Des-acyl ghrelin reduces alcohol intake and alcohol-induced reward in rodents.

The mechanisms contributing to alcohol use disorder (AUD) are complex and the orexigenic peptide ghrelin, which enhances alcohol reward, is implied as a crucial modulator. The major proportion of circulating ghrelin is however the non-octanoylated form of ghrelin, des-acyl ghrelin (DAG), whose role in reward processes is unknown. As recent studies show that DAG decreases food intake, we hypothesize that DAG attenuates alcohol-related responses in animal models. Acute and repeated DAG treatment dose-dependently decreased alcohol drinking in male and female rats. In these alcohol-consuming male rats, repeated DAG treatment causes higher levels of dopamine metabolites in the ventral tegmental area, an area central to reward processing. The role of DAG in reward processing is further supported as DAG prevents alcohol-induced locomotor stimulation, reward in the conditioned place preference paradigm, and dopamine release in the nucleus accumbens in male rodents. On the contrary, DAG does not alter the memory of alcohol reward or affect neurotransmission in the hippocampus, an area central to memory. Further, circulating DAG levels are positively correlated with alcohol drinking in female but not male rats. Studies were conducted in attempts to identify tentative targets of DAG, which currently are unknown. Data from these recombinant cell system revealed that DAG does not bind to either of the monoamine transporters, 5HT2A, CB1, or µ-opioid receptors. Collectively, our data show that DAG attenuates alcohol-related responses in rodents, an effect opposite to that of ghrelin, and contributes towards a deeper insight into behaviors regulated by the ghrelinergic signaling pathway.

Pre- and postsynaptic signatures in the prelimbic cortex associated with "alcohol use disorder" in the rat.

The transition to alcohol use disorder (AUD) involves persistent neuroadaptations in executive control functions primarily regulated by the medial prefrontal cortex. However, the neurophysiological correlates to behavioral manifestations of AUD are not fully defined. The association between cortical neuroadaptations and behavioral manifestations of addiction was studied using a multi-symptomatic operant model based on the DSM-5 diagnostic criteria for AUD. This model aimed to characterize an AUD-vulnerable and AUD-resistant subpopulation of outbred male Wistar rats and was combined with electrophysiological measurements in the prelimbic cortex (PL). Mirroring clinical observations, rats exhibited individual variability in their vulnerability to develop AUD-like behavior, including motivation to seek for alcohol (crit 1), increased effort to obtain the substance (crit 2), and continued drinking despite negative consequences (crit 3). Only a small subset of rats met all the aforementioned AUD criteria (3 crit, AUD-vulnerable), while a larger fraction was considered AUD-resilient (0 crit). The development of AUD-like behavior was characterized by disruptions in glutamatergic synaptic activity, involving decreased frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and heightened intrinsic excitability in layers 2/3 PL pyramidal neurons. These alterations were concomitant with a significant impairment in the ability of mGlu2/3 receptors to negatively regulate glutamate release in the PL but not in downstream regions like the basolateral amygdala or nucleus accumbens core. In conclusion alterations in PL synaptic activity were strongly associated with individual addiction scores, indicating their role as potential markers of the behavioral manifestations linked to AUD psychopathology.

Decoding the influence of central LEAP2 on food intake and its effect on accumbal dopamine release.

The gut-brain peptide ghrelin and its receptor are established as a regulator of hunger and reward-processing. However, the recently recognized ghrelin receptor inverse agonist, liver-expressed antimicrobial peptide 2 (LEAP2), is less characterized. The present study aimed to elucidate LEAP2s central effect on reward-related behaviors through feeding and its mechanism. LEAP2 was administrated centrally in mice and effectively reduced feeding and intake of palatable foods. Strikingly, LEAP2s effect on feeding was correlated to the preference of the palatable food. Further, LEAP2 reduced the rewarding memory of high preference foods, and attenuated the accumbal dopamine release associated with palatable food exposure and eating. Interestingly, LEAP2 was widely expressed in the brain, and particularly in reward-related brain areas such as the laterodorsal tegmental area (LDTg). This expression was markedly altered when allowed free access to palatable foods. Accordingly, infusion of LEAP2 into LDTg was sufficient to transiently reduce acute palatable food intake. Taken together, the present results show that central LEAP2 has a profound effect on dopaminergic reward signaling associated with food and affects several aspects of feeding. The present study highlights LEAP2s effect on reward, which may have applications for obesity and other reward-related psychiatric and neurological disorders.

