GLP-1 acts on habenular avoidance circuits to control nicotine intake

Glucagon-Like Peptide-1 Receptor Agonist Treatment Does Not Reduce Abuse-Related Effects of Opioid Drugs

Dependence on opioids and the number of opioid overdose deaths are serious and escalating public health problems, but medication-assisted treatments for opioid addiction remain inadequate for many patients. Glucagon-like pepide-1 (GLP-1) is a gut hormone and neuropeptide with actions in peripheral tissues and in the brain, including regulation of blood glucose and food intake. GLP-1 analogs, which are approved diabetes medications, can reduce the reinforcing and rewarding effects of alcohol, cocaine, amphetamine, and nicotine in rodents. Investigations on effects of GLP-1 analogs on opioid reward and reinforcement have not been reported. We assessed the effects of the GLP-1 receptor agonist Exendin-4 (Ex4) on opioid-related behaviors in male mice, i.e., morphine-conditioned place preference (CPP), intravenous self-administration (IVSA) of the short-acting synthetic opioid remifentanil, naltrexone-precipitated morphine withdrawal, morphine analgesia (male and female mice), and locomotor activity. Ex4 treatment had no effect on morphine-induced CPP, withdrawal, or hyperlocomotion. Ex4 failed to decrease remifentanil self-administration, if anything reinforcing effects of remifentanil appeared increased in Ex4-treated mice relative to saline. Ex4 did not significantly affect analgesia. In contrast, Ex4 dose dependently decreased oral alcohol self-administration, and suppressed spontaneous locomotor activity. Taken together, Ex4 did not attenuate the addiction-related behavioral effects of opioids, indicating that GLP-1 analogs would not be useful medications in the treatment of opioid addiction. This difference between opioids and other drug classes investigated to date may shed light on the mechanism of action of GLP-1 receptor treatment in the addictive effects of alcohol, central stimulants, and nicotine.

Recent advances in neuroepigenetic editing

A wealth of studies in the mammalian nervous system indicate the role of epigenetic gene regulation in both basic neurobiological function and disease. However, the relationship between epigenetic regulation and neuropathology is largely correlational due to the presence of mixed cell populations within brain regions and the genome-wide effects of classical approaches to manipulate the epigenome. Locus-specific epigenetic editing allows direct epigenetic regulation of specific genes to elucidate the direct causal relationship between epigenetic modifications and transcription. This review discusses some of the latest innovations in the efficacy and flexibility in this approach that hold promise for neurobiological application.

Chronic Suppression of Glucagon-Like Peptide-1 Receptor (GLP1R) mRNA Translation in the Rat Bed Nucleus of the Stria Terminalis Reduces Anxiety-Like Behavior and Stress-Induced Hypophagia, But Prolongs Stress-Induced Elevation of Plasma Corticosterone

The anterior lateral bed nucleus of the stria terminalis (alBST) expresses glucagon-like peptide-1 receptors (GLP1Rs) and receives input from caudal brainstem GLP1 neurons. GLP1 administered centrally reduces food intake and increases anxiety-like behavior and plasma corticosterone (cort) levels in rats, whereas central GLP1R antagonism has opposite effects. Anxiogenic threats and other stressors robustly activate c-fos expression in both GLP1-producing neurons and also in neurons within alBST subregions expressing GLP1R. To examine the functional role of GLP1R signaling within the alBST, adult male Sprague Dawley rats received bilateral alBST-targeted injections of an adeno-associated virus (AAV) vector expressing short hairpin RNA (shRNA) to knock down the translation of GLP1R mRNA (GLP1R-KD rats), or similar injections of a control AAV (CTRL rats). In situ hybridization revealed that GLP1R mRNA is expressed in a subset of GABAergic alBST neurons, and quantitative real-time PCR confirmed that GLP1R-KD rats displayed a significant 60% reduction in translatable GLP1R mRNA. Compared with CTRL rats, GLP1R-KD rats gained more body weight over time and displayed less anxiety-like behavior, including a loss of light-enhanced acoustic startle and less stress-induced hypophagia. Conversely, while baseline plasma cort levels were similar in GLP1R-KD and CTRL rats, GLP1R-KD rats displayed a prolonged stress-induced elevation of plasma cort levels. GLP1R-KD and CTRL rats displayed similar home cage food intake and a similar hypophagic response to systemic Exendin-4, a GLP1R agonist that crosses the blood-brain barrier. We conclude that GLP1R expressed within the alBST contributes to multiple behavioral responses to anxiogenic threats, yet also serves to limit the plasma cort response to acute stress.SIGNIFICANCE STATEMENT Anxiety is an affective and physiological state that supports threat avoidance. Identifying the neural bases of anxiety-like behaviors in animal models is essential for understanding mechanisms that contribute to normative and pathological anxiety in humans. In rats, anxiety/avoidance behaviors can be elicited or enhanced by visceral or cognitive threats that increase glucagon-like peptide-1 (GLP1) signaling from the caudal brainstem to the hypothalamus and limbic forebrain. Data reported here support a role for limbic GLP1 receptor signaling to enhance anxiety-like behavior and to attenuate stress-induced elevations in plasma cort levels in rats. Improved understanding of central GLP1 neural pathways that impact emotional responses to stress could expand potential therapeutic options for anxiety and other stress-related disorders in humans.

