title: Nicotine self-administration in rats on a progressive ratio schedule of reinforcement.
abstract: BACKGROUND
  Robust intravenous (i.v.) nicotine self-administration (SA) in rats has been reported by several laboratories, including our own, using fixed ratio (FR) schedules of reinforcement. Studies on other drugs of abuse, however, suggest that progressive ratio (PR) schedules may provide additional information not gained using FR schedules.
  
  
  OBJECTIVE
  Here, we attempt to establish and characterize nicotine SA on a PR.
  
  
  METHODS
  One study allowed animals to acquire SA on a FR at four doses of nicotine (0.02, 0.03, 0.06, 0. 09 mg/kg) before being switched to a PR. A second study examined extinction by saline substitution or pretreatment with the nicotinic antagonist, mecamylamine, including a preliminary analysis into the role of secondary reinforcers in the extinction process.
  
  
  RESULTS
  SA of nicotine on a PR was stable across repeated sessions. The number of infusions earned on a PR correlated with infusion rate on a FR; however, a large portion of the variance in SA on a PR could not be accounted for by infusion rate on a FR. Infusions on a PR increased across the same range of doses that produced a decrease in the infusion rate on a FR. Extinction of responding occurred after saline substitution or pretreatment with mecamylamine, and animals re-acquired when nicotine was again available without pretreatment. The presence of drug-paired stimuli appeared to lengthen the extinction process.
  
  
  CONCLUSIONS
  Nicotine supports stable SA on a PR. Since PR and FR schedules may measure different aspects of nicotine reinforcement, PR schedules may be valuable in further characterizing group and individual differences in nicotine reinforcement.
authors.affiliation: Department of Psychology, 412 Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Donny
authors.forename: A R
authors.initials: AR
authors.lastname: Caggiula
authors.forename: M M
authors.initials: MM
authors.lastname: Mielke
authors.forename: S
authors.initials: S
authors.lastname: Booth
authors.forename: M A
authors.initials: MA
authors.lastname: Gharib
authors.forename: A
authors.initials: A
authors.lastname: Hoffman
authors.forename: V
authors.initials: V
authors.lastname: Maldovan
authors.forename: C
authors.initials: C
authors.lastname: Shupenko
authors.forename: S E
authors.initials: SE
authors.lastname: McCallum
mesh_terms: D000818:Animals; D005108:Extinction, Psychological / Q000187:drug effects*; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009538:Nicotine / Q000008:administration & dosage*; D018722:Nicotinic Agonists / Q000008:administration & dosage*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012646:Self Administration
chemical_list: D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D008464:Mecamylamine; D009538:Nicotine