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Environmental reward-predictive cues can motivate reward-seeking behaviors. Although this influence is normally adaptive, it can become maladaptive in disordered states, such as addiction. Dopamine release in the nucleus accumbens core (NAc) is known to mediate the motivational impact of reward-predictive cues, but little is known about how other neuromodulatory systems contribute to cue-motivated behavior. Here, we examined the role of the NAc cholinergic receptor system in cue-motivated behavior using a Pavlovian-to-instrumental transfer task designed to assess the motivating influence of a reward-predictive cue over an independently-trained instrumental action. Disruption of NAc muscarinic acetylcholine receptor activity attenuated, whereas blockade of nicotinic receptors augmented cue-induced invigoration of reward seeking. We next examined a potential dopaminergic mechanism for this behavioral effect by combining fast-scan cyclic voltammetry with local pharmacological acetylcholine receptor manipulation. The data show evidence of opposing modulation of cue-evoked dopamine release, with muscarinic and nicotinic receptor antagonists causing suppression and augmentation, respectively, consistent with the behavioral effects of these manipulations. In addition to demonstrating cholinergic modulation of naturally-evoked and behaviorally-relevant dopamine signaling, these data suggest that NAc cholinergic receptors may gate the expression of cue-motivated behavior through modulation of phasic dopamine release.

Environmental reward-predictive stimuli provide a major source of motivation for instrumental reward-seeking activity and this has been linked to dopamine signaling in the nucleus accumbens (NAc). This cue-induced incentive motivation can be quite general, not restricted to instrumental actions that earn the same unique reward, and is also typically regulated by one’s current need state, such that cues only motivate actions when this is adaptive. But it is unknown whether cue-evoked dopamine signaling is similarly regulated by need state. Here we used fast-scan cyclic voltammetry to monitor dopamine concentration changes in the NAc core of rats during a Pavlovian-to-instrumental transfer (PIT) task in which the motivating influence of two cues, each signaling a distinct food reward (sucrose or food pellets), over an action earning a third unique food reward (grape-flavored polycose) was assessed in a state of hunger and of satiety. Both cues elicited a robust NAc dopamine response when hungry. The magnitude of the sucrose cue-evoked dopamine response correlated with the PIT effect that was selectively induced by this stimulus. Satiety attenuated these cue-evoked dopamine responses and behavioral responding, even though rats had never experienced the specific food rewards in this state. These data demonstrate that cue-evoked NAc core responses are sensitive to current need state, one critical variable that determines the current adaptive utility of cue-motivated behavior.

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Background: Environmental reward-predictive stimuli provide a major source of motivation for adaptive reward pursuit behavior. This cue-motivated behavior is known to be mediated by the nucleus accumbens core (NAc). The cholinergic interneurons in the NAc are tonically active and densely arborized and, thus, well-suited to modulate NAc function. But their causal contribution to adaptive behavior remains unknown. Here we investigated the function of NAc cholinergic interneurons in cue-motivated behavior.Methods: To do this, we used chemogenetics, optogenetics, pharmacology, and a translationally analogous Pavlovian-to-instrumental transfer behavioral task designed to assess the motivating influence of a reward-predictive cue over reward-seeking actions in male and female rats. Results:The data show that NAc cholinergic interneuron activity is necessary and sufficient to oppose the motivating influence of appetitive cues. Chemogenetic inhibition of NAc cholinergic interneurons augmented cue-motivated behavior. Optical stimulation of acetylcholine release from NAc cholinergic interneurons prevented cues from invigorating reward-seeking behavior, an effect that was mediated by activation of β2-containing nicotinic acetylcholine receptors.Conclusions: Thus, NAc cholinergic interneurons provide a critical regulatory influence over adaptive cue-motivated behavior and, therefore, are a potential therapeutic target for the maladaptive cue-motivated behavior that marks many psychiatric conditions, including addiction and depression. Collins et al 3Environmental reward-predictive stimuli provide a major source of motivation for adaptive reward pursuit behaviors (1). This incentive motivational value can become dysfunctional in many psychiatric disease states (2). Indeed, it can become amplified allowing cues to become potent triggers for maladaptive compulsive overeating (3), alcohol abuse (4-7), or drug seeking (8-12).Stress, anxiety, and depression (13-16) can also disrupt the motivating influence of appetitive cues, resulting in dampened or inappropriate motivation. The nucleus accumbens core (NAc) has been implicated in cue-motivated behavior (17)(18)(19). But little is known about the function of the major NAc neuromodulator acetylcholine. Such information is crucial given the purported importance of cholinergic signaling in many mental illnesses (20,21).Cholinergic interneurons provide the primary, though not exclusive (22), source of acetylcholine in the NAc (23). Despite comprising only 1-2% of the population, these large-bodied, tonically active neurons are densely arborized (24-29), making them ideally suited to modulate NAc function and associated behaviors. Cholinergic interneurons have also been shown to locally regulate striatal dopamine release (30-32). NAc cholinergic signaling is elevated under conditions that discourage vigorous reward seeking, such as satiety (33, 34), and has been implicated in anxiety-and depression-like states (35, 36) marked by blunted motivation. Cholinergic interneurons are transien...