The effect of glucagon-like peptide-1 (GLP-1) receptor agonists on substance use disorder (SUD)-related behavioural effects of drugs and alcohol: A systematic review

Glucagon-like-peptide-1 (GLP-1)-receptor agonists have been proposed as putative treatment for substance use disorders (SUD). The objective of this systematic review is to characterize the effects of GLP-1-receptor agonists on SUD-related behavioural effects of drugs, nicotine, and alcohol. The review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). A search was performed in PubMed and EMBASE on June 16, 2018. The inclusion criteria were primary studies investigating the use of GLP-1-receptor agonists on behavioural endpoints related to SUD. Seventeen studies were included, investigating the effect of the GLP-1-receptor agonists exendin-4, fluoro-exendin-4, liraglutide, AC3174 and GLP-1 (7-36) on SUD-related behavioural effects of ethanol, cocaine, amphetamine, and/or nicotine. All studies used rodents as subjects. Nine of the studies dealt with ethanol, six with cocaine, two with amphetamine, and two with nicotine. Most studies investigated acute treatment effects, finding a significant effect in all but one experiment. A few studies investigated more chronic effects on ethanol. All the studies reported sustained effects. Eleven studies tested more than one dose, finding a dose-related response in ten out of thirteen experiments. Six studies report a central effect through intra-cerebral administration or by using mice in which the central GLP-1-receptors had been inactivated. In conclusion, a solid body of evidence documents acute effects of GLP-1-receptor agonist treatment on behavioural effects of alcohol, nicotine, amphetamine and cocaine. Documentation of effect of more chronic GLP-1-receptor stimulation on these behaviours is limited.

Central GLP-1 receptors: Novel molecular targets for cocaine use disorder

Given that the search for effective pharmacotherapies for cocaine use disorder has, thus far, been fruitless, there remains a critical need for conceptually innovative approaches toward identifying new medications to treat this disease. A better understanding of the neurocircuits and neurobiological mechanisms underlying cocaine taking and seeking may identify molecular substrates that could serve as targets for novel pharmacotherapies to treat cocaine use disorder. Recent preclinical evidence suggests that glucagon-like peptide-1 (GLP-1) receptor agonists could be re-purposed to treat cocaine craving-induced relapse. This review endeavors to comprehensively summarize the current literature investigating the efficacy of GLP-1 receptor agonists in reducing the rewarding and reinforcing effects of cocaine in animal models of cocaine use disorder. The role of central endogenous GLP-1 circuits in voluntary cocaine taking and seeking is also discussed. Behavioral, neurochemical, electrophysiological and molecular biology studies indicate that central GLP-1 receptor activation functionally modulates the mesolimbic reward system and decreases addiction-like phenotypes in rodents. Overall, an emerging preclinical literature provides compelling evidence to advance GLP-1 receptor agonists into clinical trials testing the efficacy of these medications in preventing cocaine craving-induced relapse.

