Mesolimbic Reward Circuitry Research Articles

Sex differences in glutamate transmission and plasticity in reward related regions.

Disruptions in glutamate homeostasis within the mesolimbic reward circuitry may play a role in the pathophysiology of various reward related disorders such as major depressive disorders, anxiety, and substance use disorders. Clear sex differences have emerged in the rates and symptom severity of these disorders which may result from differing underlying mechanisms of glutamatergic signaling. Indeed, preclinical models have begun to uncover baseline sex differences throughout the brain in glutamate transmission and synaptic plasticity. Glutamatergic synaptic strength can be assessed by looking at morphological features of glutamatergic neurons including spine size, spine density, and dendritic branching. Likewise, electrophysiology studies evaluate properties of glutamatergic neurons to provide information of their functional capacity. In combination with measures of glutamatergic transmission, synaptic plasticity can be evaluated using protocols that induce long-term potentiation or long-term depression. This review will consider preclinical rodent literature directly comparing glutamatergic transmission and plasticity in reward related regions of males and females. Additionally, we will suggest which regions are exhibiting evidence for sexually dimorphic mechanisms, convergent mechanisms, or no sex differences in glutamatergic transmission and plasticity and highlight gaps in the literature for future investigation.

Adolescent alcohol drinking interaction with the gut microbiome: implications for adult alcohol use disorder.

Reciprocal communication between the gut microbiota and the brain, commonly referred to as the "gut-brain-axis" is crucial in maintaining overall physiological homeostasis. Gut microbiota development and brain maturation (neuronal connectivity and plasticity) appear to be synchronized and to follow the same timeline during childhood (immature), adolescence (expansion) and adulthood (completion). It is important to note that the mesolimbic reward circuitry develops early on, whereas the maturation of the inhibitory frontal cortical neurons is delayed. This imbalance can lead to increased acquirement of reward-seeking and risk-taking behaviors during adolescence, and consequently eventuate in heightened risk for substance abuse. Thus, there is high initiation of alcohol drinking in early adolescence that significantly increases the risk of alcohol use disorder (AUD) in adulthood. The underlying causes for heightened AUD risk are not well understood. It is suggested that alcohol-associated gut microbiota impairment during adolescence plays a key role in AUD neurodevelopment in adulthood. Furthermore, alcohol-induced dysregulation of microglia, either directly or indirectly through interaction with gut microbiota, may be a critical neuroinflammatory pathway leading to neurodevelopmental impairments and AUD. In this review article, we highlight the influence of adolescent alcohol drinking on gut microbiota, gut-brain axis and microglia, and eventual manifestation of AUD. Furthermore, novel therapeutic interventions via gut microbiota manipulations are discussed briefly.

Reward, motivation and brain imaging in human healthy participants - A narrative review.

Over the past 20 years there has been an increasing number of brain imaging studies on the mechanisms underlying reward motivation in humans. This narrative review describes studies on the neural mechanisms associated with reward motivation and their relationships with cognitive function in healthy human participants. The brain's meso-limbic dopamine reward circuitry in humans is known to control reward-motivated behavior in humans. The medial and lateral Pre-Frontal Cortex (PFC) integrate motivation and cognitive control during decision-making and the dorsolateral PFC (dlPFC) integrates and transmits signals of reward to the mesolimbic and meso-cortical dopamine circuits and initiates motivated behavior. The thalamus and insula influence incentive processing in humans and the motor system plays a role in response to action control. There are reciprocal relationships between reward motivation, learning, memory, imagery, working memory, and attention. The most common method of assessing reward motivation is the monetary incentive delay task (DMRT) and there are several meta-analyses of this paradigm. Genetics modulates motivation reward, and dopamine provides the basis for the interaction between motivational and cognitive control. There is some evidence that male adolescents take more risky decisions than female adolescents and that the lateralization of reward-related DA release in the ventral striatum is confined to men. These studies have implications for our understanding of natural reward and psychiatric conditions like addiction, depression and ADHD. Furthermore, the association between reward and memory can help develop treatment techniques for drug addiction that interfere with consolidation of memory. Finally, there is a lack of research on reward motivation, genetics and sex differences and this can improve our understanding of the relationships between reward, motivation and the brain.

The disruptive relationship among circadian rhythms, pain, and opioids.

