2015 — 2019 |
Flores, Cecilia |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Amphetamine in Adolescence Alters Frontal Cortex Development
DESCRIPTION (provided by applicant): Adolescence is a critical period of vulnerability to develop drug abuse. This application is about the effects of stimulant drugs in adolescence on the development of the medial prefrontal cortex (mPFC), a brain region implicated in reward, motivation, and cognition. My long-term goal is to identify mechanisms whereby exposure to drugs of abuse in adolescence, as compared to adulthood, confers a higher risk for psychopathologies later in life. The proposed experiments are designed to assess the impact of amphetamine (AMPH) exposure in adolescence on the development of the dopamine (DA) innervation to the mPFC and to determine the role that DCC receptors play in this regard. DCC receptors respond to the guidance cue, netrin-1, to organize neuronal connectivity and are highly and conspicuously expressed by DA neurons in the ventral tegmental area (VTA) across the lifespan. My work in rodents is the first to identify dcc as a gene involved specifically in th adolescent development of mPFC DA inputs, and in turn, in the maturation of local circuitry. In addition, we have shown that AMPH regulates DCC receptor expression in the VTA during early adolescence. Remarkably, this same early adolescent exposure to AMPH increases the expanse of DA fibers in the adult mPFC, but denudes these fibers of synaptic sites. These enduring effects are not observed following adult exposure to AMPH. My working hypothesis is that AMPH in adolescence, by altering the expression of DCC receptors within DA neurons, produces changes in their normal developmental trajectory, leading to their ectopic innervation and faulty synaptogenesis in the mPFC. These changes in mPFC DA innervation, in turn, induce structural and functional reorganization of mPFC local circuitry, influencing cognitive processing in adulthood. Objectives: 1) to characterize the nature of the effects of AMPH exposure in adolescence on mPFC DA innervation and on local circuitry organization and function in adulthood, 2) to determine whether AMPH- induced regulation of VTA DCC receptor expression is required for drug-induced disruption of mPFC development and to identify the underlying mechanisms, 3) to examine the consequences that the DCC- mediated AMPH-induced disruption of mPFC development has on cognitive processing in adulthood. Methods: I will combine quantitative neuroanatomical analyses with genetic manipulations to unravel the fine architecture and synaptic organization of DA circuitry. I will use in vivo microdialysis and electrophysiology to capture the functional consequences of the neuroanatomical alterations. I will use mice that lack dcc specifically within DA neurons to assess whether DCC receptors play a role in AMPH-induced disruption of mPFC development. I will perform loss- and gain-of-function experiments by manipulating netrin-1 expression in DA targets to discern how AMPH-induced changes in DCC-mediated netrin-1 signaling alter mPFC development. I will examine the effects of AMPH exposure in adolescence, and the contribution of DCC receptors, on cognitive processing in adulthood by performing tests of behavioral flexibility and behavioral inhibition, and working memory.
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1 |
2021 |
Flores, Cecilia |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Amphetamine in Adolescence Disrupts Frontal Cortex Development
Adolescence is an age of increased vulnerability to psychopathology, including drug abuse. My work concerns the molecular events underlying the maturation of the medial prefrontal cortex (mPFC) in adolescence and the effect of stimulant drugs on these processes. My ultimate goal is to unravel the molecular factors mediating risk and resilience in adolescence to the deleterious effects of drugs of abuse in males and females. Our work has focused on the impact of amphetamine (AMPH) on the development of the dopamine (DA) innervation to the mPFC. We discovered that DA axons are still growing toward the mPFC across adolescence, remaining particularly susceptible to disruption. This delayed DA axon growth is controlled by the guidance cue receptor DCC, which determines whether, when, and where DA axons stop or continue to grow. Notably, AMPH in early adolescence dysregulates DCC expression and also induces profound changes in mPFC DA synaptic connectivity/function and causes deficits in cognitive control in adulthood. Until very recently all our studies have been focused on male mice only. In addition, we have been investigating only AMPH effects of doses that reach plasma levels equivalent to those seen in recreational drug users. Our recent preliminary data suggest, however, that the vulnerability to the effects of AMPH on mPFC DA development is sex-specific. Also, recently published results show that therapeutic-like doses during this time induce opposite, even beneficial enduring effects. The experiments now proposed are designed to test the following working hypotheses: (a) that the vulnerability to AMPH-induced disruption of mPFC development at particular adolescent time windows is sexually biased, (b) that this dimorphism also impacts detrimental drug effects on adult cognitive processing, (c) that sex-specific control over DCC receptor expression in DA neurons mediates differential drug vulnerability/resilience (d) that these effects are dependent upon recreational- versus therapeutic-like exposure. Methods: To address these questions, we will conduct molecular, anatomical, neurochemical, and behavioral experiments in male and female mice. Our studies will combine dual viral transduction strategies and quantitative neuroanatomical analyses to track DA axon targeting and growth in adolescence. To measure DA function, we will use novel and temporal-sensitive measurements of in vivo DA signaling (dLIght1) in freely moving mice. To identify mechanisms underlying the dimorphic vulnerability to AMPH, we will perform gain- and loss-of-function experiments using neuron optimized CRISPR and Cre-Lox recombination strategies.
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