Opioid peptide messenger RNA expression is increased at spinal and supraspinal levels following excitotoxic spinal cord injury
Section snippets
Intraspinal microinjection
All experimental procedures were approved by the Institutional Animal Care and Use Committee of East Carolina University. The technique of intraspinal injection was similar to that described in previous reports.22., 53. In brief, male, Long–Evans rats (250–300 g) were anesthetized with a mixture of Ketamine, Acepromazine and Xylazine (0.80 ml/kg, i.p.). After the vertebral column was exposed, the spinous process and vertebral lamina were removed from one spinal level and the dura incised
Histology
The general characteristics of spinal cords following QUIS injections were similar to those described in previous reports.51., 53. Consistently, the greatest area of neuronal loss was seen in the intermediate gray matter of the cord (Fig. 1). The area of neuronal loss and extent of spinal cavitation was generally larger in animals with longer survival times. Although not specifically examined, Thionin staining also suggested the presence of inflammatory cells, reactive astrocytes and
Discussion
This study demonstrates that intraspinal injection of QUIS results in an increase in the expression of PPE mRNA and PPD mRNA in the spinal cord adjacent to the site of injection, as well as in cortical areas associated with pain processing, i.e. the cingulate cortex and the parietal cortex. This is the first evidence of changes in opioid peptide gene expression in cortical areas in response to SCI, and suggests that both spinal and supraspinal regulation of endogenous opioid peptide expression
Conclusions
The present study reveals an increase in both PPD and PPE mRNA expression in the spinal cord rostral and caudal to and ipsilateral and contralateral to the site of intraspinal QUIS injection at various time-points following injury. In addition, there is an increase in PPD expression in the parietal cortex and an increase in PPD expression in the cingulate cortex following intraspinal QUIS injection. These results further our understanding of the secondary events that occur following SCI,
Acknowledgements
This research was supported by DA03982. We thank Denise Mayer and G. W. Lanford for technical assistance.
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