title: Rat strain differences in nicotine self-administration using an unlimited access paradigm.
abstract: An effective animal model for elucidating the neurobiological basis of human smoking should simulate important aspects of this behavior. Therefore, a 23 h unlimited access nicotine self-administration model was used to compare inbred Lewis rats, which have a propensity to self-administer drugs of abuse, to inbred Fisher 344 rats and to the outbred Holtzman strain. Using this unlimited access model, 88.8% of Lewis vs. 57.1% of Holtzman rats achieved maintenance self-administration at a fixed ratio 1 (FR 1) at 0.03 mg/kg IV nicotine (P<0.05). In contrast, Fisher rats did not acquire self-administration under these conditions. Of the Lewis and Holtzman rats that achieved maintenance self-administration on an FR 1 schedule, a greater percentage of Lewis rats acquired nicotine self-administration at FR 2 (P<0.05) and progressed to FR 4 (P<0.05). Using naïve cohorts in a progressive dose reduction study, 83.3% of Lewis rats achieved maintenance at 0.0075 mg/kg nicotine as compared to 31.8% of Holtzman rats (P<0.05). Furthermore, only Lewis rats showed differences in active vs. inactive bar presses during maintenance at sequential dose reductions (P<0.001). Thus, in this unlimited access model, inbred Lewis rats will more reliably acquire nicotine self-administration than outbred Holtzman rats. Moreover, Lewis rats showed a significantly higher likelihood of continuing to self-administer nicotine in face of both increasing work requirements and decreasing drug reinforcement. Therefore, it is likely that Lewis rats would be genetically susceptible to nicotine addiction.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, 874 Union Avenue, Memphis, TN 38163, USA. vbrower@utmen.edu
authors.forename: Victoria G
authors.initials: VG
authors.lastname: Brower
authors.forename: Yitong
authors.initials: Y
authors.lastname: Fu
authors.forename: Shannon G
authors.initials: SG
authors.lastname: Matta
authors.forename: Burt M
authors.initials: BM
authors.lastname: Sharp
mesh_terms: D000818:Animals; D018678:Cholinergic Agents / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D012055:Reinforcement Schedule; D012646:Self Administration; D013045:Species Specificity
chemical_list: D018678:Cholinergic Agents; D009538:Nicotine