Antismoking agents do not contribute synergistically to semaglutide's ability to reduce alcohol intake in rats.

Preclinical studies have identified glucagon-like peptide-1 receptor (GLP-1R) agonists, and the antismoking agents varenicline and bupropion as tentative agents for treatment of alcohol use disorder (AUD). Combining different medications is a recent approach that has gained attention regarding heterogenous and difficult-to-treat diseases, like AUD. Successfully, this approach has been tested for the combination of varenicline and bupropion as it prevents relapse to alcohol drinking in rats. However, studies assessing the effects of the combination of semaglutide, an FDA-approved GLP-1R agonist for diabetes type II, and varenicline or bupropion to reduce alcohol intake in male and female rats remains to be conducted. Another approach to influence treatment outcome is to combine a medication with feeding interventions like high fat diet (HFD). While HFD reduces alcohol intake, the ability of the combination of HFD and semaglutide to alter alcohol drinking is unknown and thus the subject for a pilot study. Therefore, three intermittent alcohol drinking experiments were conducted to elucidate the effectiveness of these treatment combinations. We show that semaglutide, bupropion or HFD reduces alcohol intake in male as well as female rats. While various studies reveal beneficial effects of combinatorial pharmacotherapies for the treatment of AUD, we herein do not report any additive effects on alcohol intake by adding either varenicline or bupropion to semaglutide treatment. Neither does HFD exposure alter the ability of semaglutide to reduce alcohol intake. Although no additive effects by the combinatorial treatments are found, these findings collectively provide insight into possible monotherapeutical treatments for AUD.

Semaglutide reduces alcohol intake and relapse-like drinking in male and female rats.

BACKGROUND: Glucagon-like peptide1 receptor (GLP-1R) agonists have been found to reduce alcohol drinking in rodents and overweight patients with alcohol use disorder (AUD). However, the probability of low semaglutide doses, an agonist with higher potency and affinity for GLP-1R, to attenuate alcohol-related responses in rodents and the underlying neuronal mechanisms is unknown. METHODS: In the intermittent access model, we examined the ability of semaglutide to decrease alcohol intake and block relapse-like drinking, as well as imaging the binding of fluorescently marked semaglutide to nucleus accumbens (NAc) in both male and female rats. The suppressive effect of semaglutide on alcohol-induced locomotor stimulation and in vivo dopamine release in NAc was tested in male mice. We evaluated effect of semaglutide on the in vivo release of dopamine metabolites (DOPAC and HVA) and gene expression of enzymes metabolising dopamine (MAOA and COMT) in male mice. FINDINGS: In male and female rats, acute and repeated semaglutide administration reduced alcohol intake and prevented relapse-like drinking. Moreover, fluorescently labelled semaglutide was detected in NAc of alcohol-drinking male and female rats. Further, semaglutide attenuated the ability of alcohol to cause hyperlocomotion and to elevate dopamine in NAc in male mice. As further shown in male mice, semaglutide enhanced DOPAC and HVA in NAc when alcohol was onboard and increased the gene expression of COMT and MAOA. INTERPRETATION: Altogether, this indicates that semaglutide reduces alcohol drinking behaviours, possibly via a reduction in alcohol-induced reward and NAc dependent mechanisms. As semaglutide also decreased body weight of alcohol-drinking rats of both sexes, upcoming clinical studies should test the plausibility that semaglutide reduces alcohol intake and body weight in overweight AUD patients. FUNDING: Swedish Research Council (2019-01676), LUA/ALF (723941) from the Sahlgrenska University Hospital and the Swedish brain foundation.

Free-access intravenous alcohol self-administration in social drinkers and individuals with alcohol use disorder: Evaluation of relationships with phosphatidylethanol and self-reported alcohol consumption.

