bne-123-1-165

bne-123-1-165 - Behavioral Neuroscience 2009, Vol. 123, No....

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Demand for Food and Cocaine in Fischer and Lewis Rats Chesley J. Christensen, Stephen J. Kohut, Samantha Handler, Alan Silberberg, and Anthony L. Riley American University Fischer and Lewis rat strains often serve as animal vulnerability models for drug abuse and addiction. When these strains respond for drugs of abuse, several measures, including total drug intake, response rate and progressive-ratio breakpoints, have been reported to be strain-dependent, a result suggesting genetic differences in drug reactivity and vulnerability. The present study extends these strain compar- isons to a previously untested measure—demand analysis. In Experiment 1, four Fischer and four Lewis rats earned their daily food ration by lever pressing under a fixed-ratio schedule, the size of which was increased every three sessions from 3 to 1,000 in logarithmic steps. Consumption was plotted as a function replicated Experiment 1 except that different rats were used, and cocaine reinforced lever pressing. A between-experiment comparison showed a commodity-by-strain interaction: Fischer rats defended consump- tion with greater vigor when cocaine served as the reinforcer than did Lewis rats; for food, this relation was reversed. However, for both strains, defense of consumption of food exceeded that of cocaine. Keywords: exponential model of demand, cocaine, food, Fischer rats, Lewis rats There is evidence that genetic factors may predispose humans to drug addiction (Goldman, Oroszi, & Ducci, 2005; Haile, Kosten, & Kosten, 2007; Tsuang et al., 1996, 1998; Uhl, 2004). For example, Tsuang et al. (1998) found that an identical twin is more likely to be a drug abuser if the other twin is an abuser than a fraternal twin whose proband is an abuser. Experimental corrob- oration of this hypothesis comes from animal research that com- pares the effects of drugs of abuse in Fischer (F344) and Lewis (LEW) rats. These strains have been used as models of drug abuse in part because the physiological differences observed are often in Ambrosio, 2002). For example, F344 rats, when compared to LEW rats, exhibit greater hypothalamic-pituitary-adrenal axis activity (Dhabar, McEwen, & Spencer, 1993; Grakalic, Schindler, Bau- mann, Rice, & Riley, 2006; Kosten & Ambrosio, 2002; Stor et al., 2000), higher levels of D 2 receptors in the nucleus accumbens levels of tyrosine hydroxylase, a precursor to dopamine, in the ventral tegmental area, and higher levels of tyrosine hydroxylase in 1991). In addition, chronic cocaine results in greater adaptation of the mesolimbic protein levels in F344 rats than in LEW rats, indicating that these structures may be less resilient to neurophar- macological changes in response to chronic drug treatment in F344
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bne-123-1-165 - Behavioral Neuroscience 2009, Vol. 123, No....

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