Nii A. Addy - US grants

[unreadable] DESCRIPTION (provided by applicant): Smoking related deaths in the US number over 440,000 per year and yet there are 46.2 million smokers in US alone (CDC, 2004). Nicotine is believed to be the primary addictive component of cigarettes, and thus it is critical to gain a better understanding of the mechanisms of nicotine reward and reinforcement. Repeated nicotine administration in animals leads to behavioral changes, such as locomotor sensitization and conditioned place preference, which are thought to reflect its reinforcing properties. In addition, nicotine administration modulates neuronal activity, neurotransmitter release and downstream signaling in the mesolimbic dopamine system, specifically in the ventral tegmental area (VTA) and nucleus accumbens. The calcium-dependent protein phosphatase, calcineurin, also modulates many of the signaling processes implicated in nicotine addiction. Thus, it is important to understand the role of calcineurin in nicotine- mediated behavioral and neurochemical plasticity. The proposed experiments will 1) determine the contribution of calcineurin activity in the VTA to chronic nicotine-induced locomotor sensitization and 2) characterize the role of VTA calcineurin in nicotine-mediated signaling pathways. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): A major barrier to successfully treating cocaine addiction is the high rate of drug relapse that occurs during periods of drug withdrawal. Cocaine relapse can be precipitated by exposure to drug-associated cues that induce cocaine craving and cocaine-seeking behavior. However, to date there are no FDA approved pharmacotherapies to treat cocaine addiction. Thus it is crucial that we understand the neurobiological mechanisms of cocaine-seeking behavior to be able to identify novel therapeutic targets to prevent this relapsing disorder. Drug-associated cues evoke burst firing of ventral tegmental area (VTA) dopamine (DA) neurons that results in phasic DA release in the nucleus accumbens (NAc). Work from our laboratory has revealed that phasic DA activity in the VTA to NAc circuit, and VTA cholinergic receptor regulation of such activity, is critical for cue-induced cocaine-seeking. However, the precise mechanisms that mediate phasic dopamine release and cue-induced drug-seeking behavior during cocaine withdrawal remain poorly understood. We have previously shown that Cav1.3 L-type Ca2+ channels (LTCCs) and their downstream Ca2+-activated pathways in VTA DA neurons are critical for sensitized psychomotor behavioral responses to cocaine following periods of prolonged withdrawal. Additionally our recent findings have revealed that Cav1.3 channels facilitate the transition of DA neurons from tonic to burst firing and act through cholinergic mechanisms, strongly suggesting that recruitment of Cav1.3 channels may underlie cue-induced cocaine-seeking behavior. Thus, the goal of this R21 application is to test the hypothesis that VTA Cav1.3 mechanisms underlie cue-induced cocaine-seeking behavior by regulating phasic DA release in the NAc. To achieve this goal, we will use an innovative and integrative experimental approach using pharmacology and viral vector-mediated genetic knockdown in the VTA in combination with behavioral testing and in vivo voltammetry in the NAc, to examine cue-induced cocaine seeking during withdrawal, using the preclinical self-administration rat model. In specific aim 1, we will examine the role of VTA Cav1.3 channels in cue-induced cocaine-seeking during early and protracted withdrawal. In specific aim 2, we will examine in vivo the role of VTA Cav1.3 channels in VTA-evoked- and acetylcholine receptor-mediated phasic DA release in the NAc during early and protracted withdrawal. The mechanistic insight gained from this study will provide new understanding of the neurobiology of drug relapse and will determine whether Cav1.3 channels may serve as a potential novel therapeutic target to prevent cocaine relapse.

? DESCRIPTION (provided by applicant): Depression remains a serious health concern that affects approximately 1 in 6 individuals in the U.S. and dramatically decreases the quality of life for those struggling with the illness. However, there is still a great need for improved understanding of the neurobiological processes that mediate the pathogenesis of depression. There is also a need for more effective therapeutic interventions to treat depression. Evidence from clinical and preclinical studies strongly suggests that dopaminergic and cholinergic mechanisms likely play important roles in the pathogenesis of depression. Thus, ongoing investigations have sought to identify the neurocircuitry underlying major depressive disorder (MDD). Recent work in rodent models has revealed a novel, causal role for phasic dopamine activity in the ventral tegmental area (VTA) to nucleus accumbens (NAc) pathway in mediating susceptibility and resilience to stress. However, there remains a critical need to determine whether the mechanisms that regulate phasic dopamine activity also mediate responses to stress. Our preliminary findings demonstrate that VTA muscarinic acetylcholine receptor (mAChR) mechanisms powerfully regulate both phasic DA activity and susceptibility to stress, as revealed through neurochemical and behavioral studies in rats. However, critical gaps remain in identifying both the specific VTA mAChR subtype(s) and the primary cholinergic input into the VTA that mediates this susceptibility. The work in this proposal will use an integrative experimental approach (utilizing behavioral pharmacology, in vivo fast scan cyclic voltammetry, and in vivo optogenetics in male and female Sprague-Dawley rats) to address these gaps in scientific understanding. Behavioral examination will include the use of the chronic unpredictable stress (CUS) model, which has strong construct and face validity as a model of depression. Aim 1 will use behavioral pharmacology and in vivo voltammetry to identify the specific midbrain mAChR subtype(s) that mediate behavioral and dopaminergic responses to stress. Aim 2 will use in vivo optogenetics and behavioral analyses to identify the specific mesopontine to midbrain cholinergic pathway(s) that mediates susceptibility and resilience to chronic stress. The overarching goal of this work is to identify the neurobiological mechanisms that mediate behavioral and physiological responses to stress in order to facilitate the development of novel therapeutic interventions for depression.

