Bile acids modulate reinstatement of cocaine conditioned place preference and accumbal dopamine dynamics without compromising appetitive learning.

Psychostimulants target the dopamine transporter (DAT) to elicit their psychomotor actions. Bile acids (BAs) can also bind to DAT and reduce behavioral responses to cocaine, suggesting a potential therapeutic application of BAs in psychostimulant use disorder. Here, we investigate the potential of BAs to decrease drug-primed reinstatement when administered during an abstinence phase. To do this, after successful development of cocaine-associated contextual place preference (cocaine CPP), cocaine administration was terminated, and animals treated with vehicle or obeticholic acid (OCA). When preference for the cocaine-associated context was extinguished, mice were challenged with a single priming dose of cocaine, and reinstatement of cocaine-associated contextual preference was measured. Animals treated with OCA demonstrate a significantly lower reinstatement for cocaine CPP. OCA also impairs the ability of cocaine to reduce the clearance rate of electrically stimulated dopamine release and diminishes the area under the curve (AUC) observed with amperometry. Furthermore, the AUC of the amperometric signal positively correlates with the reinstatement index. Using operant feeding devices, we demonstrate that OCA has no effect on contextual learning or motivation for natural rewards. These data highlight OCA as a potential therapeutic for cocaine use disorder.

Turning the tide on obesity?

Genetics, ultraprocessed foods, portion distortion, sweetened beverages, screen time, food addiction, intestinal microbiota, diet culture, weight stigma, food insecurity-all have been implicated in the "obesity epidemic." More than a billion people worldwide have obesity, and many more are overweight. With the emergence of new, highly effective weight-loss drugs, might the "fat decades" become a closed chapter in the history of public health?

Serotonin modulates an inhibitory input to the central amygdala from the ventral periaqueductal gray.

Fear is an adaptive state that drives defensive behavioral responses to specific and imminent threats. The central nucleus of the amygdala (CeA) is a critical site of adaptations that are required for the acquisition and expression of fear, in part due to alterations in the activity of inputs to the CeA. Here, we characterize a novel GABAergic input to the CeA from the ventral periaqueductal gray (vPAG) using fiber photometry and ex vivo whole-cell slice electrophysiology combined with optogenetics and pharmacology. GABA transmission from this ascending vPAG-CeA input was enhanced by serotonin via activation of serotonin type 2 C (5HT2C) receptors. Results suggest that these receptors are presynaptic. Interestingly, we found that GABA release from the vPAG-CeA input is enhanced following fear learning via activation of 5HT2C receptors and that this pathway is dynamically engaged in response to aversive stimuli. Additionally, we characterized serotonin release in the CeA during fear learning and recall for the first time using fiber photometry coupled to a serotonin biosensor. Together, these findings describe a mechanism by which serotonin modulates GABA release from ascending vPAG GABA inputs to the CeA and characterize a role for this pathway in fear.

Genetics and neurobiology of eating disorders.

Eating disorders (anorexia nervosa, bulimia nervosa and binge-eating disorder) are a heterogeneous class of complex illnesses marked by weight and appetite dysregulation coupled with distinctive behavioral and psychological features. Our understanding of their genetics and neurobiology is evolving thanks to global cooperation on genome-wide association studies, neuroimaging, and animal models. Until now, however, these approaches have advanced the field in parallel, with inadequate cross-talk. This review covers overlapping advances in these key domains and encourages greater integration of hypotheses and findings to create a more unified science of eating disorders. We highlight ongoing and future work designed to identify implicated biological pathways that will inform staging models based on biology as well as targeted prevention and tailored intervention, and will galvanize interest in the development of pharmacologic agents that target the core biology of the illnesses, for which we currently have few effective pharmacotherapeutics.

Kappa opioid receptor and dynorphin signaling in the central amygdala regulates alcohol intake.