BACKGROUND: The free-access (FA) intravenous alcohol self-administration (IV-ASA) paradigm is an experimental approach that can identify modulators of alcohol consumption in humans. Moreover, the outcome measures of IV-ASA paradigms are associated with self-reported alcohol intake using the timeline follow-back method (TLFB). To evaluate how FA IV-ASA reflects drinking in real life, we examined the relationship between an objective marker of recent alcohol intake, phosphatidylethanol in blood (B-PEth), and TLFB and measures obtained during IV-ASA in individuals with alcohol use disorder (AUD) and social drinkers (SD). We also explored the associations between these measures and gut-brain peptides involved in AUD pathophysiology. METHODS: Thirty-eight participants completed a laboratory session in which they self-administered alcohol intravenously. The safety limit was 200 mg%, and main outcomes were mean and peak breath alcohol concentrations (BrAC). Blood samples were drawn prior to IV-ASA and subjective alcohol effects were rated during the experiment. RESULTS: The study sample comprised 24 SD and 14 participants with DSM-5 mild AUD. Although BrACs were not associated with B-PEth or TLFB in the full sample or AUD subgroup, there was an association with TLFB in SD. In both subgroups, BrACs were associated with alcohol craving but with differential timing. Total ghrelin levels were higher in AUD participants than in SD. CONCLUSIONS: No associations between B-PEth levels and achieved BrACs were observed in the mild AUD group, the SD group, or the full sample. The ability for FA IV-ASA to reflect recent drinking was confirmed only for TLFB in SD, whereas there were no associations within the smaller subsample of participants with mild AUD or in the full sample. Further studies that include a larger AUD sample are warranted. The association of BrACs with craving for alcohol suggests that the IV-ASA method may be useful for assessing interventions that target craving. This could be explored by using the FA IV-ASA model to evaluate the effects on craving of approved pharmacotherapies for AUD.

The therapeutic potential of glucagon-like peptide-1 for persons with addictions based on findings from preclinical and clinical studies.

Although the multifaceted mechanisms underlying alcohol use disorder (AUD) have been partially defined, the neurobiological complexity of this disorder is yet to be unraveled. One of the systems that have gained attention in recent times is the gut-brain axis. Although numerous peptides participate in this axis, glucagon-like peptide-1 (GLP-1) plays a central role. GLP-1 is a crucial anorexigenic peptide, with potent abilities to reduce food intake and body weight. The physiological complexity of GLP-1 entails glucose homeostasis, gastrointestinal motility, and the release of insulin and glucagon. As reviewed in this study, acute or repeated treatment with GLP-1 receptor (GLP-1R) agonists decreases alcohol consumption in rodents. Moreover, the abilities of alcohol to promote hyperlocomotion, dopamine release in the nucleus accumbens, and reward in the conditioned place preference paradigm are all suppressed by GLP-1R ligands. Moreover, activation of GLP-1R suppresses the motivation to consume alcohol, alcohol-seeking behaviors, and relapse drinking in male rodents. Similarly, abstinence symptoms experienced during alcohol withdrawal are attenuated by activation of the GLP-1 pathway. On a similar note, the activation of GLP-1 receptors within areas of the brain that are processing reward modulates these alcohol-related responses. Another area that is crucial for this ability is the nucleus of the solitary tract, which is where GLP-1 is produced and from which GLP-1-containing neurons project to areas of reward. These findings may have clinical relevance as AUD is associated with polymorphisms in GLP-1-related genes. Although a GLP-1R agonist does not alter alcohol intake in AUD patients, it reduces this consumption in a sub-population of obese AUD individuals. Given the uncertainty of this outcome, additional clinical studies of obese AUD patients should explore the effects of the GLP-1R agonists on alcohol intake and body weight. Furthermore, GLP-1 receptors modulate the behavioral and neurochemical responses to addictive drugs. Taken together, these preclinical and clinical findings imply that the GLP-1 pathway plays a role in the complex mechanisms regulating alcohol and drug consumption patterns, unveiling a novel aspect of addiction medicine.

Animal studies reveal that the ghrelin pathway regulates alcohol-mediated responses.

