This investigation illuminates a pivotal function of GLP-1 signalling in a murine model of alcohol consumption and subsequent resumption of alcohol intake following alcohol withdrawal. Specifically, we showed that systemic liraglutide administration mitigates the return to alcohol drinking and anxiety-like behavior, memory impairments, and synapse loss in male mice during alcohol withdrawal. The alignment of our rodent findings with recent clinical studies indicating that the GLP-1 analogue liraglutide reduces alcohol consumption in type 2 diabetes patients (Kalra et al., American Diabetes Association Annual Meeting 2011, Poster 1029) corroborates the data on alcohol-related behavior. Our results thus build on previous studies by underlining the significant role of GLP-1 receptors in an animal model of alcohol withdrawal and resumption of alcohol consumption.
The free-choice bottle model represents a non-invasive, straightforward experimental design for self-administration, mimicking human alcohol consumption patterns [32]. We observed that liraglutide attenuated both alcohol consumption and preference in mice, without influencing overall fluid intake during the experimental period. A notable finding of this study is the enduring reduction in alcohol consumption and preference by liraglutide following a two-week withdrawal period, implying a potentially sustained regulatory process. Previous research has noted a reduction in alcohol intake following acute pharmacological activation of the GLP-1 receptor using Exendin-4 in a two-bottle selection experiment [29]. Exendin-4 and liraglutide have also been found to decrease alcohol intake in vervet monkeys [33]. further suggesting that GLP-1 receptor activation in the brain inhibits alcohol consumption in rodents and non-human primates.
Consistent alcohol intoxication invariably impairs learning and memory processes, mediated by specific neural circuits [34]. Evidence indicates that initial exposure to alcohol may augment hippocampal function, thereby contributing to addiction development. In accordance with the self-administration hypothesis, withdrawal from alcohol results in deficits in learning and memory[35, 36]. Our study discovered that liraglutide ameliorated learning and memory impairments caused by alcohol withdrawal in mice exposed to alcohol. Observations from human adolescent studies indicate that heavy alcohol consumption correlates with poorer cognitive function across a wide range of neuropsychological assessments, encompassing learning, memory, attention, executive functioning, and impulsivity [37]. We also examined the anxiety-like behavior in mice exposed to alcohol. Alcohol dependence often leads to anxiety and depression-like behaviors, particularly in newborns and adolescents [38]. Our findings clearly demonstrate the ameliorative effect of liraglutide on alcohol-induced anxiety.
Our findings clearly demonstrate the ameliorative effect of liraglutide on alcohol-induced anxiety. [39], thus suggesting that GLP-1 receptor activation may modulate alcohol-related behaviors by influencing reward circuits. To this point, the engagement of the amygdala, hypothalamus, medial prefrontal cortex, and hippocampus in reward behavior has been documented [40]. Our findings reveal a significant diminution in the expression levels of synaptic transport-related proteins in the mPFC and HP regions during withdrawal in mice exposed to alcohol.
In the central nervous system, AMPA receptors comprise functional tetramers formed from diverse combinations of four subunits (GluA1-4), with GluA1 being the predominant subunit in neuronal synaptic and extra-synaptic AMPA receptors [41, 42]. The amplification of GluA1 expression and its phosphorylation are commonly proposed mechanisms for drug action in the study of Alzheimer's disease, depression, and addiction. An increase in the phosphorylation of the GluA1 receptor appears to be a counteractive mechanism against the pathophysiological features of Alzheimer's disease and depression [43]. Our study found that, while the total protein expression of GluA1 in the alcohol group remained unchanged compared to the control group, the expression of p-GluA1 diminished. Liraglutide treatment elevated p-GluA1 levels compared to those in the alcohol-only group, suggesting normalization of synaptic transmission.
Synaptophysin, which is expressed extensively in all nerve terminals—especially at the presynaptic membrane—is widely recognized as a crucial marker of synaptogenesis and synaptic plasticity. PSD-95, a synaptic protein, serves to stabilize dendritic spines at the postsynaptic membrane. We noted significant disparities in the expression of SYN and PSD-95 among groups; however, liraglutide treatment led to increased expression of SYN and PSD-95 compared to the alcohol group. Furthermore, we quantified the relative expression level of VGluT1 in the mPFC and HP regions post alcohol withdrawal and found that liraglutide treatment heightened VGluT1 expression compared to the alcohol group. VGluT1 plays a crucial role in central nervous system learning and memory, primarily by influencing synaptic Glu transport and long-term potentiation. Reduction of VGluT1 expression in the hippocampus can instigate changes in dendritic structure, thereby reducing synaptic connectivity, leading to neurofibrillary lesions and impairments in learning and memory [44]. To corroborate these findings, we assessed dendritic spine density using Golgi staining. We observed a reduction in dendritic spine density in mice exposed to alcohol, which was ameliorated by liraglutide treatment. These findings further substantiate the deleterious impact of alcohol on synaptic numbers and function in mice and the therapeutic potential of liraglutide in treating AUD. Previous studies have highlighted the protective effect of chronic treatment with GLP-1 receptor agonists on synapses in various disease models [45]. Our study augments this body of research by demonstrating that alcohol-induced synaptic damage can be mitigated by liraglutide.
In conclusion, our findings suggest that liraglutide can mitigate alcohol consumption and ameliorate learning and anxiety in mice exposed to alcohol. The therapeutic effect of liraglutide may be achieved by safeguarding synapses and enhancing synaptic transmission in the mPFC and HP regions. These results provide a foundation and an innovative research avenue for future investigations into the effects and mechanisms of AUD, as well as potential novel pharmaceutical interventions for this disorder.
Statement of Ethics
This study protocol was reviewed and approved by the Ethics committee of Zhengzhou university, approval number ZZUIRBGZR2017-459.