Susan L Andersen - US grants

DESCRIPTION (provided by applicant): Attention-deficit/hyperactivity disorder (ADHD) affects attention and motor capacities in approximately 6% of school-aged children, making it the most prevalent childhood disorder. ADHD can be treated effectively with stimulants including methylphenidate (MPH; RitalinTM), which are indirect dopamine (DA) agonists, and their use is rising. However, the use of such stimulants has been limited by concerns over their abuse or the possible role they play as a "gateway" to the abuse of other substances. Recent clinical data show that ADHD children treated with stimulants experience an 85% reduction in substance abuse compared with those who do not receive pharmacotherapy. The interpretation of these clinical observations, however, is difficult since effectively treated ADHD patients have improved psychosocial and academic skills that reduce other risk factors, such as social impairment. In addition, they do not address potential mechanisms leading to alternative interpretations including the possibility that early treatment with MPH can imprint on the underlying neurobiological substrate of stimulant abuse. In other words, juvenile exposure to MPH potentially can produce enduring effects on the neurobiology of the developing brain that outlast the period of drug treatment itself. Some of these questions can potentially be answered using animal models and it has been shown that chronic exposure to stimulant drugs, such as MPH, causes long-lasting increases in rewarding effects, thereby increasing vulnerability to substance abuse. However, these studies have been performed in adult animals limiting their interpretation for drug treatment in juvenile (developing) brains. We have, therefore, developed an animal model using MPH exposure in juvenile rats. In this model, MPH exposure made moderate doses of cocaine aversive and high doses less rewarding later in life demonstrating reduced vulnerability to stimulant abuse. Thus, our results indicate that imprinting and/or age differences in pharmacokinetics of MPH could mediate its enduring effects. In the proposed set of studies we endeavor to determine: 1) the age-related contribution of bioavailability of MPH to cocaine reward later in life; 2) the effect of chronic MPH treatment on dopamine release in the pre-pubertal rat; 3) whether pre-pubertal exposure to MPH changes dopamine receptor expression; and 4) the role of dopamine in the underlying mechanism of MPH-induced changes in the pre-pubertal rat.

DESCRIPTION (provided by applicant): In this I/START application from a junior investigator, we propose to use magnetic resonance imaging (MRI) in animals to test the hypothesis that early exposure to methylphenidate (MPH) alters neurobiological development. Stimulants, such as MPH, are the treatment of choice for children with Attention Deficit/Hyperactivity Disorder (ADHD), which is one of the most prevalent childhood disorders and affects an average of 6% of the population. Even though stimulants have been used to treat ADHD since the 1950' s, we know very little about the long-term enduring effects of pharmacotherapy on the developing brain. Research on this topic has become even more imperative, as children are being treated more aggressively and earlier (as young as 2 years of age) with pharmacotherapy for ADHD. From the adult preclinical literature, we know that exposure to stimulants produces enduring changes in the underlying neurobiology and neuroanatomy of the reward systems. In our animal model of childhood exposure to stimulants, we have shown that pre-pubertal exposure to the stimulant MPH produces different - even opposite - enduring changes than post-pubertal exposure (Andersen et al., 2002). This increase in the aversive properties of cocaine following pre-pubertal MPH exposure parallels clinical observations of reduced substance use disorder in adolescents who had received pharmacotherapy for their ADHD (Biederman et al., 1999). Funding from the I/START initiative will enable the PI to expand her basic research interests as a developmental psychopharmacologist to the more clinically relevant domain of neuroimaging. Preliminary MRI data will be collected and analyzed in animals that have been exposed to MPH pre-pubertally for the "proof of concept" that early medication produces enduring and specific changes in brain activity. These important pilot data will then serve as the basis for an R01 application that will determine the nature and mechanism by which early drug exposure imprints on brain activity in rats and humans.

