Ghrelin receptor antagonist JMV2959 blunts cocaine and oxycodone drug-seeking, but not self-administration, in male rats.

The drug overdose crisis has spawned serious health consequences, including the increased incidence of substance use disorders (SUDs), conditions manifested by escalating medical and psychological impairments. While medication management is a key adjunct in SUD treatment, this crisis has crystallized the need to develop additional therapeutics to facilitate extended recovery from SUDs. The "hunger hormone" ghrelin acts by binding to the growth hormone secretagogue receptor 1α (GHS1αR) to control homeostatic and hedonic aspects of food intake and has been implicated in the mechanisms underlying SUDs. Preclinical studies indicate that GHS1αR antagonists and inverse agonists suppress reward-related signaling associated with cocaine and opioids. In the present study, we found that the GHS1αR antagonist JMV2959 was efficacious to suppress both cue-reinforced cocaine and oxycodone drug-seeking, but not cocaine or oxycodone self-administration in male Sprague-Dawley rats. These data suggest a role of the ghrelin-GHS1αR axis in mediating overlapping reward-related aspects of cocaine and oxycodone and premises the possibility that a GHS1αR antagonist may be a valuable therapeutic strategy for relapse vulnerability in SUDs.

µ-opioid receptor agonists and psychedelics: pharmacological opportunities and challenges.

Opioid misuse and opioid-involved overdose deaths are a massive public health problem involving the intertwined misuse of prescription opioids for pain management with the emergence of extremely potent fentanyl derivatives, sold as standalone products or adulterants in counterfeit prescription opioids or heroin. The incidence of repeated opioid overdose events indicates a problematic use pattern consistent with the development of the medical condition of opioid use disorder (OUD). Prescription and illicit opioids reduce pain perception by activating µ-opioid receptors (MOR) localized to the central nervous system (CNS). Dysregulation of meso-corticolimbic circuitry that subserves reward and adaptive behaviors is fundamentally involved in the progressive behavioral changes that promote and are consequent to OUD. Although opioid-induced analgesia and the rewarding effects of abused opioids are primarily mediated through MOR activation, serotonin (5-HT) is an important contributor to the pharmacology of opioid abused drugs (including heroin and prescription opioids) and OUD. There is a recent resurgence of interest into psychedelic compounds that act primarily through the 5-HT2A receptor (5-HT 2A R) as a new frontier in combatting such diseases (e.g., depression, anxiety, and substance use disorders). Emerging data suggest that the MOR and 5-HT2AR crosstalk at the cellular level and within key nodes of OUD circuitry, highlighting a major opportunity for novel pharmacological intervention for OUD. There is an important gap in the preclinical profiling of psychedelic 5-HT2AR agonists in OUD models. Further, as these molecules carry risks, additional analyses of the profiles of non-hallucinogenic 5-HT2AR agonists and/or 5-HT2AR positive allosteric modulators may provide a new pathway for 5-HT2AR therapeutics. In this review, we discuss the opportunities and challenges associated with utilizing 5-HT2AR agonists as therapeutics for OUD.

Discovery of Novel Oleamide Analogues as Brain-Penetrant Positive Allosteric Serotonin 5-HT2C Receptor and Dual 5-HT2C/5-HT2A Receptor Modulators.

The serotonin 5-HT2A receptor (5-HT2AR) and 5-HT2CR localize to the brain and share overlapping signal transduction facets that contribute to their roles in cognition, mood, learning, and memory. Achieving selective targeting of these receptors is challenged by the similarity in their 5-HT orthosteric binding pockets. A fragment-based discovery approach was employed to design and synthesize novel oleamide analogues as selective 5-HT2CR or dual 5-HT2CR/5-HT2AR positive allosteric modulators (PAMs). Compound 13 (JPC0323) exhibited on-target properties, acceptable plasma exposure and brain penetration, as well as negligible displacement to orthosteric sites of ∼50 GPCRs and transporters. Furthermore, compound 13 suppressed novelty-induced locomotor activity in a 5-HT2CR-dependent manner, suggesting 5-HT2CR PAM, but not 5-HT2AR, activity at the level of the whole organism at the employed doses of 13. We discovered new selective 5-HT2CR PAMs and first-in-class 5-HT2CR/5-HT2AR dual PAMs that broaden the pharmacological toolbox to explore the biology of these vital receptors.

