Conditioned Stimulus Form Does Not Explain Failures to See Pavlovian-Instrumental-Transfer With Ethanol-Paired Conditioned Stimuli

Conditioned stimulus effects on paired or alternative reinforcement depend on presentation duration: Implications for conceptualizations of craving

Conditioned stimuli (CS) associated with alcohol ingestion are thought to play a role in relapse by producing a craving that in turn increases motivation to drink which increases ethanol-seeking and disrupts other ongoing behavior. Alternatively, such CS may provide information indicating a likely increase in the density of the paired unconditioned stimulus and simultaneously elicit behavior that may be incompatible with other ongoing behavior, i.e., approach toward the CS. To explore these possibilities, rats were trained to respond for ethanol or food in two different components of the same session after which a light above the ethanol-lever was lighted twice during each component and each light presentation was followed by ethanol delivery. The duration of this CS was 10 s initially and then increased to 30 s, then to 100 s, and finally returned to 30 s. The change in responding for ethanol or food was compared to a matched period immediately preceding CS presentation. The CS presentation increased responding to ethanol, and this effect increases with longer CS presentations. In contrast, the CS presentation decreased responding to food, and this effect decreases with longer CS presentations. These results appear to support the informational account of CS action rather than simply a change in the motivation to seek and consume ethanol. This suggests that craving as it is commonly understood likely represents multiple behavioral processes, not simply increased desire for alcohol and that reports of craving likely reflect labeling based upon past experiences rather than a cause of future drug-taking.

Under the influence of the environment: Children's responding invigorated and biased by predictive cues

Cues that signal motivationally significant consequences can elevate responding and bias choice. A task known as Pavlovian-to-instrumental transfer (PIT) has been used to assess the influence of these cues on independently trained responses and to study the effect of drug-related and food-related cues on behavior in adult populations, but it has not yet been employed in children. This study aimed to develop a simple computer task to study PIT in children. Participants, aged 7-11 years, observed a screen in which different pairings of distinct cartoon images and specific outcomes were presented (images of foods and drinks in Experiment 1 and images of pets in Experiment 2). After this, the participants pressed two keys, each consistently reinforced with one of the two outcomes. Finally, the children pressed both keys in the absence of any outcome, and each cartoon image was presented periodically so that the effect of these cues on behavior could be measured. Experiment 1 showed that the cartoons' presentations biased responding toward the key that was trained with the same outcome as the cartoon being presented, that is, outcome-specific PIT. Experiment 2 replicated this finding and also showed that a cartoon trained with an outcome different from that reinforcing the responses elevated performance of both responses relative to a cartoon that was not paired with any outcome in training, that is, general PIT. These findings are consistent with those reported in the adult population and might be a useful tool to study the early development of maladaptive behaviors.

Effects of rat strain and method of inducing ethanol drinking on Pavlovian-Instrumental-Transfer with ethanol-paired conditioned stimuli

Ethanol-paired conditioned stimuli (CSs) are widely thought to invigorate ethanol responding, and thus, precipitate relapse to drinking. However, preclinical studies investigating this issue using Pavlovian-Instrumental-Transfer (PIT) procedures have had mixed results, with some studies finding PIT while others did not. The studies failing to show PIT used Lewis rats and induced ethanol drinking using a post-prandial drinking procedure. The present experiments examined whether either of these two variables influenced the magnitude of PIT observed. In the first experiment, ethanol drinking in Lewis rats was induced using either sucrose fading or post-prandial drinking. In the second experiment, ethanol drinking was induced using post-prandial drinking in either Long-Evans Hooded or Lewis rats. In both experiments, rats were trained to respond for ethanol under a random interval schedule. Subsequently with the lever removed, 2-min light presentations were paired with ethanol deliveries. Finally, with the lever returned, the effect of light presentations on responding was tested while responding was in extinction. Light presentations similarly affected responding in Lewis rats regardless of the method of drinking induction. Likewise, light presentations similarly affected responding in both Lewis and Long-Evans Hooded rats. Neither ethanol induction method nor rat strain affected the magnitude of PIT observed, and thus, neither likely explains previous failures to observe PIT with ethanol-maintained behavior.

Outcome-specific Pavlovian-to-instrumental transfer (PIT) with alcohol cues and its extinction

The acquired motivational impact of conditioned stimuli has been studied using the Pavlovian-to-instrumental transfer (PIT) task, where a cue paired with a reward is consistently shown to energize responses separately trained with that same reward ("specific" PIT). However, most alcohol studies have shown that alcohol-related cues elevate responses trained with either the same alcohol reward or with other non-alcoholic rewards ("general" PIT). The effects of extinction on this alcohol PIT effect have not been fully explored. We tested the hypothesis that cues signaling different-tasting alcohols might acquire specific craving reactions for those alcohols leading to specific PIT, but that these effects might be sensitive to extinction. Three experiments examined the specificity of PIT using alcohol and non-alcohol outcomes. Rats first consumed different-flavored alcohol solutions in their home cages. Then they were trained to perform two responses, each reinforced with distinctly flavored solutions, using a Polycose fading procedure. The outcomes were sweet (4% sucrose) or salty (0.9% NaCl) ethanol (10% v/v) solutions (Experiments 1 and 2) or one plain or salty alcohol vs. a non-alcoholic sweet solution (Experiment 3). Then, two cues were each differentially paired with these outcomes. In PIT tests, animals performed both responses in the presence and absence of these cues without any rewards. Experiments 1, 2, and 3 showed that a cue paired with a flavored alcohol produced a small but consistent bias toward the response trained with the same alcohol solution (specific PIT). Experiment 2 showed that extinction eliminated this effect. Experiment 3 demonstrated that specific PIT occurred when contrasting salty, or plain, alcohol to a non-alcoholic solution. These results provide evidence that alcohol-related stimuli can elicit craving for specific types of alcohol (as revealed by specific PIT), but that this effect is sensitive to extinction. This paradigm of contrasting two distinctly flavored alcohols may be an especially useful animal model of alcohol addiction.

Nicotine as a discriminative stimulus for ethanol use

Abused drugs reinforce behavior; i.e., they increase the probability of the behavior preceding their administration. Abused drugs can also act as discriminative stimuli; i.e., they can set the occasion for responding reinforced by another event. Thus, one abused drug could come to set the occasion for the use of another and this functional relationship may play a role in polysubstance abuse, where common patterns of use could result in this relationship. Here we establish nicotine (0.4mg/kg, ip 5-min pre-session) as a discriminative stimulus for behavior reinforced by ethanol (0.1ml 8% w/v po, versus food) and determine the ability of nicotine (0.02-0.4mg/kg), varenicline (0.1-3.0mg/kg), and ethanol (250 and 500mg/kg) to control responding for ethanol. We compare these results to those from rats where nicotine signaled food was available (and ethanol was not). Nicotine came to function as a discriminative stimulus. Nicotine and varenicline produced dose-dependent increases in responding on the nicotine-appropriate lever while ethanol produced responding on the vehicle-appropriate lever. Whether this responding occurred on the lever that produced ethanol or food access depended on the training condition. These results demonstrate that a drug can come to set the occasion for use of another and suggest that this behavioral mechanism could play an important role in the maintenance of and recovery from polysubstance abuse, depending on the pattern of use.