Modulation of cue-triggered reward seeking by cholinergic signaling in the dorsomedial striatum

Nucleus accumbens core acetylcholine receptors modulate the balance of flexible and inflexible cue-directed motivation

Sign-tracking is a conditioned response where animals interact with reward-predictive cues due to the cues having motivational value, or incentive salience. The nucleus accumbens core (NAc) has been implicated in mediating the sign-tracking response. Additionally, acetylcholine (ACh) transmission throughout the striatum has been attributed to both incentive motivation and behavioral flexibility. Here, we demonstrate a role for NAc ACh receptors in the flexibility of sign-tracking. Sign-tracking animals were exposed to an omission contingency, in which vigorous sign-tracking was punished by reward omission. Animals rapidly adjusted their behavior, but they maintained sign-tracking in a less vigorous manner that did not cancel reward. Within this context of sign-tracking being persistent yet flexible in structure, blockade of NAc nicotinic receptors (nAChRs) led to a persistence in the initial sign-tracking response during omission followed by a period of change in the makeup of sign-tracking, whereas blockade of muscarinic receptors (mAChRs) oppositely enhanced the omission-related development of the new sign-tracking behaviors. Later, once omission learning had occurred, nAChR blockade uniquely led to reduced sign-tracking and elevated reward-directed behaviors instead. These results indicate that NAc ACh receptors have opposing roles in maintaining learned patterns of sign-tracking, with nAChRs having a special involvement in regulating the structure of the sign-tracking response.

Double dissociation of perirhinal nicotinic acetylcholine receptors and dopamine D2 receptors in modulation of object memory consolidation by nicotine, cocaine and their conditioned stimuli

There are indications that drug conditioned stimuli (CS) may activate neurochemical systems of memory modulation that are activated by the drugs themselves. To directly test this hypothesis, a cholinergic nicotinic receptor antagonist (mecamylamine; MEC: 0, 10 or 30 µg/side) and a dopamine D2 receptor antagonist (l-741,626: 0, 0.63, 2.5 µg/side) were infused in the perirhinal cortex (PRh) to block modulation of object recognition memory consolidation induced by 0.4 mg/kg nicotine, 20 mg/kg cocaine, or their CSs. To establish these CSs, male Sprague-Dawley rats were confined for 2 h in a chamber, the CS+, after injections of 0.4 mg/kg nicotine, or 20 mg/kg cocaine, and in another chamber, the CS-, after injections of vehicle. This was repeated over 10 days (5 drug/CS+ and 5 vehicle/CS- pairings in total). It was found that the memory enhancing action of post-sample nicotine was blocked by intra-PRh infusions of both MEC doses, and 30 µg/side MEC also blocked the memory enhancing action of the nicotine CS. Interestingly, intra-PRh MEC did not block the memory enhancing effect of cocaine, nor that of the cocaine CS. In contrast, the memory enhancing action of post-sample cocaine administration was blocked by both l-741,626 doses, and 2.5 µg/side also blocked the effect of the cocaine CS, but not the memory effects of nicotine or of the nicotine CS. This functional double dissociation strongly indicates that drug CSs modulate memory consolidation by activating neural systems that are activated by the drugs themselves.

Nicotinic and muscarinic acetylcholine receptor antagonism dose-dependently decreases sign- but not goal-tracking behavior in male rats

RATIONALE

Acetylcholinergic antagonists have shown some promise in reducing addiction-related behaviors in both preclinical and clinical studies. However, the psychological mechanisms by which these drugs are able to affect addictive behavior remain unclear. A particular key process for the development of addiction is the attribution of incentive salience to reward-related cues, which can be specifically measured in animals using a Pavlovian conditioned approach procedure. When confronted with a lever that predicts food delivery, some rats engage with the lever directly (i.e., they sign track), indicating attribution of incentive-motivational properties to the lever itself. In contrast, others treat the lever as a predictive cue and approach the location of impending food delivery (i.e., they goal track), without treating the lever itself as a reward.

OBJECTIVES

We tested whether systemic antagonism of the either nicotinic or muscarinic acetylcholine receptors would selectively affect sign- or goal-tracking behavior, indicating a selective effect on incentive salience attribution.

METHODS

A total of 98 male Sprague Dawley rats were either given the muscarinic antagonist scopolamine (100, 50, or 10 µg/kg i.p.) or the nicotinic antagonist mecamylamine (0.3, 1.0, or 3 mg/kg i.p.) before being trained on a Pavlovian conditioned approach procedure.

RESULTS

Scopolamine dose-dependently decreased sign tracking behavior and increased goal-tracking behavior. Mecamylamine reduced sign-tracking but did not affect goal-tracking behavior.

CONCLUSIONS

Antagonism of either muscarinic or nicotinic acetylcholine receptors can reduce incentive sign-tracking behavior in male rats. This effect appears to be specifically due to a reduction in incentive salience attribution since goal-tracking either increased or was not affected by these manipulations.