A serotonergic biobehavioral signature differentiates cocaine use disorder participants administered mirtazapine.

Cocaine use disorder (CUD) patients display heterogenous symptoms and unforeseeable responses to available treatment approaches, highlighting the need to identify objective, accessible biobehavioral signatures to predict clinical trial success in this population. In the present experiments, we employed a task-based behavioral and pharmacogenetic-fMRI approach to address this gap. Craving, an intense desire to take cocaine, can be evoked by exposure to cocaine-associated stimuli which can trigger relapse during attempted recovery. Attentional bias towards cocaine-associated words is linked to enhanced effective connectivity (EC) from the anterior cingulate cortex (ACC) to hippocampus in CUD participants, an observation which was replicated in a new cohort of participants in the present studies. Serotonin regulates attentional bias to cocaine and the serotonergic antagonist mirtazapine decreased activated EC associated with attentional bias, with greater effectiveness in those CUD participants carrying the wild-type 5-HT2CR gene relative to a 5-HT2CR single nucleotide polymorphism (rs6318). These data suggest that the wild-type 5-HT2CR is necessary for the efficacy of mirtazapine to decrease activated EC in CUD participants and that mirtazapine may serve as an abstinence enhancer to mitigate brain substrates of craving in response to cocaine-associated stimuli in participants with this pharmacogenetic descriptor. These results are distinctive in outlining a richer "fingerprint" of the complex neurocircuitry, behavior and pharmacogenetics profile of CUD participants which may provide insight into success of future medications development projects.

Heightened cocaine-seeking in male rats associates with a distinct transcriptomic profile in the medial prefrontal cortex.

Drug overdose deaths involving cocaine have skyrocketed, an outcome attributable in part to the lack of FDA-approved medications for the treatment of cocaine use disorder (CUD), highlighting the need to identify new pharmacotherapeutic targets. Vulnerability to cocaine-associated environmental contexts and stimuli serves as a risk factor for relapse in CUD recovery, with individual differences evident in the motivational aspects of these cues. The medial prefrontal cortex (mPFC) provides top-down control of striatal circuitry to regulate the incentive-motivational properties of cocaine-associated stimuli. Clinical and preclinical studies have identified genetic variations that impact the degree of executive restraint over drug-motivated behaviors, and we designed the present study to employ next-generation sequencing to identify specific genes associated with heightened cue-evoked cocaine-seeking in the mPFC of male, outbred rats. Rats were trained to stably self-administer cocaine, and baseline cue-reinforced cocaine-seeking was established. Rats were phenotyped as either high cue (HC) or low cue (LC) responders based upon lever pressing for previously associated cocaine cues and allowed 10 days of abstinence in their home cages prior to mPFC collection for RNA-sequencing. The expression of 309 genes in the mPFC was significantly different in HC vs. LC rats. Functional gene enrichment analyses identified ten biological processes that were overrepresented in the mPFC of HC vs. LC rats. The present study identifies distinctions in mPFC mRNA transcripts that characterizes individual differences in relapse-like behavior and provides prioritized candidates for future pharmacotherapeutics aimed to help maintain abstinence in CUD. In particular the Htr2c gene, which encodes the serotonin 5-HT2C receptor (5-HT2CR), is expressed to a lower extent in HC rats, relative to LC rats. These findings build on a plethora of previous studies that also point to the 5-HT2CR as an attractive target for the treatment of CUD.

Safety and Preliminary Efficacy of Lorcaserin for Cocaine Use Disorder: A Phase I Randomized Clinical Trial.