Excessive alcohol drinking has been shown to modify brain circuitry to predispose individuals for future alcohol abuse. Previous studies have implicated the central nucleus of the amygdala (CeA) as an important site for mediating the somatic symptoms of withdrawal and for regulating alcohol intake. In addition, recent work has established a role for both the Kappa Opioid Receptor (KOR) and its endogenous ligand dynorphin in mediating these processes. However, it is unclear whether these effects are due to dynorphin or KOR arising from within the CeA itself or other input brain regions. To directly examine the role of preprodynorphin (PDYN) and KOR expression in CeA neurons, we performed region-specific conditional knockout of these genes and assessed the effects on the Drinking in the Dark (DID) and Intermittent Access (IA) paradigms. Conditional gene knockout resulted in sex-specific responses wherein PDYN knockout decreased alcohol drinking in both male and female mice, whereas KOR knockout decreased drinking in males only. We also found that neither PDYN nor KOR knockout protected against anxiety caused by alcohol drinking. Lastly, a history of alcohol drinking did not alter synaptic transmission in PDYN neurons in the CeA of either sex, but excitability of PDYN neurons was increased in male mice only. Taken together, our findings indicate that PDYN and KOR signaling in the CeA plays an important role in regulating excessive alcohol consumption and highlight the need for future studies to examine how this is mediated through downstream effector regions.

Anatomical and Functional Characterization of Central Amygdala Glucagon-Like Peptide 1 Receptor Expressing Neurons.

Glucagon-like peptide 1 receptors (GLP-1Rs) are highly expressed in the brain and are responsible for mediating the acute anorexigenic actions of widely prescribed GLP-1R agonists. Neurobiological efforts to localize the hypophagic effects of GLP-1R agonists in the brain have mainly focused on the hypothalamus and hindbrain. In this study, we performed a deep anatomical and neurophysiological characterization of GLP-1Rs in the central nucleus of the amygdala (CeA). At an mRNA level, we found that Glp1r is diffusely coexpressed in known CeA subpopulations like protein kinase c δ (Prkcd), somatostatin (Sst), or tachykinin2 (Tac2). At a cellular level, we used Glp1r-Cre mice and viral Cre-dependent tracing to map the anatomical positions of GLP-1R cells across the rostral-caudal axis of the CeA and in CeA subdivisions. We found that Glp1r CeA cells are highly enriched in the medial subdivision of the CeA (CeM). Using whole cell patch clamp electrophysiology, we found that Glp1r CeA neurons are characterized by the presence of Ih-like currents and resemble a low threshold bursting neuronal subtype in response to hyperpolarizing and depolarizing current injections. We observed sex differences in the magnitude of Ih-like currents and membrane capacitance. At rest, we observed that nearly half of Glp1r CeA neurons are spontaneously active. We observed that active and inactive neurons display significant differences in excitability even when normalized to an identical holding potential. Our data are the first to deeply characterize the pattern of Glp1r in the CeA and study the neurophysiological characteristics of CeA neurons expressing Glp1r. Future studies leveraging these data will be important to understanding the impact of GLP-1R agonists on feeding and motivation.

Manipulations of Central Amygdala Neurotensin Neurons Alter the Consumption of Ethanol and Sweet Fluids in Mice.

The central nucleus of the amygdala plays a significant role in alcohol use and other affective disorders; however, the genetically-defined neuronal subtypes and projections that govern these behaviors are not well known. Here we show that neurotensin neurons in the central nucleus of the amygdala of male mice are activated by in vivo ethanol consumption and that genetic ablation of these neurons decreases ethanol consumption and preference in non-ethanol-dependent animals. This ablation did not impact preference for sucrose, saccharin, or quinine. We found that the most robust projection of the central amygdala neurotensin neurons was to the parabrachial nucleus, a brain region known to be important in feeding behaviors, conditioned taste aversion, and alarm. Optogenetic stimulation of projections from these neurons to the parabrachial nucleus is reinforcing, and increases ethanol drinking as well as consumption of sucrose and saccharin solutions. These data suggest that this central amygdala to parabrachial nucleus projection influences the expression of reward-related phenotypes and is a novel circuit promoting consumption of ethanol and palatable fluids.SIGNIFICANCE STATEMENT Alcohol use disorder (AUD) is a major health burden worldwide. Although ethanol consumption is required for the development of AUD, much remains unknown regarding the underlying neural circuits that govern initial ethanol intake. Here we show that ablation of a population of neurotensin-expressing neurons in the central amygdala decreases intake of and preference for ethanol in non-dependent animals, whereas the projection of these neurons to the parabrachial nucleus promotes consumption of ethanol as well as other palatable fluids.