Pain behavior and the systems that mediate opioid analgesia and opioid reward processing display circadian rhythms. Moreover, the pain system and opioid processing systems, including the mesolimbic reward circuitry, reciprocally interact with the circadian system. Recent work has demonstrated the disruptive relationship among these three systems. Disruption of circadian rhythms can exacerbate pain behavior and modulate opioid processing, and pain and opioids can influence circadian rhythms. This review highlights evidence demonstrating the relationship among the circadian, pain, and opioid systems. Evidence of how disruption of one of these systems can lead to reciprocal disruptions of the other is then reviewed. Finally, we discuss the interconnected nature of these systems to emphasize the importance of their interactions in therapeutic contexts.

Development of VU6019650: A Potent, Highly Selective, and Systemically Active Orthosteric Antagonist of the M5 Muscarinic Acetylcholine Receptor for the Treatment of Opioid Use Disorder.

The muscarinic acetylcholine receptor (mAChR) subtype 5 (M5) represents a novel potential target for the treatment of multiple addictive disorders, including opioid use disorder. Through chemical optimization of several functional high-throughput screening hits, VU6019650 (27b) was identified as a novel M5 orthosteric antagonist with high potency (human M5 IC50 = 36 nM), M5 subtype selectivity (>100-fold selectivity against human M1-4) and favorable physicochemical properties for systemic dosing in preclinical addiction models. In acute brain slice electrophysiology studies, 27b blocked the nonselective muscarinic agonist oxotremorine-M-induced increases in neuronal firing rates of midbrain dopamine neurons in the ventral tegmental area, a part of the mesolimbic dopaminergic reward circuitry. Moreover, 27b also inhibited oxycodone self-administration in male Sprague-Dawley rats within a dose range that did not impair general motor output.

Historical and Modern Evidence for the Role of Reward Circuitry in Emergence.

Increasing evidence supports a role for brain reward circuitry in modulating arousal along with emergence from anesthesia. Emergence remains an important frontier for investigation, since no drug exists in clinical practice to initiate rapid and smooth emergence. This review discusses clinical and preclinical evidence indicating a role for two brain regions classically considered integral components of the mesolimbic brain reward circuitry, the ventral tegmental area and the nucleus accumbens, in emergence from propofol and volatile anesthesia. Then there is a description of modern systems neuroscience approaches to neural circuit investigations that will help span the large gap between preclinical and clinical investigation with the shared aim of developing therapies to promote rapid emergence without agitation or delirium. This article proposes that neuroscientists include models of whole-brain network activity in future studies to inform the translational value of preclinical investigations and foster productive dialogues with clinician anesthesiologists.

Differential effects of intra-ventral tegmental area ghrelin and glucagon-like peptide-1 on the stimulatory action of D-amphetamine and cocaine-induced ethanol intake in male Sprague Dawley rats

In order to further elucidate the role of mesolimbic peptides in the expression of ethanol reward, the present study investigated the effects of ghrelin and glucagon-like peptide-1 (GLP-1) on ethanol intake, in addition to ethanol intake stimulated by systemic d-amphetamine or cocaine treatment. While a number of studies suggest that ghrelin plays an important role in mesolimbic reward, emerging data now indicate that GLP-1 receptor mechanisms inhibit reward signaling, possibly by directly or indirectly inhibiting ghrelinergic activity within the mesolimbic system. In the present study all rats were initially habituated to a 6% ethanol solution. We then demonstrated that intraperitoneal injections of d-amphetamine and cocaine increased ethanol intake compared to the vehicle condition. In subsequent testing we examined the effects of ventral tegmental area (VTA) ghrelin or vehicle paired with a fixed dose of d-amphetamine or vehicle. In separate rats we then investigated the impact of the GLP-1 agonist exendin-4 (Ex-4), injected into the VTA, on ethanol intake alone, or when Ex-4 was co-administered with d-amphetamine or cocaine. Our results indicated that VTA ghrelin significantly increased ethanol intake, and most importantly, potentiated the effect of d-amphetamine and cocaine on ethanol consumption. Conversely, VTA Ex-4 inhibited ethanol intake and antagonized the stimulatory effect of d-amphetamine and cocaine on ethanol consumption. In a final study we further demonstrated that VTA Ex-4 treatment significantly inhibited the combined stimulatory effects of ghrelin paired with d-amphetamine or ghrelin paired with cocaine. Overall our findings are consistent with a critical role for both ghrelin and GLP-1 receptor mechanisms in mesolimbic ethanol reward circuitry. Moreover, our results further suggest that ghrelin and GLP-1 modulate the stimulatory effect of psychostimulants on ethanol intake.