Background and Objectives: Preclinical studies show serotonin (5-HT) 5-HT2C receptor (5-HT2CR) agonists reduce cocaine-seeking and cocaine intake. This study examined safety of the 5-HT2CR agonist lorcaserin administered with cocaine in participants with cocaine use disorder (CocUD). Secondarily, subjective response to cocaine and choice of cocaine vs. money were examined. Methods: A double-blind, randomized, placebo-controlled trial of 25 inpatient non-treatment seeking participants with CocUD. Participants were randomized to either lorcaserin (n = 17) or placebo (n = 8). Primary outcome measures included cardiovascular measures and plasma cocaine levels. Secondary measures of subjective response to cocaine were assessed using a visual analog scale (VAS) and cocaine vs. money progressive ratio choice sessions. Results: Thirteen randomized participants were included in the final analysis. No serious or unexpected adverse events were related to lorcaserin. There were no significant interactions between cocaine and lorcaserin on cardiovascular measures, plasma cocaine, or subjective ratings. After multiple comparisons correction, cocaine significantly increased blood pressure, heart rate, and QTc. Lorcaserin significantly decreased VAS ratings of "feel irritable," "feel hungry," and "I am craving." For the cocaine vs. money choice procedure, there was a significant interaction between choice (cocaine vs. money) and lorcaserin. Participants treated with lorcaserin were more likely to choose cocaine. Discussion and Conclusions: This study showed safety of lorcaserin administered with cocaine but lack of efficacy to reduce the reinforcing effects of cocaine. Scientific Significance: This study is the first to show a disconnect between effects of 5-HT2CR agonists on craving and cocaine choice in human cocaine users.

Subanesthetic ketamine with an AMPAkine attenuates motor impulsivity in rats.

The concept of 'impulse control' has its roots in early psychiatry and today has progressed into a well-described, although poorly understood, multidimensional endophenotype underlying many neuropsychiatric disorders (e.g., attention deficit hyperactivity disorder, schizophrenia, substance use disorders). There is mounting evidence suggesting that the cognitive and/or behavioral dimensions underlying impulsivity are driven by dysfunctional glutamate (Glu) neurotransmission via targeted ionotropic Glu receptor (GluR) [e.g., N-methyl-D-aspartate receptor (NMDAR), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)] mechanisms and associated synaptic alterations within key brain nodes. Ketamine, a noncompetitive NMDAR antagonist and FDA-approved for treatment-resistant depression, induces a 'glutamate burst' that drives resculpting of the synaptic milieu, which lasts for several days to a week. Thus, we hypothesized that single and repeated treatment with a subanesthetic ketamine dose would normalize motor impulsivity. Next, we hypothesized that AMPAR positive allosteric modulation, alone or in combination with ketamine, would attenuate impulsivity and provide insight into the mechanisms underlying GluR dysfunction relevant to motor impulsivity. To measure motor impulsivity, outbred male Sprague-Dawley rats were trained on the one-choice serial reaction time task. Rats pretreated with single or repeated (3 days) administration of ketamine (10 mg/kg; i.p.; 24-h pretreatment) or with the AMPAkine HJC0122 (1 or 10 mg/kg; i.p.; 30-min pretreatment) exhibited lower levels of motor impulsivity vs. control. Combination of single or repeated ketamine plus HJC0122 also attenuated motor impulsivity vs. control. We conclude that ligands designed to promote GluR signaling represent an effective pharmacological approach to normalize impulsivity and subsequently, neuropsychiatric disorders marked by aberrant impulse control.

Blunted prefrontal signature of proactive inhibitory control in cocaine use disorder.

BACKGROUND: Impulsivity is an established risk factor for substance use disorder (SUD). Integral to SUD recovery is proactive control (leveraging information about a potential need for behavioral restraint to marshal increased cognitive resources toward inhibition) when cues for drug use are unavoidable. However, proactive control is little studied in SUD, and is merely inferred from post-error performance adjustments. METHODS: We probed covert neurocircuit signatures of proactive control in persons with SUD, as well as the moderating effects of incentives for successfully exerting proactive control. We administered a Monetary Incentive Stop Task (MIST) during functional magnetic resonance imaging of adults with cocaine use disorder (CUD; n = 21) and healthy controls (n = 21). The MIST blended the reward and loss-anticipatory cues of the Monetary Incentive Delay (MID) Task with a variant of the Stop-Signal Task, in which target color signaled whether or not withholding a response might be necessary. RESULTS: In controls, but not in CUD participants, targets that signaled a potential need to stop (as a contrast with targets that signaled no need to stop) activated portions of right operculum akin to activation commonly elicited by stop signals, despite no actual stop signal. Across all participants, this proactive control activation did not relate to task behavior or to questionnaire impulsivity. Anticipatory incentive cues did not recruit ventral striatum. CONCLUSIONS: These data suggest that persons with CUD show blunted covert signatures of attention and proactive control. This potentially accounts in part for the role of poor executive function in relapse vulnerability.

Discovery of 4-Phenylpiperidine-2-Carboxamide Analogues as Serotonin 5-HT2C Receptor-Positive Allosteric Modulators with Enhanced Drug-like Properties.

