Nicotine self-administration in rats on a progressive ratio schedule of reinforcement |
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Authors: | E C Donny A R Caggiula M M Mielke S Booth M A Gharib A Hoffman V Maldovan C Shupenko S E McCallum |
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Institution: | (1) Department of Psychology, 412 Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260, USA e-mail: Tonypsy@vms.cis.pitt.edu, Tel.: +1-412-6244561, Fax: +1-412-6244428, US;(2) University of Pittsburgh, Cancer Institute, Pittsburgh, PA 15260, USA, US |
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Abstract: | Rationale: 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.
Received: 28 December 1998 / Final version: 14 June 1999 |
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Keywords: | Nicotine Self-administration Progressive ratio Rodents Reinforcement Extinction |
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