title: Hedonic and motivational responses to food reward are unchanged in rats with neuropathic pain.
abstract: Rewards influence responses to acute painful stimuli, but the relationship of chronic pain to hedonic or motivational aspects of reward is not well understood. We independently evaluated hedonic qualities of sweet or bitter tastants and motivation to seek food reward in rats with experimental neuropathic pain induced by L5/6 spinal nerve ligation. Hedonic response was measured by implantation of intraoral catheters to allow passive delivery of liquid solutions, and "liking/disliking" responses were scored according to a facial reactivity scale. Spinal nerve ligation rats did not differ from controls in either "liking" or "disliking" reactions to intraoral sucrose or quinine, respectively, at postsurgery day 21, suggesting no differences in perceived hedonic value of sweet or bitter tastants. To assess possible motivational deficits during acute and chronic pain, we used fixed- and progressive-ratio response paradigms of sucrose pellet presentation in rats with transient inflammatory or chronic neuropathic pain. Assessment of response acquisition and break points under the progressive ratio schedule revealed no differences between sham and spinal nerve ligation rats for up to 120 days after injury. However, rats with inflammation showed decrements in lever pressing and break points on days 1 and 2 after complete Freund adjuvant injection that normalized by day 4, consistent with transient ongoing pain. Thus, although acute ongoing inflammatory pain may transiently reduce reward motivation, we did not detect influences of chronic neuropathic pain on hedonic or motivational responses to food rewards. Adaptations that allow normal reward responding to food regardless of chronic pain may be of evolutionary benefit to promote survival.
authors.affiliation: Department of Pharmacology, University of Arizona, Tucson, AZ, USA.|Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: Alec
authors.initials: A
authors.lastname: Okun
authors.affiliation: Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: McKinzie
authors.affiliation: Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Witkin
authors.affiliation: Department of Pharmacology, University of Arizona, Tucson, AZ, USA.
authors.forename: Bethany
authors.initials: B
authors.lastname: Remeniuk
authors.affiliation: Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: Omar
authors.initials: O
authors.lastname: Husein
authors.affiliation: Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Gleason
authors.affiliation: Department of Pharmacology, University of Arizona, Tucson, AZ, USA.
authors.forename: Janice
authors.initials: J
authors.lastname: Oyarzo
authors.affiliation: Department of Pharmacology, University of Arizona, Tucson, AZ, USA.
authors.forename: Edita
authors.initials: E
authors.lastname: Navratilova
authors.affiliation: Department of Psychology, University of Arizona, Tucson, AZ, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: McElroy
authors.affiliation: Department of Psychology, University of Arizona, Tucson, AZ, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Cowen
authors.affiliation: Neuroscience Discovery Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN, USA.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Kennedy
authors.affiliation: Department of Pharmacology, University of Arizona, Tucson, AZ, USA.
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D005108:Extinction, Psychological / Q000502:physiology; D005502:Food; D005620:Freund's Adjuvant / Q000633:toxicity; D008297:Male; D009042:Motivation / Q000502:physiology*; D009437:Neuralgia / Q000209:etiology / Q000503:physiopathology* / Q000523:psychology*; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D013127:Spinal Nerves / Q000293:injuries; D013395:Sucrose / Q000008:administration & dosage; D013649:Taste / Q000187:drug effects; D013997:Time Factors
chemical_list: D013395:Sucrose; D005620:Freund's Adjuvant