The Effects of Repeated Morphine Treatment on the Endogenous Cannabinoid System in the Ventral Tegmental Area.

The therapeutic utility of opioids is diminished by their ability to induce rewarding behaviors that may lead to opioid use disorder. Recently, the endogenous cannabinoid system has emerged as a hot topic in the study of opioid reward but relatively little is known about how repeated opioid exposure may affect the endogenous cannabinoid system in the mesolimbic reward circuitry. In the present study, we investigated how sustained morphine may modulate the endogenous cannabinoid system in the ventral tegmental area (VTA) of Sprague Dawley rats, a critical region in the mesolimbic reward circuitry. Studies here using proteomic analysis and quantitative real-time PCR (qRT-PCR) found that the VTA expresses 32 different proteins or genes related to the endogenous cannabinoid system; three of these proteins or genes (PLCγ2, ABHD6, and CB2R) were significantly affected after repeated morphine exposure (CB2R was only detected by qRT-PCR but not proteomics). We also identified that repeated morphine treatment does not alter either anandamide (AEA) or 2-arachidonoylglycerol (2-AG) levels in the VTA compared to saline treatment; however, there may be diminished levels of anandamide (AEA) production in the VTA 4 h after a single morphine injection in both chronic saline and morphine pretreated cohorts. Treating the animals with an inhibitor of 2-AG degradation significantly decreased repeated opioid rewarding behavior. Taken together, our studies reveal a potential influence of sustained opioids on the endocannabinoid system in the VTA, suggesting that the endogenous cannabinoid system may participate in the opioid-induced reward.

Alcohol dependence activates ventral tegmental area projections to central amygdala in male mice and rats.

The neural adaptations that occur during the transition to alcohol dependence are not entirely understood but may include a gradual recruitment of brain stress circuitry by mesolimbic reward circuitry that is activated during early stages of alcohol use. Here, we focused on dopaminergic and nondopaminergic projections from the ventral tegmental area (VTA), important for mediating acute alcohol reinforcement, to the central nucleus of the amygdala (CeA), important for alcohol dependence-related negative affect and escalated alcohol drinking. The VTA projects directly to the CeA, but the functional relevance of this circuit is not fully established. Therefore, we combined retrograde and anterograde tracing, anatomical, and electrophysiological experiments in mice and rats to demonstrate that the CeA receives input from both dopaminergic and nondopaminergic projection neurons primarily from the lateral VTA. We then used slice electrophysiology and fos immunohistochemistry to test the effects of alcohol dependence on activity and activation profiles of CeA-projecting neurons in the VTA. Our data indicate that alcohol dependence activates midbrain projections to the central amygdala, suggesting that VTA projections may trigger plasticity in the CeA during the transition to alcohol dependence and that this circuit may be involved in mediating behavioral dysregulation associated with alcohol dependence.

Psychedelics as an emerging novel intervention in the treatment of substance use disorder: a review.

Classical psychedelics are a group of drugs characterized by their activation of the serotonin-2A (5-hydroxytryptamine-2A; 5-HT2A) receptor and the unique hallucinogenic and mystical-type experiences that result. After a substantial period of restrictions limiting investigations into the therapeutic potential of psychedelics, a relatively recent recommencement of interest has sparked the burgeoning possibility for these drugs to play a part in the treatment of a wide array of psychopathologies. One of the most promising is in the study of addiction. Evidence has emerged that psychedelic agents may provide a novel avenue for the clinical treatment of patients dealing with substance use disorders (SUD). These serotonergic hallucinogens have displayed remarkable and enduring positive outcomes in this area, even when administered as one or two doses. The neural targets for these psychedelics are varied and underlie a complex mechanism of action-modulating multiple neural networks. It is believed that these agents allow for the reorganization of disordered neural pathways in the default mode network and attenuate maladaptive signaling in mesolimbic reward circuitry. The aim of this review is to examine the current standing of evidence regarding psychedelic psychopharmacology and to provide an overview of the use and effectiveness of these drugs in the treatment of SUD, alcohol use disorder, and for smoking cessation.

E-cigarettes, nicotine, the lung and the brain: multi-level cascading pathophysiology.

