Involvement of cholecystokinin within craving for cocaine: role of cholecystokinin receptor ligands

Food addiction, hormones and blood biomarkers in humans: A systematic literature review

BACKGROUND

Food addiction may play a role in rising obesity rates in connection with obesogenic environments and processed food availability, however the concept of food addiction remains controversial. While animal studies show evidence for addictive processes in relation to processed foods, most human studies are psychologically focussed and there is a need to better understand evidence for biological mechanisms of food addiction in humans. Several key hormones are implicated in models of food addiction, due to their key roles in feeding, energy metabolism, stress and addictive behaviours. This systematic literature review examines evidence for relationships between food addiction, hormones and other blood biomarkers.

METHODS

A series of literature searches was performed in Scopus, PsychInfo, MedLine, ProQuest, CINAHL and Web of Science. A total of 3111 articles were found, of which 1045 were duplicates. Articles were included if they contained a psychometric measurement of food addiction, such as the Yale Food Addiction Scale, as well as addressed the association between FA and hormones or blood biomarkers in humans. Articles were assessed for eligibility by two independent reviewers.

RESULTS

Sixteen studies were identified that examined relationships between food addiction and blood biomarkers, published between 2015 and 2021. Significant findings were reported for leptin, ghrelin, cortisol, insulin and glucose, oxytocin, cholesterol, plasma dopamine, thyroid stimulating hormone (TSH), haemoglobin A1c (HbA1c), triglyceride (TG), amylin, tumour necrosis factor alpha (TNF- α) and cholecystokinin (CCK). Methodological issues included small sample sizes and variation in obesity status, sex and mental health-related comorbidities. Due to methodological limitations, definite connections between FA, hormones and other blood biomarkers cannot yet be determined.

CONCLUSION

This systematic review identified preliminary evidence linking FA symptoms to hormones and other blood biomarkers related to feeding, addiction, and stress. However, due to the small number of studies and methodological limitations, further research is needed to evaluate biopsychosocial models of FA and to resolve controversies.

Neural circuit mechanisms of the cholecystokinin (CCK) neuropeptide system in addiction

Given historical focus on the roles for cholecystokinin (CCK) as a peripheral hormone controlling gastrointestinal processes and a brainstem peptide regulating food intake, the study of CCK as a limbic neuromodulator coordinating reward-seeking and emotional behavior remains underappreciated. Furthermore, localization of CCK to specialized interneurons throughout the hippocampus and cortex relegated CCK to being examined primarily as a static cell type marker rather than a dynamic functional neuromodulator. Yet, over three decades of literature have been generated by efforts to delineate the central mechanisms of addiction-related behaviors mediated by the CCK system across the striatum, amygdala, hypothalamus, and midbrain. Here, we cover fundamental findings that implicate CCK neuron activity and CCK receptor signaling in modulating drug intake and drug-seeking (focusing on psychostimulants, opioids, and alcohol). In doing so, we highlight the few studies that indicate sex differences in CCK expression and corresponding drug effects, emphasizing the importance of examining hormonal influences and sex as a biological variable in translating basic science discoveries to effective treatments for substance use disorders in human patients. Finally, we point toward understudied subcortical sources of endogenous CCK and describe how continued neurotechnology advancements can be leveraged to modernize understanding of the neural circuit mechanisms underlying CCK release and signaling in addiction-relevant behaviors.

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Involvement of the Dorsal Vagal Complex in Alcohol-Related Behaviors