Cigarette smoking, type 2 diabetes mellitus, and glucagon-like peptide-1 receptor agonists as a potential treatment for smokers with diabetes: An integrative review

Tobacco use disorder (TUD), in particular cigarette smoking, contributes significantly to the macro- and micro-vascular complications of type 2 diabetes mellitus (DM). Persons with DM who regularly use tobacco products are twice as likely to experience mortality and negative health outcomes. Despite these risks, TUD remains prevalent in persons with DM. The objective of this integrative review is to summarize the relationship between TUD and DM based on epidemiological and preclinical biological evidence. We conclude with a review of the literature on the glucagon-like peptide-1 (GLP-1) as a potential treatment target for addressing comorbid TUD in smokers with DM.

Activation of glucagon-like peptide-1 receptors in the nucleus accumbens attenuates cocaine seeking in rats

Recent evidence indicates that activation of glucagon-like peptide-1 (GLP-1) receptors reduces cocaine-mediated behaviors and cocaine-evoked dopamine release in the nucleus accumbens (NAc). However, no studies have examined the role of NAc GLP-1 receptors in the reinstatement of cocaine-seeking behavior, an animal model of relapse. Here, we show that systemic infusion of a behaviorally relevant dose of the GLP-1 receptor agonist exendin-4 penetrated the brain and localized with neurons and astrocytes in the NAc. Administration of exendin-4 directly into the NAc core and shell subregions significantly attenuated cocaine priming-induced reinstatement of drug-seeking behavior. These effects were not due to deficits in operant responding or suppression of locomotor activity as intra-accumbal exendin-4 administration had no effect on sucrose-seeking behavior. To determine the effects of GLP-1 receptor activation on neuronal excitability, exendin-4 was bath applied to ex vivo NAc slices from cocaine-experienced and saline-experienced rats following extinction of cocaine-taking behavior. Exendin-4 increased the frequency of action potential firing of NAc core and shell medium spiny neurons in cocaine-experienced rats while no effect was observed in saline controls. In contrast, exendin-4 did not affect the frequency or amplitude of spontaneous excitatory postsynaptic currents or alter the paired-pulse ratios of evoked excitatory postsynaptic currents. These effects were not associated with altered expression of GLP-1 receptors in the NAc following cocaine self-administration. Taken together, these findings indicate that increased activation of GLP-1 receptors in the NAc during cocaine abstinence increases intrinsic, but not synaptic, excitability of medium spiny neurons and is sufficient to reduce cocaine-seeking behavior.

Glucagon-like peptide-1 receptors within the nucleus of the solitary tract regulate alcohol-mediated behaviors in rodents

The ability of glucagon-like peptide-1 (GLP-1) to reduce food intake involves activation of GLP-1 receptors (GLP-1R) in the nucleus of the solitary tract (NTS). It has also been demonstrated that systemic administration of GLP-1R agonists attenuates alcohol-mediated behaviors via, to date, unknown mechanisms. Therefore, we evaluated the effects of NTS-GLP-1R activation by exendin-4 (Ex4) on alcohol-induced locomotor stimulation, accumbal dopamine release and memory of alcohol reward in the conditioned place preference (CPP) model in mice. Moreover, the ability of Ex4 infusion into the NTS on alcohol intake was explored in rats. Ex4 into the NTS inhibits the acute effects of alcohol as measured by alcohol-induced locomotor stimulation, accumbal dopamine release and the memory consolidation of alcohol reward in the CPP paradigm. In addition, NTS-Ex4 dose-dependently decreases alcohol intake in rats consuming alcohol for 12 weeks. Pharmacological suppression of GLP-1R in the NTS prevents the ability of systemic Ex4 to block the alcohol-induced locomotor stimulation in mice. These data add a functional role of GLP-1R within the NTS, involving alcohol-related behaviors. In addition, they may provide insight into the GLP-1R containing brain areas that modulate the ability of GLP-1R agonists to reduce alcohol reinforcement. Collectively, this further supports GLP-1R as potential treatment targets for alcohol use disorder.