Tobacco smoking is highly addictive and causes respiratory disease, cardiovascular disease and multiple types of cancer. Electronic-cigarettes (e-cigarettes) are non-combustible tobacco alternatives that aerosolize nicotine and flavouring agents in a propylene glycol-vegetable glycerine vehicle. They were originally envisaged as a tobacco cessation aid, but whether or not they help people to quit tobacco use is controversial. In this review, we have compared and contrasted what is known regarding the effects of nicotine on the lungs vs. the effects of nicotine in the brain in the context of addiction. Critically, both combustible tobacco products and e-cigarettes contain nicotine, a highly addictive, plant-derived alkaloid that binds to nicotinic acetylcholine receptors (nAChRs). Nicotine's reinforcing properties are primarily mediated by activation of the brain's mesolimbic reward circuitry and release of the neurotransmitter dopamine that contribute to the development of addiction. Moreover, nicotine addiction drives repeated intake that results in chronic pulmonary exposure to either tobacco smoke or e-cigarettes despite negative respiratory symptoms. Beyond the brain, nAChRs are also highly expressed in peripheral neurons, epithelia and immune cells, where their activation may cause harmful effects. Thus, nicotine, a key ingredient of both conventional and electronic cigarettes, produces neurological effects that drive addiction and may damage the lungs in the process, producing a complex, multilevel pathological state. We conclude that vaping needs to be studied by multi-disciplinary teams that include pulmonary and neurophysiologists as well as behaviourists and addiction specialists to fully understand their impact on human physiology.

Differential color tuning of the mesolimbic reward system

Visual wavelengths are not only associated with the subjective experience of color but also have long been thought to regulate affect. Here we examined the attracting rewarding properties of opposite ends of the wavelength spectrum, as well as their individual variation. As reward is multifaceted, we sought convergent evidence from subjective and objective behavioral and attentional indices, as well as its neural reward system bases. On average, short (blue) relative to long (red) wavelengths were judged subjectively more pleasant and had objectively greater behavioral and attentional salience, regulating speed of simple color discriminations and perception of temporal order. Consistent with reward, these color effects were magnified following monetary reinforcement. Pronounced individual differences in color effects were related to reward but not punishment sensitivity, with blue relative to red preference associated with high relative to low reward sensitivity. An fMRI study revealed these individual differences were supported by color-dependent functional coupling between the visual cortices and mesolimbic reward circuitry. Our findings reveal the reward bases of color, demonstrating color is a potent regulator of perception, action, and neural dynamics.

Endocannabinoid genetic variation enhances vulnerability to THC reward in adolescent female mice.

Adolescence represents a developmental period with the highest risk for initiating cannabis use. Little is known about whether genetic variation in the endocannabinoid system alters mesolimbic reward circuitry to produce vulnerability to the rewarding properties of the exogenous cannabinoid Δ9-tetrahydrocannabinol (THC). Using a genetic knock-in mouse model (FAAHC/A) that biologically recapitulates the human polymorphism associated with problematic drug use, we find that in adolescent female mice, but not male mice, this FAAH polymorphism enhances the mesolimbic dopamine circuitry projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and alters cannabinoid receptor 1 (CB1R) levels at inhibitory and excitatory terminals in the VTA. These developmental changes collectively increase vulnerability of adolescent female FAAHC/A mice to THC preference that persists into adulthood. Together, these findings suggest that this endocannabinoid genetic variant is a contributing factor for increased susceptibility to cannabis dependence in adolescent females.

Pharmacological Antagonism of T-Type Calcium Channels Constrains Rebound Burst Firing in Two Distinct Subpopulations of GABA Neurons in the Rat Ventral Tegmental Area: Implications for α-Lipoic Acid.

The ventral tegmental area (VTA) is a midbrain region highly involved in motivation and reward. A large body of work has investigated synaptic plasticity and ion channel excitability in this area, which has strong implication in drug abuse. We recently provided electrophysiological and pharmacological evidence that the CaV3.1 isoform of T-type voltage-gated calcium channels contributes to the excitability of VTA dopamine (DA) neurons. However, the role of T-channels in excitability of VTA gamma-amino-butyric acid (GABA) neurons remained unaddressed. Here, with a population study of rat VTA GABA neurons, we provide evidence that T-channels contribute to rebound spiking activity in two phenotypically distinct subpopulations of GABAergic neurons, each with differing electrophysiological characteristics. Additionally, we provide the first study to investigate the effect of α-lipoic acid (ALA) on ion channels in mesolimbic reward circuitry. Taken together, our population study and pharmacology experiments implicate T-channels as a target for therapies aimed at tempering VTA and mesolimbic circuit excitability.

