The tendency to sign-track predicts cue-induced reinstatement during nicotine self-administration, and is enhanced by nicotine but not ethanol

RATIONALE

Some individuals are particularly responsive to reward-associated stimuli ("cues"), including the effects of these cues on craving and relapse to drug-seeking behavior. In the cases of nicotine and alcohol, cues may acquire these abilities via the incentive-enhancing properties of the drug.

OBJECTIVES

To determine the interaction between cue-responsivity and nicotine reinforcement, we studied the patterns of nicotine self-administration in rats categorized based on their tendency to approach a food-predictive cue ("sign-trackers") or a reward-delivery location ("goal-trackers"). In a second experiment, we determined whether nicotine and ethanol altered the incentive value of a food cue.

METHODS

Rats were classified as sign- or goal-trackers during a Pavlovian conditioned approach paradigm. Rats then self-administered intravenous nicotine (0.03 mg/kg infusions) followed by extinction and cue-induced reinstatement tests. We also tested the effects of nicotine (0.4 mg/kg base s.c.) or ethanol (0.7 g/kg i.p.) on the approach to, and reinforcing efficacy of, a food cue.

RESULTS

Sign-trackers showed greater reinstatement in response to a nicotine cue. Further, nicotine enhanced sign-tracking but not goal-tracking to a food cue and also enhanced responding for the food cue during the conditioned reinforcement test. Conversely, ethanol reduced sign-tracking and increased goal-tracking, but had no effect on conditioned reinforcement.

CONCLUSIONS

Our studies demonstrate that the tendency to attribute incentive value to a food cue predicts enhanced cue-induced reinstatement. Additionally, the incentive value of food cues is differentially modulated by nicotine and ethanol, which may be related to the reinforcing effects of these drugs.

Sign-tracking to an appetitive cue predicts incubation of conditioned fear in rats

Although post-traumatic stress disorder (PTSD) and addiction are very different disorders, both are characterized by hyperreactivity to trauma- or drug-related cues, respectively. We investigated whether an appetitive conditioning task, Pavlovian conditioned approach, which predicts vulnerability to reinstatement of cocaine-seeking, also predicts fear incubation, which may be a marker for vulnerability to PTSD. We classified rats based on whether they learned to approach and interact with a food predictive cue (sign-trackers), or, whether upon cue presentation they went to the location of impending food delivery (goal-trackers). Rats were then exposed to extensive Pavlovian tone-shock pairings, which causes the fear response to increase or "incubate" over time. We found that the fear incubation effect was only present in sign-trackers. The behavior of goal-trackers was more consistent with a normal fear response-it was most robust immediately after training and decayed slowly over time. Sign-trackers also had lower levels of brain-derived neurotrophic factor (BDNF) protein in the prefrontal cortex than goal-trackers. These results indicate that, while many factors likely contribute to the disproportionate co-occurrence of PTSD and substance abuse, one such factor may be a core psychological trait that biases some individuals to attribute excessive motivational significance to predictive cues, regardless of the emotional valence of those cues. High levels of BDNF in the prefrontal cortex may be protective against developing excessive emotional and motivational responses to salient cues.

Effects of nucleus accumbens core and shell lesions on autoshaped lever-pressing

Certain Pavlovian conditioned stimuli (CSs) paired with food unconditioned stimuli (USs) come to elicit approach and even consumption-like behaviors in rats (sign-tracking). We investigated the effects of lesions of the nucleus accumbens core (ACbC) or shell (ACbS) on the acquisition of sign-tracking in a discriminative autoshaping procedure in which presentation of one lever CS was followed by delivery of sucrose, and another was not. Although we previously found that bilateral lesions of the whole ACb disrupted the initial acquisition of sign-tracking, neither ACbC or ACbS lesions affected the rate or percentage of trials in which rats pressed the CS+. In addition, detailed video analysis showed no effect of either lesion on the topography of the sign-tracking conditioned response (CR). These and other results from lesion studies of autoshaping contrast with those from previous sign-tracking experiments that used purely visual cues (Parkinson et al., 2000a,b), suggesting that the neural circuitry involved in assigning incentive value depends upon the nature of the CS.

Adolescent cannabinoid exposure effects on natural reward seeking and learning in rats

RATIONALE

Adolescence is characterized by endocannabinoid (ECB)-dependent refinement of neural circuits underlying emotion, learning, and motivation. As a result, adolescent cannabinoid receptor stimulation (ACRS) with phytocannabinoids or synthetic agonists like "Spice" cause robust and persistent changes in both behavior and circuit architecture in rodents, including in reward-related regions like medial prefrontal cortex and nucleus accumbens (NAc).