Neurobiological and Neurophysiological Mechanisms Underlying Nicotine Seeking and Smoking Relapse

Tobacco-related morbidity and mortality continue to be a significant public health concern. Unfortunately, current FDA-approved smoking cessation pharmacotherapies have limited efficacy and are associated with high rates of relapse. Therefore, a better understanding of the neurobiological and neurophysiological mechanisms that promote smoking relapse is needed to develop novel smoking cessation medications. Here, we review preclinical studies focused on identifying the neurotransmitter and neuromodulator systems that mediate nicotine relapse, often modeled in laboratory animals using the reinstatement paradigm, as well as the plasticity-dependent neurophysiological mechanisms that facilitate nicotine reinstatement. Particular emphasis is placed on how these neuroadaptations relate to smoking relapse in humans. We also highlight a number of important gaps in our understanding of the neural mechanisms underlying nicotine reinstatement and critical future directions, which may lead toward the development of novel, target pharmacotherapies for smoking cessation.

Vagal Interoceptive Modulation of Motivated Behavior

In addition to regulating the ingestion and digestion of food, sensory feedback from gut to brain modifies emotional state and motivated behavior by subconsciously shaping cognitive and affective responses to events that bias behavioral choice. This focused review highlights evidence that gut-derived signals impact motivated behavior by engaging vagal afferents and central neural circuits that generally serve to limit or terminate goal-directed approach behaviors, and to initiate or maintain behavioral avoidance.

Molecular Mechanisms Associated with Nicotine Pharmacology and Dependence

Tobacco dependence is a leading cause of preventable disease and death worldwide. Nicotine, the main psychoactive component in tobacco cigarettes, has also been garnering increased popularity in its vaporized form, as derived from e-cigarette devices. Thus, an understanding of the molecular mechanisms underlying nicotine pharmacology and dependence is required to ascertain novel approaches to treat drug dependence. In this chapter, we review the field's current understanding of nicotine's actions in the brain, the neurocircuitry underlying drug dependence, factors that modulate the function of nicotinic acetylcholine receptors, and the role of specific genes in mitigating the vulnerability to develop nicotine dependence. In addition to nicotine's direct actions in the brain, other constituents in nicotine and tobacco products have also been found to alter drug use, and thus, evidence is provided to highlight this issue. Finally, currently available pharmacotherapeutic strategies are discussed, along with an outlook for future therapeutic directions to achieve to the goal of long-term nicotine cessation.

Preproglucagon Neurons in the Nucleus of the Solitary Tract Are the Main Source of Brain GLP-1, Mediate Stress-Induced Hypophagia, and Limit Unusually Large Intakes of Food

Centrally administered glucagon-like peptide 1 (GLP-1) supresses food intake. Here we demonstrate that GLP-1-producing (PPG) neurons in the nucleus tractus solitarii (NTS) are the predominant source of endogenous GLP-1 within the brain. Selective ablation of NTS PPG neurons by viral expression of diphtheria toxin subunit A substantially reduced active GLP-1 concentrations in brain and spinal cord. Contrary to expectations, this loss of central GLP-1 had no significant effect on the ad libitum feeding of mice, affecting neither daily chow intake nor body weight or glucose tolerance. Only after bigger challenges to homeostasis were PPG neurons necessary for food intake control. PPG-ablated mice increased food intake after a prolonged fast and after a liquid diet preload. Consistent with our ablation data, acute inhibition of hM₄Di-expressing PPG neurons did not affect ad libitum feeding; however, it increased refeeding intake after fast and blocked stress-induced hypophagia. Additionally, chemogenetic PPG neuron activation through hM₃Dq caused a strong acute anorectic effect. We conclude that PPG neurons are not involved in primary intake regulation but form part of a secondary satiation/satiety circuit, which is activated by both psychogenic stress and large meals. Given their hypophagic capacity, PPG neurons might be an attractive drug target in obesity treatment.

