Regina M. Carelli - US grants

DESCRIPTION (provided by applicant): Numerous studies implicate a critical role of the nucleus accumbens (NAc) and its dopaminergic input in goal-directed behavior for cocaine and 'natural' (e.g., food/water) rewards. The PI has used electrophysiological recording procedures in behaving rats to investigate underlying cellular mechanisms mediating reward-seeking behavior. To examine the role of dopamine (DA) in this process, fast scan cyclic voltammetry (FSCV) was used, a technique that allows direct measurement of DA in the NAc on a subsecond time scale with micron spatial resolution. Thus, FSCV provides chemical information temporally analogous to data obtained from electrophysiology. Working with R. Mark Wightman, changes in DA efflux were uncovered in the NAc during key aspects of reward-seeking involving natural rewards (e.g., sucrose), intracranial self-stimulation (ICSS) and cocaine self-administration. In order to make definitive statements about the relationship between specific types of cellular discharges and DA, this grant was originally submitted as a Cutting Edge Basic Research Award to develop and apply the technology to measure changes in NAc cell firing and NAc DA from the same electrode in behaving rats. This combined approach enabled the first unique view of real-time, spatially resolved concentration fluctuations of DA in conjunction with changes in cell firing during behavior. In the last funding period key factors were determined that control rapid DA signaling (using FSCV alone) and its relationship to NAc cell firing during behavior (using the combined technique). Here, 4 specific aims are proposed to build upon that work. Aim1 will use FSCV alone to determine if rapid DA release is altered during a cocaine/sucrose multiple schedule when animals switch from responding for one versus the other reward. Thus, we will determine if DA release within specific locations occurs uniformly during operant responding for both rewards, or if distinct subregions exist in the NAc at which DA release selectively occurs depending upon reinforcer type. Aim 2 will build upon prior work by the PI and determine the effects of interruption of drug access (cocaine abstinence) on rapid DA signaling in the NAc. Our prior electrophysiology studies revealed a heightened activation of NAc cell firing following 1-month cocaine abstinence. Here, we will incorporate drug abstinence and reinstatement procedures to determine if interruption of cocaine self-administration enhances rapid DA release during subsequent cocaine-seeking behavior. Although the NAc is clearly linked with reward, less is known about its role in aversion. Aim 3 will use the combined voltammetry/electrophysiology technique to determine the precise relationship between rapid DA signaling and NAc cell firing during intra-oral infusions of a rewarding (sucrose) vs. aversive (quinine) tastant. Aim 4 will expand that study and apply our improved iontophoresis method in conjunction with the combined voltammetry/electrophysiology technology to determine potential causal links between rapid DA signaling and NAc cell firing during rewarding and aversive situations. PUBLIC HEALTH RELEVANCE: Cocaine addiction is a serious problem in the United States, yet strategies to treat cocaine abuse are limited. The significance of this research is that it will provide unprecedented information regarding the actions of rewarding (e.g., cocaine) and aversive substances on dopamine release and the activity of brain cells in the nucleus accumbens (NAc), a brain structure known to be crucially involved in mediating the reinforcing actions of abused substances. The information obtained from the present application will provide insight into the neurobiological mechanisms mediating cocaine addiction and thereby aid in the development of pharmacological agents to treat human drug addiction.