OBJECTIVES AND METHODS

Here, we examine persistent effects of ACRS with the cannabinoid receptor 1/2 specific agonist WIN55-212,2 (WIN; 1.2 mg/kg/day, postnatal day (PD) 30-43), on natural reward-seeking behaviors and ECB system function in adult male Long Evans rats (PD 60+).

RESULTS

WIN ACRS increased palatable food intake, and altered attribution of incentive salience to food cues in a sign-/goal-tracking paradigm. ACRS also blunted hunger-induced sucrose intake, and resulted in increased anandamide and oleoylethanolamide levels in NAc after acute food restriction not seen in controls. ACRS did not affect food neophobia or locomotor response to a novel environment, but did increase preference for exploring a novel environment.

CONCLUSIONS

These results demonstrate that ACRS causes long-term increases in natural reward-seeking behaviors and ECB system function that persist into adulthood, potentially increasing liability to excessive natural reward seeking later in life.

Premature responding is associated with approach to a food cue in male and female heterogeneous stock rats

RATIONALE

Disorders of behavioral regulation, including attention deficit hyperactivity disorder (ADHD) and drug addiction, are in part due to poor inhibitory control, attentional deficits, and hyper-responsivity to reward-associated cues.

OBJECTIVES

To determine whether these traits are related, we tested genetically variable male and female heterogeneous stock rats in the choice reaction time (CRT) task and Pavlovian conditioned approach (PavCA). Sex differences in the response to methylphenidate during the CRT were also assessed.

METHODS

In the CRT task, rats were required to withhold responding until one of two lights indicated whether responses into a left or right port would be reinforced with water. Reaction time on correct trials and premature responses were the operational definitions of attention and response inhibition, respectively. Rats were also pretreated with oral methylphenidate (0, 2, 4 mg/kg) during the CRT task to determine whether this drug would improve performance. Subsequently, during PavCA, presentation of an illuminated lever predicted the delivery of a food pellet into a food-cup. Lever-directed approach (sign-tracking) and food-cup approach (goal-tracking) were the primary measures, and rats were categorized as "sign-trackers" and "goal-trackers" using an index based on these measures.

RESULTS

Sign-trackers made more premature responses than goal-trackers but showed no differences in reaction time. There were sex differences in both tasks, with females having higher sign-tracking, completing more CRT trials, and making more premature responses after methylphenidate administration.

CONCLUSIONS

These results indicate that response inhibition is related to reward-cue responsivity, suggesting that these traits are influenced by common genetic factors.

Sign-tracking behavior is difficult to extinguish and resistant to multiple cognitive enhancers

The attribution of incentive-motivational value to drug-related cues underlies relapse and craving in drug addiction. One method of addiction treatment, cue-exposure therapy, utilizes repeated presentations of drug-related cues in the absence of drug (i.e., extinction learning); however, its efficacy has been limited due to an incomplete understanding of extinction and relapse processes after cues have been imbued with incentive-motivational value. To investigate this, we used a Pavlovian conditioned approach procedure to screen for rats that attribute incentive-motivational value to reward-related cues (sign-trackers; STs) or those that do not (goal-trackers; GTs). In Experiment 1, rats underwent Pavlovian extinction followed by reinstatement and spontaneous recovery tests. For comparison, a separate group of rats underwent PCA training followed by operant conditioning, extinction, and tests of reinstatement and spontaneous recovery. In Experiment 2, three cognitive enhancers (sodium butyrate, D-cycloserine, and fibroblast growth factor 2) were administered following extinction training to facilitate extinction learning. STs but not GTs displayed enduring resistance to Pavlovian, but not operant, extinction and were more susceptible to spontaneous recovery. In addition, none of the cognitive enhancers tested affected extinction learning. These results expand our understanding of extinction learning by demonstrating that there is individual variation in extinction and relapse processes and highlight potential difficulties in applying extinction-based therapies to drug addiction treatment in the clinic.

Individual differences in food cue responsivity are associated with acute and repeated cocaine-induced vocalizations, but not cue-induced vocalizations

RATIONALE

Individuals prone to attribute incentive salience to food-associated stimuli ("cues") are also more sensitive to cues during drug seeking and drug taking. This may be due in part to a difference in sensitivity to the affective or other stimulus properties of the drug. In rats, these properties are associated with 50-kHz ultrasonic vocalizations (USVs), in that they are elicited during putative positive affective and motivational states, including in response to drugs of abuse.

OBJECTIVES

We sought to determine whether individual differences in the tendency to attribute incentive salience to a food cue (as measured by approach) were associated with differences in cocaine-induced USVs. We also tested whether the food cue would elicit USVs and if this response was related to approach to the food cue.

