The role of corticotropin-releasing factor in binge-like ethanol consumption

Previous research establishes a crucial role for corticotropin releasing factor (CRF) in ethanol dependence. Recent evidence demonstrates a role for the CRF type 1 receptor (CRF1R) in the modulation of binge-like ethanol consumption by non-dependent animals, a behavior which can precede ethanol dependence. The goal of this dissertation was to further characterize the role of the CRF system in binge-like ethanol consumption. The role of the CRF receptors in binge-like ethanol consumption were pharmacologically investigated in Chapter 2. In Chapter 3, the effects of binge-like ethanol consumption on CRF expression was assessed using immunohistochemistry techniques. CRF is known to signal through two pathways, the hypothalamic pathway that activates the hypothalamic-pituitary-adrenal (HPA) axis response to stressors, and the extrahypothalamic pathway that includes limbic regions such as the amygdala, which is involved in drug-taking behaviors. Thus, in Chapter 4, the involvement of the HPA axis in binge-like ethanol consumption was assessed using a series of pharmacological and surgical techniques to manipulate HPA axis function and radioimmunoassay techniques to observe the effects of binge-like ethanol consumption on the HPA axis. Based on the results of previous chapters, in Chapter 5, the involvement of the central nucleus of the amygdala was assessed using immunohistochemistry, electrophysiology and pharmacology approaches to manipulate the CRF system. Results show that binge-like ethanol consumption by non-dependent animals selectively alters CRF signaling in the CeA, and that the CRF1R in this brain region is necessary for binge-like levels of ethanol intake to occur. In tandem with data suggesting that the CRF system does not modulate non-binge-like ethanol consumption, these observations suggest that binge-like ethanol consumption, like dependence-induced ethanol consumption, recruits the CRF system of the CeA. Therefore, we hypothesize that recruitment of the CRF system during binge-like ethanol consumption leads to transient neuroadaptations in the amygdala, and these changes in CRF signaling become permanent with repeated binges and eventually culminate in ethanol dependence. The implications of this hypothesis are discussed in the context of the leading theory of alcohol dependence

Functional Alterations in the Dorsal Raphe Nucleus Following Acute and Chronic Ethanol Exposure

Alcoholism is a pervasive disorder perpetuated in part to relieve negative mood states like anxiety experienced during alcohol withdrawal. Emerging evidence demonstrates a role for the serotonin-rich dorsal raphe (DR) in anxiety following ethanol withdrawal. The current study examined the effects of chronic ethanol vapor exposure on the DR using slice electrophysiology in male DBA2/J mice. We found that chronic ethanol exposure resulted in deficits in social approach indicative of increased anxiety-like behavior at both 24 h and 7 days post-ethanol exposure. At 24 h post-ethanol exposure, we observed increased excitability and decreased spontaneous inhibitory transmission (inhibitory postsynaptic currents, IPSCs) in the DR. At 7 days post-ethanol exposure, we observed increased spontaneous and miniature excitatory transmission (excitatory postsynaptic currents, EPSCs). Because acute ethanol alters GABA transmission in other brain regions, we assessed the effects of ex vivo ethanol (50 mM) on miniature IPSCs (mIPSCs) in the DR 24-h post-ethanol exposure. Bath application of ethanol enhanced the amplitude of mIPSCs in cells from ethanol-naive and chronic intermittent ethanol-exposed (CIE) mice, but significantly enhanced the frequency of mIPSCs only in cells from CIE mice, suggesting that DR neurons are more sensitive to the inhibitory effects of acute ethanol following CIE. On the basis of these findings, we hypothesize that net excitation of DR neurons following chronic ethanol exposure contributes to enhanced anxiety during ethanol withdrawal, and that increased sensitivity of DR neurons to subsequent ethanol exposure may mediate acute ethanol's ability to relieve anxiety during ethanol withdrawal

