Repeated swim stress increases pain-induced expression of c-Fos in the rat lumbar cord.
We have previously demonstrated that repeated swim stress produces a long-lasting cutaneous hyperalgesia in rats. We have now looked at c-Fos expression in the spinal lumbar cord of male Sprague-Dawley rats subjected to 10-20 min daily sessions of forced swimming for 3 consecutive days. Control rats were subjected to sham swimming or were completely naive. Forty-eight hours later, nociception was assessed by recording for 90 min the nociceptive behavior evoked the injection of 1% formalin in the hind paw. Thirty min later, the rats' spinal cords were removed for c-Fos immunocytochemistry. Total pain scores were 45% higher in swim stressed rats compared to control animals due an increased nociceptive behavior during last 70 min of the recording period. In addition, the number of c-Fos-immunoreactive nuclei was 40% higher in the lumbar ipsilateral dorsal horn (L4-L5) of swim stressed rats than in controls, being the highest relative increase, relative to the control groups, observed in laminae III-IV, followed by laminae V-VI, with the smallest difference in laminae I-II. c-Fos expression in the contralateral dorsal horn was higher in swim stressed rats than in sham and nai;ve rats. In the absence of a nociceptive stimulus, a low level of c-Fos expression was observed mainly in laminae I, II, V, and VI, being higher in swim stressed rats than in sham rats. These findings suggest that repeated inescapable and uncontrollable stress could induce a sensitization and activation of sensory neurons at the spinal level.
Quintero
Luis
L
Section of Pharmacology, Institute of Clinical Investigation, School of Medicine, University of Zulia, Apartado Postal 1151, Maracaibo 4001-A, Venezuela.
Cuesta
Maria Cecilia
MC
Silva
Jose Antonio
JA
Arcaya
Jose Luis
JL
Pinerua-Suhaibar
Lorena
L
Maixner
William
W
Suarez-Roca
Heberto
H
D000818:Animals; D015415:Biomarkers / Q000032:analysis; D005786:Gene Expression Regulation / Q000502:physiology; D008297:Male; D010146:Pain / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry / Q000378:metabolism*; D013312:Stress, Physiological / Q000378:metabolism*; D013550:Swimming / Q000502:physiology*
D015415:Biomarkers; D016760:Proto-Oncogene Proteins c-fos