METHODS

In experiment 1, rats underwent Pavlovian conditioned approach (PavCA) training where they learned to associate a cue (an illuminated lever) with the delivery of a food pellet into a food cup. Subjects were categorized based on their approach to the cue ("sign-trackers") or to the food cup ("goal-trackers"). Rats subsequently underwent nine testing days in which they were given saline or cocaine (10 mg/kg i.p) and placed into a locomotor chamber. In experiment 2, rats were first tested in the locomotor chambers for one saline-treated day followed by one cocaine-treated day and then trained in PavCA. USVs were recorded from a subset of individuals during the last day of PavCA to determine if the food cue would elicit USVs.

RESULTS

Sign-trackers produced 5-24 times more cocaine-induced 50 kHz USVs compared to goal-trackers for all days of experiment 1, and this response sensitized with repeated cocaine, only in sign-trackers. Similarly in experiment 2, individuals that produced the most cocaine-induced USVs on a single exposure also showed the greatest tendency to sign-track during PavCA. Lastly, while sign-trackers produced more USVs during PavCA generally, the cue itself did not elicit additional USVs in sign- or goal-trackers.

CONCLUSIONS

These results indicate a robust and consistent relationship between approach to a food cue and cocaine-induced USV production. Thus, these USVs may index the neurobiological differences underlying the behavioral distinctions of sign- and goal-trackers.

Establishing a model for assessing DNA damage in murine brain cells as a molecular marker of chemotherapy-associated cognitive impairment

AIMS

Chemotherapy-associated cognitive impairment often follows cancer chemotherapy. We explored chemotherapy-induced DNA damage in the brain cells of mice treated with 5-fluorouracil (5FU), an antineoplastic agent, to correlate the extent of DNA damage to behavioral functioning in an autoshaping-operant mouse model of chemotherapy-induced learning and memory deficits (Foley et al., 2008).

MAIN METHODS

Male, Swiss-Webster mice were injected once with saline or 75 mg/kg 5FU at 0, 12, and 24h and weighed every 24h. Twenty-four h after the last injection, the mice were tested in a two-day acquisition and the retention of a novel response task for food reinforcement. Murine brain cells were analyzed for the presence of single- and double-strand DNA breaks by the single cell gel electrophoresis assay (the Comet assay).

KEY FINDINGS

We detected significant differences (p<0.0001) for all DNA damage characteristics (DNA "comet" tail shape, migration pattern, tail moment and olive moments) between control mice cohort and 5FU-treated mice cohort: tail length - 119 vs. 153; tail moment - 101 vs. 136; olive moment - 60 vs. 82, correspondingly. We found a positive correlation between increased response rates (r=0.52, p<0.05) and increased rate of errors (r=0.51, p<0.05), and DNA damage on day 1. For all 15 mice (saline-treated and 5FU-treated mice), we found negative correlations between DNA damage and weight (r=-0.75, p<0.02).

SIGNIFICANCE

Our results indicate that chemotherapy-induced DNA damage changes the physiological status of the brain cells and may provide insights to the mechanisms for cognitive impairment after cancer chemotherapy.

Role of prefrontal 5-HT in the strain-dependent variation in sign-tracking behavior of C57BL/6 and DBA/2 mice

RATIONALE

The expression of sign-tracking (ST) phenotype over goal-tracking (GT) phenotype has been associated to different aspects of impulsive behavior, and depletions of brain serotonin (5-HT) have been shown to selectively increase impulsive action as well as ST.

OBJECTIVES

The present study aimed at testing the relationship between reduced brain 5-HT availability and expression of ST phenotype in a genetic model of individual variation in brain 5-HT functionality. Inbred DBA/2J (DBA) mice are homozygous for the allelic variant of the TPH-2 gene causing lower brain 5-HT function in comparison with C57BL/6J (C57) inbred mice.

MATERIALS

Young adult (10 weeks) and adult (14 weeks) C57 and DBA mice were trained in a Pavlovian conditioned approach (PCA) paradigm. Lever-directed (ST) and magazine-directed (GT) responses were measured in 12 daily conditioning sessions. In a second experiment, effect of the medial prefrontal cortex (mPFC) 5-HT depletion by the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) was assessed on acquisition of ST phenotype in adult C57 mice, according to their higher 5-HT functionality compared to DBA mice.

RESULTS

Young adult mice of both strains developed ST phenotype, but only adult DBA mice developed ST phenotype. 5-HT depletion in the mPFC of adult C57 mice completely changed their phenotype, as shown by their increased ST.