Potent and Selective Peptide-based Inhibition of the G Protein Gαq

In contrast to G protein-coupled receptors, for which chemical and peptidic inhibitors have been extensively explored, few compounds are available that directly modulate heterotrimeric G proteins. Active Gα q binds its two major classes of effectors, the phospholipase C (PLC)-β isozymes and Rho guanine nucleotide exchange factors (RhoGEFs) related to Trio, in a strikingly similar fashion: a continuous helix-turn-helix of the effectors engages Gα q within its canonical binding site consisting of a groove formed between switch II and helix α3. This information was exploited to synthesize peptides that bound active Gα q in vitro with affinities similar to full-length effectors and directly competed with effectors for engagement of Gα q A representative peptide was specific for active Gα q because it did not bind inactive Gα q or other classes of active Gα subunits and did not inhibit the activation of PLC-β3 by Gβ 1 γ 2 In contrast, the peptide robustly prevented activation of PLC-β3 or p63RhoGEF by Gα q ; it also prevented G protein-coupled receptor-promoted neuronal depolarization downstream of Gα q in the mouse prefrontal cortex. Moreover, a genetically encoded form of this peptide flanked by fluorescent proteins inhibited Gα q -dependent activation of PLC-β3 at least as effectively as a dominant-negative form of full-length PLC-β3. These attributes suggest that related, cell-penetrating peptides should effectively inhibit active Gα q in cells and that these and genetically encoded sequences may find application as molecular probes, drug leads, and biosensors to monitor the spatiotemporal activation of Gα q in cells

Lateral Hypothalamus GABAergic Neurons Modulate Consummatory Behaviors Regardless of the Caloric Content or Biological Relevance of the Consumed Stimuli

It was recently reported that activation of a subset of lateral hypothalamus (LH) GABAergic neurons induced both appetitive (food-seeking) and consummatory (eating) behaviors in vGat-ires-cre mice, while inhibition or deletion of GABAergic neurons blunted these behaviors. As food and caloric-dense liquid solutions were used, the data reported suggest that these LH GABAergic neurons may modulate behaviors that function to maintain homeostatic caloric balance. Here we report that chemogenetic activation of this GABAergic population in vGat-ires-cre mice increased consummatory behavior directed at any available stimulus, including those entailing calories (food, sucrose, and ethanol), those that do not (saccharin and water), and those lacking biological relevance (wood). Chemogenetic inhibition of these neurons attenuated consummatory behaviors. These data indicate that LH GABAergic neurons modulate consummatory behaviors regardless of the caloric content or biological relevance of the consumed stimuli

Mu Opioid Receptor Modulation of Dopamine Neurons in the Periaqueductal Gray/Dorsal Raphe: A Role in Regulation of Pain

The periaqueductal gray (PAG) is a brain region involved in nociception modulation, and an important relay center for the descending nociceptive pathway through the rostral ventral lateral medulla. Given the dense expression of mu opioid receptors and the role of dopamine in pain, the recently characterized dopamine neurons in the ventral PAG (vPAG)/dorsal raphe (DR) region are a potentially critical site for the antinociceptive actions of opioids. The objectives of this study were to (1) evaluate synaptic modulation of the vPAG/DR dopamine neurons by mu opioid receptors and to (2) dissect the anatomy and neurochemistry of these neurons, in order to assess the downstream loci and functions of their activation. Using a mouse line that expresses eGFP under control of the tyrosine hydroxylase (TH) promoter, we found that mu opioid receptor activation led to a decrease in inhibitory inputs onto the vPAG/DR dopamine neurons. Furthermore, combining immunohistochemistry, optogenetics, electrophysiology, and fast-scan cyclic voltammetry in a TH-cre mouse line, we demonstrated that these neurons also express the vesicular glutamate type 2 transporter and co-release dopamine and glutamate in a major downstream projection structure—the bed nucleus of the stria terminalis. Finally, activation of TH-positive neurons in the vPAG/DR using Gq designer receptors exclusively activated by designer drugs displayed a supraspinal, but not spinal, antinociceptive effect. These results indicate that vPAG/DR dopamine neurons likely play a key role in opiate antinociception, potentially via the activation of downstream structures through dopamine and glutamate release

Glutamatergic mechanisms associated with stress-induced amygdala excitability and anxiety-related behavior

The neural factors underlying individual differences in susceptibility to chronic stress remain poorly understood. Preclinical studies demonstrate that mouse strains vary greatly in anxiety-related responses to chronic stress in a manner paralleled by differential stress-induced changes in glutamatergic signaling in the basolateral amygdala (BLA). Previous work has also shown that alterations in the amygdala gene expression of the GluN1 NMDA and the GluK1 kainate receptors are associated with stress-induced alterations in anxiety-like behavior in the C57BL/6J mouse strain. Using in vivo behavioral pharmacological and ex vivo physiological approaches, the aim of the current study was to further elucidate changes in glutamate neurotransmission in the BLA caused by stress and to test the functional roles of GluN1 and GluK1 in mediating stress-related changes in behavior. Results showed that stress-induced alterations in anxiety-like behavior (light/dark exploration test) were absent following bilateral infusion of the GluK1 agonist ATPA into the BLA. Intra-BLA infusion of the competitive NMDA antagonist AP5 produced a generalized behavioral disinhibition/locomotor hyperactivity, irrespective of stress. Slice electrophysiological recordings showed that ATPA augmented BLA GABAergic neurotransmission and that stress increased the amplitude of network-dependent spontaneous excitatory postsynaptic currents and amplitude of GABAergic miniature inhibitory postsynaptic currents in BLA. These findings could indicate stress-induced BLA glutamatergic neuronal network hyperexcitability and a compensatory increase in GABAergic neurotransmission, suggesting that GluK1 agonism augmented GABAergic inhibition to prevent behavioral sequelae of stress. Current data could have implications for developing novel therapeutic approaches, including GluK1 agonists, for stress-related 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 24 hour 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-hour 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