Alcohol use disorder (AUD) is often described as repeated phases of binge drinking, compulsive alcohol-taking, craving for alcohol during withdrawal, and drinking with an aim to a reduce the negative consequences. Although multifaceted, alcohol-induced reward is one aspect influencing the former three of these. The neurobiological mechanisms regulating AUD processes are complex and one of these systems is the gut-brain peptide ghrelin. The vast physiological properties of ghrelin are mediated via growth hormone secretagogue receptor (GHSR, ghrelin receptor). Ghrelin is well known for its ability to control feeding, hunger, and metabolism. Moreover, ghrelin signaling appears central for alcohol-mediated responses; findings reviewed herein. In male rodents GHSR antagonism reduces alcohol consumption, prevents relapse drinking, and attenuates the motivation to consume alcohol. On the other hand, ghrelin increases the consumption of alcohol. This ghrelin-alcohol interaction is also verified to some extent in humans with high alcohol consumption. In addition, either pharmacological or genetic suppression of GHSR decreases several alcohol-related effects (behavioral or neurochemical). Indeed, this suppression blocks the alcohol-induced hyperlocomotion and dopamine release in nucleus accumbens as well as ablates the alcohol reward in the conditioned place preference model. Although not fully elucidated, this interaction appears to involve areas central for reward, such as the ventral tegmental area (VTA) and brain nodes targeted by VTA projections. As reviewed briefly, the ghrelin pathway does not only modulate alcohol-mediated effects, it regulates reward-related behaviors induced by addictive drugs. Although personality traits like impulsivity and risk-taking behaviors are common in patients with AUD, the role of the ghrelin pathway thereof is unknown and remains to be studied. In summary, the ghrelin pathway regulates addiction processes like AUD and therefore the possibility that GHSR antagonism reduces alcohol or drug-taking should be explored in randomized clinical trials.

Abstinence-Induced Nicotine Seeking Relays on a Persistent Hypoglutamatergic State within the Amygdalo-Striatal Neurocircuitry.

Nicotine robustly sustains smoking behavior by acting as a primary reinforcer and by enhancing the incentive salience of the nicotine-associated stimuli. The motivational effects produced by environmental cues associated with nicotine delivery can progressively manifest during abstinence resulting in reinstatement of nicotine seeking. However, how the activity in reward neuronal circuits is transformed during abstinence-induced nicotine seeking is not yet fully understood. In here we used a contingent nicotine and saline control self-administration model to disentangle the contribution of cue-elicited seeking responding for nicotine after drug abstinence in male Wistar rats. Using ex vivo electrophysiological recordings and a network analysis approach, we defined temporal and brain-region specific amygdalo-striatal glutamatergic alterations that occur during nicotine abstinence. The results from this study provide critical evidence indicating a persistent hypoglutamatergic state within the amygdalo-striatal neurocircuitry over protracted nicotine abstinence. During abstinence-induced nicotine seeking, electrophysiological recordings showed progressive neuroadaptations in dorsal and ventral striatum already at 14-d abstinence while neuroadaptations in subregions of the amygdala emerged only after 28-d abstinence. The observed neuroadaptations pointed to a brain network involving the amygdala and the dorsolateral striatum (DLS) to be implied in cue-induced reinstatement of nicotine seeking. Together these data suggest long-lasting neuroadaptations that might reflect neuroplastic changes responsible to abstinence-induced nicotine craving. Neurophysiological transformations were detected within a time window that allows therapeutic intervention advancing clinical development of preventive strategies in nicotine addiction.

Ghrelin activates the mesolimbic dopamine system via nitric oxide associated mechanisms in the ventral tegmental area.