CONCLUSIONS

These findings indicate that ST phenotype can be the expression of a transitory late developmental stage and that genetic factors determine persistence of this phenotype in adulthood. These findings also support a role of 5-HT transmission in PFC in constraining development of ST phenotype.

Behavioral predictors of alcohol drinking in a neurodevelopmental rat model of schizophrenia and co-occurring alcohol use disorder

Alcohol use disorder commonly occurs in patients with schizophrenia and contributes greatly to its morbidity. Unfortunately, the neural and behavioral underpinnings of alcohol drinking in these patients are not well understood. In order to begin to understand the cognitive and reward-related changes that may contribute to alcohol drinking, this study was designed to address: 1) latent inhibition; 2) conditioning; and 3) extinction of autoshaping in a neurodevelopmental rat model with relevance to co-occurring schizophrenia and alcohol use disorders, the neonatal ventral hippocampal lesioned (NVHL) rat. NVHL lesions (or sham surgeries) were performed on post-natal day 7 (PND7) and animals were given brief exposure to alcohol during adolescent (PND 28-42). Latent inhibition of autoshaping, conditioning and extinction were assessed between PND 72-90. On PND90 animals were given alcohol again and allowed to establish stable drinking. Latent inhibition of autoshaping was found to be prolonged in the NVHL rats; the NVHL rats pre-exposed to the lever stimulus were slower to acquire autoshaping than sham pre-exposed rats. NVHL rats that were not pre-exposed to the lever stimulus did not differ during conditioning, but were slower to extinguish conditioned responding compared to sham controls. Finally, the NVHL rats from both groups drank significantly more alcohol than sham rats, and the extent of latent inhibition predicted future alcohol intake in the pre-exposed animals. These findings suggest that the latent inhibition of autoshaping procedure can be used to model cognitive- and reward-related dysfunctions in schizophrenia, and these dysfunctions may contribute to the development of co-occurring alcohol use.

Experimental predictions drawn from a computational model of sign-trackers and goal-trackers

Gaining a better understanding of the biological mechanisms underlying the individual variation observed in response to rewards and reward cues could help to identify and treat individuals more prone to disorders of impulsive control, such as addiction. Variation in response to reward cues is captured in rats undergoing autoshaping experiments where the appearance of a lever precedes food delivery. Although no response is required for food to be delivered, some rats (goal-trackers) learn to approach and avidly engage the magazine until food delivery, whereas other rats (sign-trackers) come to approach and engage avidly the lever. The impulsive and often maladaptive characteristics of the latter response are reminiscent of addictive behaviour in humans. In a previous article, we developed a computational model accounting for a set of experimental data regarding sign-trackers and goal-trackers. Here we show new simulations of the model to draw experimental predictions that could help further validate or refute the model. In particular, we apply the model to new experimental protocols such as injecting flupentixol locally into the core of the nucleus accumbens rather than systemically, and lesioning of the core of the nucleus accumbens before or after conditioning. In addition, we discuss the possibility of removing the food magazine during the inter-trial interval. The predictions from this revised model will help us better understand the role of different brain regions in the behaviours expressed by sign-trackers and goal-trackers.

Effects of orbitofrontal cortex lesions on autoshaped lever pressing and reversal learning

A cue associated with a rewarding event can trigger behavior towards the cue itself due to the cue acquiring incentive value through its pairing with the rewarding outcome (i.e., sign-tracking). For example, rats will approach, press, and attempt to "consume" a retractable lever conditioned stimulus (CS) that signals delivery of a food unconditioned stimulus (US). Attending to food-predictive CSs is important when seeking out food, and it is just as important to be able to modify one's behavior when the relationships between CSs and USs are changed. Using a discriminative autoshaping procedure with lever CSs, the present study investigated the effects of orbitofrontal cortex (OFC) lesions on sign-tracking and reversal learning. Insertion of one lever was followed by sucrose delivery upon retraction, and insertion of another lever was followed by nothing. After the acquisition phase, the contingencies between the levers and outcomes were reversed. Bilateral OFC lesions had no effect on the acquisition of sign-tracking. However, OFC-lesioned rats showed substantial deficits in acquiring sign-tracking compared to sham-lesioned rats once the stimulus-outcome contingencies were reversed. Over the course of reversal learning, OFC-lesioned rats were able to reach comparable levels of sign-tracking as sham-lesioned rats. These findings suggest that OFC is not necessary for the ability of a CS to acquire incentive value and provide more evidence that OFC is critical for modifying behavior appropriately following a change in stimulus-outcome contingencies.

