Brian A. Baldo - US grants

amylin; ethology; nucleus accumbens; eating; chordate locomotion; behavioral /social science research tag; laboratory rat; nutrition related tag;

DESCRIPTION (provided by applicant): Obesity is currently one of the major public health problems in the United States. Over 65% of the U.S. adult population is overweight. Obesity puts individuals at considerable risk for many disorders, such as heart disease, hypertension, diabetes, stroke, and certain types of cancer. Although there are a number of complex factors contributing to this trend, such as genetic predisposition, inactivity, lifestyle changes, and economic factors, the abundance and over consumption of calorically dense foods such as fats and sweets is largely responsible. Ingestion of food is required for survival, yet overabundance of energy-dense food has led to conditions that actually threaten survival. In the past decade, specific brain and peripheral systems involved in appetite control, particularly within the hypothalamus, have been discovered and characterized. However, relatively little is known about how brain networks involved in emotional regulation, executive function, and conscious control of behavior interact with hypothalamic energy balance-sensing systems. This would seem an important area of obesity research, as cognitive control, decision-making, and modulation of emotional responses in relation to the desire to eat are major determinants for the control of appetite in humans. Our work focuses on the role of the nucleus accumbens, a region within the ventral striatum, in the control of food motivation and food reward. We have shown that two main systems, one governed by endogenous opioid peptides and one by amino acid (GABA and glutamate) receptors, control certain aspects of ingestive behavior via connections with the lateral hypothalamus and other forebrain and brainstem regions. We aim to expand these investigations to study how cortical systems (i.e. the amygdala, gustatory cortex and prefrontal cortex) interact with ventral striatum and hypothalamus in the regulation of ingestive behavior. We will employ behavioral, pharmacological, neuroanatomical and molecular methodologies to address this question within an integrated, interdisciplinary framework.

DESCRIPTION (provided by applicant): The current 'epidemic'of obesity has been called one of the leading public health concerns worldwide. Despite recent progress in the discovery of discrete hypothalamic peptide systems that control food intake, little is known about the manner in which cognitive/affective processing coordinates with hypothalamic energy balance systems to control behavioral output. Hence, this proposal focuses on characterizing functional interactions between the medial prefrontal cortex, a brain region mediating 'executive'control over behavioral output and affective responses, and hypothalamic substrates mediating the homeostatic control of feeding. This proposal is informed by our recent discovery of a novel, specific role of medial prefrontal cortex (mPFC) in controlling feeding microstructure. We find that producing temporary lesions in mPFC fundamentally alters the manner in which rats organize behavioral responses with respect to ingestive behavior. We aim to investigate the behavioral mechanisms and anatomical specificity associated with this effect, and to examine how inactivating mPFC influences the response to hypothalamic administration of orexigenic and anorexic peptides. To obtain a functional anatomical correlate of these behavioral studies, we will investigate the manner in which temporary lesions of the mPFC alter brain activation (measured using Fos expression) associated with feeding. Relevance to public health: These studies have the potential to reveal how the parts of the brain controlling decision-making and impulsivity (such as the prefrontal cortex) can interact with, and perhaps overwhelm, the systems that regulate food intake in response to energy needs. This could lead to fundamentally dysregulated feeding behavior. It is interesting that brain imaging studies have shown alterations in prefrontal cortex function in association with eating disorders and obesity. Our work may help understand how these cortical alterations are ultimately translated into behavioral changes.

DESCRIPTION (provided by applicant): The current 'epidemic'of obesity has been called one of the leading public health concerns worldwide. Despite recent progress in the discovery of discrete hypothalamic peptide systems that control food intake, little is known about the manner in which cognitive/affective processing coordinates with hypothalamic energy balance systems to control behavioral output. Hence, this proposal focuses on characterizing functional interactions between the medial prefrontal cortex, a brain region mediating 'executive'control over behavioral output and affective responses, and hypothalamic substrates mediating the homeostatic control of feeding. This proposal is informed by our recent discovery of a novel, specific role of medial prefrontal cortex (mPFC) in controlling feeding microstructure. We find that producing temporary lesions in mPFC fundamentally alters the manner in which rats organize behavioral responses with respect to ingestive behavior. We aim to investigate the behavioral mechanisms and anatomical specificity associated with this effect, and to examine how inactivating mPFC influences the response to hypothalamic administration of orexigenic and anorexic peptides. To obtain a functional anatomical correlate of these behavioral studies, we will investigate the manner in which temporary lesions of the mPFC alter brain activation (measured using Fos expression) associated with feeding. Relevance to public health: These studies have the potential to reveal how the parts of the brain controlling decision-making and impulsivity (such as the prefrontal cortex) can interact with, and perhaps overwhelm, the systems that regulate food intake in response to energy needs. This could lead to fundamentally dysregulated feeding behavior. It is interesting that brain imaging studies have shown alterations in prefrontal cortex function in association with eating disorders and obesity. Our work may help understand how these cortical alterations are ultimately translated into behavioral changes.

