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.

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.

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.

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.

Effects of sub-chronic amylin receptor activation on alcohol-induced locomotor stimulation and monoamine levels in mice.

RATIONALE: Amylin receptors consist of the calcitonin receptor (CTR) and one of three receptor activity-modifying proteins (RAMPs). The identification of amylin receptors in areas processing reward, namely laterodorsal tegmental area (LDTg), ventral tegmental area (VTA), and nucleus accumbens (NAc), has attributed them a role as reward regulators. Indeed, acute activation of amylin receptors by the amylin receptor agonist salmon calcitonin (sCT) attenuates alcohol-induced behaviours in rodents. OBJECTIVES: The effects of long-term administration of sCT on alcohol-related behaviours and the molecular mechanisms underlying these processes are not yet elucidated. To fill this knowledge gap, we investigated the effects of sub-chronic sCT treatment on the locomotor stimulatory responses to alcohol in mice and the molecular pathways involved. METHODS: We assessed the behavioural effects of sub-chronic sCT treatment by means of locomotor activity experiments in mice. We used western blot to identify changes of the CTR levels and ex vivo biochemical analysis to detect changes in monoamines and their metabolites. RESULTS: After discontinuation for 5 days of sCT treatment, alcohol did not induce locomotor stimulation in mice pre-treated with sCT when compared with vehicle, without altering secondary behavioural parameters of the locomotor activity experiment or the protein levels of the CTR in reward-related areas in the same set of animals. Moreover, repeated sCT treatment altered monoaminergic neurotransmission in various brain areas, including increased serotonin and decreased dopamine turnover in the VTA. Lastly, we identified a differential effect of repeated sCT and acute alcohol administration on alcohol-induced locomotion in mice, where sCT initially attenuated and later increased this alcohol response. It was further found that this treatment combination did not affect secondary behavioural parameters measured in this locomotor activity experiments. CONCLUSIONS: These data suggest that sub-chronic sCT treatment differentially alters the ability of alcohol to cause locomotor stimulation, possibly through molecular mechanisms involving various neurotransmitter systems and not the CTR levels per se.