Dopamine-dependent, swimming-induced paralysis arises as a consequence of loss of function mutations in the RUNX transcription factor RNT-1.

Dopamine (DA) is a neurotransmitter with actions across phylogeny that modulate core behaviors such as motor activity, reward, attention, and cognition. Perturbed DA signaling in humans is associated with multiple disorders, including addiction, ADHD, schizophrenia, and Parkinson's disease. The presynaptic DA transporter exerts powerful control on DA signaling by efficient clearance of the neurotransmitter following release. As in vertebrates, Caenorhabditis elegans DAT (DAT-1) constrains DA signaling and loss of function mutations in the dat-1 gene result in slowed crawling on solid media and swimming-induced paralysis (Swip) in water. Previously, we identified a mutant line, vt34, that exhibits robust DA-dependent Swip. vt34 exhibits biochemical and behavioral phenotypes consistent with reduced DAT-1 function though vt34; dat-1 double mutants exhibit an enhanced Swip phenotype, suggesting contributions of the vt34-associated mutation to additional mechanisms that lead to excess DA signaling. SNP mapping and whole genome sequencing of vt34 identified the site of the molecular lesion in the gene B0412.2 that encodes the Runx transcription factor ortholog RNT-1. Unlike dat-1 animals, but similar to other loss of function rnt-1 mutants, vt34 exhibits altered male tail morphology and reduced body size. Deletion mutations in both rnt-1 and the bro-1 gene, which encodes a RNT-1 binding partner also exhibit Swip. Both vt34 and rnt-1 mutations exhibit reduced levels of dat-1 mRNA as well as the tyrosine hydroxylase ortholog cat-2. Although reporter studies indicate that rnt-1 is expressed in DA neurons, its re-expression in DA neurons of vt34 animals fails to fully rescue Swip. Moreover, as shown for vt34, rnt-1 mutation exhibits additivity with dat-1 in generating Swip, as do rnt-1 and bro-1 mutations, and vt34 exhibits altered capacity for acetylcholine signaling at the neuromuscular junction. Together, these findings identify a novel role for rnt-1 in limiting DA neurotransmission and suggest that loss of RNT-1 may disrupt function of both DA neurons and body wall muscle to drive Swip.

Central Amygdala Prepronociceptin-Expressing Neurons Mediate Palatable Food Consumption and Reward.

Food palatability is one of many factors that drives food consumption, and the hedonic drive to feed is a key contributor to obesity and binge eating. In this study, we identified a population of prepronociceptin-expressing cells in the central amygdala (PnocCeA) that are activated by palatable food consumption. Ablation or chemogenetic inhibition of these cells reduces palatable food consumption. Additionally, ablation of PnocCeA cells reduces high-fat-diet-driven increases in bodyweight and adiposity. PnocCeA neurons project to the ventral bed nucleus of the stria terminalis (vBNST), parabrachial nucleus (PBN), and nucleus of the solitary tract (NTS), and activation of cell bodies in the central amygdala (CeA) or axons in the vBNST, PBN, and NTS produces reward behavior but did not promote feeding of palatable food. These data suggest that the PnocCeA network is necessary for promoting the reinforcing and rewarding properties of palatable food, but activation of this network itself is not sufficient to promote feeding.

Metallo-ß-lactamase Domain-Containing Protein 1 (MBLAC1) Is a Specific, High-Affinity Target for the Glutamate Transporter Inducer Ceftriaxone.

Ceftriaxone, a ß-lactam antibiotic, has been reported to act independently of its antimicrobial actions to normalize perturbed central nervous system glutamate levels, principally by elevating expression of glial glutamate transporters. Identification of a specific, high-affinity target for ceftriaxone could significantly impact therapeutic development for multiple brain disorders, ranging from neurodegenerative disorders to addiction. Recently, we identified a glial-expressed Caenorhabditis elegans gene, swip-10, that encodes a metallo-ß-lactamase domain-containing protein, and limits glutamate-dependent changes in dopamine neuron excitability. Bioinformatic analyses identified MBLAC1 as the likely mammalian orthologue of swip-10. Using cyanogen bromide immobilized ceftriaxone for affinity capture experiments and backscattering interferometry to monitor MBLAC1 binding of unmodified ceftriaxone, we obtained evidence for specific, high affinity (KD = 2.2 µM) binding of ceftriaxone to MBLAC1. We discuss our findings with respect to MBLAC1 as a potentially exclusive, high-affinity binding partner of ceftriaxone in the CNS, and the path forward in the development of novel, MBLAC1-based therapeutics.