Besides enhanced feeding, the orexigenic peptide ghrelin activates the mesolimbic dopamine system to cause reward as measured by locomotor stimulation, dopamine release in nucleus accumbens shell (NAcS), and conditioned place preference. Although the ventral tegmental area (VTA) appears to be a central brain region for this ghrelin-reward, the underlying mechanisms within this area are unknown. The findings that the gaseous neurotransmitter nitric oxide (NO) modulate the ghrelin enhanced feeding, led us to hypothesize that ghrelin increases NO levels in the VTA, and thereby stimulates reward-related behaviors. We initially demonstrated that inhibition of NO synthesis blocked the ghrelin-induced activation of the mesolimbic dopamine system. We then established that antagonism of downstream signaling of NO in the VTA, namely sGC, prevents the ability of ghrelin to stimulate the mesolimbic dopamine system. The association of ghrelin to NO was further strengthened by in vivo electrochemical recordings showing that ghrelin enhances the NO release in the VTA. Besides a GABAB -receptor agonist, known to reduce NO and cGMP, blocks the stimulatory properties of ghrelin. The present series of experiments reveal that ablated NO signaling, through pharmacologically inhibiting the production of NO and/or cGMP, prevents the ability of ghrelin to induced reward-related behaviors.

Role of the ghrelin system in alcohol use disorder and alcohol-associated liver disease: A narrative review.

Unhealthy alcohol consumption is a global health problem. Adverse individual, public health, and socioeconomic consequences are attributable to harmful alcohol use. Epidemiological studies have shown that alcohol use disorder (AUD) and alcohol-associated liver disease (ALD) are the top two pathologies among alcohol-related diseases. Consistent with the major role that the liver plays in alcohol metabolism, uncontrolled drinking may cause significant damage to the liver. This damage is initiated by excessive fat accumulation in the liver, which can further progress to advanced liver disease. The only effective therapeutic strategies currently available for ALD are alcohol abstinence or liver transplantation. Any molecule with dual-pronged effects at the central and peripheral organs controlling addictive behaviors and associated metabolic pathways are a potentially important therapeutic target for treating AUD and ALD. Ghrelin, a hormone primarily derived from the stomach, has such properties, and regulates both behavioral and metabolic functions. In this review, we highlight recent advances in understanding the peripheral and central functions of the ghrelin system and its role in AUD and ALD pathogenesis. We first discuss the correlation between blood ghrelin concentrations and alcohol use or abstinence. Next, we discuss the role of ghrelin in alcohol-seeking behaviors and finally its role in the development of fatty liver by metabolic regulations and organ crosstalk. We propose that a better understanding of the ghrelin system could open an innovative avenue for improved treatments for AUD and associated medical consequences, including ALD.

Activation of glucagon-like peptide-1 receptors reduces the acquisition of aggression-like behaviors in male mice.

Aggression is a complex social behavior, which is provoked in the defense of limited resources including food and mates. Recent advances show that the gut-brain hormone ghrelin modulates aggressive behaviors. As the gut-brain hormone glucagon-like peptide-1 (GLP-1) reduces food intake and sexual behaviors its potential role in aggressive behaviors is likely. Therefore, we investigated a tentative link between GLP-1 and aggressive behaviors by combining preclinical and human genetic-association studies. The influence of acute or repeated injections of a GLP-1 receptor (GLP-1R) agonist, exendin-4 (Ex4), on aggressive behaviors was assessed in male mice exposed to the resident-intruder paradigm. Besides, possible mechanisms participating in the ability of Ex4 to reduce aggressive behaviors were evaluated. Associations of polymorphisms in GLP-1R genes and overt aggression in males of the CATSS cohort were assessed. In male mice, repeated, but not acute, Ex4 treatment dose-dependently reduced aggressive behaviors. Neurochemical and western blot studies further revealed that putative serotonergic and noradrenergic signaling in nucleus accumbens, specifically the shell compartment, may participate in the interaction between Ex4 and aggression. As high-fat diet (HFD) impairs the responsiveness to GLP-1 on various behaviors the possibility that HFD blunts the ability of Ex4 to reduce aggressive behaviors was explored. Indeed, the levels of aggression was similar in vehicle and Ex4 treated mice consuming HFD. In humans, there were no associations between polymorphisms of the GLP-1R genes and overt aggression. Overall, GLP-1 signaling suppresses acquisition of aggressive behaviors via central neurotransmission and additional studies exploring this link are warranted.

Insight into the role of the gut-brain axis in alcohol-related responses: Emphasis on GLP-1, amylin, and ghrelin.