DESCRIPTION (provided by applicant): This application examines the underlying signaling mechanisms that are involved in impulsivity as it changes across development (juvenile, adolescent, and adult), sex, pathology, and drug exposure. The overarching goal of this application is to: To identify dysfunctional neuronal circuit(s) and signaling mechanisms associated with impulsive behaviors and identify novel prevention approaches for intervention. We propose a multi-faceted approach that encompasses behavioral and molecular analyses to examine neuronal function within well-defined neural pathways in the rodent brain of both males and females. We have two Co-PIs, who will be running different aspects of these projects indepdently and interdependently at various times within the 5 year period. We build on our new data that show that elevated D1 dopamine receptors in the prelimbic prefrontal cortex of the rat increase impulsivity and other risky behaviors. Aim 1 will identify and confirm neuronal pathways underlying impulsivity using both a reward-associated impulsivity task of impulsive choice (e.g., delayed discounting) and a motor-related task of impulsive action (e.g., the stop signal reaction time task). We will analyze receptors on projections from the prelimbic prefrontal cortex, the basolateral amygdala, and the orbital frontal cortex as they innervate the nucleus accumbens and the basolateral amygdala. Differential expression levels of D1 and alpha2A noradrenergic receptors are hypothesized to mediate these behaviors. We will use laser microdissection (LMD) and quantitative, real-time PCR for this initial assessment, followed by mechanistic confirmation with experimental use of viral vectors that selectively over-express these receptors in glutamate neurons in a given region. In Aim 2, we will determine effective doses (ED50s) of methylphenidate, atomoxetine, and guanficine on impulsivity at different ages and across sex. Due to their different selectivity for dopamine and alpha2A receptors, we expect that different signaling pathways will be uniquely activated at different ages. The derived ED50s will then be used in a juvenile exposure paradigm that is predicted to effectively prevent impulsive behaviors in adulthood. In Aim 3, samples from Aim 1 (viral over-expression) and Aim 2 (preventative interventions) will be analyzed with a bioinformatics approach with microarray and microRNAs analyses to identify convergent signaling pathways involved in impulsive behaviors and its effective intervention. Together, these studies will provide information on the developmental profile of the mechanisms underlying impulsivity as it is influenced by sex and medication. PUBLIC HEALTH RELEVANCE: We will use laser microdissection of glutamate neurons in specific projection pathways into the nucleus accumbens to identify the underlying signaling mechanisms that are associated with impulsive choice and action. Drug treatments determined to be effective in reducing impulsive behaviors will be coupled with genetic engineering to identify novel cell signaling pathways with microarrays and microMRNA analyses. The goal of the proposed work is to elucidate a preventative therapeutic approach to impulsive behaviors.

DESCRIPTION (provided by applicant): Substance use typically begins in mid-adolescence, but when it occurs earlier in adolescence/late childhood, drug use is associated with significant, life-long addiction liability. Identification of at-risk individuals is vital for early intervention/prevention and may have the greatest impact on reducing addiction long-term. However, this approach requires an understanding of the mechanism of risk and the proof should be causal, and not correlational, as in previous studies. In addition, this understanding needs to be extended to immature females, where extreme little is know about neural changes and drug sensitivity. Here, we propose to build on our substantial preliminary data that utilizes highly novel and innovative approaches to show the following: a) elevated D1 dopamine receptor expression on glutamatergic neurons in the prelimbic prefrontal cortex (plPFC) is observed in adolescent male rats relative to younger and older rats, and is associated with increased sensitivity to drug-associated cues at this age; b) gene engineered elevations in D1 receptors on glutamate neurons with a lentiviral vector (CamKII.D1) in the plPFC increases preferences to cocaine-associated cues; c) gene engineered D1 receptor expression on both GABA and glutamate neurons (Synapsin.D1) does not enhance drug-cue sensitivity; d) novelty-seeking in juvenile rats correlates with preferences for cocaine-associated environments (r=0.87); e) D1 dopamine receptors produce age-dependent changes in blood flow patterns that most likely reflect the distribution of D1 receptors on glutamate and GABA neurons. In a set of studies that are highly consistent with # PA-07-226, we propose to use these two viral vectors to increase (a) or decrease (b) sensitivity to drug-related cues to experimentally show that D1 receptor location on glutamate neurons is the risk mechanism (Aim I). These same animals will also show that the original, strong drug-cue associations are more difficult to extinguish and reinstate more strongly as a result of D1 receptors on glutamate neurons within the plPFC (Aim I). Aim II will determine whether novelty-seeking in juvenile animals can serve as an behavioral metric to identify increased drug-cue sensitivity and how this relates to D1 receptors. Aim IV, which runs concurrently, will use the CamKII.D1 virus and novelty-seeking to determine whether pharmacoMRI can identify this biomarker of risk through unique blood flow patterns. Aim III will determine whether a more benign environment at the time of initial drug exposure (e.g., home- cage) can reduce drug-seeking in other more salient environments later in life. Together, these studies will determine how a single biomarker predicts risk for substance use and influence enduring risk of drug abuse. PUBLIC HEALTH RELEVANCE: The goal of the proposed research is to determine whether elevated expression of the D1 dopamine receptor in the prefrontal cortex contributes to vulnerability to substance use in developing animals and can serve as a biomarker for early detection. D1 dopamine receptors are transiently over-expressed on specific neurons (e.g., glutamate) during adolescence, which is hypothesized to underlie enhanced vulnerability to cocaine at this stage. Here, we will use gene engineering to manipulate D1 receptor expression to conclusively show that this receptor underlies increased sensitivity to the initial formation of cocaine-associations and their maintenance, which may be detected by behavioral screening early and/or detected with pharmacoMRI and associated blood flow changes.