The Atypical MAP Kinase SWIP-13/ERK8 Regulates Dopamine Transporters through a Rho-Dependent Mechanism.

The neurotransmitter dopamine (DA) regulates multiple behaviors across phylogeny, with disrupted DA signaling in humans associated with addiction, attention-deficit/ hyperactivity disorder, schizophrenia, and Parkinson's disease. The DA transporter (DAT) imposes spatial and temporal limits on DA action, and provides for presynaptic DA recycling to replenish neurotransmitter pools. Molecular mechanisms that regulate DAT expression, trafficking, and function, particularly in vivo, remain poorly understood, though recent studies have implicated rho-linked pathways in psychostimulant action. To identify genes that dictate the ability of DAT to sustain normal levels of DA clearance, we pursued a forward genetic screen in Caenorhabditis elegans based on the phenotype swimming-induced paralysis (Swip), a paralytic behavior observed in hermaphrodite worms with loss-of-function dat-1 mutations. Here, we report the identity of swip-13, which encodes a highly conserved ortholog of the human atypical MAP kinase ERK8. We present evidence that SWIP-13 acts presynaptically to insure adequate levels of surface DAT expression and DA clearance. Moreover, we provide in vitro and in vivo evidence supporting a conserved pathway involving SWIP-13/ERK8 activation of Rho GTPases that dictates DAT surface expression and function.SIGNIFICANCE STATEMENT Signaling by the neurotransmitter dopamine (DA) is tightly regulated by the DA transporter (DAT), insuring efficient DA clearance after release. Molecular networks that regulate DAT are poorly understood, particularly in vivo Using a forward genetic screen in the nematode Caenorhabditis elegans, we implicate the atypical mitogen activated protein kinase, SWIP-13, in DAT regulation. Moreover, we provide in vitro and in vivo evidence that SWIP-13, as well as its human counterpart ERK8, regulate DAT surface availability via the activation of Rho proteins. Our findings implicate a novel pathway that regulates DA synaptic availability and that may contribute to risk for disorders linked to perturbed DA signaling. Targeting this pathway may be of value in the development of therapeutics in such disorders.

Sequence determinants of the Caenhorhabditis elegans dopamine transporter dictating in vivo axonal export and synaptic localization.

The monoamine neurotransmitter dopamine (DA) acts across phylogeny to modulate both simple and complex behaviors. The presynaptic DA transporter (DAT) is a major determinant of DA signaling capacity in ensuring efficient extracellular DA clearance. In humans, DAT is also a major target for prescribed and abused psychostimulants. Multiple structural determinants of DAT function and regulation have been defined, though largely these findings have arisen from heterologous expression or ex vivo cell culture studies. Loss of function mutations in the gene encoding the Caenhorhabditis elegans DAT (dat-1) produces rapid immobility when animals are placed in water, a phenotype termed swimming-induced paralysis (Swip). The ability of a DA neuron-expressed, GFP-tagged DAT-1 fusion protein (GFP::DAT-1) to localize to synapses and rescue Swip in these animals provides a facile approach to define sequences supporting DAT somatic export and function in vivo. In prior studies, we found that truncation of the last 25 amino acids of the DAT-1 C-terminus (Δ25) precludes Swip rescue, supported by a deficit in GFP::DAT-1 synaptic localization. Here, we further defined the elements within Δ25 required for DAT-1 export and function in vivo. We identified two conserved motifs (584KW585 and 591PYRKR595) where mutation results in a failure of GFP::DAT-1 to be efficiently exported to synapses and restore DAT-1 function. The 584KW585 motif conforms to a sequence proposed to support SEC24 binding, ER export from the endoplasmic reticulum (ER), and surface expression of mammalian DAT proteins, whereas the 591PYRKR595 sequence conforms to a 3R motif identified as a SEC24 binding site in vertebrate G-protein coupled receptors. Consistent with a potential role of SEC24 orthologs in DAT-1 export, we demonstrated DA neuron-specific expression of a sec-24.2 transcriptional reporter. Mutations of the orthologous C-terminal sequences in human DAT (hDAT) significantly reduced transporter surface expression and DA uptake, despite normal hDAT protein expression. Although, hDAT mutants retained SEC24 interactions, as defined in co-immunoprecipitation studies. However, these mutations disrupted the ability of SEC24D to enhance hDAT surface expression. Our studies document an essential role of conserved DAT C-terminal sequences in transporter somatic export and synaptic localization in vivo, that add further support for important roles for SEC24 family members in efficient transporter trafficking.