Instrumental and Pavlovian Mechanisms in Alcohol Use Disorder

Purpose of Review

Current theories of alcohol use disorders (AUD) highlight the importance of Pavlovian and instrumental learning processes mainly based on preclinical animal studies. Here, we summarize available evidence for alterations of those processes in human participants with AUD with a focus on habitual versus goal-directed instrumental learning, Pavlovian conditioning, and Pavlovian-to-instrumental transfer (PIT) paradigms.

Recent Findings

The balance between habitual and goal-directed control in AUD participants has been studied using outcome devaluation or sequential decision-making procedures, which have found some evidence of reduced goal-directed/model-based control, but little evidence for stronger habitual responding. The employed Pavlovian learning and PIT paradigms have shown considerable differences regarding experimental procedures, e.g., alcohol-related or conventional reinforcers or stimuli.

Summary

While studies of basic learning processes in human participants with AUD support a role of Pavlovian and instrumental learning mechanisms in the development and maintenance of drug addiction, current studies are characterized by large variability regarding methodology, sample characteristics, and results, and translation from animal paradigms to human research remains challenging. Longitudinal approaches with reliable and ecologically valid paradigms of Pavlovian and instrumental processes, including alcohol-related cues and outcomes, are warranted and should be combined with state-of-the-art imaging techniques, computational approaches, and ecological momentary assessment methods.

Effects of hM4Di activation in CamKII basolateral amygdala neurons and CNO treatment on sensory-specific vs. general PIT: refining PIT circuits and considerations for using CNO

BACKGROUND

Pavlovian stimuli can influence instrumental behaviors via phenomena such as Pavlovian-to-instrumental transfer (PIT). PIT arises via dissociable processes as sensory-specific PIT (SS-PIT) and general PIT. The basolateral amygdala (BLA) mediates SS-PIT, but not general PIT. However, the specific BLA neuronal populations involved are unknown.

AIMS

To determine the contribution of glutamatergic BLA neurons to the expression of SS-PIT and to the recall of sensory-specific properties of stimulus-outcome associations.

METHODS

BLA neurons were transduced with virus containing either GFP or hM4Di, driven by the CamKII promoter. Rats were then tested for SS and general PIT and subsequently for expression of Pavlovian outcome devaluation effects and conditioned taste aversion following injections of vehicle or clozapine-N-oxide (CNO, the hM4Di agonist).

RESULTS

CNO selectively blocked SS-PIT in the hM4Di-expressing group, but not controls, without altering expression of Pavlovian outcome devaluation or sensory-specific taste aversion in either group. Unexpectedly, CNO disrupted general PIT in both groups.

CONCLUSIONS

CamKII BLA neurons mediate the expression of SS-PIT by enabling Pavlovian stimuli to trigger recall of the correct action-outcome associations rather than by mediating recall of the sensory-specific properties of the stimulus-outcome association. Separately, our data demonstrate that CNO alone is sufficient to disrupt affective, but not sensory-specific processes, an effect that was not due to generalized motor disruption. This non-specific effect on general PIT may be related to CNO-induced shifts in internal state. Together, these data identify BLA CamKII neurons as critical for the expression of SS-PIT and reveal important considerations for using CNO to study general affective motivation.

Beta-arrestin 1 regulation of reward-motivated behaviors and glutamatergic function

The two highly homologous non-visual arrestins, beta-arrestin 1 and 2, are ubiquitously expressed in the central nervous system, yet knowledge of their disparate roles is limited. While beta-arrestin 2 (βarr2) has been implicated in several aspects of reward-related learning and behavior, very little is known about the behavioral function of beta-arrestin 1 (βarr1). Using mice lacking βarr1, we focused on the role of this scaffolding and signal transduction protein in reward-motivated behaviors and in striatal glutamatergic function. We found that βarr1 KO mice were both slower in acquiring cocaine self-administration and in extinguishing this behavior. They also showed deficits in learning tasks supported by a natural food reward, suggesting a general alteration in reward processing. We then examined glutamatergic synaptic strength in WT and KO medium spiny neurons (MSNs) of the Nucleus Accumbens (NAc) shell in naïve animals, and from those that underwent cocaine self-administration. An increase in the AMPA/NMDA (A/N) ratio and a relative lack of GluN2B-enriched NMDARs was found in naïve KO vs WT MSNs. Applying Lim Domain Kinase (LIMK1), the kinase that phosphorylates and inactivates cofilin, to these cells, showed that both βarr1 and LIMK regulate the A/N ratio and GluN2B-NMDARs. Cocaine self-administration increased the A/N ratio and GluN2B-NMDARs in WT MSNs and, although the A/N ratio also increased in KO MSNs, this was accompanied by fewer GluN2B-NMDARs and an appearance of calcium-permeable AMPARs. Finally, to examine the consequences of reduced basal GluN2B-NMDARs in reward-processing seen in KO mice, we chronically infused ifenprodil, a GluN2B antagonist, into the NAc shell of WT mice. This intervention substantially reduced food-motivated behavior. Together these findings identify a previously unknown role of βarr1 in regulating specific reward-motivated behaviors and glutamatergic function.