Justin M. Moscarello, Ph.D. - US grants

DESCRIPTION (provided by applicant): A large body of evidence implicates the mesocroticolimbic dopamine (DA) system, specifically the medial prefrontal cortex (mPFC) and nucleus accumbens (NAcc) in the neurobiology of natural (e.g. food) and artificial (e.g.drug) reinforcement, as well as motivational states associated with goal-seeking. However, relatively little has been established about how these two brain regions interact as a function of alterations in motivational state or reinforcer magnitude, or how such interactions modify the output of goal-direceted behavior. The current proposal is therefore intended to better understand the functional relationship between the mPFC and NAcc as it relates motivated behavior. The project has three specific aims. First, to build upon preliminary data obtained with c-Fos (a protein marker of neuronal activation) by employing in vivo microdialysis to further understand the interaction between mPFC and NAcc as a function of manipulations of motivational state and reinforcer magnitude. Second, to assess the effects of chemical inhibition and excitation of both mPFC and NAcc as it pertains to multiple behavioral indices of motivation (i.e. progressive ratio reponding for food reinforcement;conditioned approach behavior in an operant runway). Third, to assess the effects of D1/D2 antagonism in both mPFC and NAcc with respect to performance in the same behavioral assays. Understanding of the functional relationship between mPFC and NAcc as it pertains to motivation will provide crucial evidence about the processes by which the nervous system serves to organize behavior. Ample research in humans and in animals suggests that the brain regions under study in this proposal are crucial mediators of addiction, as well as other behavioral disorders with a motivational component. Thus, a complete understanding of how these brain areas function is necessary in order to fully address a number of important issues of public health.

Excessive fear, a central component of many anxiety disorders, can have deleterious effects on both psychological and physical wellbeing. Treatments for anxiety disorders often endeavor to supplant fear-based reactions with instrumental actions that can be thought of as active coping strategies. Thus, the capacity to transition from reactive fear to active coping has clear clinical significance [unreadable] understanding the biological basis of this process could provide a sound platform for advancements in the treatment of anxiety-related psychopathologies. Signaled active avoidance learning can offer important insights into this transitional process. In this form of conditioning, subjects are trained to avoid an unconditioned stimulus (US) by performing an instrumental action when a predictive conditioned stimulus (CS) is presented. Interestingly, an initial Pavlovian fear reaction, freezing, predominates through early training and constrains the development of active behaviors during CS presentation. Over the course of learning freezing is suppressed, allowing active avoidance responses to become manifest. It is this very suppression of freezing that this proposal seeks to examine, as it represents a compelling model of the transition from reactive to active behavioral states. A neurobiological understanding of this phenomenon could shed light on the substrates of anxiety and resilience, and thus has ample translational potential. The ventromedial prefrontal cortex (vmPFC) is involved in the suppression of maladaptive or inappropriate behaviors, whereas the central nucleus of the amygdala (CeA) is crucial for CS evoked freezing. vmPFC cells form synapses on the neurons that comprise the intercalated cell masses of the amygdala (ITC), which are an inhibitory population that in turn project to the cells of the CeA. The basic hypothesis that this proposal will pursue is that vmPFC exerts feed-forward inhibition on CeA during signaled avoidance learning, thus suppressing CS-evoked freezing and allowing the subject to execute an instrumental avoidance response when the CS is presented. To explore this hypothesis, three specific aims are proposed: 1) to ascertain the role of vmPFC and Cea in the suppression of freezing during signaled avoidance learning, 2) to identify the role of the ITC, and of the vmPFC projection to those neurons, and 3) to determine the timing and nature of vmPFC involvement in the suppression of freezing. Experiments proposed under the first two aims will involve traditional lesion techniques, while the final aim will be explored using the light-activated inhibitory molecule Archaerhodopsin-3. This blend of conventional (lesion) and cutting edge (optogenetic) methodologies will allow for a detailed and precise exploration of the proposed model, thus shedding light on the neuroboiogical substrates of a clinically relevant behavioral phenomenon.

PROJECT SUMMARY/ABSTRACT Avoidance is a hallmark symptom contributing to the deleterious impact of many anxiety disorders. Despite this, there are major gaps in our understanding of the neural circuits underlying avoidant behavior. A mechanistic account of this key symptom would advance progress toward brain-based innovations for the treatment of pathological anxiety. Signaled active avoidance (SAA) is a behavioral procedure for rats in which a highly persistent avoidance response is triggered by a conditioned stimulus (CS) associated with an aversive unconditioned stimulus (US). Because the avoidance response prevents US delivery, acquisition of SAA causes the US to transition from an imminent threat early in training to a remote threat later in training, once the response has become more frequent. Ethologically inspired models for aversive emotion suggest that this change in threat imminence is consistent with a shift from fear to anxiety, indicating that SAA expression is mediated by an anxiety-like state. The overarching hypothesis of this proposal is that neural circuits of anxiety-like behavior play a central role in SAA. Previous work implicates the bed nucleus of the stria terminalis (BNST) in anxiety. To generate preliminary data for the overarching hypothesis of this proposal, an initial experiment was conducted using an inhibitory DREADD (designer receptor exclusively activated by designer drugs) to inactivate BNST neurons in rats performing SAA. This manipulation demonstrated that BNST is necessary for the maintenance of the avoidance response. The proposed studies will build on this result by dissecting the function of a circuit mechanism for active avoidance, comprised of BNST and key regions that provide it with synaptic input (prefrontal cortex, basal amygdala). Given that avoidant coping is a behavioral disturbance common to many anxiety disorders, this work has clear relevance to public health. Discovery of an avoidance circuitry could provide a novel target for innovative therapeutic interventions for pathological anxiety. The goal of this work is to generate rigorous preclinical data that accelerates clinical advancement.