Abstract: Project #1 The proportion of users of sweet-flavored and mentholated tobacco products (including menthol cigarettes) has increased dramatically, especially within the adolescent population, raising concerns that flavors may facilitate the initiation of tobacco product use and promote nicotine addiction. An additional concern is the recent introduction of synthetic cooling agents that may have effects similar to menthol. Children and adolescents are conditioned, through prior experience, to associate sweet and cooling flavors (fruit, candy, mints, etc.) with high sweetener content (sugar or artificial sweeteners). However, the role of flavors in the initiation of tobacco product use is difficult to study in humans, especially in adolescents and never-users. The goal of this project is to use our adolescent and adult rodent models of inhaled and smokeless tobacco product use, and of oral flavor-paired nicotine self-administration, to examine whether sweet and cooling flavors in tobacco products enhance nicotine use behavior and addiction. We will determine whether early flavor exposure and early flavorant associations with sweeteners influence subsequent nicotine choice and initiation, maintenance, and relapse to paired nicotine and flavorant intake. In Aim 1, we will examine sweet and cooling flavor exposure and conditioning effects on nicotine choice and use. In this aim, we will examine (A) the effects of conditioning to sweet flavors and cooling flavors on nicotine aversion and flavor preference and (B) the effects of characterizing sweet and cooling flavor exposure on the initiation and maintenance of nicotine-taking and relapse to nicotine-seeking. We will also use in-vivo voltammetry to examine reward-related dopamine signaling responses to flavorants, as these signals could serve as a biomarker for the ability of flavorants to enhance nicotine use and addiction. In Aim 2, we will examine the effects of synthetic cooling agents on respiratory irritation caused by electronic cigarette vapors ? effects that could potentially facilitate nicotine intake and use. The results of this work; (1) will provide the FDA with understanding of sweet and cooling flavor effects on the initiation and persistence of nicotine taking, and (2) could be used to guide policy decision on the regulation of sweet and cooling flavors in tobacco products.

Individuals with substance use disorders (SUDs) have a higher prevalence of mood and anxiety disorders, and those with mood disorders also have a higher prevalence for SUDs. Periods of drug abstinence are also associated with increased irritability, heightened anxiety, and increased mood disorder symptoms. Further, repeated exposure to either drugs of abuse or stress is associated with mood-related disorders. Thus, the comorbidity between substance abuse and mood disorders is an ongoing challenge for the field. There is a need for both improved understanding of mechanisms mediating this comorbidity and a need for novel and effective therapeutic targets. Research continues to reveal overlapping mechanisms, notably in brain reward pathways, mediating both SUDs and mood-related disorders. In humans, L-type calcium channel (LTCC) genes have been identified as candidate risk genes for cocaine dependence, major depressive disorder, and heightened anxiety. In rodent models, we have found that activation of L-type calcium channels (LTCCs) in the ventral tegmental area (VTA) enhances cocaine-related, depression-like, anxiety-like, and anhedonic behavior, while also inducing social deficits. We have also found that LTCC blockade leads to decreased drug-seeking behavior via regulation of dopamine signaling in the nucleus accumbens (NAc). However, the field still lacks in depth understanding of LTCC mechanisms in neuropsychiatric disorders. More specifically, there is very limited understanding of LTCC mechanisms mediating depression and anxiety-related phenotypes induced by exposure to drugs of abuse or chronic stress ? represent a gap in scientific knowledge. Our preliminary findings have revealed that LTCC blockade in cocaine abstinent or chronic stress exposed rats induces anxiolytic-like and antidepressant-like effects. In the current proposal, we will integrate intravenous drug self- administration and chronic unpredictable stress (CUS) paradigms with behavioral pharmacology and in vivo electrochemistry (voltammetry) in male and female rats to: 1) Determine whether LTCC blockade produces anxiolytic-like and antidepressant-like effects and promotes social interaction during cocaine abstinence, via regulation of DA signaling and, 2) Determine whether LTCC blockade attenuates the anxiogenic and anhedonic effects, and the social interaction deficits, of CUS. In this proposal, we will identify the underlying mechanisms by which LTCC blockade may serve as a novel therapeutic intervention to alleviate mood disorder symptoms associated with repeated exposure to cocaine or stress.