous findings, stretching reduced locomotor function in both naltrexone and saline groups. However, the loss of locomotor function appeared earlier in the naltrexone group. Animals in both groups had a similar rate of recovery following the termination of stretching. Interestingly, the administration of naltrexone did not influence acute thermal cutaneous nociceptive responses as measured by a tail-flick assay but caused a significant increase in spasticity following stretch.
Conclusions
The results of this study suggest that the endogenous opioid system plays a role in modulating the negative impact of muscle stretch on spinal cord motor circuitry that is vulnerable due to loss of descending input. The observed actions of the broad-spectrum opioid antagonist naltrexone imply that pharmaceuticals targeting the endogenous opioid system post-SCI may have unintended consequences. |
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ISSN: | 1362-4393 1476-5624 |
DOI: | 10.1038/s41393-021-00705-6 |