Voluntary alcohol access during adolescence/early adulthood, but not during adulthood, causes faster omission contingency learning

In omission contingency training, rodents learn to suppress their natural tendency to approach or touch a reward-predictive cue (termed "autoshaping" or "sign-tracking" responses) if the approach/touching responses lead to the omission of the reward. Previous research has shown that high levels of alcohol exposure (through alcohol vapor exposure) or adolescent alcohol consumption (with some versions of the omission contingency task) can lead to faster omission contingency learning. However, the alcohol exposure procedures and/or omission contingency task parameters differed between these different demonstrations. It was unclear whether the same voluntary alcohol consumption procedures during adolescence/early adulthood and/or adulthood would lead to faster omission contingency learning in one or both age groups. Here, rats received 6 weeks of chronic intermittent access to 20% alcohol or water from PND 26-66 (adolescence/early adulthood in Exp. 1) or PND 68-108 (adulthood in Exp. 2) and began behavioral training (autoshaping training followed by omission contingency training) several days later. We found no evidence that alcohol access at either age altered the number of trials with a sign-tracking response on the levers during autoshaping training. However, alcohol access during adolescence/early adulthood, but not during adulthood, led to faster learning to withhold responding on the lever under omission contingencies during the subsequent phase. We also found no evidence that the level of alcohol consumption was correlated with sign-tracking behavior in the autoshaping phase or with the suppression of lever-pressing during the omission contingency phase. Our results suggest that adolescent/early adult rats have increased vulnerability, compared with adults, to some long-term behavioral effects of voluntary alcohol consumption.

Elucidating the role of D4 receptors in mediating attributions of salience to incentive stimuli on Pavlovian conditioned approach and conditioned reinforcement paradigms

The power of drug-associated cues to instigate drug 'wanting' and consequently promote drug seeking is a corner stone of contemporary theories of addiction. Gambling disorder has recently been added to the pantheon of addictive disorders due to the phenomenological similarities between the diseases. However, the neurobiological mechanism that may mediate increased sensitivity towards conditioned stimuli in addictive disorders is unclear. We have previously demonstrated using a rodent analogue of a simple slot machine that the dopamine D4 receptor is critically engaged in controlling animals' attribution of salience to stimuli associated with reward in this paradigm, and consequently may represent a target for the treatment of gambling disorder. Here, we investigated the role of acute administration of a D4 receptor agonist on animals' responsivity to conditioned stimuli on both a Pavlovian conditioned approach (autoshaping) and a conditioned reinforcement paradigm. Following training on one of the two tasks, separate cohorts of rats (male and female) were administered a dose of PD168077 shown to be maximally effective at precipitating errors in reward expectancy on the rat slot machine task (10mg/kg). However, augmenting the activity of the D4 receptors in this manner did not alter behaviour on either task. These data therefore provide novel evidence that the D4 receptor does not alter incentive motivation in response to cues on simple behavioural tasks.

Effects of predictive and incentive value manipulation on sign- and goal-tracking behavior

When a neutral stimulus is repeatedly paired with an appetitive reward, two different types of conditioned approach responses may develop: a sign-tracking response directed toward the neutral cue, or a goal-tracking response directed toward the location of impending reward delivery. Sign-tracking responses have been postulated to result from attribution of incentive value to conditioned cues, while goal-tracking reflects the assignment of only predictive value to the cue. We therefore hypothesized that sign-tracking rats would be more sensitive to manipulations of incentive value, while goal-tracking rats would be more responsive to changes in the predictive value of the cue. We tested sign- and goal-tracking before and after devaluation of a food reward using lithium chloride, and tested whether either response could be learned under negative contingency conditions that precluded any serendipitous reinforcement of the behavior that might support instrumental learning. We also tested the effects of blocking the predictive value of a cue using simultaneous presentation of a pre-conditioned cue. We found that sign-tracking was sensitive to outcome devaluation, while goal-tracking was not. We also confirmed that both responses are Pavlovian because they can be learned under negative contingency conditions. Goal-tracking was almost completely blocked by a pre-conditioned cue, while sign-tracking was much less sensitive to such interference. These results indicate that sign- and goal-tracking may follow different rules of reinforcement learning and suggest a need to revise current models of associative learning to account for these differences.

Nicotine Produces a High-Approach, Low-Avoidance Phenotype in Response to Alcohol-Associated Cues in Male Rats

BACKGROUND

Nicotine and alcohol use are highly comorbid. Modulation of drug-paired extrinsic and intrinsic cues likely plays a role in this interaction, as cues can acquire motivational properties and augment drug seeking. The motivational properties of cues can be measured through Pavlovian conditioning paradigms, in which cues either elicit approach following pairing with the reinforcing properties of alcohol or elicit avoidance following pairing with the aversive consequences of alcohol. The present experiments tested whether nicotine would enhance the incentive properties of an appetitive ethanol (EtOH) cue and diminish the avoidance of an aversive EtOH cue in Pavlovian paradigms.