The neurobiological mechanisms that regulate the development and maintenance of alcohol use disorder (AUD) are complex and involve a wide variety of within and between systems neuroadaptations. While classic reward, preoccupation, and withdrawal neurocircuits have been heavily studied in terms of AUD, viable treatment targets from this established literature have not proven clinically effective as of yet. Therefore, examination of additional neurocircuitries not classically studied in the context of AUD may provide novel therapeutic targets. Recent studies demonstrate that various neuropeptides systems are important modulators of alcohol reward, seeking, and intake behaviors. This includes neurocircuitry within the dorsal vagal complex (DVC), which is involved in the control of the autonomic nervous system, control of intake of natural rewards like food, and acts as a relay of interoceptive sensory information via interactions of numerous gut-brain peptides and neurotransmitter systems with DVC projections to central and peripheral targets. DVC neuron subtypes produce a variety of neuropeptides and transmitters and project to target brain regions critical for reward such as the mesolimbic dopamine system as well as other limbic areas important for the negative reinforcing and aversive properties of alcohol withdrawal such as the extended amygdala. This suggests the DVC may play a role in the modulation of various aspects of AUD. This review summarizes the current literature on neurotransmitters and neuropeptides systems in the DVC (e.g., norepinephrine, glucagon-like peptide 1, neurotensin, cholecystokinin, thyrotropin-releasing hormone), and their potential relevance to alcohol-related behaviors in humans and rodent models for AUD research. A better understanding of the role of the DVC in modulating alcohol related behaviors may lead to the elucidation of novel therapeutic targets for drug development in AUD.

Does endogenous cholecystokinin modulate alcohol intake?

Alcohol use disorder or alcoholism is characterized by uncontrollable alcohol use and intoxication, as well as a heightened state of anxiety after alcohol withdrawal. Ethanol-associated stimuli also drive the urge to drink by means of classical conditioning. Alcoholism has been considered a dopamine (DA) dysregulation syndrome that involves the activity of the central amygdala circuitry of anxiety. Cholecystokinin (CCK) is the most abundant neuropeptide in the mammal brain, where it activates two receptors, CCK₁ and CCK₂. Genetic evidence relates CCK₁ receptors to alcoholism in humans. CCK₂ activity has been associated with the onset of human anxiety. CCK modulates DA release in the nucleus accumbens (NAc) and it is expressed in the γ-aminobutyric acid (GABA)-expressing basket interneurons in the cerebral cortex. CCK interacts with serotonin (5-HT) neurotransmission through 5-HT₃ receptors to regulate mesocorticolimbic pathways and with GABA to attenuate anxiety in the amygdala. Finally, CCK stimulates the release of orexins and oxytocin in the hypothalamus, two relevant hypothalamic neuropeptides involved in signaling satiety for ethanol and well-being respectively. Given the "dimmer-switch" function of endogenous CCK in the neurotransmission by 5-HT, DA, GABA, and glutamate in normal and pathological behaviors (Ballaz and Bourin, 2020), we hypothesize that CCK adjusts functioning of the reward and anxiety circuitries altered by ethanol. This review gathers data supporting this hypothesis, and suggests mechanisms underlying a role for endogenous CCK in alcoholism.

Cholecystokinin-Mediated Neuromodulation of Anxiety and Schizophrenia: A "Dimmer-Switch" Hypothesis

Cholecystokinin (CCK), the most abundant brain neuropeptide, is involved in relevant behavioral functions like memory, cognition, and reward through its interactions with the opioid and dopaminergic systems in the limbic system. CCK excites neurons by binding two receptors, CCK1 and CCK2, expressed at low and high levels in the brain, respectively. Historically, CCK2 receptors have been related to the induction of panic attacks in humans. Disturbances in brain CCK expression also underlie the physiopathology of schizophrenia, which is attributed to the modulation by CCK1 receptors of the dopamine flux in the basal striatum. Despite this evidence, neither CCK2 receptor antagonists ameliorate human anxiety nor CCK agonists have consistently shown neuroleptic effects in clinical trials. A neglected aspect of the function of brain CCK is its neuromodulatory role in mental disorders. Interestingly, CCK is expressed in pivotal inhibitory interneurons that sculpt cortical dynamics and the flux of nerve impulses across corticolimbic areas and the excitatory projections to mesolimbic pathways. At the basal striatum, CCK modulates the excitability of glutamate, the release of inhibitory GABA, and the discharge of dopamine. Here we focus on how CCK may reduce rather than trigger anxiety by regulating its cognitive component. Adequate levels of CCK release in the basal striatum may control the interplay between cognition and reward circuitry, which is critical in schizophrenia. Hence, it is proposed that disturbances in the excitatory/ inhibitory interplay modulated by CCK may contribute to the imbalanced interaction between corticolimbic and mesolimbic neural activity found in anxiety and schizophrenia.

