title: Behavioral evidence of thermal hyperalgesia and mechanical allodynia induced by intradermal cinnamaldehyde in rats.
abstract: TRPA1 agonists cinnamaldehyde (CA) and mustard oil (allyl isothiocyanate=AITC) induce heat hyperalgesia and mechanical allodynia in human skin, and sensitize responses of spinal and trigeminal dorsal horn neurons to noxious skin heating in rats. TRPA1 is also implicated in cold nociception. We presently used behavioral methods to investigate if CA affects sensitivity to thermal and mechanical stimuli in rats. Unilateral intraplantar injection of CA (5-20%) induced a significant, concentration-dependent reduction in latency for ipsilateral paw withdrawal from a noxious heat stimulus, peaking (61.7% of pre-injection baseline) by 30 min with partial recovery at 120 min. The highest dose of CA also significantly reduced the contralateral paw withdrawal latency. CA significantly reduced mechanical withdrawal thresholds of the injected paw that peaked sooner (3 min) and was more profound (44.4% of baseline), with no effect contralaterally. Bilateral intraplantar injections of CA resulted in a significant cold hyperalgesia (cold plate test) and a weak enhancement of innocuous cold avoidance (thermal preference test). The data are consistent with roles for TRPA1 in thermal (hot and cold) hyperalgesia and mechanical allodynia.
authors.affiliation: Department of Neurophysiology, Beritashvili Inst. Physiology, Tbilisi, Georgia, USA.
authors.forename: Merab G
authors.initials: MG
authors.lastname: Tsagareli
authors.forename: Nana
authors.initials: N
authors.lastname: Tsiklauri
authors.forename: Karen L
authors.initials: KL
authors.lastname: Zanotto
authors.forename: Mirela Iodi
authors.initials: MI
authors.lastname: Carstens
authors.forename: Amanda H
authors.initials: AH
authors.lastname: Klein
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Sawyer
authors.forename: Gulnazi
authors.initials: G
authors.lastname: Gurtskaia
authors.forename: Elene
authors.initials: E
authors.lastname: Abzianidze
authors.forename: E
authors.initials: E
authors.lastname: Carstens
mesh_terms: D000171:Acrolein / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D017487:Ankyrins; D001522:Behavior, Animal / Q000187:drug effects*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D003080:Cold Temperature; D006358:Hot Temperature; D006930:Hyperalgesia / Q000523:psychology*; D007271:Injections, Intradermal; D008297:Male; D010146:Pain / Q000523:psychology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D014110:Touch
chemical_list: D017487:Ankyrins; D002120:Calcium Channel Agonists; D015220:Calcium Channels; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; C480976:Trpa1 protein, rat; D000171:Acrolein; C012843:cinnamaldehyde