Abstract
Drug addiction is often associated with impulsivity and altered behavioural responses to both primary and conditioned rewards. Here we investigated whether selectively bred alcohol-preferring (P) and alcohol-nonpreferring (NP) rats show differential levels of impulsivity and conditioned behavioural responses to food incentives. P and NP rats were assessed for impulsivity in the 5-choice serial reaction time task (5-CSRTT), a widely used translational task in humans and other animals, as well as Pavlovian conditioned approach to measure sign- and goal-tracking behaviour. Drug-naïve P and NP rats showed similar levels of impulsivity on the 5-CSRTT, assessed by the number of premature, anticipatory responses, even when the waiting interval to respond was increased. However, unlike NP rats, P rats were faster to enter the food magazine and spent more time in this area. In addition, P rats showed higher levels of goal-tracking responses than NP rats, as measured by the number of magazine nose-pokes during the presentation of a food conditioned stimulus. By contrast, NP showed higher levels of sign-tracking behaviour than P rats. Following a 4-week exposure to intermittent alcohol we confirmed that P rats had a marked preference for, and consumed more alcohol than, NP rats, but were not more impulsive when re-tested in the 5-CSRTT. These findings indicate that high alcohol preferring and drinking P rats are neither intrinsically impulsive nor do they exhibit impulsivity after exposure to alcohol. However, P rats do show increased goal-directed behaviour to food incentives and this may be associated with their strong preference for alcohol.
Highlights
Impulsivity, the tendency to exhibit unduly premature or risky behaviour, has been associated with addiction to several drugs of abuse including alcohol but the directionality of thisPLOS ONE | DOI:10.1371/journal.pone.0131016 June 22, 2015Goal Tracking and Alcohol PreferenceGSK, Cambridge Cognition, Lilly, Lundbeck and Merck
P rats showed faster response latencies to collect food reward, spent more time nose-poking in the food magazine in the 5-choice serial reaction time task (5-CSRTT), and showed increased goal-tracking responses in an appetitive Pavlovian conditioning task compared with NP rats
These findings demonstrate that vulnerability to alcohol intake is not predicted by increased levels of motor impulsivity on the 5-CSRTT, unlike psychostimulants [13,28] but instead by increased goal-directed behaviour to food incentives
Summary
Impulsivity, the tendency to exhibit unduly premature or risky behaviour, has been associated with addiction to several drugs of abuse including alcohol but the directionality of this. We initially hypothesised that P rats might show high levels of impulsivity in the 5-choice serial reaction time task (5-CSRTT) prior to any opportunity to drink alcohol, in comparison with NP rats This hypothesis was based on the association between alcohol abuse and heightened impulsivity in humans [6,7], and the finding that impulsivity in the 5-CSRTT is positively correlated with ethanol drinking in several strains of mice [8,9,10] and an analogous task in humans [8,11]. To further characterise P and NP rats we investigated whether they were differentially impaired in the acquisition of appetitive Pavlovian conditioning since this has been shown to predict measures of stimulant self-administration and the incentive salience of drug-associated stimuli [22,23] In this task, some subjects will approach the location in which the reward is delivered, showing a goal-tracking response while others develop an approach response towards the CS predictive of reward delivery and interact with it (sign-trackers). In the present study we assessed P and NP rats in an intermittent 2-bottle choice drinking procedure prior to re-testing in the 5-CSRTT, in order both to validate and replicate the drinking phenotype observed in these lines in our laboratory and to investigate if chronic access to alcohol in the P rats would impact on our measure of impulsivity
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