The unappreciated roles of the cholecystokinin receptor CCK(1) in brain functioning

The CCK(1) receptor is a G-protein-coupled receptor activated by the sulfated forms of cholecystokinin (CCK), a gastrin-like peptide released in the gastrointestinal tract and mammal brain. A substantial body of research supports the hypothesis that CCK(1)r stimulates gallbladder contraction and pancreatic secretion in the gut, as well as satiety in brain. However, this receptor may also fulfill relevant roles in behavior, thanks to its widespread distribution in the brain. The strategic location of CCK(1)r in mesolimbic structures and specific hypothalamic and brainstem nuclei lead to complex interactions with neurotransmitters like dopamine, serotonin, and glutamate, as well as hypothalamic hormones and neuropeptides. The activity of CCK(1)r maintains adequate levels of dopamine and regulates the activity of serotonin neurons of raphe nuclei, which makes CCK(1)r an interesting therapeutic target for the development of adjuvant treatments for schizophrenia, drug addiction, and mood disorders. Unexplored functions of CCK(1)r, like the transmission of interoceptive sensitivity in addition to the regulation of hypothalamic hormones and neurotransmitters affecting emotional states, well-being, and attachment behaviors, may open exciting roads of research. The absence of specific ligands for the CCK(1) receptor has complicated the study of its distribution in brain so that research about its impact on behavior has been published sporadically over the last 30 years. The present review reunites all this body of evidence in a comprehensive way to summarize our knowledge about the actual role of CCK in the neurobiology of mental illness.

Interaction between cholecystokinin and the fibroblast growth factor system in the ventral tegmental area of selectively bred high- and low-responder rats

Individual differences in the locomotor response to novelty have been linked to basal differences in dopaminergic neurotransmission. Mesolimbic dopaminergic outputs are regulated by cholecystokinin (CCK), a neuropeptide implicated in anxiety. In turn, CCK expression is regulated by fibroblast growth factor-2 (FGF2), which has recently been identified as an endogenous regulator of anxiety. FGF2 binds to the high-affinity fibroblast growth factor receptor-1 (FGF-R1) to regulate the development and maintenance of dopamine neurons in the ventral tegmental area (VTA). However, the relationship between the FGF and CCK systems in the VTA is not well understood. Therefore, we utilized the selectively-bred low-responder (bLR; high-anxiety) and high-responder (bHR; low-anxiety) rats to examine the effects of repeated (21-day) FGF2 treatment on CCK and FGF-R1 mRNA in the rostral VTA (VTAr). In vehicle-treated controls, both CCK and FGF-R1 mRNA levels were increased in the VTAr of bLR rats relative to bHR rats. Following FGF2 treatment, however, bHR-bLR differences in CCK and FGF-R1 mRNA expression were eliminated, due to decreased CCK mRNA levels in the VTAr of bLR rats and increased FGF-R1 expression in bHR rats. Differences after FGF2 treatment may denote distinct interactions between the CCK and FGF systems in the VTAr of bHR vs. bLR rats. Indeed, significant correlations between CCK and FGF-R1 mRNA expression were found in bHR, but not bLR rats. Colocalization studies suggest that CCK and FGF-R1 are coexpressed in some VTAr neurons. Taken together, our findings suggest that the FGF system is poised to modulate both CCK and FGF-R1 expression in the VTAr, which may be associated with individual differences in mesolimbic pathways associated with anxiety-like behavior.