METHODS

In experiment 1, male Long-Evans rats with or without prior chronic intermittent access to EtOH were administered nicotine or saline injections prior to Pavlovian conditioned approach (PavCA) sessions, during which conditioned approach to the cue ("sign-tracking") or the EtOH delivery location ("goal-tracking") was measured. In experiment 2, male Long-Evans rats were administered nicotine or saline injections prior to pairing a flavor cue with increasing doses of EtOH (i.p.) in an adaptation of the conditioned taste avoidance (CTA) paradigm.

RESULTS

Results from PavCA indicate that, regardless of EtOH exposure, nicotine enhanced responding elicited by EtOH-paired cues with no effect on a similar cue not explicitly paired with EtOH. Furthermore, nicotine reduced sensitivity to EtOH-induced CTA, as indicated by a rightward shift in the dose-response curve of passively administered EtOH. The ED₅₀ , or the dose of EtOH that produced a 50% reduction in intake relative to baseline, was significantly higher in nicotine-treated rats compared to saline-treated rats.

CONCLUSIONS

We conclude that nicotine increases the approach and diminishes the avoidance elicited by Pavlovian cues paired, respectively, with the reinforcing and aversive properties of EtOH consumption in male rats. As such, nicotine may enhance alcoholism liability by engendering an attentional bias toward cues that predict the reinforcing outcomes of drinking.

Learning not to respond: Role of the hippocampus in withholding responses during omission training

Autoshaping is a Pavlovian learning paradigm in which rats experience pairings of a CS and a US independently of their behavior. When the CS is a lever inserted into the test cage and the US is food delivered to an adjacent magazine, many rats acquire a lever-pressing response called 'sign-tracking' even though that response has no effect on the occurrence of either the CS or the US. Since these lever presses are always followed by the US, it has been suggested that sign-tracking could be due to unintended reinforcement of the response. To eliminate the possibility of such instrumental learning the omission schedule, in which a response to the CS cancels the US, was introduced. Previous research has shown that training rats on autoshaping and switching them to an omission schedule generally reduces but does not eliminate sign-tracking, suggesting that it may be due to both Pavlovian and instrumental learning. In the present study naive rats trained on an omission schedule sign-tracked less than a control group exposed to random, unpaired CS and US presentations, suggesting that they learned to withhold the lever press response because of the negative contingency between that response and the US. In a second experiment rats with dorsal hippocampus lesions sign-tracked more than sham-lesioned rats on omission schedules, suggesting that this case of learning not to respond is hippocampus-based. This conclusion is consistent with many previous findings on the inability of hippocampal rats to withhold or suppress responding, and with studies suggesting that one form of extinction of learned responses in normal rats is due to competition from hippocampus-based learning not to respond.

Effects of dopamine receptor antagonism and amphetamine-induced psychomotor sensitization on sign- and goal-tracking after extended training

The dopamine system is important for incentive salience attribution, where motivational value is assigned to conditioned cues that predict appetitive reinforcers. However, the role of dopamine in this process may change with extended training. We tested the effects of dopamine D1-like and D2-like receptor antagonism on the expression of sign-tracking and goal-tracking conditioned responses following extended Pavlovian conditioned approach (PCA) training. We also tested if amphetamine-induced psychomotor sensitization accelerates the enhanced acquisition of sign-tracking that is observed with extended training. In experiment 1, 24 male Long-Evans rats received 20 PCA sessions in which one lever (CS+, 10 s) predicted 0.2 ml sucrose (10 %, w/v) delivery and the other lever (CS-) did not. SCH-23390 (D1-like antagonist) or eticlopride (D2-like antagonist) were administered before non-reinforced behavioural tests at doses of 0, 0.01, and 0.1 mg/kg (s.c.). In experiment 2, rats received vehicle or 2 mg/kg amphetamine (i.p.) for 7 days (n = 12/group). Ten days later, they received 16 PCA training sessions. Both doses of SCH-23390 reduced sign- and goal-tracking, but also reduced locomotor behaviour. A low dose of eticlopride (0.01 mg/kg) selectively reduced goal-tracking, without affecting sign-tracking or locomotor behaviour. Amphetamine produced psychomotor sensitization, and this did not affect the acquisition of sign- or goal-tracking. Following extended PCA training, dopamine D2-like receptor activity is required for the expression of goal-tracking but not sign-tracking. Psychomotor sensitization to amphetamine did not impact incentive salience attribution; however, more selective manipulations of the dopamine system may be needed.