Механизмы контроля потребления алкоголя: экспрессия генов ноцицептин/каппа-опиоидной системы в мозге крыс

Каппа-опиоидная и ноцицептиновая системы играют важную роль в модуляции функций дофаминергической системы «награды», однако их роль в механизмах формирования аддиктивного поведения до конца не ясна. Цель исследования: сравнить уровни мРНК каппа-опиоидного (OPRK1) и ноцицептинового (OPRL1) рецепторов, а также их эндогенных лигандов - препродинорфина (PDYN) и препроноцицептина (PDYN) в мозге животных с различным уровнем предпочтения алкоголя. Методы: потребление алкоголя у половозрелых крыс-самцов Wistar регистрировали с 60-го по 85-й дни жизни в модели «свободный выбор» между водой и 10% раствором этанола. Относительный уровень мРНК в структурах мозга определяли на 86-й день жизни методом ПЦР в реальном времени. Результаты: Экспрессия мРНК PDYN и PNOC в стриатуме, и OPRK1 и OPRL1 в миндалине была достоверно выше у «отвергающих», т.е. контролирующих потребление алкоголя на постоянно низком уровне животных, по сравнению с «предпочитающими», увеличившими потребление алкоголя в течение эксперимента. Заключение: более высокий уровень экспрессии генов эндогенных опиоидов PDYN и PNOC и их рецепторов в исследованных областях мозга может обусловливать меньшую гедоническую привлекательность алкоголя, играя превентивную роль и снижая риск злоупотребления алкоголем Kappa-opioidergic and nociceptinergic systems both inhibit the mesolimbic reward circuitry but their role in mechanisms of addictive behavior still is not well understood. Objective of the study was to compare expression of kappa opioid and nociceptin receptor genes (OPRK1 and OPRL1, respectively) and their endogenous ligands, preprodynorphin (PDYN) and prepronociceptin (PNOC), in the mesolimbic areas of rats with high and low voluntary alcohol consumption. Methods. Individually housed male Wistar rats were given a 25-day-long two-bottle (10% ethanol/water) free choice trial. mRNA levels were measured using the real-time polymerase chain reaction (qPCR). Results. Alcohol preferring rats progressively increased their ethanol consumption over the course of experiment while non-preferring, low-drinking animals controlled their alcohol intake near the baseline level. Alcohol non-preferring rats were identified to have significantly higher levels of PDYN and PNOC mRNA in the striatum and OPRK1 and OPRL1 mRNA in the amygdala compared to ethanol preferring animals. Conclusion. We suggested that higher levels of the “anti-reward opioid system” gene expression in mesolimbic structures may blunt the hedonic response to alcohol and thus preclude the increase in alcohol preference and uncontrolled excessive alcohol intake.

Divergent associations between ghrelin and neural responsivity to palatable food in hyperphagic and hypophagic depression

BackgroundThe neurobiological mechanisms involved in divergent appetitive phenotypes in major depressive disorder (MDD) are not well understood, although recent data suggest disruption in mesolimbic reward circuitry. Ghrelin, an orexigenic hormone, has been shown to modulate the reward circuitry. We aimed to investigate the relationship between acylated ghrelin levels and the neural response to food stimuli in individuals with hyperphagic and hypophagic MDD in remission. MethodsWomen with hyperphagic MDD (n = 10), hypophagic MDD (n = 18), and healthy controls (HC; n = 18) underwent fMRI scanning during which they viewed images of food. The fMRI session was followed by a standardized meal, appetite ratings, and serial blood draws. ResultsIn individuals with hyperphagic MDD, greater change in acylated ghrelin in response to a meal was associated with increased BOLD response to high-calorie food in the bilateral ventral tegmental area and left hypothalamus. In contrast, negative associations were observed between acylated ghrelin AUC and BOLD activity in the right hypothalamus in the hypophagic MDD group. LimitationsUnbalanced group sizes with a relatively small sample in the hyperphagic MDD group. ConclusionsIn the absence of differences in absolute ghrelin levels between the hyperphagic MDD and HC groups, results in hyperphagic MDD might suggest a ghrelinergic signaling mechanism for increased appetite during an MDD episode in this group. Our findings shed light on interactions between appetite hormones and mesolimbic circuitry which could contribute to development of therapeutic targets for opposing appetite phenotypes in depression.

Valuation of knowledge and ignorance in mesolimbic reward circuitry.

