title: Effects of acute stressors on itch- and pain-related behaviors in rats.
abstract: Many acute stressors reduce pain, a phenomenon called stress-induced antinociception (SIA). Stress also is associated with increased scratching in chronic itch conditions. We investigated effects of acute stressors on facial itch and pain using a recently introduced rat model. Under baseline (no-swim) conditions, intradermal (id) cheek microinjection of the pruritogen serotonin (5-HT) selectively elicited hindlimb scratch bouts, whereas the algogen mustard oil (allyl isothiocyanate [AITC]) selectively elicited ipsilateral forepaw swipes, directed to the cheek injection site. To test effects of swim stress, rats received id cheek microinjection of 5-HT (1%), AITC (10%), or vehicle, and were then subjected to one of the following swim conditions: (1) weak SIA (W-SIA), (2) naltrexone-sensitive SIA (intermediate or I-SIA), or (3) naltrexone-insensitive SIA (strong or S-SIA). After the swim, we recorded the number of hindlimb scratch bouts and forelimb swipes directed to the cheek injection site, as well as facial grooming by both forepaws. Under S-SIA, AITC-evoked swiping and 5-HT-evoked scratching were both reduced. I-SIA reduced AITC-evoked swiping with no effect on 5-HT-evoked scratching. Facial grooming immediately post-swim was suppressed by S-SIA, but not I- or W-SIA. W-SIA tended to equalize scratching and swiping elicited by 5-HT and AITC compared with no-swim controls, suggesting altered itch and pain processing. Exercise (wheel-running), novelty, cold exposure, and fear (shaker table), key components of swim stress, differentially affected tail-flick latencies and 5-HT-evoked swiping and scratching behavior. Thus, itch and pain can be simultaneously suppressed by a combination of acute stress-related factors via an opioid-independent mechanism.
authors: Department of Neurobiology, Physiology and Behavior, University of California-Davis, Davis, CA, USA.
authors: Jessica Marie
authors: JM
authors: Spradley
authors: Auva
authors: A
authors: Davoodi
authors: Mirela Iodi
authors: MI
authors: Carstens
authors: Earl
authors: E
authors: Carstens
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D006120:Grooming / Q000502:physiology; D007271:Injections, Intradermal; D007509:Irritants / Q000008:administration & dosage; D017879:Isothiocyanates / Q000008:administration & dosage; D008297:Male; D009271:Naltrexone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D059225:Nociception / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D011537:Pruritus / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000008:administration & dosage; D013315:Stress, Psychological / Q000503:physiopathology*
chemical_list: D007509:Irritants; D017879:Isothiocyanates; D009292:Narcotic Antagonists; D012701:Serotonin; D009271:Naltrexone; C004471:allyl isothiocyanate