Alcohol use disorder (AUD) contributes substantially to global morbidity and mortality. Given the heterogenicity of this brain disease, available pharmacological treatments only display efficacy in sub-set of individuals. The need for additional treatment options is thus substantial and is the goal of preclinical studies unraveling neurobiological mechanisms underlying AUD. Although these neurobiological processes are complex and numerous, one system gaining recent attention is the gut-brain axis. Peptides of the gut-brain axis include anorexigenic peptide like glucagon-like peptide-1 (GLP-1) and amylin as well as the orexigenic peptide ghrelin. In animal models, agonists of the GLP-1 or amylin receptor and ghrelin receptor (GHSR) antagonists reduce alcohol drinking, relapse drinking, and alcohol-seeking. Moreover, these three gut-brain peptides modulate alcohol-related responses (behavioral and neurochemical) in rodents, suggesting that the alcohol reduction may involve a suppression of alcohol's rewarding properties. Brain areas participating in the ability of these gut-brain peptides to reduce alcohol-mediated behaviors/neurochemistry involve those important for reward. Human studies support these preclinical studies as polymorphisms of the genes encoding for GLP-1 receptor or the ghrelin pathway are associated with AUD. Moreover, a GLP-1 receptor agonist decreases alcohol drinking in overweight patients with AUD and an inverse GHSR agonist reduces alcohol craving. Although preclinical and clinical studies reveal an interaction between the gut-brain axis and AUD, additional studies should explore this in more detail.

An Overview of Appetite-Regulatory Peptides in Addiction Processes; From Bench to Bed Side.

There is a substantial need for new pharmacological treatments of addiction, and appetite-regulatory peptides are implied as possible candidates. Appetite regulation is complex and involves anorexigenic hormones such as glucagon-like peptide-1 (GLP-1) and amylin, and orexigenic peptides like ghrelin and all are well-known for their effects on feeding behaviors. This overview will summarize more recent physiological aspects of these peptides, demonstrating that they modulate various aspects of addiction processes. Findings from preclinical, genetic, and experimental clinical studies exploring the association between appetite-regulatory peptides and the acute or chronic effects of addictive drugs will be introduced. Short or long-acting GLP-1 receptor agonists independently attenuate the acute rewarding properties of addictive drugs or reduce the chronic aspects of drugs. Genetic variation of the GLP-1 system is associated with alcohol use disorder. Also, the amylin pathway modulates the acute and chronic behavioral responses to addictive drugs. Ghrelin has been shown to activate reward-related behaviors. Moreover, ghrelin enhances, whereas pharmacological or genetic suppression of the ghrelin receptor attenuates the responses to various addictive drugs. Genetic studies and experimental clinical studies further support the associations between ghrelin and addiction processes. Further studies should explore the mechanisms modulating the ability of appetite-regulatory peptides to reduce addiction, and the effects of combination therapies or different diets on substance use are warranted. In summary, these studies provide evidence that appetite-regulatory peptides modulate reward and addiction processes, and deserve to be investigated as potential treatment target for addiction.

Salmon Calcitonin Attenuates Some Behavioural Responses to Nicotine in Male Mice.

The behavioural responses to nicotine involve appetite-regulatory hormones; however, the effects of the anorexigenic hormone amylin on reward-related behaviours induced by nicotine remain to be established. Previous studies have shown that the amylinergic pathway regulates behavioural responses to alcohol, amphetamine and cocaine. Here, we evaluated the effects of salmon calcitonin (sCT), an amylin and calcitonin receptor (CTR) agonist, on nicotine-induced locomotor stimulation and sensitisation as well as dopamine release in the nucleus accumbens (NAc) shell. Moreover, we investigated the effects of sCT on the acquisition and expression of nicotine-induced reward in the conditioned place preference (CPP) paradigm. Finally, we performed Western Blot experiments in an attempt to identify the levels of the amylin receptor components CTRa, CTRb, and RAMP1 in reward-related areas of mice responding differently to repeated injections of sCT and nicotine in the locomotor sensitisation test. We found that sCT blocked nicotine's stimulatory and dopamine-releasing effects and prevented its ability to cause locomotor sensitisation. On the other hand, sCT did not alter nicotine-induced acquisition and expression of CPP. Lastly, sCT-nicotine treated mice from the locomotor sensitisation experiment displayed higher levels of total CTR, i.e. CTRa and CTRb together, in the reward-processing laterodorsal tegmental area (LDTg) of the brain compared to mice treated with vehicle-nicotine. Overall, the present data reveal that activation of CTR or/and amylin receptors attenuates certain nicotine-induced behaviours in male mice, further contributing to the understanding of appetite-regulatory peptides in reward regulation.