Neuropeptide Regulation of Signaling and Behavior in the BNST

Recent technical developments have transformed how neuroscientists can probe brain function. What was once thought to be difficult and perhaps impossible, stimulating a single set of long range inputs among many, is now relatively straight-forward using optogenetic approaches. This has provided an avalanche of data demonstrating causal roles for circuits in a variety of behaviors. However, despite the critical role that neuropeptide signaling plays in the regulation of behavior and physiology of the brain, there have been remarkably few studies demonstrating how peptide release is causally linked to behaviors. This is likely due to both the different time scale by which peptides act on and the modulatory nature of their actions. For example, while glutamate release can effectively transmit information between synapses in milliseconds, peptide release is potentially slower [See the excellent review by Van Den Pol on the time scales and mechanisms of release (van den Pol, 2012)] and it can only tune the existing signals via modulation. And while there have been some studies exploring mechanisms of release, it is still not as clearly known what is required for efficient peptide release. Furthermore, this analysis could be complicated by the fact that there are multiple peptides released, some of which may act in contrast. Despite these limitations, there are a number of groups making progress in this area. The goal of this review is to explore the role of peptide signaling in one specific structure, the bed nucleus of the stria terminalis, that has proven to be a fertile ground for peptide action

Repeated Cycles of Binge-Like Ethanol Drinking in Male C57BL/6J Mice Augments Subsequent Voluntary Ethanol Intake But Not Other Dependence-Like Phenotypes

Recently, procedures have been developed to model specific facets of human alcohol abuse disorders, including those that model excessive binge-like drinking (i.e., “drinking in the dark”, or DID procedures) and excessive dependence-like drinking (i.e., intermittent ethanol vapor exposure). Similar neuropeptide systems modulate excessive ethanol drinking stemming from both procedures, raising the possibility that both paradigms are actually modeling the same phenotypes and triggering the same central neuroplasticity. Therefore, the goal of the present project was to study the effects of a history of binge-like ethanol drinking, using DID procedures, on phenotypes that have previously been described with procedures to model dependence-like drinking

Corticotropin Releasing Factor Signaling in the Central Amygdala is Recruited during Binge-Like Ethanol Consumption in C57BL/6J Mice

A well-established body of work indicates a crucial role for corticotropin releasing factor (CRF) in neurobiological responses associated with excessive dependence-like ethanol drinking in ethanol vapor exposed rodents. Recent evidence demonstrates a role for CRF in the modulation of binge-like ethanol consumption by non-dependent mice, a behavior which can precede ethanol dependence. The CRF circuitry that is engaged by binge-like ethanol exposure, however, is unknown. Using converging approaches, we provide evidence that, similar to ethanol vapor-induced increases in ethanol intake, CRF signaling in the central nucleus of the amygdala (CeA) is engaged during binge-like ethanol consumption by C57BL/6J mice. Specifically, we found that binge-like consumption of an ethanol solution (20% ethanol v/v) was attenuated by pretreatment with the CRF1R antagonists antalarmin, (4-ethyl-[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amino-1-butanol (LWH-63), and NBI-27914 at doses (30 mg/kg, i.p.) that did not alter non-binge-like ethanol consumption. Binge-like ethanol consumption resulted in significant increases of CRF immunoreactivity in the CeA immediately following ethanol drinking and 18-24 h following ethanol removal and also blocked the ability of CRF to enhance GABAergic transmission in the CeA 18-24 h following ethanol removal. Pretreatment with bilateral injections of antalarmin (1 μg/ 0.5 μl per side) into the CeA, but not the adjacent basolateral amygdala (BLA), significantly attenuated binge-like ethanol consumption. These findings suggest that CRF signaling in the CeA is recruited during excessive ethanol intake, prior to the development of dependence. We hypothesize that plastic changes in CRF signaling develop with repeated binge-like drinking episodes, contributing to the transition to dependence