title: C-fiber mechanical stimulus-response functions are different in inflammatory versus neuropathic hyperalgesia in the rat.
abstract: To compare changes in primary afferent nociceptors associated with inflammatory versus neuropathic hyperalgesia, we evaluated in rats the mechanical stimulus-response function of isolated C-fiber primary afferent nociceptors to 10-s stimuli of differing mechanical strengths; 36 fibers after prostaglandin E2, 28 fibers from streptozotocin-diabetic rats and 46 fibers from control, non-treated rats were examined. Intradermal injection of prostaglandin E2 decreased mechanical threshold of 19 of 35 (54%) C-fibers. C-fibers that demonstrated a decrease in the mechanical threshold after prostaglandin E2 also showed an increased response to suprathreshold stimuli. The increase in the number of action potentials in prostaglandin E2-treated C-fibers was greatest at lower magnitude stimulus intensities, i.e. near threshold; the response to higher magnitude stimulus intensities was unchanged from that in control animals. In contrast, an increase in the number of action potentials seen in C-fibers from streptozotocin-diabetic rats was not seen at low-magnitude stimulus intensities; rather, a pronounced increase in response was seen at high-magnitude stimulus intensities. The von Frey hair thresholds for C-fibers in streptozotocin-diabetic rats were not different from those in control C-fibers. These data suggest that the changes in mechanical stimulus-response function of C-fibers are different in inflammatory compared to neuropathic mechanical hyperalgesia. These differences may underlie some of the differences in clinical features between inflammatory and neuropathic hyperalgesias.
authors.affiliation: Department of Anatomy, University of California, San Francisco 94143-0452, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Ahlgren
authors.forename: J F
authors.initials: JF
authors.lastname: Wang
authors.forename: J D
authors.initials: JD
authors.lastname: Levine
mesh_terms: D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000150:complications* / Q000503:physiopathology; D003929:Diabetic Neuropathies / Q000150:complications*; D015232:Dinoprostone / Q000494:pharmacology*; D006930:Hyperalgesia / Q000209:etiology* / Q000503:physiopathology*; D007249:Inflammation / Q000139:chemically induced / Q000150:complications; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects* / Q000502:physiology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values
chemical_list: D015232:Dinoprostone