Targeting the serotonin (5-HT) 5-HT2C receptor (5-HT2CR) allosteric site to potentiate endogenous 5-HT tone may provide novel therapeutics to alleviate the impact of costly, chronic diseases such as obesity and substance use disorders. Expanding upon our recently described 5-HT2CR-positive allosteric modulators (PAMs) based on the 4-alkylpiperidine-2-carboxamide scaffold, we optimized the undecyl moiety at the 4-position with variations of cyclohexyl- or phenyl-containing fragments to reduce rotatable bonds and lipophilicity. Compound 12 (CTW0415) was discovered as a 5-HT2CR PAM with improved pharmacokinetics and reduced off-target interactions relative to our previous series of molecules. The in vivo efficacy of compound 12 to potentiate the effects of a selective 5-HT2CR agonist was established in a drug discrimination assay. Thus, 12 is reported as a 5-HT2CR PAM with characteristics suitable for in vivo pharmacological studies to further probe the biological and behavioral mechanisms of allosteric modulation of a receptor important in several chronic diseases.

Methylation Patterns of the HTR2A Associate With Relapse-Related Behaviors in Cocaine-Dependent Participants.

Relapse during abstinence in cocaine use disorder (CUD) is often hastened by high impulsivity (predisposition toward rapid unplanned reactions to stimuli without regard to negative consequences) and high cue reactivity (e.g., attentional bias towards drug reward stimuli). A deeper understanding of the degree to which individual biological differences predict or promote problematic behaviors may afford opportunities for clinical refinement and optimization of CUD diagnostics and/or therapies. Preclinical evidence implicates serotonin (5-HT) neurotransmission through the 5-HT2A receptor (5-HT2AR) as a driver of individual differences in these relapse-related behaviors. Regulation of 5-HT2AR function occurs through many mechanisms, including DNA methylation of the HTR2A gene, an epigenetic modification linked with the memory of gene-environment interactions. In the present study, we tested the hypothesis that methylation of the HTR2A may associate with relapse-related behavioral vulnerability in cocaine-dependent participants versus healthy controls. Impulsivity was assessed by self-report (Barratt Impulsiveness Scale; BIS-11) and the delay discounting task, while levels of cue reactivity were determined by performance in the cocaine-word Stroop task. Genomic DNA was extracted from lymphocytes and the bisulfite-treated DNA was subjected to pyrosequencing to determine degree of methylation at four cytosine residues of the HTR2A promoter (-1439, -1420, -1224, -253). We found that the percent methylation at site -1224 after correction for age trended towards a positive correlation with total BIS-11 scores in cocaine users, but not healthy controls. Percent methylation at site -1420 negatively correlated with rates of delay discounting in healthy controls, but not cocaine users. Lastly, the percent methylation at site -253 positively correlated with attentional bias toward cocaine-associated cues. DNA methylation at these cytosine residues of the HTR2A promoter may be differentially associated with impulsivity or cocaine-associated environmental cues. Taken together, these data suggest that methylation of the HTR2A may contribute to individual differences in relapse-related behaviors in CUD.

Inherent Motor Impulsivity Associates with Specific Gene Targets in the Rat Medial Prefrontal Cortex.

High impulsivity characterizes a myriad of neuropsychiatric diseases, and identifying targets for neuropharmacological intervention to reduce impulsivity could reveal transdiagnostic treatment strategies. Motor impulsivity (impulsive action) reflects in part the failure of "top-down" executive control by the medial prefrontal cortex (mPFC). The present study profiled the complete set of mRNA molecules expressed from genes (transcriptome) in the mPFC of male, outbred rats stably expressing high (HI) or low (LI) motor impulsivity based upon premature responses in the 1-choice serial reaction time (1-CSRT) task. RNA-sequencing identified expression of 18 genes that was higher in the mPFC of HI vs. LI rats. Functional gene enrichment revealed that biological processes related to calcium homeostasis and G protein-coupled receptor (GPCR) signaling pathways, particularly glutamatergic, were overrepresented in the mPFC of HI vs. LI rats. Transcription factor enrichment identified mothers against decapentaplegic homolog 4 (SMAD4) and RE1 silencing transcription factor (REST) as overrepresented in the mPFC of HI rats relative to LI rats, while in silico analysis predicted a conserved SMAD binding site within the voltage-gated calcium channel subunit alpha1 E (CACNA1E) promoter region. qRT-PCR analyses confirmed that mRNA expression of CACNA1E, as well as expression of leucyl and cystinyl aminopeptidase (LNPEP), were higher in the mPFC of HI vs. LI rats. These outcomes establish a transcriptomic landscape in the mPFC that is related to individual differences in motor impulsivity and propose novel gene targets for future impulsivity research.

