Dynamic variations of c-Fos expression in the spinal cord exposed to intramuscular hypertonic saline-induced muscle nociception.
BACKGROUND
Numerous studies focus on intramuscular (i.m.) injection of hypertonic saline-induced muscle pain and nociception. The spatio-temporal characteristics and dynamic variation of spinal neuronal activities elicited by i.m. hypertonic saline remain unknown.


METHODS
The spatio-temporal variations of c-Fos expression in the lumbar spinal cord exposed to i.m. injection of 5.8% saline were investigated in male rats.


RESULTS
After a unilateral i.m. 5.8% saline injection, c-Fos expression in dorsal horn of spinal L4-6 segments was significantly enhanced bilaterally (p < 0.05 and p < 0.001). These 5.8% saline-induced bilateral spinal Fos expression occurred rapidly 0.5 h following the i.m. injection, and reached the peak levels within 1 h, which declined gradually and returned to the control levels within 8 h. Compared with intact rats without i.m. insults, no significant influence of the spinalization on spinal c-Fos expression was found. However, the 5.8% saline-induced increases in Fos expression in intact and spinalized rats differed significantly. During muscle nociception, the c-Fos expression within the superficial layer (laminae I-II) and the deep layer (laminae V-VI) in spinalized rats were significantly lower and higher than that of in intact rats (p < 0.05 and p < 0.001). Fentanyl (20 μg/kg, intraperitoneal) completely attenuated the 5.8% saline intramuscularly induced increases in c-Fos expression in laminae III-VI (p < 0.001), but not laminae I-II.


CONCLUSIONS
It is suggested that spinal nociceptive neuronal activities in superficial and deep layers may differently be modulated by endogenous descending facilitation and inhibition, respectively.
Center for Biomedical Research on Pain (CBRP), College of Medicine, Xi'an Jiaotong University, China.
Y-K
YK
Chen
J
J
Lei
L
L
Jin
Y-X
YX
Tan
H-J
HJ
You
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D005283:Fentanyl / Q000494:pharmacology; D007839:Functional Laterality / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects; D016762:Genes, fos / Q000187:drug effects / Q000502:physiology*; D007150:Immunohistochemistry; D007273:Injections, Intramuscular; D008297:Male; D059352:Musculoskeletal Pain / Q000139:chemically induced* / Q000235:genetics*; D059225:Nociception / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*
D000701:Analgesics, Opioid; D012462:Saline Solution, Hypertonic; D005283:Fentanyl