title: Diet-induced obesity and diet-resistant rats: differences in the rewarding and anorectic effects of D-amphetamine.
abstract: BACKGROUND
  Obesity is a leading public health problem worldwide. Multiple lines of evidence associate deficits in the brain reward circuit with obesity.
  
  
  OBJECTIVE
  Whether alterations in brain reward sensitivity precede or are a consequence of obesity is unknown. This study aimed to investigate both innate and obesity-induced differences in the sensitivity to the effects of an indirect dopaminergic agonist.
  
  
  METHODS
  Rats genetically prone to diet-induced obesity (DIO) and their counterpart diet-resistant (DR) were fed a chow diet, and their response to D-amphetamine on intracranial self-stimulation and food intake were assessed. The same variables were then evaluated after exposing the rats to a high-fat diet, after DIO rats selectively developed obesity. Finally, gene expression levels of dopamine receptors 1 and 2 as well as tyrosine hydroxylase were measured in reward-related brain regions.
  
  
  RESULTS
  In a pre-obesity state, DIO rats showed innate decreased sensitivity to the reward-enhancing and anorectic effects of D-amphetamine, as compared to DR rats. In a diet-induced obese state, the insensitivity to the potentiating effects of D-amphetamine on intracranial self-stimulation (ICSS) threshold persisted and became more marked in DIO rats, while the anorectic effects were comparable between genotypes. Finally, innate and obesity-induced differences in the gene expression of dopamine receptors were observed.
  
  
  CONCLUSIONS
  Our results demonstrate that brain reward deficits antedate the development of obesity and worsen after obesity is fully developed, suggesting that these alterations represent vulnerability factors for its development. Moreover, our data suggests that the reward-enhancing and anorectic effects of D-amphetamine are dissociable in the context of obesity.
authors.affiliation: Laboratory of Addictive Disorders, Departments of Pharmacology and Psychiatry, Boston University School of Medicine, 72 E Concord St, R-612 or R-618, Boston, MA, 02118, USA.
authors.forename: Marta
authors.initials: M
authors.lastname: Valenza
authors.forename: Luca
authors.initials: L
authors.lastname: Steardo
authors.forename: Pietro
authors.initials: P
authors.lastname: Cottone
authors.forename: Valentina
authors.initials: V
authors.lastname: Sabino
mesh_terms: D000273:Adipose Tissue / Q000187:drug effects; D000818:Animals; D001067:Appetite Depressants / Q000494:pharmacology*; D001823:Body Composition / Q000187:drug effects; D003913:Dextroamphetamine / Q000494:pharmacology*; D004032:Diet; D059305:Diet, High-Fat; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D005260:Female; D015870:Gene Expression; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects; D009765:Obesity / Q000209:etiology* / Q000523:psychology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000096:biosynthesis / Q000235:genetics; D017448:Receptors, Dopamine D2 / Q000096:biosynthesis / Q000235:genetics; D012201:Reward; D012653:Self Stimulation; D014446:Tyrosine 3-Monooxygenase / Q000096:biosynthesis / Q000235:genetics; D017557:Ventral Tegmental Area / Q000187:drug effects
chemical_list: D001067:Appetite Depressants; D018765:Dopamine Uptake Inhibitors; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D014446:Tyrosine 3-Monooxygenase; D003913:Dextroamphetamine