Numerous investigations indicate that the nucleus accumbens (Acb) is crucially involved in mediating the reinforcing actions of drugs of abuse such as cocaine and `natural' reinforcers such as food and water. We recently completed a series of studies that examined the activity of the same Acb neurons in rats responding on multiple schedules for either two distinct `natural' reinforcers (water and food), or one of those `natural' reinforcers and the intravenous self-administration of cocaine (Carelli et al., 2000; Appendix D). The results showed that the majority of neurons tested exhibited similar, overlapping neuronal firing patterns across the two `natural' reinforcer conditions. In contrast, the majority of neurons examined (> 90%) exhibited differential, nonoverlapping firing patterns relative to operant responding for water (or food) vs. cocaine reinforcement. Given these findings, four experiments are proposed in this application to provide critical information regarding factors that influence and/or control Acb reinforcement-related cell firing in behaving animals. Exp. 1 will determine the anatomic distribution of neurons in the Acb that selectively encode information related to water vs. cocaine reinforcement. This will be accomplished by the strategic positioning of microelectrodes into the core, shell and/or rostral pole of the Acb, and the specific `marking' of wires from which reinforcer selective cell firing was recorded during a water/cocaine multiple schedule. Exp. 2 will extend that study and determine if reinforcer selective cell firing is apparent during initial exposure to cocaine or if it is a direct consequence of repeated self-administration experience. Information gained in those studies will be expanded in Exps. 3 & 4 by determining the effects of interruption of drug access (abstinence) on cocaine selective cell firing. This is a critical issue since cocaine addiction in humans is typically characterized by periods of abstinence from drug taking and relapse (Gawin, 1991; O'Brien et al., 1992). Specifically, Exp. 3 will determine the firing properties of Acb neurons following various periods of cocaine abstinence (2, 4 and 8 weeks). Exp. 4 will determine the effects of cocaine abstinence on the associative properties of Acb cell firing documented in a number of published reports by the PI. Results of Exp. 4 will be directly relevant to understanding the biological basis of stimulus control in cocaine addiction reported to be a major contributor to problems in human drug abusers (O'Brien et al., 1992; Childress et al., 1999). Collectively, these studies will provide important insight into the functional organization of the Acb and its role in reinforcement-related processing in behaving animals.

DESCRIPTION (provided by applicant): The DSM-IV recognizes the emergence of negative affect (e.g., dysphoria, irritability, anhedonia) in addiction, postulated to play a key role in craving and relapse. Prior rewarding experiences (e.g., food, job) become devalued as the addict continues to seek and use drug despite harmful outcomes. Dissecting the neural mechanisms underlying this detrimental consequence of addiction is critical since it may lead to novel treatments that ameliorate negative affective states associated with drug use and decrease the drive for the drug. The nucleus accumbens (NAc) plays a key role in reward processing and NAc neurons encode the critical features of natural and cocaine directed behaviors. Importantly, this processing is highly dynamic and profoundly altered by a variety of factors including drug abstinence. However, understanding the neural basis of natural reward devaluation by cocaine, the development of aversive affect associated with this devaluation, and the potential alteration of this processing by abstinence, has been limited. The Carelli lab began addressing these issues using an animal model developed in the last funding period. NAc activity was examined in rats during intraoral infusion of a sweet taste alone or following devaluation (i.e., when it predicted delayed cocaine availability). Rats exhibited aversive taste reactivity (e.g., gapes) during infusion of the devalued sweet, similar to infusion of quinine, a bitter, aversive tastant. This shift in palatability corresponded to an alteration in NAc activity; cells that previously responded with inhibition during infusion of the sweet shifted to excitatory activity during infusion of the cocaine-devalued tastant. This excitatory response profile is typically observed during quinine infusion, indicating that the once palatable sweet taste becomes aversive following its association with impending cocaine availability, and NAc neurons encode this aversive state. Critically, the expression of this aversion to the sweet taste predicted the subsequent motivation to self- administer cocaine. Likewise, a shift (from increase to decrease) in NAc dopamine (DA) was observed as the aversive state developed. These intriguing findings suggest that cocaine-conditioned cues elicit a cocaine-need state that is aversive, is encoded by a distinct subset of NAc cells and rapid DA signaling, and promotes cocaine seeking. Here, three specific aims are proposed. We will determine the effects of experimenter- controlled cocaine abstinence on NAc cell firing (Aim 1) and rapid DA release (Aim 2) during presentation of a natural reward that predicts delayed cocaine access. Aim 3 will expand those findings and determine a possible neural mechanism of natural reward devaluation in our model; we will determine if the shift from increased to decreased DA is necessary for the development and/or expression of cocaine-induced negative affect. The proposed studies will provide novel insight into neurobiological mechanisms mediating the emergence negative affective states and the associated devaluation of natural rewards by cocaine, and the effects of abstinence on this phenomenon.