An extended history of drug self-administration results in multiple sources of control over drug seeking behavior

It is widely recognized that across the development of drug addiction, cues associated with drug use come to exert increasing control over drug seeking and taking behaviors. However, there remain gaps in our knowledge regarding how the different types of drug related cues affect drug seeking and taking behaviors, and how the emergence of cue control over these behaviors relates to the onset of drug seeking compulsions. This paper reviews the literature on drug self-administration in animals to address these gaps. It first identifies the different types of cues that acquire control over reward seeking behavior generally, and examines whether the same types of cues acquire control over drug seeking behavior specifically. It then examines how the role of drug related cues in motivating and reinforcing drug seeking behavior changes across an extended drug-taking history, with a particular focus on the case of nicotine. The evidence reviewed shows that, after an extended history of drug taking, drug seeking behaviors are controlled by contextual cues associated with the development of drug seeking habits, response contingent cues that accompany delivery of the drug, as well as internal states that correlate with levels of drug intake. These multiple sources of control over drug seeking are discussed in relation to the generation of an addicted phenotype in animal models and the hypothesized progression from internal control over drug use to compulsive drug seeking.

Gut-brain axis and addictive disorders: A review with focus on alcohol and drugs of abuse

Due to the limited efficacy of existing medications for addictive disorders including alcohol use disorder (AUD), the need for additional medications is substantial. Potential new medications for addiction can be identified through investigation of the neurochemical substrates mediating the ability of drugs of abuse such as alcohol to activate the mesolimbic dopamine system. Interestingly, recent studies implicate neuropeptides of the gut-brain axis as modulators of reward and addiction processes. The present review therefore summarizes the current studies investigating the ability of the gut-brain peptides ghrelin, glucagon-like peptide-1 (GLP-1), amylin and neuromedin U (NMU) to modulate alcohol- and drug-related behaviors in rodents and humans. Extensive literature demonstrates that ghrelin, the only known orexigenic neuropeptide to date, enhances reward as well as the intake of alcohol, and other drugs of abuse, while ghrelin receptor antagonism has the opposite effects. On the other hand, the anorexigenic peptides GLP-1, amylin and NMU independently inhibits reward from alcohol and drugs of abuse in rodents. Collectively, these rodent and human studies imply that central ghrelin, GLP-1, amylin and NMU signaling may contribute to addiction processes. Therefore, the need for randomized clinical trials investigating the effects of agents targeting these aforementioned systems on drug/alcohol use is substantial.

Transcriptomic Characterization of the Human Habenula Highlights Drug Metabolism and the Neuroimmune System

Due to size and accessibility, most information about the habenula is derived from rodent studies. To better understand the molecular signature of the habenula we characterized the genes that have high expression in the habenula. We compared anatomical expression profiles of three normal adult human brains and four fetal brains. We used gene set enrichment analyses to determine if genes annotated to specific molecular functions, cellular components, and biological processes are enriched in the habenula. We also tested gene sets related to depression and addiction to determine if they uniquely involve the habenula. As expected, we observed high habenular expression of GPR151, nicotinic cholinergic receptors, and cilia-associated genes (medial division). Genes identified in genetic studies of smoking and associated with nicotine response were enriched in the habenula. Genes associated with major depressive disorder did not have enriched expression in the habenula but genes negatively correlated with hedonic well-being were, providing a link to anhedonia. We observed enrichment of genes associated with diseases that are comorbid with addictions (hematopoiesis, thrombosis, liver cirrhosis, pneumonia, and pulmonary fibrosis) and depression (rheumatoid arthritis, multiple sclerosis, and kidney disease). These inflammatory diseases mark a neuroimmune signature that is supported by genes associated with mast cells, acute inflammatory response, and leukocyte migration. We also found enrichment of cytochrome p450 genes suggesting the habenula is uniquely sensitive to endogenous and xenobiotic compounds. Our results suggest the habenula receives negative reward signals from immune and drug processing molecules. This is consistent with the habenular role in the "anti-reward" system and suggests it may be a key bridge between autoimmune disorders, drug use, and psychiatric diseases.

