title: Comparison of cocaine reinforcement in lean and obese Zucker rats: Relative potency and reinstatement of extinguished operant responding.
abstract: Evidence indicates that obese individuals exhibit alterations in brain-reward function that are anatomically and functionally similar to what has been observed in drug addicts, which could theoretically make obese individuals vulnerable to drug abuse and drug abusers vulnerable to overeating. However, few studies have investigated the cross-generality of these phenotypes. We recently reported that the reinforcing effectiveness (i.e., value) of a fat was greater in obese Zucker rats than in their lean counterparts, but found no differences in the reinforcing effectiveness of cocaine between groups, suggesting psychostimulant reinforcement is similar in lean and obese Zucker rats. However, it is unknown if other aspects of reinforcement such as cocaine's potency as a reinforcer or its reinstating effects differ in lean and obese Zucker rats.
  
  
  
  The current study compared cocaine's potency as a reinforcer in lean and obese Zucker rats self-administering intravenous cocaine (0.06-1.0mg/kg/inj), and subsequently tested these subjects in cue- (light) and drug-primed (intraperitoneal cocaine; 10mg/kg) reinstatement of extinguished operant responding.
  
  
  
  All rats acquired cocaine self-administration and generated "inverted-U" dose-response functions. Following extinction of responding, the cue- and drug-primes increased lever-pressing in both groups (i.e., reinstatement). No significant differences in the reinforcing potency or reinstating effects of cocaine were observed as a function of obesity.
  
  
  
  These results, combined with our previous observations, demonstrate that cocaine's reinforcing effects are comparable in lean and obese Zucker rats and do not support the hypothesis that obesity is associated with an altered reinforcing effect of psychostimulants.
authors.affiliation: Dept. of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, MS 39216 United States; Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, The University of Mississippi Medical Center, Jackson, MS 39216, United States. Electronic address: s52drew@gmail.com.
authors.forename: E Andrew
authors.initials: EA
authors.lastname: Townsend
authors.affiliation: Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, The University of Mississippi Medical Center, Jackson, MS 39216, United States.
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Freeman
mesh_terms: D061605:Administration, Intravenous; D000818:Animals; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D003042:Cocaine / Q000008:administration & dosage*; D019970:Cocaine-Related Disorders; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D003463:Cues; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D058999:Drug-Seeking Behavior / Q000502:physiology; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology; D008297:Male; D009765:Obesity / Q000503:physiopathology / Q000523:psychology*; D011619:Psychotropic Drugs / Q000008:administration & dosage; D011924:Rats, Zucker; D012201:Reward; D012646:Self Administration; D013045:Species Specificity; D016019:Survival Analysis
chemical_list: D000697:Central Nervous System Stimulants; D018765:Dopamine Uptake Inhibitors; D011619:Psychotropic Drugs; D003042:Cocaine
keywords: Cocaine; Obesity; Self-administration; Zucker rat