Reward uncertainty attributes incentive value to reward proximal cues, while amphetamine sensitization reverts attention to more predictive reward distal cues

Slot-machine gambling incorporates numerous audiovisual cues prior to and during reward delivery (e.g. spinning wheels, flashing lights, celebratory sounds). Over time, these cues may motivate playing and even elicit cravings and relapse in those affected by gambling disorder. Animal studies suggest a heightened attraction to these cues despite diminished predictive ability under reward uncertainty, as evidenced by sign-tracking behavior in rats. Repeated amphetamine administration may also enhance the incentive value attributed to cues. Here, we explored the impact of reward uncertainty and prior amphetamine sensitization on the relative attractiveness and conditioned reinforcing properties of serial Pavlovian cues with different degrees of predictive and incentive value in rats. Animals were sensitized through repeated injections of amphetamine (1-4 mg/kg) or saline and then trained in a Pavlovian autoshaping task involving two sequential lever-auditory cue combinations (CS1, CS2) under Certain (100%-1) or Uncertain (50%-1-2-3) reward conditions. Subsequently, we evaluated the impact of acute amphetamine exposure on cue attraction. Our results suggest that Uncertainty alone enhanced attraction towards the reward-proximal CS2. However, combined sensitization and Uncertainty reversed cue preference relative to Uncertainty alone, enhancing attraction towards the more predictive reward-distal CS1. Both cues acquired conditioned reinforcing properties, despite the CS2 being otherwise ignored in all groups besides Uncertainty. However, combined sensitization and Uncertainty increased the reinforcing value of both cues and doubled the amount of interaction with the CS1 lever per presentation. Our results imply competitive mechanisms for attributing incentive value to gambling-related cues between reward uncertainty, prior amphetamine sensitization, and acute amphetamine administration.

Effort-motivated behavior resolves paradoxes in appetitive conditioning

Motivated behavior has long been studied by psychologists, ethologists, and neuroscientists. To date, many scientists agree with the view that cue and reward attraction is the product of a dopamine-dependent unconscious process called incentive salience or "wanting". This process allows the influence of multiple factors such as hunger and odors on motivational attraction. In some cases, however, the resulting motivated behavior differs from what the incentive salience hypothesis would predict. I argue that seeking behavior under reward uncertainty illustrates this situation: Organisms do not just "want" (appetite-based attraction) cues that are inconsistent or associated with reward occasionally, they "hope" that those cues will consistently predict reward procurement in the ongoing trial. Said otherwise, they become motivated to invest time and energy to find consistent cue-reward associations despite no guarantee of success (effort-based attraction). A multi-test comparison of performance between individuals trained under uncertainty and certainty reveals behavioral paradoxes suggesting that the concept of incentive salience cannot fully account for responding to inconsistent cues. A mathematical model explains how appetite-based and effort-based attractions might combine their effects.

Activation of 5-HT1A and 5-HT7 receptors enhanced a positively reinforced long-term memory

Memory is one of the most important capabilities of our mind since it determines our individuality. Memory formation involves different stages: acquisition, consolidation and retrieval. There are many studies about early stages, however little is known about memory retrieval. Retrieval is the use of learned information and represents a big problem in patients with memory deficits where the main issue is that they can learn but cannot remember. Previous findings have demonstrated that 5-hydroxytryptamine (5-HT) is a neurotransmitter involved in memory process. Hence, here we are exploring the role of 5-HT in memory retrieval by using its metabolic precursor l-tryptophan and several ligands at 5-HT1A and 5-HT7 receptors. Experimental protocol consisted of evaluating conditioned responses (%CR) after one week of interruption following autoshaping sessions for memory formation; a decrease of %CR was interpreted as memory decay. Systemic administration of: (1) l-tryptophan (50 and 100 mg/kg), (2) 5-HT1A receptor agonist 8-OH-DPAT (0.031 and 0.062 mg/kg), (3) the selective antagonist 5-HT1A receptor WAY 100635 (0.3 and 0.6 mg/kg), (4) the 5-HT7 receptor agonist, LP 211, in a dose-dependent manner (1, 2.5, 5.0 and 10.0 mg/kg) enhanced memory retrieval. Further, the 5-HT7 receptor antagonist, SB 269970 (10.0 mg/kg), had no effect. Finally, SB 269970 (10.0 mg/kg) significantly blocked memory retrieval enhancement produced by 10.0 mg/kg LP 211, but not that induced by 2.5 mg/kg LP 211.These results, taken together, suggest that activation of 5-HT1A and 5-HT7 receptors enhanced memory retrieval and these receptors may be therapeutic targets to improve long-term memory retrieval.