Glucagon-like peptide-1 receptor activation in the ventral tegmental area attenuates cocaine seeking in rats

Novel molecular targets are needed to develop new medications for the treatment of cocaine addiction. Here we investigated a role for glucagon-like peptide-1 (GLP-1) receptors in the reinstatement of cocaine-seeking behavior, an animal model of relapse. We showed that peripheral administration of the GLP-1 receptor agonist exendin-4 dose dependently reduced cocaine seeking in rats at doses that did not affect ad libitum food intake, meal patterns or body weight. We also demonstrated that systemic exendin-4 penetrated the brain where it putatively bound receptors on both neurons and astrocytes in the ventral tegmental area (VTA). The effects of systemic exendin-4 on cocaine reinstatement were attenuated in rats pretreated with intra-VTA infusions of the GLP-1 receptor antagonist exendin-(9-39), indicating that the suppressive effects of systemic exendin-4 on cocaine seeking were due, in part, to activation of GLP-1 receptors in the VTA. Consistent with these effects, infusions of exendin-4 directly into the VTA reduced cocaine seeking. Finally, extinction following cocaine self-administration was associated with decreased preproglucagon mRNA expression in the caudal brainstem. Thus, our study demonstrated a novel role for GLP-1 receptors in the reinstatement of cocaine-seeking behavior and identified behaviorally relevant doses of a GLP-1 receptor agonist that selectively reduced cocaine seeking and did not produce adverse effects.

Nicotine aversion is mediated by GABAergic interpeduncular nucleus inputs to laterodorsal tegmentum

Nicotine use can lead to dependence through complex processes that are regulated by both its rewarding and aversive effects. Recent studies show that aversive nicotine doses activate excitatory inputs to the interpeduncular nucleus (IPN) from the medial habenula (MHb), but the downstream targets of the IPN that mediate aversion are unknown. Here we show that IPN projections to the laterodorsal tegmentum (LDTg) are GABAergic using optogenetics in tissue slices from mouse brain. Selective stimulation of these IPN axon terminals in LDTg in vivo elicits avoidance behavior, suggesting that these projections contribute to aversion. Nicotine modulates these synapses in a concentration-dependent manner, with strong enhancement only seen at higher concentrations that elicit aversive responses in behavioral tests. Optogenetic inhibition of the IPN-LDTg connection blocks nicotine conditioned place aversion, suggesting that the IPN-LDTg connection is a critical part of the circuitry that mediates the aversive effects of nicotine.

Systemic and Intra-Habenular Activation of the Orphan G Protein-Coupled Receptor GPR139 Decreases Compulsive-Like Alcohol Drinking and Hyperalgesia in Alcohol-Dependent Rats

GPR139 is an orphan G protein-coupled receptor (GPCR) that is expressed mainly in the brain, with the highest expression in the medial habenula. The modulation of GPR139 receptor function has been hypothesized to be beneficial in the treatment of some mental disorders, but behavioral studies have not yet provided causal evidence of the role of GPR139 in brain dysfunction. Because of the high expression of GPR139 in the habenula, a critical brain region in addiction, we hypothesized that GPR139 may play role in alcohol dependence. Thus, we tested the effect of GPR139 receptor activation using the selective, brain-penetrant receptor agonist JNJ-63533054 on addiction-like behaviors in alcohol-dependent male rats. Systemic administration of JNJ-63533054 (30 mg/kg but not 10 mg/kg, p.o.) reversed the escalation of alcohol self-administration in alcohol-dependent rats, without affecting water or saccharin intake in dependent rats or alcohol intake in nondependent rats. Moreover, systemic JNJ-63533054 administration decreased withdrawal-induced hyperalgesia, without affecting somatic signs of alcohol withdrawal. Further analysis demonstrated that JNJ-63533054 was effective only in a subgroup of dependent rats that exhibited compulsive-like alcohol drinking. Finally, site-specific microinjection of JNJ-63533054 in the habenula but not interpeduncular nucleus (IPN) reduced both alcohol self-administration and withdrawal-induced hyperalgesia in dependent rats. These results provide robust preclinical evidence that GPR139 receptor activation reverses key addiction-like behaviors in dependent animals, suggest that GPR139 may be a novel target for the treatment of alcohol use disorder, and demonstrate that GPR139 is functionally relevant in regulating mammalian behavior.