A ghrelin receptor antagonist reduces the ability of ghrelin, alcohol or amphetamine to induce a dopamine release in the ventral tegmental area and in nucleus accumbens shell in rats.

The orexigenic peptide ghrelin increases the release of dopamine in the nucleus accumbens (NAc) shell via central ghrelin receptors, especially those located in the ventral tegmental area (VTA). The activity of the VTA dopamine neurons projecting to NAc shell, involves somatodendritic dopamine release within the VTA. However, the effects of ghrelin on the concomitant dopamine release in the VTA and NAc shell is unknown. It is further unknown whether addictive drugs, such as alcohol and amphetamine, enhance the dopamine levels in both these areas via ghrelin receptor dependent mechanisms. Thus, the effects of a ghrelin receptor antagonist, JMV2959, on the ability of i) central ghrelin ii) systemic alcohol or iii) systemic amphetamine to increase the dopamine release in the VTA and in the NAc shell in rats by using in vivo microdialysis was explored. We showed that systemic administration of JMV2959 blocks the ability of central ghrelin to increases dopamine release in the VTA and the NAc shell, and reduces the alcohol- and amphetamine-induced dopamine release in both these areas. Locomotor activity studies was then conducted in an attempt to correlate the ghrelin-induced dopamine release in the VTA to a behavioural outcome. These revealed that local infusion of a dopamine D1 receptor antagonist into the VTA blocks the ability of central ghrelin to cause a locomotor stimulation in mice. Collectively, this study adds to the growing body of evidence indicating that ghrelin signalling modulates the ability of ghrelin, and addictive drugs, to activate the mesoaccumbal dopamine pathway.

Effects of a selective long-acting amylin receptor agonist on alcohol consumption, food intake and body weight in male and female rats.

Alcohol use disorder is a complex neuropsychiatric disorder affecting both males and females worldwide; however, the efficacy of current pharmacotherapies varies. Recent advances show that gut-brain peptides, like amylin, regulate alcohol behavioural responses by acting on brain areas involved in alcohol reward processes. Thus, the activation of amylin receptors (AMYRs) by salmon calcitonin (sCT) decreases alcohol behaviours in male rodents. Given that sCT also activates the sole calcitonin receptor (CTR), studies of more selective AMYR agonists in both male and female rodents are needed to explore amylinergic modulation of alcohol behaviours. Therefore, we investigated the effects of repeated administration of a selective long-acting AMYR agonist, NNC0174-1213 (AM1213), on alcohol, water and food intake, as well as body weight in male and female rats chronically exposed to alcohol. We confirm our previous studies with sCT in male rats, as repeated AM1213 administration for 2 weeks initially decreased alcohol intake in both male and female rats. However, this reduction ceases in both sexes on later sessions, accompanied by an increase in males. AM1213 reduced food intake and body weight in both male and female rats, with sustained body weight loss in males after discontinuation of the treatment. Moreover, AM1213 administration for 3 or 7 days, differentially altered dopamine, serotonin and their metabolites in the reward-related areas in males and females, providing tentative, but different, downstream mechanism through which selective activation of AMYR may alter alcohol intake. Our data provide clarified insight into the importance of AMYRs for alcohol intake regulation in both sexes.

An amylin and calcitonin receptor agonist modulates alcohol behaviors by acting on reward-related areas in the brain.