DESCRIPTION (provided by applicant): The goal of this proposal is to evaluate a potential new target for the treatment of schizophrenia and other psychiatric disorders that involve aberrant nucleus accumbens (Acb) function: the Acb-localized AMY1 receptor. This receptor binds members of the calcitonin family of peptides, including amylin, salmon calcitonin, and calcitonin gene-related peptide (CGRP). Despite the fact that the Acb possesses among the densest concentrations of this receptor in the brain, the evidence that the Acb-localized amylin receptor represents a unique receptor subtype, and the finding that amylin in the Acb produces potent behavioral effects reminiscent of functional dopamine antagonism, there has been no research exploring the effects of Acb amylin receptor manipulations on schizophrenia-like information-processing deficits. This is a surprising omission given that that hyperdopaminergia within Acb is widely thought to contribute to the symptomatology of schizophrenia, but antipsychotic drugs that can selectively influence dopamine transmission in Acb without concomitantly altering DA signaling in other sites and/or causing potent side-effects are not available. The Acb-localized AMY1 receptor represents an attractive target with which to enact such an anatomically specific pharmacotherapy for schizophrenia. The present proposal seeks to explore this hypothesis by evaluating in animal models of deficient prepulse inhibition (PPI) the effects of stimulating and antagonizing the Acb AMY1 receptor in rats. PPI is the normal diminution of the startle response that occurs when a weak prestimulus immediately precedes the startling stimulus, and is an operational measure of core information-filtering deficits that are seen in schizophrenia, Tourette's Syndrome, Obsessive-compulsive disorder, and certain other mental illnesses. PPI is among the most well-validated preclinical paradigms with which to assess antipsychotic efficacy, as drugs that normalize PPI deficits in animals successfully treat clinical PPI deficits. The present studies will determine if stimulation of Acb AMY1 receptors improves baseline or deficient PPI (induced by psychotomimetic drugs such as amphetamine or phencyclidine), and/or if agonists for this receptor augment the efficacy of clinically prescribed antipsychotic medications in the PPI paradigm. Finally, we will explore whether the family of amylin-related genes is regulated by isolation rearing, a developmental manipulation in rats that is known to produce schizophrenia-like PPI deficits in adulthood. In the course of this last study, we will also determine whether amylin-related genes themselves are developmentally regulated. PUBLIC HEALTH RELEVANCE: The direct translational implication of the proposed work would be the identification of a novel target for antipsychotic drug development, to use in the treatment of schizophrenia, which affects 1% of the population worldwide. Schizophrenia is a devastating chronic illness characterized by hallucinations, delusions, affective dysregulation, and thought disorder. Current treatments, albeit helpful, are not completely effective and produce serious side effects including weight gain, insulin resistance, and diabetes. By virtue of its selective localization in one of the brain regions most likely to underlie many schizophrenic symptoms the AMY1 receptor represents a powerful new putative candidate for producing antipsychotic effects. Moreover, because stimulation of AMY receptors promotes weight loss, this drug target has the potential be free of or even reverse one of the most problematic side-effects of current antipsychotics (weight gain, insulin resistance and diabetes).

? DESCRIPTION (provided by applicant): The public health impact of substance abuse is enormous and widespread; adverse consequences include mortality, morbidity including debilitating physical and psychological symptoms, and loss of productivity. Existing drugs are not completely effective and often characterized by adverse side effects; hence, there is a great need to discover new neurochemical targets for the development of addiction therapeutics. As a neurochemical class, peptides are understudied relative to classic neuromodulators such as dopamine. Yet, work on a relatively small number of a priori-identified peptides show that they play profound functional roles across the addiction cycle. The next generation of anti-addiction medications could very conceivably be based on yet undiscovered peptides with specific functional roles in the addiction cycle. In this proposal, we aim to apply a cutting-edge mass spectrometry (MS)-based analytic platform to discover new peptides (peptidomic discovery), and characterize already-known peptides with unprecedented precision, across two drug states: acute cocaine intoxication and peak cocaine withdrawal. The technological platform consists of the following methods: 1. Shotgun peptidomics approach based on gas-phase tandem MS fragmentation methods coupled with isobaric tagging to rapidly quantify a large number of neuropeptides; 2. Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) of thin tissue slices using a novel gold-nanoparticle matrix, in correlation with in situ hybridization, to map the spatial distribution of peptide fluxes and enable co-localization wih dopamine signals; 3. Affinity-enhanced microdialysis using innovative magnetic nanoparticles to massively amplify the recovery of peptide efflux from the central nervous system (CNS) extracellular space, thereby improving sensitivity and temporal resolution; 4. Synthesis of any novel peptides discovered, and behavioral testing of these sequences in a well- validated brain stimulation-reward threshold procedure. These methods are highly advanced, and some new innovations have never been tried before in mammalian tissues. Hence, considering the time constraints of the R21 grant mechanism, our first goal is to refine and optimize the technological platform by specifically focusing on simultaneous ?-opioid, ?-opioid, and dopamine co-transmission in the nucleus accumbens (Acb) and prefrontal cortex (PFC) during acute cocaine intoxication and peak cocaine withdrawal. This type of combinatorial analysis in both brain sites has never been attempted. Our work has the potential to reveal crucial insights regarding an important opponent-process theory in addiction biology, positing diverse and opposing ?- opioid actions relative to ?-opioid/dopamine actions across the addiction cycle. Choosing acute cocaine intoxication and peak withdrawal offers the strongest test of the theory. Insights gained from these analyses could translate into uniquely effective combinatorial treatment strategies. Our second goal is to test any new peptide sequences discovered in the MS-based shotgun peptidomic analysis in the subsequent stages of our platform, as time permits. This plan will allow us to refine a powerful, technologically advanced platform for peptidomic discovery, and achieve unprecedented 'vertical integration' from the transcriptional to the behavioral levels. At the same time, our studies will ask a discrete question of great scientific importance regarding the interplay among opioid peptides and dopamine in distinct cocaine-associated states.