The pursuit of knowledge is a basic feature of human nature. However, in domains ranging from health to finance people sometimes choose to remain ignorant. Here, we show that valence is central to the process by which the human brain evaluates the opportunity to gain information, explaining why knowledge may not always be preferred. We reveal that the mesolimbic reward circuitry selectively treats the opportunity to gain knowledge about future favorable outcomes, but not unfavorable outcomes, as if it has positive utility. This neural coding predicts participants' tendency to choose knowledge about future desirable outcomes more often than undesirable ones, and to choose ignorance about future undesirable outcomes more often than desirable ones. Strikingly, participants are willing to pay both for knowledge and ignorance as a function of the expected valence of knowledge. The orbitofrontal cortex (OFC), however, responds to the opportunity to receive knowledge over ignorance regardless of the valence of the information. Connectivity between the OFC and mesolimbic circuitry could contribute to a general preference for knowledge that is also modulated by valence. Our findings characterize the importance of valence in information seeking and its underlying neural computation. This mechanism could lead to suboptimal behavior, such as when people reject medical screenings or monitor investments more during bull than bear markets.

Evaluating anhedonia in the activity-based anorexia (ABA) rat model

Patients suffering anorexia nervosa (AN) become anhedonic, in other words, unable or unwilling to derive normal pleasures and avoid rewarding outcomes, most profoundly in food intake. The neurobiological underpinnings of anhedonia are likely to involve mesolimbic reward circuitry. We propose here that this circuitry and its involvement in AN can be investigated using the activity-based anorexia (ABA) rodent model that recapitulates many of the characteristics of the human condition, most notably rapid weight loss. Preference for sweetened water was used to assay hedonic processing in female Sprague-Dawley rats exposed to the ABA protocol, which involves free access to running wheels paired with time-limited access to food. This protocol uncovered a transient anhedonia in only one quarter of cases; however, exposure to running wheels alone was associated with a rapid aversion to sweetened water (F1.833, 20.17 = 78.29, p < .0001), and time-limited food access alone did not impact preference (F2.205, 24.25 = 0.305, p = .761). High levels of running wheel activity prior to the onset of food restriction increased susceptibility to body weight loss in ABA (F10,196.129 = 2.069, p = .029) and food anticipatory activity predicted subsequent food intake only for rats that were resistant to body weight loss (r = 0.44, p = .001). These data are inconsistent with the hypothesis that anhedonia underscores the precipitous weight loss in ABA, however, they highlight the predictive nature of hyperactivity in susceptibility to the ABA paradigm. These results will help inform the neurobiological framework of ABA and provide insight into the mechanisms of reward relevant to feeding and weight loss.

F163. Inflammation is Associated With Mesolimbic Reward Circuitry in Major Depression

Growing evidence implicates immune dysregulation in major depressive disorder (MDD), which impacts mood state via changes in a central ‘reward circuit’ that includes dopaminergic projections from the ventral tegmental area to nucleus accumbens (VTA–NAc).

Selective inhibition of M5 muscarinic acetylcholine receptors attenuates cocaine self-administration in rats.

Cocaine use disorder (CUD) remains a debilitating health problem in the United States for which there are no Food and Drug Administration-approved treatment options. Accumulating anatomical and electrophysiological evidence indicates that the muscarinic acetylcholine receptor (mAChR) subtype 5 (M5 ) plays a critical role in the regulation of the mesolimbic dopaminergic reward circuitry, a major site of action for cocaine and other psychostimulants. In addition, M5 knockout mice exhibit reduced cocaine self-administration behaviors with no differences in sugar pellet-maintained responding relative to wild-type mice. These findings suggest that selective inhibition of M5 mAChR may provide a novel pharmacological approach for targeting CUD. Recently, we reported the synthesis and characterization of ML375, a selective negative allosteric modulator (NAM) for the rat and human M5 mAChR with optimized pharmacokinetic properties for systemic dosing in rodents. In the present study, male Sprague-Dawley rats were trained to self-administer intravenous cocaine (0.1-0.75mg/kg/infusion) under a 10-response fixed ratio or a progressive ratio schedule of reinforcement. Under both schedules of reinforcement, ML375 produced dose-related reductions in cocaine self-administration. ML375 also modestly reduced sugar pellet-maintained responding on the 10-response, fixed ratio schedule but had no effect under a progressive ratio schedule of reinforcement. Further, ML375 did not affect general motor output as assessed by a rotarod test. Collectively, these results provide the first demonstration that selective inhibition of M5 using the M5 NAM ML375 can attenuate both the reinforcing effects and the relative strength of cocaine and suggest that M5 NAMs may represent a promising, novel treatment approach for CUD.