title: Altered sucrose self-administration following injection of melanocortin receptor agonists and antagonists into the ventral tegmental area.
abstract: OBJECTIVE
  Alpha-melanocyte stimulating hormone (αMSH) and agouti-related protein (AgRP) are antagonistic neuropeptides that play an important role in the control of feeding and body weight through their central actions on the melanocortin-3 and melanocortin-4 receptors. Increasing evidence indicates that αMSH and AgRP can interact with the mesolimbic dopamine system to regulate feeding as well as other behaviors. For example, we have shown previously that injection of melanocortin receptor agonists and antagonists into the ventral tegmental area (VTA) alters both normal home-cage feeding and the intake of sucrose solutions, but it remains unknown whether αMSH and AgRP can also act in the VTA to affect reward-related feeding.
  
  
  METHODS
  We tested whether injection of the melanocortin receptor agonist, MTII, or the melanocortin receptor antagonist, SHU9119, directly into the VTA affected operant responding maintained by sucrose pellets in self-administration assays.
  
  
  RESULTS
  Injection of MTII into the VTA decreased operant responding maintained by sucrose pellets on both fixed ratio and progressive ratio schedules of reinforcement, whereas SHU9119 increased operant responding under fixed ratio, but not progressive ratio schedules. MTII also increased and SHU9119 decreased 24-h home-cage food intake.
  
  
  CONCLUSIONS
  This study demonstrates that αMSH and AgRP act in the VTA to affect sucrose self-administration. Thus, it adds critical information to the growing literature showing that in addition to their well-characterized role in controlling "need-based" feeding, αMSH and AgRP can also act on the mesolimbic dopamine system to control reward-related behavior.
authors.affiliation: Department of Biology, Georgia State University, Atlanta, GA, 30303, USA.
authors.forename: Laranci
authors.initials: L
authors.lastname: Shanmugarajah
authors.affiliation: Department of Biology, Georgia State University, Atlanta, GA, 30303, USA.
authors.forename: Anna I
authors.initials: AI
authors.lastname: Dunigan
authors.affiliation: Department of Biology, Georgia State University, Atlanta, GA, 30303, USA.|Neuroscience Institute, Georgia State University, Atlanta, GA, 30303, USA.
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Frantz
authors.affiliation: Department of Biology, Georgia State University, Atlanta, GA, 30303, USA. aroseberry@gsu.edu.|Neuroscience Institute, Georgia State University, Atlanta, GA, 30303, USA. aroseberry@gsu.edu.|Center for Obesity Reversal, State University, Atlanta, GA, 30303, USA. aroseberry@gsu.edu.
authors.forename: Aaron G
authors.initials: AG
authors.lastname: Roseberry
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D004435:Eating / Q000187:drug effects / Q000502:physiology; D007276:Injections, Intraventricular; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D044105:Receptor, Melanocortin, Type 4 / Q000819:agonists* / Q000037:antagonists & inhibitors*; D012201:Reward; D012646:Self Administration; D013395:Sucrose / Q000008:administration & dosage*; D017557:Ventral Tegmental Area / Q000187:drug effects* / Q000378:metabolism; D000521:alpha-MSH / Q000008:administration & dosage / Q000031:analogs & derivatives
chemical_list: D044105:Receptor, Melanocortin, Type 4; C105974:acetyl-norleucyl(4)-(aspartyl(5)-histidyl(6)-phenylalanyl(7)-arginyl(8)-tryptophyl(9)-lysyl(10))cyclo-alpha-MSH(4-10)amide; C103272:SHU 9119; D013395:Sucrose; D000521:alpha-MSH; D009074:Melanocyte-Stimulating Hormones
keywords: Dopamine; Feeding; MC3R; Melanocortin; Self-administration; VTA; αMSH