Alcohol causes stimulatory behavioral responses by activating reward-processing brain areas including the laterodorsal (LDTg) and ventral tegmental areas (VTA) and the nucleus accumbens (NAc). Systemic administration of the amylin and calcitonin receptor agonist salmon calcitonin (sCT) attenuates alcohol-mediated behaviors, but the brain sites involved in this process remain unknown. Firstly, to identify potential sCT sites of action in the brain, we used immunohistochemistry after systemic administration of fluorescent-labeled sCT. We then performed behavioral experiments to explore how infused sCT into the aforementioned reward-processing brain areas affects acute alcohol-induced behaviors in mice and chronic alcohol consumption in rats. We show that peripheral sCT crosses the blood brain barrier and is detected in all the brain areas studied herein. sCT infused into the LDTg attenuates alcohol-evoked dopamine release in the NAc shell in mice and reduces alcohol intake in rats. sCT into the VTA blocks alcohol-induced locomotor stimulation and dopamine release in the NAc shell in mice and decreases alcohol intake in rats. Lastly, sCT into the NAc shell prevents alcohol-induced locomotor activity in mice. Our data suggest that central sCT modulates the ability of alcohol to activate reward-processing brain regions.

Activation of the amylin pathway modulates cocaine-induced activation of the mesolimbic dopamine system in male mice.

Besides food intake reduction, activation of the amylin pathway by salmon calcitonin (sCT), an amylin and calcitonin receptor agonist, inhibits alcohol-mediated behaviors in rodents. This involves brain areas processing reward, i.e. the laterodorsal (LDTg), ventral tegmental area (VTA) and nucleus accumbens (NAc). However, the effects of stimulation of the amylin pathway on behaviors caused by cocaine and the brain areas involved in these processes have not yet been investigated. We therefore explored in male mice, the effects of systemic administration of sCT on cocaine-induced locomotor stimulation, dopamine release in the NAc and cocaine reward, as well as reward-dependent memory of cocaine, in the conditioned place preference (CPP) paradigm. Moreover, the outcome of systemic sCT and cocaine co-administration for five days on locomotor activity was investigated. Lastly, the impact of sCT infusions into the LDTg, VTA, NAc shell or core on cocaine-evoked locomotor stimulation was explored. We found that sCT attenuated cocaine-induced locomotor stimulation and accumbal dopamine release, without altering cocaine's rewarding properties or reward-dependent memory retrieval in the CPP paradigm. Five days of cocaine administration caused locomotor stimulation in mice pre-treated with vehicle, but not with sCT. In mice infused with vehicle into the aforementioned reward-related areas, cocaine caused locomotor stimulation, a response that was not evident following sCT infusions. The current findings suggest a novel role for the amylinergic pathway as regulator of cocaine-evoked activation of the mesolimbic dopamine system, opening the way for the investigation of the amylin signalling in the modulation of other drugs of abuse.

Activation of glucagon-like peptide-1 receptors and skilled reach foraging.

Glucagon-like peptide-1 receptor (GLP-1R) agonists, such as exendin-4 (Ex4), liraglutide and dulaglutide, regulate glucose homeostasis and are thus used to treat diabetes type II. GLP-1 also contributes towards a variety of additional physiological functions, including suppression of reward and improvement of learning. Acute activation of GLP-1R in the nucleus accumbens (NAc) shell, an area essential for motivation, reduces the motivation to consume sucrose or alcohol when assessed in a simple motor task. However, the effects of repeated administration of the different GLP-1R agonists on behaviours in a more complex motor task are unknown. The aim was therefore to investigate the effects of repeated Ex4, liraglutide or dulaglutide on the motivation and learning of a complex motor tasks such as skilled reach foraging in the Montoya staircase test. To explore the neurophysiological correlates of the different GLP-1R agonists on motivation, ex vivo electrophysiological recordings were conducted. In rats with an acquired skilled reach performance, Ex4 or liraglutide but not dulaglutide reduced the motivation of skilled reach foraging. In trained rats, Ex4 infusion into NAc shell decreased this motivated behaviour, and both Ex4 and liraglutide supressed the evoked field potentials in NAc shell. In rats without prior Montoya experience, dulaglutide but not Ex4 or liraglutide enhanced the learning of skilled reach foraging. Taken together, these findings indicate that the tested GLP-1R agonists have different behavioural outcomes depending on the context.