Suppression of cocaine relapse-like behaviors upon pimavanserin and lorcaserin co-administration.

Cocaine use disorder (CUD) is a major public health challenge for which there are no pharmacotherapeutics approved by the United States Food and Drug Administration (FDA). The propensity to relapse in CUD involves several vulnerability factors including sensitivity to cues associated with cocaine-taking. Serotonin (5-hydroxytryptamine, 5-HT) neurotransmission, particularly through the 5-HT2A receptor (5-HT2AR) and 5-HT2C receptor (5-HT2CR), is mechanistically linked to cocaine-seeking in preclinical models. In the present experiments, we employed self-administration assays in male rats to investigate whether acute and/or repeated administration of the FDA-approved selective 5-HT2AR antagonist/inverse agonist pimavanserin, selective 5-HT2CR agonist lorcaserin or their combination would alter cocaine intake and/or cocaine-seeking behavior. We found that acute administration of lorcaserin, but not pimavanserin, attenuated cocaine intake while pimavanserin plus lorcaserin did not impact cocaine self-administration. In contrast, 10-days of repeated administration of pimavanserin, lorcaserin, or pimavanserin plus lorcaserin during forced abstinence from cocaine self-administration, blunted cocaine-seeking, similar to the acute administration of each ligand. Taken together, these data reveal the efficacy of repeated treatment with pimavanserin plus lorcaserin to attenuate factors important to relapse-like behaviors in rodent models of CUD. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Serotonin 5-HT2C Receptor Cys23Ser Single Nucleotide Polymorphism Associates with Receptor Function and Localization In Vitro.

A non-synonymous single nucleotide polymorphism of the human serotonin 5-HT2C receptor (5-HT2CR) gene that converts a cysteine to a serine at amino acid codon 23 (Cys23Ser) appears to impact 5-HT2CR pharmacology at a cellular and systems level. We hypothesized that the Cys23Ser alters 5-HT2CR intracellular signaling via changes in subcellular localization in vitro. Using cell lines stably expressing the wild-type Cys23 or the Ser23 variant, we show that 5-HT evokes intracellular calcium release with decreased potency and peak response in the Ser23 versus the Cys23 cell lines. Biochemical analyses demonstrated lower Ser23 5-HT2CR plasma membrane localization versus the Cys23 5-HT2CR. Subcellular localization studies demonstrated O-linked glycosylation of the Ser23 variant, but not the wild-type Cys23, may be a post-translational mechanism which alters its localization within the Golgi apparatus. Further, both the Cys23 and Ser23 5-HT2CR are present in the recycling pathway with the Ser23 variant having decreased colocalization with the early endosome versus the Cys23 allele. Agonism of the 5-HT2CR causes the Ser23 variant to exit the recycling pathway with no effect on the Cys23 allele. Taken together, the Ser23 variant exhibits a distinct pharmacological and subcellular localization profile versus the wild-type Cys23 allele, which could impact aspects of receptor pharmacology in individuals expressing the Cys23Ser SNP.

In Vivo and In Vitro Analyses of Novel Peptidomimetic Disruptors for the Serotonin 5-HT2C Receptor Interaction With Phosphatase and Tensin Homolog.

Hypofunction of the serotonin (5-HT) 5-HT2C receptor (5-HT2CR) has been implicated in a variety of disorders including substance use disorders. As such, approaches to enhance 5-HT2CR signaling display therapeutic potential. In the present study, we show that disruption of the 5-HT2CR interaction with the protein phosphatase and tensin homolog (PTEN) via peptidomimetics enhances 5-HT2CR-mediating signaling in vitro and potentiates selective 5-HT2CR agonists in behavioral rodent models. Overall, the present study provides further evidence that 5-HT2CR activity can be modulated through an allosteric protein-protein interaction. This work provides the groundwork for the continued exploration of protein-protein interactions that can allosterically modulate this critical receptor and other important G protein-coupled receptors (GPCRs) for new therapeutic development through mechanisms that may display clinical utility.