Serotonin engages an anxiety and fear-promoting circuit in the extended amygdala.

Serotonin (also known as 5-hydroxytryptamine (5-HT)) is a neurotransmitter that has an essential role in the regulation of emotion. However, the precise circuits have not yet been defined through which aversive states are orchestrated by 5-HT. Here we show that 5-HT from the dorsal raphe nucleus (5-HTDRN) enhances fear and anxiety and activates a subpopulation of corticotropin-releasing factor (CRF) neurons in the bed nucleus of the stria terminalis (CRFBNST) in mice. Specifically, 5-HTDRN projections to the BNST, via actions at 5-HT2C receptors (5-HT2CRs), engage a CRFBNST inhibitory microcircuit that silences anxiolytic BNST outputs to the ventral tegmental area and lateral hypothalamus. Furthermore, we demonstrate that this CRFBNST inhibitory circuit underlies aversive behaviour following acute exposure to selective serotonin reuptake inhibitors (SSRIs). This early aversive effect is mediated via the corticotrophin-releasing factor type 1 receptor (CRF1R, also known as CRHR1), given that CRF1R antagonism is sufficient to prevent acute SSRI-induced enhancements in aversive learning. These results reveal an essential 5-HTDRN→CRFBNST circuit governing fear and anxiety, and provide a potential mechanistic explanation for the clinical observation of early adverse events to SSRI treatment in some patients with anxiety disorders.

Nociceptin receptor antagonist SB 612111 decreases high fat diet binge eating.

Binge eating is a dysregulated form of feeding behavior that occurs in multiple eating disorders including binge-eating disorder, the most common eating disorder. Feeding is a complex behavioral program supported through the function of multiple brain regions and influenced by a diverse array of receptor signaling pathways. Previous studies have shown the overexpression of the opioid neuropeptide nociceptin (orphanin FQ, N/OFQ) can induce hyperphagia, but the role of endogenous nociceptin receptor (NOP) in naturally occurring palatability-induced hyperphagia is unknown. In this study we adapted a simple, replicable form of binge eating of high fat food (HFD). We found that male and female C57BL/6J mice provided with daily one-hour access sessions to HFD eat significantly more during this period than those provided with continuous 24h access. This form of feeding is rapid and entrained. Chronic intermittent HFD binge eating produced hyperactivity and increased light zone exploration in the open field and light-dark assays respectively. Treatment with the potent and selective NOP antagonist SB 612111 resulted in a significant dose-dependent reduction in binge intake in both male and female mice, and, unlike treatment with the serotonin selective reuptake inhibitor fluoxetine, produced no change in total 24-h food intake. SB 612111 treatment also significantly decreased non-binge-like acute HFD consumption in male mice. These data are consistent with the hypothesis that high fat binge eating is modulated by NOP signaling and that the NOP system may represent a promising novel receptor to explore for the treatment of binge eating.

Dynorphin Controls the Gain of an Amygdalar Anxiety Circuit.

Kappa opioid receptors (KORs) are involved in a variety of aversive behavioral states, including anxiety. To date, a circuit-based mechanism for KOR-driven anxiety has not been described. Here, we show that activation of KORs inhibits glutamate release from basolateral amygdala (BLA) inputs to the bed nucleus of the stria terminalis (BNST) and occludes the anxiolytic phenotype seen with optogenetic activation of BLA-BNST projections. In addition, deletion of KORs from amygdala neurons results in an anxiolytic phenotype. Furthermore, we identify a frequency-dependent, optically evoked local dynorphin-induced heterosynaptic plasticity of glutamate inputs in the BNST. We also find that there is cell type specificity to the KOR modulation of the BLA-BNST input with greater KOR-mediated inhibition of BLA dynorphin-expressing neurons. Collectively, these results provide support for a model in which local dynorphin release can inhibit an anxiolytic pathway, providing a discrete therapeutic target for the treatment of anxiety disorders.

