Environmental cues can serve as triggers for various pathological behaviors, including drug seeking and compulsive overeating. Indeed, there is growing evidence that the behavioral influence of drug-paired cues becomes dysregulated in addiction, accounting for the progressive nature of this disorder. Obesity and drug addiction are major intractable public health problems in the US, accounting for hundreds of billions of dollars in costs associated with health care, crime, incarceration and law enforcement. Effective approaches to prevent and/or treat these disorders are therefore badly needed. The long-term goal of this research proposal is to advance our understanding of the basic neural substrates of cue-triggered reward seeking to gain insight into how such pathological states arise and determine what can be done to combat them. Addictive substances are thought to hijack the normal role of reward-predictive stimuli in adaptive decision making. Research has identified two distinct functions of such cues. First, they provide a nonspecific motivational function, indiscriminately invigorating reward-seeking behaviors. This motivational function is gated by physiological need, such that, for instance, shifting an organism from hunger-to-satiety will suppress the motivational impact of a food-associated cue. Second, reward-predictive cues can bias decision processes to favor actions with which they share a common outcome. Recent studies in rodents and humans have established that these processes are mediated by distinct corticostriatal circuits including the nucleus accumbens core (NAc), which supports the general motivational process, and the dorsomedial striatum (DMS), which supports the outcome-specific, action biasing process. However, much remains unknown regarding the specific neurochemical underpinnings of these aspects of cue-motivated behavior. Here we provide an in-depth and hypothesis-driven investigation of the involvement of dopamine and acetylcholine, the two main striatal neuromodulators. While it is known that cue-motivated behavior is accompanied by phasic striatal dopamine signaling, the proposed research will provide critical tests of whether these events are causally linked. The contributions of acetylcholine to motivated behavior are even less well understood, though there is evidence that striatal acetylcholine is involved in the homeostatic regulation of feeding behavior. Importantly, recent in vitro studies have shown that acetylcholine plays an important, but complex, role in modulating striatal dopamine release through its actions at nicotinic acetylcholine receptors on dopamine terminals. While this work has been crucial in characterizing the neuromodulatory relationship, its ultimate behavioral significance is not known. The current proposal will apply a highly integrative approach to investigate the potentially region- and function-specific roles of dopamine and acetylcholine and their interaction in cue-motivated behavior by combining sophisticated behavioral analysis with pharmacological and optogenetic manipulations, and in vivo neurochemical analysis of striatal acetylcholine and dopamine systems.
Cues associated with rewarding events, like palatable food or addictive drugs; acquire powerful behavioral effects that allow them to motivate reward seeking behavior and bias decisions about action selection in favor of anticipated goals. Cue-triggered reward seeking is known to depend on transmission of the neuromodulator dopamine in an area of the brain called the striatum. There has been a recent surge of elegant basic science research showing that striatal dopamine signaling is regulated by acetylcholine, another neuromodulator, suggesting that these neurochemical systems work together to mediate motivated behavior. The current proposal uses state-of-the-art techniques to probe and monitor striatal neurotransmission to test this important hypothesis, which may have significant implications for the treatment and prevention of drug addiction.
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