Cingulo-hippocampal effective connectivity positively correlates with drug-cue attentional bias in opioid use disorder.

Individuals with opioid use disorder (OUD) often relapse when exposed to opioid-related cues. Previous functional magnetic resonance imaging (fMRI) studies have identified neuronal corticolimbic changes related to drug cue reactivity in OUD. However, the corresponding manner in which brain regions interact is still unclear. Effective (directional) connectivity was analyzed using dynamic causal modeling of fMRI data acquired from 27 OUD participants (13 with OUD and 14 with OUD and cocaine use disorder [OUD+CUD]), while performing an opioid-word Stroop task. Participants were shown opioid and neutral words presented in different colors and were instructed to indicate word color but ignore word meaning. The effects of opioid words relative to neutral words on effective connectivity and on behavioral reaction time were defined as modulatory change and attentional bias, respectively. For all the 27 participants, left anterior cingulate cortex (ACC) to right hippocampus effective connectivity exhibited the largest modulatory change, which was positively correlated with attentional bias. The findings for the ACC to hippocampus EC were consistent across OUD and CUD found in a previous study.

Profile of cortical N-methyl-D-aspartate receptor subunit expression associates with inherent motor impulsivity in rats.

Impulsivity is a multifaceted behavioral manifestation with implications in several neuropsychiatric disorders. Glutamate neurotransmission through the N-methyl-D-aspartate receptors (NMDARs) in the medial prefrontal cortex (mPFC), an important brain region in decision-making and goal-directed behaviors, plays a key role in motor impulsivity. We discovered that inherent motor impulsivity predicted responsiveness to D-cycloserine (DCS), a partial NMDAR agonist, which prompted the hypothesis that inherent motor impulsivity is associated with the pattern of expression of cortical NMDAR subunits (GluN1, GluN2A, GluN2B), specifically the protein levels and synaptosomal trafficking of the NMDAR subunits. Outbred male Sprague-Dawley rats were identified as high (HI) or low (LI) impulsive using the one-choice serial reaction time task. Following phenotypic identification, mPFC synaptosomal protein was extracted from HI and LI rats to assess the expression pattern of the NMDAR subunits. Synaptosomal trafficking and stabilization for the GluN2 subunits were investigated by co-immunoprecipitation for postsynaptic density 95 (PSD95) and synapse associated protein 102 (SAP102). HI rats had lower mPFC GluN1 and GluN2A, but higher GluN2B and pGluN2B synaptosomal protein expression versus LI rats. Further, higher GluN2B:PSD95 and GluN2B:SAP102 protein:protein interactions were detected in HI versus LI rats. Thus, the mPFC NMDAR subunit expression pattern and/or synaptosomal trafficking associates with high inherent motor impulsivity. Increased understanding of the complex regulation of NMDAR balance within the mPFC as it relates to inherent motor impulsivity may lead to a better understanding of risk factors for impulse-control disorders.

Convergent neural connectivity in motor impulsivity and high-fat food binge-like eating in male Sprague-Dawley rats.

Food intake is essential for survival, but maladaptive patterns of intake, possibly encoded by a preexisting vulnerability coupled with the influence of environmental variables, can modify the reward value of food. Impulsivity, a predisposition toward rapid unplanned reactions to stimuli, is one of the multifaceted determinants underlying the etiology of dysregulated eating and its evolving pathogenesis. The medial prefrontal cortex (mPFC) is a major neural director of reward-driven behavior and impulsivity. Compromised signaling between the mPFC and nucleus accumbens shell (NAcSh) is thought to underlie the cognitive inability to withhold prepotent responses (motor impulsivity) and binge intake of high-fat food (HFF) seen in binge eating disorder. To explore the relationship between motor impulsivity and binge-like eating in rodents, we identified high (HI) and low impulsive (LI) rats in the 1-choice serial reaction time task and employed a rat model of binge-like eating behavior. HFF binge rats consumed significantly greater calories relative to control rats maintained on continual access to standard food or HFF. HI rats repeatedly exhibited significantly higher bingeing on HFF vs. LI rats. Next, we employed dual viral vector chemogenetic technology which allows for the targeted and isolated modulation of ventral mPFC (vmPFC) neurons that project to the NAcSh. Chemogenetic activation of the vmPFC to NAcSh pathway significantly suppressed motor impulsivity and binge-like intake for high-fat food. Thus, inherent motor impulsivity and binge-like eating are linked and the vmPFC to NAcSh pathway serves as a 'brake' over both behaviors.