Behavioral and cortical EEG evaluations confirm the roles of both CCKA and CCKB receptors in mouse CCK-induced anxiety

This study investigated the roles of cholecystokinin (CCK)(A) and CCK(B) receptors on CCK-4-induced anxiety-like behaviors in mice through behavioral and neural evaluations. Anxiety-like behaviors in mice were induced by an intracerebroventricular (i.c.v.) administration of CCK-4, which can bind to both CCK(A) and CCK(B) receptors. The effects of CCK(A) and CCK(B) receptor antagonists (devazepide and CI-988, respectively) were examined using mouse anxiety tests (elevated-plus maze and light-dark box) and also by examining neuronal activities through EEG monitoring and c-Fos immunohistochemistry in the cortex and amygdala. CCK-4 (3 μg/kg of body weight i.c.v.) significantly induced mouse anxiety-like behaviors in the anxiety tests and also affected their EEG patterns with respect to pre-drug tracing, resulting in increase in spectral power in relative power distribution in the delta and theta bands (0.5-5 Hz frequency bands) and also in increase in c-Fos immunopositive neuron counts. These CCK-4 effects were completely suppressed by 1.0mg/kg CCK(B) receptor antagonist, CI-988, while the same amount of CCK(A) receptor antagonist, devazepide was partly able to suppress the same effects. These findings indicated that not only CCK(B) receptors but also CCK(A) receptors in the brain play important roles in regulating anxiety-like behaviors in mice. The present study also proposed a possibility that cortical EEG is useful for assessing anxiety.

Correlating human and animal studies of cocaine abuse and gene expression

Gene expression changes resulting from cocaine abuse in both humans and animal models have been studied for several decades. Although human studies have been very useful at illuminating cocaine-related expression changes, there are many factors complicating these studies, including the difficulty of obtaining high-quality postmortem brain tissue and patient comorbidities. Animal models of cocaine abuse have served as valuable additions to human data and allow examination of specific aspects of cocaine abuse, including immediate early gene expression and the molecular effects of abstinence and relapse. In total, human and animal studies of cocaine abuse have uncovered gene expression changes in the brain related to a number of molecular functions, including the extracellular matrix, synaptic communication and neuroplasticity, receptors, ion channels and transporters, oligodendrocytes and myelin, apoptosis and cell death, mitochondrial function, signal transduction, and transcription factors. In addition, the mitogen-activated protein kinase and synaptic long-term potentiation signal transduction pathways are highlighted as pathways in which multiple components are altered by cocaine. Pathways and processes affected by changes in gene expression that overlap among multiple species may be promising pharmacotherapeutic targets for reducing the behavioral effects of cocaine abuse and the relapse potential observed in humans.

Regional brain cholecystokinin changes as a function of rough-and-tumble play behavior in adolescent rats

Brain cholecystokinin (CCK) levels have been shown to be elevated in animals defeated during adult social aggression. The present experiment evaluated whether similar effects are evident in prolonged bouts of juvenile social-play fighting, which tend to switch from largely positive to some negative affect after approximately 15 min into a half-hour play session, as indexed by a gradual shift from positively valenced 50 kHz ultrasonic vocalizations (USVs) to negatively valenced 20 kHz USVs. Given the role of CCK in both positive and negative emotional events, we examined levels of CCK-8 in tissue homogenates from 14 brain areas in animals 6h after a 30 min play bout compared to no-play control animals tested similarly in isolation for 30 min. As with patterns observed following adult defeat, significantly higher CCK levels were evident after play in the posterior neo-cortex compared to no-play control animals (+26%). Levels of CCK were also elevated in the midbrain (+35%). However, unlike in adult aggression, CCK levels were reduced in the hypothalamus (-40%) and basal forebrain (-24%) as compared to no-play animals. Posterior cortex CCK levels were positively correlated to the duration that each animal was pinned (r = +.50) which suggests that elevated CCK in the posterior cortex may be related to the negative aspects of play. Hypothalamic CCK levels were negatively related to dorsal contacts and pins (r's = -.57), and suggest that the lower CCK levels may reflect the more positive valenced aspects of play. The data indicate that CCK utilization in the brain is dynamically responsive to rough-and-tumble play.