DESCRIPTION (provided by applicant): This application is to request funding for the 2011 Gordon Research Conference on Catecholamines at Bates College in Lewiston, ME, August 7-12, 2011. The 2011 Gordon Research Conference on Catecholamines will take place in Lewiston, ME in August 2011. This small conference, held every other year, is an ideal forum for exploring new developments in the field of catecholamines. It is also an excellent opportunity for junior investigators and trainees to interact with established investigators in a relaxed atmosphere. The evaluations of recent conferences highlight the strong impact this meeting typically has on emerging as well as established scientists. As the funds allocated by the Gordon Conference organization are limited, we are requesting funding from other sources. We are hoping that the results of our requests enable us to support speakers and discussion leaders as well as a large number of junior investigators to participate in the meeting. The conference includes two plenary talks, by Dr. Peter Kalivas and Dr. Barry Everitt. The preliminary program includes a large number of junior scientists and women, and the sessions planned include: 1) Advances in Catecholamine Methods, 2) Catecholamines and Synaptic Transmission, 3) Catecholamines in Reward and Drug Addiction, 4) Cognitive Effects of Catecholamines, 5) Catecholamines in Neuropsychiatic Disorders, 6) Neuroethology and Catecholamines, 7) Catecholamines: Secretory Mechanisms, 8) Catecholamines and Epigenetics and 9) Catecholamines and Learning. The themes covered in the 2011 Gordon Conference on Catecholamines are highly relevant to understanding the neurobiological bases of drug addiction and a variety of neurological and neuropsychiatric disorders including schizophrenia, affective disorders, bipolar disorder, OCD, and Parkinson's disease. This forum will provide a unique opportunity to discuss recent advances in the understanding of how catecholamine systems may contribute to the pathophysiology and treatment of those conditions. The fact that a large proportion of the participants are junior investigators and a significant number will be graduate students and postdocs ensure that this conference may have an impact on how future generations of neuroscientists view these issues. PUBLIC HEALTH RELEVANCE: This application is to request funding for the 2011 Gordon Research Conference on Catecholamines at Bates College in Lewiston, ME, August 7-12, 2011. The catecholamines dopamine (DA), norepinephrine (NE) and epinephrine play critical roles in the peripheral and central nervous systems, and alterations in catecholamine function result in human disease states including cardiovascular disease and neuropsychiatric disorders such as drug addiction, Parkinson's Disease, schizophrenia, depression, and ADHD. The 2011 Catecholamine Gordon Conference will illuminate leading research in catecholamine neurobiology as well as catecholamine function and dysfunction that can lead to novel advances in our understanding of human disease states.

DESCRIPTION (provided by applicant): To effectively secure resources necessary for survival, animals must learn to evaluate the costs and benefits of their behaviors. The mesolimbic dopamine (DA) system, in particular its projection to the nucleus accumbens (NAc), is uniquely situated to process this type of value-related information. Electrophysiology studies in behaving animals show that DA neurons encode specific characteristics of predicted rewards including the cost of, probability of, delay to, and magnitude of future rewards. Likewise, electrochemistry studies employing fast scan cyclic voltammetry (FSCV) have shown that DA release in the NAc encodes similar distinct features of predicted reward values including response costs, delays, magnitude, and risk. Those studies support the seminal theory by Schultz and colleagues that the mesolimbic DA system serves as a prediction error learning signal and as such plays a key role in decision making related to reward. However, there are several critical issues regarding the role of the mesolimbic DA system, particularly its projection to the NAc, in decision making that remain largely unknown. First, although electrophysiology studies are highly informative, it has been less clear precisely how these neural signals translate into DA release in NAc subregions (core versus shell). Differential DA release dynamics across NAc subregions would indicate that although the mesolimbic DA system is involved in decision making and appear to follow reward prediction theory, distinct functional aspects of this processing exist in target regions of the NAc. Second, although electrophysiology and electrochemistry studies have been highly informative, those approaches provide information that is strictly correlational in nature. Additional studies are needed to determine if rapid DA signaling in the NAc is causally linked with decision making behavior. Finally, numerous studies indicate that exposure to abused substances such as cocaine alter decision making behavior, particularly impulsive choices during delay discounting tasks. However, it is not known if a history of cocaine alters rapid DA release in specific NAc subregions during cues that signal those choices. To resolve these issues, three specific aims are proposed. Aim 1 will fully characterize rapid DA release dynamics in the NAc core versus shell during decision making tasks involving changes in magnitude, delay and during delay discounting. Aim 2 will determine if NAc core vs. shell rapid DA release during cues that signal high value options is causally linked to behavioral choices for those options using optogenetic tools. Aim 3 will build upon prior aims and determine the effects of cocaine self-administration experience on rapid DA release dynamics in the NAc core versus shell during delay discounting. Collectively, the proposed studies will provide unprecedented insight into how mesolimbic DA in key target regions of the NAc encode and control decision making behaviors, and how a history of cocaine can alter decision making, a detrimental consequence of repeated drug use.