GLP-1 signaling and alcohol-mediated behaviors; preclinical and clinical evidence

Alcohol addiction, affecting approximately four percent of the population, contributes significantly to the global burden of diseases and is a substantial cost to the society. The neurochemical mechanisms regulating alcohol mediated behaviors is complex and in more recent years a new physiological role of the gut-brain peptides, traditionally known to regulate appetite and food intake, have been suggested. Indeed, regulators of alcohol-mediated behaviors. One of these gut-brain peptides is the annorexigenic peptide glucagon-like peptide-1 (GLP-1), Preclinical studies show that GLP-1 receptor activation, either by GLP-1 or analogues, attenuate the ability of alcohol to activate the mesolimbic dopamine system as well as decrease alcohol consumption and operant self-administration. In further support for the endogenous GLP-1 system in addiction processes are the experimental data showing that a GLP-1 receptor antagonist increases alcohol intake. Moreover, GLP-1 receptor agonists prevent the ability of other addictive drugs to activate the mesolimbic dopamine system. The number of clinical studies is limited, but show i) that genetic variation in the GLP-1 receptor gene is associated with alcohol addiction as well as increased alcohol infusion in humans, ii) that plasma levels of GLP-1 are associated with the subjective experience of cocaine and iii) that a GLP-1 receptor agonist reduces alcohol intake in patients with type-2 diabetes mellitus. These experimental and clinical studies raises the concern that clinically available GLP-1 receptor agonists deserves to be tested as potential treatments of patients with addictive disorders including alcohol addiction. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Advancing Pharmacotherapy Development from Preclinical Animal Studies

Animal models provide rapid, inexpensive assessments of an investigational drug's therapeutic potential. Ideally, they support the plausibility of therapeutic efficacy and provide a rationale for further investigation. Here, I discuss how the absence of clear effective-ineffective categories for alcohol use disorder (AUD) medications and biases in the clinical and preclinical literature affect the development of predictive preclinical alcohol dependence (AD) models. Invoking the analogical argument concept from the philosophy of science field, I discuss how models of excessive alcohol drinking support the plausibility of clinical pharmacotherapy effects. Even though these models are not likely be completely discriminative, they are sensitive to clinically effective medications and have revealed dozens of novel medication targets. In that context, I discuss recent preclinical work on GLP-1 receptor agonists, phosphodiesterase inhibitors, glucocorticoid receptor antagonists, nociception agonists and antagonists, and CRF1 antagonists. Clinically approved medications are available for each of these drug classes. I conclude by advocating a translational approach in which drugs are evaluated highly congruent preclinical models and human laboratory studies. Once translation is established, I suggest the burden is to develop hypothesis-based therapeutic interventions maximizing the impact of the confirmed pharmacotherapeutic effects in the context of additional variables falling outside the model.

Retrograde inhibition by a specific subset of interpeduncular α5 nicotinic neurons regulates nicotine preference

Repeated exposure to drugs of abuse can produce adaptive changes that lead to the establishment of dependence. It has been shown that allelic variation in the α5 nicotinic acetylcholine receptor (nAChR) gene CHRNA5 is associated with higher risk of tobacco dependence. In the brain, α5-containing nAChRs are expressed at very high levels in the interpeduncular nucleus (IPN). Here we identified two nonoverlapping α5 ⁺ cell populations (α5- ^Amigo1 and α5- ^Epyc ) in mouse IPN that respond differentially to nicotine. Chronic nicotine treatment altered the translational profile of more than 1,000 genes in α5- ^Amigo1 neurons, including neuronal nitric oxide synthase (Nos1) and somatostatin (Sst). In contrast, expression of few genes was altered in the α5- ^Epyc population. We show that both nitric oxide and SST suppress optically evoked neurotransmitter release from the terminals of habenular (Hb) neurons in IPN. Moreover, in vivo silencing of neurotransmitter release from the α5- ^Amigo1 but not from the α5- ^Epyc population eliminates nicotine reward, measured using place preference. This loss of nicotine reward was mimicked by shRNA-mediated knockdown of Nos1 in the IPN. These findings reveal a proaddiction adaptive response to chronic nicotine in which nitric oxide and SST are released by a specific α5⁺ neuronal population to provide retrograde inhibition of the Hb-IPN circuit and thereby enhance the motivational properties of nicotine.