? DESCRIPTION (provided by applicant): Loss of inhibitory control over appetitively motivated behavior, sometimes manifested as `bingeing', is a phenotype present in multiple psychiatric conditions. It is widely assumed that bingeing emerges from the dysregulated function of frontal-executive control mechanisms that govern subcortical motivation systems; nevertheless, specific neuropharmacological mechanisms and circuit connections are not clearly understood. One clue derives from the fact that opiate antagonist drugs are among the only pharmacotherapies with some efficacy in improving inhibitory control across a wide variety of psychiatric disorders with binge features. Hence, opioid actions within frontal circuits could be a crucial substrate underlying binge-type pathologies. To date, however, opioid effects in frontal cortex have been almost completely overlooked. In the previous funding period, we discovered that µ-opioid receptor (µOR) stimulation in rat ventromedial prefrontal cortex (PFC) - an area analogous to those showing abnormal responses in a variety of disorders with binge features - engenders robust non-homeostatic feeding and hyperactivity, increased food motivation in a progressive-ratio task, and robust `impulsivity-like' impairments in a PFC-sensitive task of inhibitory control. These effects were not reproduced by a wide array of monoamine receptor agonists or antagonists, demonstrating unique actions of µORs relative to other PFC modulatory systems. Furthermore, dual-site drug microinfusion studies revealed that PFC µOR signaling engages appetitive drive via feeding/arousal circuits in the lateral-perifornical hypothalamic region (LH-PeF), including the hypocretin/orexin system, while concurrently causing activation of an AMPA-coded PFC?nucleus accumbens shell (AcbSh) circuit that limits food motivation. Finally, we found that repeated episodes of sweetened-fat `gorging' sensitize AcbSh GABA systems, potentially blunting the effect the PFC?AcbSh `limiter circuit'. Based on these findings, we propose a novel network model stating that loss of control over appetitive behavior occurs when subcortical systems are driven by excessive PFC-µOR signaling, and/or when there is an imbalance in the PFC?LH-PeF (`appetitive-driver') and PFC?AcbSh (`appetitive limiter') pathways. Moreover, we propose that palatable food gorging causes neuroplastic changes in AcbSh amino-acid (glutamate, GABA) systems that blunt incoming PFC signals, curbing the influence of the `limiter circuit', thereby allowing appetitive behavior to go unchecked. In this way, the neuroadaptations caused by intense reward-driven feeding could engage a vicious cycle, leading to further binge-like behavior. We will test this working hypothesis with a combination of classic pharmacology experiments and studies using virally introduced Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). These engineered receptors permit the activation of G-proteins with a synthetic ligand; thus, neuronal activity can be modulated within specific populations of virally transduced neurons. Using a dual-virus approach, we will target DREADD expression to PFC neurons specifically projecting either to the AcbSh or to the hypothalamus, and selectively manipulate these tagged neurons in rats performing operant tasks of food motivation and inhibitory control. Furthermore, using classic pharmacology + DREADD experiments, we will test the hypothesis that palatable-food bingeing desensitizes vmPFC?AcbSh `limiter circuit' and perhaps amplifies the vmPFC?hypothalamus `appetitive-driver' circuit. Using receptor antagonists, we will examine the role of endogenous µ-opioid and hypocretin/orexin transmission in mediating PFC-driven food motivation and impulsivity. Finally, we will explore possible gender differences in PFC-µOR control of food motivation and food impulsivity.