? DESCRIPTION (provided by applicant): The present proposal is a continuation of an interdisciplinary, predoctoral training program in research on substance abuse currently in its 24th year as a NIDA-supported training grant. The objective continues to be the preparation of individuals for careers that require broad knowledge and research expertise in addiction science, with emphasis on the abuse of drugs and alcohol (alone or in combination), consistent with the Collaborative Research on Addiction at NIH (CRAN). To reflect that perspective, the proposed program is re-titled, Predoctoral Training in Addiction Science. Only predoctoral trainees with an established interest in pursuing research related to substance abuse are selected from a substantial pool of competitive applicants at the University of North Carolina, Chapel Hill (UNC-CH). The environment at UNC-CH provides optimal resources for training in addiction science. First, the training program includes a core of faculty mentors whose research and teaching activities provide a broad spectrum of research training opportunities. These include research programs focusing on motivated behaviors, opioid and cytokine neurobiology, the neuropharmacology and neurobiological effects of abused substances, investigations of the immune system and of HIV/AIDS and drug abuse, behavioral genetics of drug abuse and vulnerability and impulsivity. The addition of mentors from the Clinical Psychology program and from UNC's Obstetrics & Gynecology Department brings new research opportunities in translational areas that will enrich the trainees' knowledge in substance abuse treatment. Research laboratories are located within the Psychology Department, the Psychiatry Department, the School of Pharmacy and the Center for Alcohol Studies. Second, all trainees receive formal training in basic neural and behavioral sciences and statistics. More focused training related to addiction science takes place through several interdepartmental courses and seminars and extensive laboratory research. Third, the program offers many opportunities for professional development through a yearlong Seminar in Addiction Science which trainees take part in every year as they progress through the program. The Seminar in Addiction Science provides a) training in grant writing, b) practice in making research presentations, c) numerous presentations by outside scientists in addiction science and d) introduction of a range of career options. Fourth, the trainees regularly present their research at national meetings and receive training in teaching skills. Finally, UNC-CH is committed to maintaining ethical conduct in research and instruction and this topic is integrated from a variety of sources and takes place over the course of the entire training period. Over the last 10 years, 24 trainees have received their PhD (average time to degree: 5.2 yrs.) and the program has successfully trained several individuals from underrepresented groups. Upon completion of the program, trainees have established careers within addiction science, in both academic and research-intensive settings.