Regional brain cholecystokinin changes as a function of friendly and aggressive social interactions in rats

Cholecystokinin (CCK) is the most abundant neuropeptide in the mammalian brain, and has been implicated in the regulation of a diversity of emotions and motivations including negative affect and stress responses. In this experiment, we assayed levels of CCK (CCK4/5 and CCK8) from tissue homogenates in intruder animals 6 h after resident-intruder inter-male aggression. Intruder animals that demonstrated submissive behavior (freezing and 22-kHz ultrasonic vocalizations) had higher levels of CCK in the tegmentum and posterior cortex as compared to non-submissive (i.e., "Friendly") intruder animals. Ultrasonic vocalizations (22-kHz) were positively correlated with CCK levels in the tegmentum, posterior cortex and pituitary. These data suggest that CCK may play a role in the generation of negative affective states indexed by 22-kHz ultrasonic calls in certain regions of the brain.

5-(Tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-Based Cholecystokinin Receptor Antagonists: Reversal of CCK1 Receptor Subtype Selectivity toward CCK2 Receptors

With the aim of reversing selectivity or antagonist/agonist functionality in the 5-(tryptophylamino)-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-derived potent and highly selective CCK(1) antagonists, a series of 4-benzyl and 4-methyl derivatives have been synthesized. Whereas the introduction of the benzyl group led, in all cases, to complete loss of the binding affinity, the incorporation of the methyl group gave a different result depending on the stereochemistry of the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine scaffold. Thus, the introduction of the methyl group into the (4aS,5R)-diastereoisomers, giving a (4S)-configuration, produced a 3-fold increase in the CCK(1) binding potency and selectivity. However, the same structural manipulation in the opposite (4aR,5S)-stereochemistry, leading to a (4R,4aR,5S)-configuration, produced reversal of the selectivity for CCK(1) to the CCK(2) receptors. The replacement of the Boc group at the tryptophan moiety by a 2-adamantyloxycarbonyl group also contributed to that reversal. The resulting compounds displayed moderate CCK(2) antagonist activity in rat and human receptors, and a very small partial agonist effect on the production of inositol phosphate in COS-7 cells transfected with the wild-type human CCK(2) receptor.

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

Reactivation of cocaine conditioned place preference induced by stress is reversed by cholecystokinin-B receptors antagonist in rats

The effects of different cholecystokinin (CCK) receptor antagonists (devazepide and L365,260) on cocaine or stress-induced reactivation of cocaine conditioned place preference (CPP) were investigated in rats. After receiving alternate injection of cocaine (10 mg/kg) and saline for 8 consecutive days, the rats spent more time in the drug-paired side (cocaine CPP) on day 9. These animals did not show cocaine CPP on day 31 following saline-paired training daily from days 10 to 30 (21-day extinction). However, a single injection of cocaine (10 mg/kg) or 15 min of intermittent footshock could reinstate CPP on day 32 with significant more time spent in the drug-paired side in comparison with that on day 0. Systemic injection of CCK-A receptor antagonists, devazepide (0.1 and 1 mg/kg, i.p.), 30 min before cocaine priming, significantly attenuated cocaine-induced reinstatement of CPP, while CCK-B receptor antagonist, L365,260 (0.1 and 1 mg/kg, i.p.), did not show a similar effect. In contrast, pretreatment with L365,260 (0.1 and 1 mg/kg, i.p.) but not devazepide (0.1 and 1 mg/kg, i.p.) significantly blocked stress-induced reinstatement of CPP. In another experiment, CCK-A or B receptor antagonists were infused into nucleus accumbens or amygdala to determine which brain area are involved in the role of different CCK receptors in stress or drug-induced relapse to cocaine seeking. The results show that infusion of the devazepide (10 microg) into the nucleus accumbens significantly inhibited the cocaine-induced reinstatement of CPP, while infusion of devazepide (1 and 10 microg) into amygdala did not affect cocaine-induced reactivation of CPP. Interestingly, infusion of L365,260 (1 and 10 microg) into both nucleus accumbens or amygdala significantly attenuated or blocked stress-induced reinstatement of CPP. These findings demonstrate that CCK-A and B receptor have different roles in relapse to drug craving and further suggest that the brain areas involved in the CCK receptors on reinstatement of drug seeking are not identical. CCK-B receptor antagonists might be of some value in the treatment and prevention of relapse to stress-induced to drug craving following long-term detoxification.