Quantifying the instrumental and noninstrumental underpinnings of Pavlovian responding with the Price equation

The Price equation is a mathematical expression of selectionist and non-selectionist pressures on biological, cultural, and behavioral change. We use it here to specify instrumental and noninstrumental behaviors as they arise within the context of the Pavlovian autoshaping procedure, for rats trained under reward certainty and reward uncertainty. The point of departure for this endeavor is that some portion of autoshaped behavior referred to as goal-tracking appears instrumental-a function of resource attainment (the individual approaches the location where the unconditioned stimulus is to be delivered). By contrast, some other portion of autoshaped behavior referred to as sign-tracking is noninstrumental-irrelevant to making contact with the to-be-delivered unconditioned stimulus. A Price equation model is proposed that unifies our understanding of Pavlovian autoshaping behavior by isolating operant and respondent influences on goal-tracking (instrumental) and sign-tracking (noninstrumental) behavior.

Dose-dependent effects of alcohol injections on omission-contingency learning have an inverted-U pattern

Previous examinations of the long-term effects of alcohol exposure on omission-contingency learning have produced mixed results across different age or sex groups, with evidence for faster learning or no effect. However, none of these experiments made comparisons using the same exposure-dose across the age/sex groups. Here, we exposed rats to 6 weeks of alcohol injections (3 days/week, 1.75 or 3.5 g/kg/24-h, i.p. broken up into 2 injections/day) in adolescent/early adult males or females (PND27-66) or adult males (PND62-101). We then tested the rats in autoshaping and omission-contingency tasks. In contrast to our hypotheses, the low 1.75-g/kg/24-h dose led to slower omission learning and the higher 3.5-g/kg/24-h dose had no effect. There were no age- or sex-differences in omission learning. Additionally, during autoshaping training, rats exposed in adolescence/early adulthood had a faster shift to sign-tracking in their sign-tracking/goal-tracking ratios than rats exposed in adulthood, with no consistent effect of alcohol exposure or sex-differences. Our results suggest complex effects of alcohol on the neural substrates of omission-contingency learning at different doses, which will require future investigation.

Translations in Stimulus-Stimulus Pairing: Autoshaping of Learner Vocalizations

Stimulus-stimulus pairing (SSP) is a procedure used by behavior analysis practitioners that capitalizes on respondent conditioning processes to elicit vocalizations. These procedures usually are implemented only after other, more customary methods (e.g., standard echoic training via modeling) have been exhausted. Unfortunately, SSP itself has mixed research support, probably because certain as-yet-unidentified procedural variations are more effective than others. Even when SSP produces (or increases) vocalizations, its effects can be short-lived. Although specific features of SSP differ across published accounts, fundamental characteristics include presentation of a vocal stimulus proximal with presentation of a preferred item. In the present article, we draw parallels between SSP procedures and autoshaping, review factors shown to affect autoshaping, and interpret autoshaping research for suggested SSP tests and applications. We then call for extended use and reporting of SSP in behavior-analytic treatments. Finally, three bridges created by this article are identified: basic-applied, respondent-operant, and behavior analysis with other sciences.

Memory reconsolidation impairments in sign-tracking to an audiovisual compound stimulus

Studies of memory reconsolidation of pavlovian memories have typically employed unimodal conditioned stimuli, despite the use of multimodal compound stimuli in other settings. Here we studied sign-tracking behaviour to a compound audiovisual stimulus. First, we observed not unexpectedly that sign-tracking was poorer to the audiovisual compound than to unimodal visual stimuli. Then, we showed that, depending on the parameters of compound stimulus re-exposure at memory reactivation, systemic MK-801 treatment either impaired extinction to improve sign-tracking at test, or disrupted reconsolidation to impair test behaviour. When memory reactivation consisted of re-exposure to only the auditory component of the compound stimulus, we observed sign-tracking impairments following MK-801 treatment, but only under certain test conditions. This was in contrast to the consistent impairment following reactivation with the full audiovisual compound. Moreover, the parameters of auditory stimulus presentation to enable MK-801-induced impairment at test varied depending on whether the stimulus was presented within or outside the training context. These findings suggest that behaviour under the control of appetitive pavlovian compound stimuli can be modulated by targeting both extinction and reconsolidation, and that it is not necessary to re-expose to the full compound stimulus in order to achieve a degree of modulation of behaviour.