Research Project
9636527
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.