Project Summary/Abstract Investigations in humans and animal models show maladaptive brain pathologies that are a consequence of repeated drug use. Neuroimaging studies show that specific regions of the prefrontal cortex (PFC), critical for cognitive processing, are dampened (i.e., become ?offline?) in human addicts. Given the critical role of the PFC in cognition, and its anatomic link to brain ?reward? structures such as the nucleus accumbens (NAc), the inability to abstain from drug taking may stem in part from deficits in associative learning induced by the drug. Rodent studies support this view. For example, research in the Carelli lab has revealed that rats with a history of cocaine self-administration are able to learn first-order (Pavlovian) associations, but are then unable to use that information to flexibly alter habitual actions. Critically, these deficits in behavior are linked to decreases in neural signaling in the prelimbic (PrL) cortex and NAc core during first order conditioning that may underlie the subsequent cocaine-induced deficits in behavioral flexibility. Thus, one effective treatment strategy for addiction may be to ?restore? alterations in neural signaling in the PFC and associated regions that are a consequence of repeated drug use. One innovative approach that holds great promise in this regard is Non-Invasive Brain Stimulation (NIBS). Indeed, recent data indicates that NIBS that targets PFC regions in human addicts can modulate cortical excitability, and dampen drug craving. Recently, working in collaboration with an expert in NIBS, we developed a rat model of one form of NIBS, transcranial alternating current stimulation (tACS). Here, exogenous electric fields resulting from tACS can be used to modulate cortical oscillations in brain (for example, those that are disrupted following a history of cocaine) by simply applying mild alternating electrical currents to the skull. While NIBS such as tACS holds great promise, virtually no information is known about how it can modulate neural systems to reverse cocaine-induced deficits, since rodent models of this approach are lacking. Therefore, the overall goal of this exploratory R21 application is to apply our tACS approach in combination with our well-established electrophysiology methods (spike and local field potential) to examine if tACS can ?re-adjust? neural signaling in the PrL and NAc core and ameliorate cocaine-induced deficits in flexible behaviors. Aim 1 will determine if tACS can reverse cocaine-induced alterations in flexible behavior and associated shifts in neural encoding in PrL and NAc core in male rats. Aim 2 will determine if tACS reverses cocaine-induced alterations in flexible behavior and associated shifts in neural encoding in the PrL and NAc core in female rats; estrous cycle will be also tracked to determine if it is related to behavioral flexibly and tACS actions. This application is highly innovative in that it will provide novel insight into how tACS can modulate neural signaling and cocaine-induced deficits in associative learning across sexes, and, since this approach is ?noninvasive? (i.e., electrical stimulation is applied to screws mounted on the skull, not in brain), holds great translational value.

Project Summary/Abstract The ability to seek out situations that elicit pleasure and avoid those that lead to aversion or discomfort is a fundamental ability we all share, yet dysfunctional hedonic processing is prevalent in numerous psychiatric illnesses including substance use disorders (SUDs), alcohol abuse, and depression. As such, it is critical to understand the basic neural mechanisms underlying aversive affective states to ultimately apply treatment strategies to restore normal hedonic processing and aid in the recovery of maladaptive behaviors in mental illness. Here, we seek to understand the role of ?top-down? medial prefrontal cortex (mPFC) to nucleus accumbens (NAc) processing of innate and conditioned negative affective processing, incorporating electrophysiology, optogenetics, and a rat transcranial alternating current stimulation (tACS) method we developed. We focus on one type of behavior (taste reactivity, TR), measured in innate (unconditioned) situations and during conditioned taste aversion (CTA) and its extinction (restoration of positive affect). Notably, TR has exceptional translational value since it is preserved across species with similar behaviors present in rats, nonhuman primates and humans. Using electrophysiology, we will first determine how oscillatory, coordinated rhythms in mPFC and NAc circuitry are linked to affective processing in real time in the naïve state, how this signaling shifts when the sweet becomes devalued through CTA, and when it is restored in extinction. Since human and animal studies indicate that strengthening the mPFC can reduce negative affect we will then determine if strengthening these circuits using two distinct approaches can restore positive affect and associated neural function. We will use optogenetics (channelrhodopsin) to determine if targeted optical strengthening of infralimbic (IL)-NAc shell and/or prelimbic (PrL)-NAc core is sufficient to reduce negative affect and enhance CTA extinction. We will also examine if our novel rat transcranial alternating current (tACS) system, a relatively noninvasive approach with great translational value, can also modulate disrupted cortical oscillations in CTA, strengthen overall mPFC-NAc circuit coherence, and determine if this approach can increase positive affect. In both optogenetics and tACS studies, we will focus on 20 Hz (beta) frequency given its role in ?top-down? cognitive control as well as 80 Hz (gamma) frequency given studies that implicate this signaling in reward processing. Collectively, this multi-faceted approach will provide important insight into how mPFC-NAc systems modulate normal hedonic processing, how these systems are disrupted as negative affective states emerge and provide the foundation for the ultimate goal of developing methods to restore aberrant circuit function and hasten recovery from negative emotional states.