Acute blockade of the Caenorhabditis elegans dopamine transporter DAT-1 by the mammalian norepinephrine transporter inhibitor nisoxetine reveals the influence of genetic modifications of dopamine signaling in vivo.

Modulation of neurotransmission by the catecholamine dopamine (DA) is conserved across phylogeny. In the nematode Caenorhabditis elegans, excess DA signaling triggers Swimming-Induced Paralysis (Swip), a phenotype first described in animals with loss of function mutations in the presynaptic DA transporter (dat-1). Swip has proven to be a phenotype suitable for the identification of novel dat-1 mutations as well as the identification of novel genes that impact DA signaling. Pharmacological manipulations can also induce Swip, though the reagents employed to date lack specificity and potency, limiting their use in evaluation of dat-1 expression and function. Our lab previously established the mammalian norepinephrine transporter (NET) inhibitor nisoxetine to be a potent antagonist of DA uptake conferred by DAT-1 following heterologous expression. Here we demonstrate the ability of low (µM) concentrations of nisoxetine to trigger Swip within minutes of incubation, with paralysis dependent on DA release and signaling, and non-additive with Swip triggered by dat-1 deletion. Using nisoxetine in combination with genetic mutations that impact DA release, we further demonstrate the utility of the drug for demonstrating contributions of presynaptic DA receptors and ion channels to Swip. Together, these findings reveal nisoxetine as a powerful reagent for monitoring multiple dimensions of DA signaling in vivo, thus providing a new resource that can be used to evaluate contributions of dat-1 and other genes linked to DA signaling without the potential for compensations that attend constitutive genetic mutations.

Glial Expression of the Caenorhabditis elegans Gene swip-10 Supports Glutamate Dependent Control of Extrasynaptic Dopamine Signaling.

Glial cells play a critical role in shaping neuronal development, structure, and function. In a screen for Caenorhabditis elegans mutants that display dopamine (DA)-dependent, Swimming-Induced Paralysis (Swip), we identified a novel gene, swip-10, the expression of which in glia is required to support normal swimming behavior. swip-10 mutants display reduced locomotion rates on plates, consistent with our findings of elevated rates of presynaptic DA vesicle fusion using fluorescence recovery after photobleaching. In addition, swip-10 mutants exhibit elevated DA neuron excitability upon contact with food, as detected by in vivo Ca(2+) monitoring, that can be rescued by glial expression of swip-10. Mammalian glia exert powerful control of neuronal excitability via transporter-dependent buffering of extracellular glutamate (Glu). Consistent with this idea, swip-10 paralysis was blunted in mutants deficient in either vesicular Glu release or Glu receptor expression and could be phenocopied by mutations that disrupt the function of plasma membrane Glu transporters, most noticeably glt-1, the ortholog of mammalian astrocytic GLT1 (EAAT2). swip-10 encodes a protein containing a highly conserved metallo-ß-lactamase domain, within which our swip-10 mutations are located and where engineered mutations disrupt Swip rescue. Sequence alignments identify the CNS-expressed gene MBLAC1 as a putative mammalian ortholog. Together, our studies provide evidence of a novel pathway in glial cells regulated by swip-10 that limits DA neuron excitability, DA secretion, and DA-dependent behaviors through modulation of Glu signaling.

Genetics and Epigenetics of Eating Disorders.

Eating disorders (EDs) are serious psychiatric conditions influenced by biological, psychological, and sociocultural factors. A better understanding of the genetics of these complex traits and the development of more sophisticated molecular biology tools have advanced our understanding of the etiology of EDs. The aim of this review is to critically evaluate the literature on the genetic research conducted on three major EDs: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). We will first review the diagnostic criteria, clinical features, prevalence, and prognosis of AN, BN, and BED, followed by a review of family, twin, and adoption studies. We then review the history of genetic studies of EDs covering linkage analysis, candidate gene association studies, genome-wide association studies, and the study of rare variants in EDs. Our review also incorporates a translational perspective by covering animal models of ED-related phenotypes. Finally, we review the nascent field of epigenetics of EDs and a look forward to future directions for ED genetic research.