Fos expression in the medullary dorsal horn of the rat after chronic constriction injury to the infraorbital nerve.
Chronic constriction injury to the rat's infraorbital nerve (IoN-CCI) induces asymmetric face grooming directed to the injured nerve territory and, beginning at 7-12 days postoperative, hyperresponsiveness to mechanical stimulation in this territory (B.P. Vos, A.M. Strassman, and R.J. Maciewicz, 1994, J. Neurosci. 14:2708-2723). To examine central mechanisms involved in these behavioral alterations, changes in nonevoked and mechanical stimulation-evoked fos-like immunoreactivity (fos-LI) following IoN-CCI were quantified in the medullary dorsal horn. Following the appearance of hyperresponsiveness in IoN-CCI rats, experimental and matched sham-operated rats were anesthetized with urethane and received either no stimulation or repeated stimulation with either a 2- or 15-g von Frey hair applied to the hairy skin between vibrissae B3-4/C3-4 on the operated side. Unstimulated IoN-CCI rats had increased fos-LI in laminae I-IV of the ipsilateral medullary dorsal horn. In both groups, mechanical stimulation produced a distinct pattern of fos-LI in the ipsilateral medullary dorsal horn, the quantity of which was related to stimulus intensity. For both stimulus intensities, the total amount and the rostrocaudal spread of evoked fos-LI were significantly larger in IoN-CCI rats. In IoN-CCI rats, stimulation-evoked increases in fos-LI were proportionally larger in laminae I-II than in III-IV. This laminar effect was also present in sham-operated rats but only for 15-g stimulation. Neither condition nor stimulus intensity affected fos-LI in the contralateral medullary dorsal horn. Positive correlations were found between the behavioral parameters of increased trigeminal nociceptive activity and the total amount of fos-LI in the ipsilateral medullary dorsal horn. The results demonstrate that IoN-CCI induces significant alterations in the central processing of afferent signals, which may underlie behavioral manifestations of increased nociceptive activity.
Vos
B P
BP
Department of Neurology, Massachusetts General Hospital, Boston.
Strassman
A M
AM
D000704:Analysis of Variance; D000818:Animals; D002908:Chronic Disease; D003251:Constriction, Pathologic; D006120:Grooming / Q000502:physiology*; D008297:Male; D009419:Nerve Tissue Proteins / Q000032:analysis*; D009437:Neuralgia / Q000209:etiology / Q000523:psychology*; D009915:Orbit / Q000294:innervation*; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry*; D013314:Stress, Mechanical; D014276:Trigeminal Nerve / Q000503:physiopathology
D009419:Nerve Tissue Proteins; D016760:Proto-Oncogene Proteins c-fos