bne-123-1-156 - Behavioral Neuroscience 2009, Vol. 123, No....

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Strain Differences in Patterns of Drug-Intake During Prolonged Access to Cocaine Self-Administration Kevin B. Freeman The University of Mississippi Medical Center David N. Kearns, Stephen J. Kohut, and Anthony L. Riley American University The current study examined possible interactions between genetic factors and prolonged drug access by testing the Fischer (F344), Lewis (LEW), and Wistar rat strains in a prolonged access cocaine self- administration (SA) procedure. Before prolonged access, the strains did not differ in breakpoints for food or cocaine with progressive ratio (PR) testing. The LEW and Wistar rats acquired cocaine SA faster than the F344s. With prolonged access to cocaine SA, the LEW and Wistar rats showed comparable within-session patterns that were higher at the outset of each session and decreased to a stable baseline. Alternatively, the F344 rats began sessions with lower intake and increased their rate of intake during the session. The F344 and Wistar rats took more drug per session than the LEW rats but did not differ from each other. Following prolonged access, the strains did not differ in breakpoints for food, but the Wistar rats had higher breakpoints for cocaine than the F344 rats. Possible underpinnings for the observed strain differences are discussed. Keywords: Fischer, Lewis, Wistar, cocaine, self-administration Genetic factors appear to play a significant role in a person’s likelihood to abuse drugs (Goldman, Oroszi, & Ducci, 2005; Haile, Kosten, & Kosten, 2007; Uhl, 2004; Tsuang et al., 1996, 1998). However, the potential for human models in the characterization of these genetic contributions is largely limited to correlational anal- yses with genetically related users, a factor that complicates the assessment of other variables that could, by interacting with ge- netic factors, enhance the likelihood of abusing drugs. To that end, animal models have been developed to investigate the relative roles of genetics and other factors in the acquisition and mainte- nance of drug-taking behaviors. In this context, the Lewis (LEW) and Fischer (F344) rat strains have been used extensively, in part, because they exhibit a number of key baseline differences in the neuropharmacological substrates on which drugs of abuse are known to produce their effects (see levels of the D 2 receptor in the nucleus accumbens (NAc) than LEW rats, although there are no differences in levels of D 1 (Flores, of tyrosine hydroxylase, an enzyme necessary for the synthesis of dopamine and norepinephrine, are higher in the NAc and lower in the ventral tegmental area (VTA) in F344 rats relative to LEW rats (Beitner-Johnson, Guitart, & Nestler, 1991; Guitart, Beitner- Johnson, Marby, Kosten, & Nestler, 1992; response to chronic cocaine, F344 rats exhibit greater degrees of
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This note was uploaded on 10/16/2011 for the course PSYCH 101 taught by Professor Brown,b during the Spring '08 term at BYU.

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bne-123-1-156 - Behavioral Neuroscience 2009, Vol. 123, No....

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