Binge-Type Eating in Rats is Facilitated by Neuromedin U Receptor 2 in the Nucleus Accumbens and Ventral Tegmental Area.

Binge-eating disorder (BED) is the most common eating disorder, characterized by rapid, recurrent overconsumption of highly palatable food in a short time frame. BED shares an overlapping behavioral phenotype with obesity, which is also linked to the overconsumption of highly palatable foods. The reinforcing properties of highly palatable foods are mediated by the nucleus accumbens (NAc) and the ventral tegmental area (VTA), which have been implicated in the overconsumption behavior observed in BED and obesity. A potential regulator of binge-type eating behavior is the G protein-coupled receptor neuromedin U receptor 2 (NMUR2). Previous research demonstrated that NMUR2 knockdown potentiates binge-type consumption of high-fat food. We correlated binge-type consumption across a spectrum of fat and carbohydrate mixtures with synaptosomal NMUR2 protein expression in the NAc and VTA of rats. Synaptosomal NMUR2 protein in the NAc demonstrated a strong positive correlation with binge intake of a "lower"-fat (higher carbohydrate) mixture, whereas synaptosomal NMUR2 protein in the VTA demonstrated a strong negative correlation with binge intake of an "extreme" high-fat (0% carbohydrate) mixture. Taken together, these data suggest that NMUR2 may differentially regulate binge-type eating within the NAc and the VTA.

Endogenous Serotonin 5-HT2A and 5-HT2C Receptors Associate in the Medial Prefrontal Cortex.

The 5-HT2A receptor (5-HT2AR) and 5-HT2CR are localized to the same neurons within the medial prefrontal cortex (mPFC), which regulates executive function, decision-making, and reward-guided learning and memory processes. The 5-HT2AR and 5-HT2CR coimmunoprecipitate in the mPFC of male Sprague-Dawley rats, while in vitro studies demonstrate the presence of a physical interaction between the 5-HT2AR and 5-HT2CR. The purpose of this study was to identify mPFC subregions in which the 5-HT2AR and 5-HT2CR physically interact ex vivo in the male Sprague-Dawley rat. We established the expression patterns of 5-HT2AR and 5-HT2CR in layers I-VI of the anterior cingulate cortex (ACC), prelimbic (PL), and infralimbic (IL) subregions using double-label fluorescence immunohistochemistry in male rats. We then employed the proximity ligation assay (PLA) to test the hypothesis that the 5-HT2AR and 5-HT2CR form a close, physical association within these mPFC subregions. Our results demonstrate subregion- and layer-specific expression of the 5-HT2AR and 5-HT2CR proteins using immunofluorescence and single recognition PLA, and a spatially close (within 40 nm) interaction between the 5-HT2AR and 5-HT2CR that occurs along a dorsal-ventral gradient in the rat mPFC.

Design, Synthesis, and Characterization of 4-Undecylpiperidine-2-carboxamides as Positive Allosteric Modulators of the Serotonin (5-HT) 5-HT2C Receptor.

An impaired signaling capacity of the serotonin (5-HT) 5-HT2C receptor (5-HT2CR) has been implicated in the neurobehavioral processes that promote relapse vulnerability in cocaine use disorder (CUD). Restoration of the diminished 5-HT2CR signaling through positive allosteric modulation presents a novel therapeutic approach. Several new molecules with the 4-alkylpiperidine-2-carboxamide scaffold were designed, synthesized, and pharmacologically evaluated, leading to the discovery of selective 5-HT2CR positive allosteric modulators (PAMs). Compound 16 (CYD-1-79) potentiated 5-HT-evoked intracellular calcium release in cells stably expressing the human 5-HT2CR but not the 5-HT2AR cells. A topographically distinct allosteric site was identified based on the newly solved 5-HT2CR structure. Compound 16 modulated 5-HT2CR-mediated spontaneous ambulation, partially substituted for the training dose of the 5-HT2CR agonist WAY163909, synergized with a low dose of WAY163909 to substitute fully for the stimulus effects of WAY163909, and attenuated relapse vulnerability as assessed in a rodent self-administration model, indicating its therapeutic promise for CUD.