title: Basal and touch-evoked fos-like immunoreactivity during experimental inflammation in the rat.
abstract: Fos-immunoreactivity can readily be induced in spinal cord neurones by noxious, but to a much more limited extent, by innocuous peripheral stimuli. The present study has investigated whether low intensity stimuli and electrical stimulation of A beta afferents elicit greater c-fos expression during the behavioural sensory hypersensitivity generated by experimental peripheral inflammation. We have examined the time-course of c-fos expression after inflammation produced by either an intra-plantar injection of the irritant turpentine oil or of complete Freund's adjuvant (CFA). In the former case, a significant initial expression in all dorsal horn laminae was followed by a gradual decrease, whereas after CFA injection, an initial expression limited to the superficial laminae subsequently extended into the deep laminae, with a decrease at 24 h and an increase in labelling at later times. Low intensity touch stimuli repeated for 10 min, when applied at 24 h and 48 h after CFA injection, elicited a significant increase in the number of Fos-immunoreactive neurons in both the superficial and deep laminae of the dorsal horn compared to non-inflamed animals. Electrical stimulation of the sciatic nerve 24 h post-CFA injection, at a strength sufficient only to activate A beta-afferents fibres (100 microA, 50 microseconds, 10 min), also elicited a significant increase in labelling relative to the same stimuli applied in control animals, especially in laminae V-VI. The present results demonstrate that low intensity cutaneous stimuli elicit a significantly greater increase in c-fos expression in dorsal horn neurons during peripheral inflammation and that A beta-afferent input contributes to this, a finding that may relate to the allodynia experienced during inflammation.
authors.affiliation: Department of Anatomy and Developmental Biology, University College London, UK.
authors.forename: Q P
authors.initials: QP
authors.lastname: Ma
authors.forename: C J
authors.initials: CJ
authors.lastname: Woolf
mesh_terms: D000344:Afferent Pathways / Q000503:physiopathology; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D004558:Electric Stimulation; D005528:Foot; D005620:Freund's Adjuvant; D007150:Immunohistochemistry; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism*; D007267:Injections; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds; D013997:Time Factors; D014110:Touch / Q000502:physiology*; D014425:Turpentine / Q000494:pharmacology
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D005620:Freund's Adjuvant; D014425:Turpentine