DESCRIPTION (provided by applicant): We propose to advance the use and interpretation of near-infrared spectroscopy (NIRS) technology by determining the faithfulness to which NIRS localizes patterns of blood flow relevant to addiction-related processes. Importantly, these NIRS signals will be simultaneously collected with behavioral measures of addiction (e.g., self-administration) in real-time. Currently, the use of functional magnetic resonance (fMRI) for the study of small mammals is difficult and relatively impractical for the majority of researchers. Our goal is to provide a poor man's functional imaging device that will be available for a modest cost and is readily accessible and easy to implement. Simply stated, our intent is to rapidly increase our knowledge base about blood flow changes in animals that could be readily translated to understanding human processing of drug-related information. In the proposed research, we will use a multi-faceted approach including NIRS, MFI, and intravenous self- administration of cocaine to determine whether localized assessment with NIRS is a useful alternative to fMRI to determine changes in blood flow. We will extend the utility of the NIRS approach to freely moving animals that are actively self-administering cocaine. Both the significance and innovation of this approach is relevant for the CEBRA due to the development of innovative technology to rapidly advance our understanding of blood flow change in animal models. Aims Proposed: * Specific Aim 1. To establish the similarities in blood flow changes detected by fMRI and NIRS. * Specific Aim II: To determine whether we can use NIRS to monitor neuronal activity in real-time in freely moving animals.

Early adolescent exposure to marijuana has been associated with increased addiction and mental illness, suggesting that marijuana use is a gateway to adverse outcomes. However, research on the effects of early marijuana exposure is hampered by the need for a robust rodent inhalation exposure paradigm and a clearly defined sensitive period of exposure. Program announcement # 14-162 recognizes these fundamental gaps in our knowledge, as well as the need for studies on the exposure to different potencies and constituencies of cannabis/cannabinoids in both sexes. Marijuana is composed of two main constituencies of interest: ?9-tetrahydrocannabinol (THC; the `high') or the cannabidiols (CBD; `medicinal marijuana'). The long-term goal is to identify key factors that are predictive of THC/CBD effects to develop improved strategies to reduce the unwanted, long-term effects of developmental marijuana exposure. The overall objective in this R21 application is to establish how different levels of inhaled marijuana constituents influence pharmacokinetics across age to identify a sensitive period when risky behaviors are effected by THC/CBD exposure in rats. Specifically, the central hypothesis is that higher levels of THC exposure will increase, and CBD exposure will reduce, respectively, risky behavior and addiction as a function of age of exposure and sex. The rationale for these studies is based on clinical observations that exposure to marijuana during early adolescence has been associated with increased addiction. Preliminary data show that exposure to inhaled 6% THC- containing NIDA marijuana cigarettes (0.02% CBD) produced age-dependent changes in THC blood levels and memory deficits, with the greatest impairment in early adolescence. Impairment on this same memory task predicts later cocaine self-administration. The central hypothesis will be tested by pursuing two specific aims: 1) determine the age- and sex- dependent effects on drug levels in rats following acute and chronic exposure to passive inhalation of different THC/CBD potencies in early adolescence, late adolescence and adulthood; and 2) determine early behavioral predictors of addiction risk following THC/CBD inhalation exposure. Whether a risky behavior is present before or after (or both) exposure to three different combinations of inhaled THC/CBD and then increases the amount of cocaine self- administration will be investigated. The approach is innovative, in the applicant's opinion, because the inhaled effects of CBD and/or THC on development have been neglected. The proposed research is significant because it is expected to address the classic ?chicken or the egg? question that is raised by the gateway hypothesis with the pre-/post- behavioral assessments. Successful development of an inhalation paradigm and the identification of a sensitive period will be used in future studies that examine the effects of marijuana exposure on brain development with anatomical and functional MRI.