One of the more daunting problems associated with treating drug addiction is the high incidence of relapse, which has been reported to occur in up to 90% of addicted individuals. Relapse is often precipitated by exposure to stressful events; thus highlighting the need for basic science research to characterize the neural circuits by which stress affects motivated behavior. Previous studies suggest that the dopamine cells of the ventral tegmental area (VTA) are well situated to mediate the interaction between stress and motivation, but to date this has not been directly tested. Therefore, the primary goal of the research plan in this K99/R00 'Pathway to Independence Award' proposal is to assess how stress-related peptides, aversive cues, and stressful stimuli directly affect phasic dopamine release, which is the pattern of dopamine release directly associated with promoting motivated behavior. To address this goal, fast-scan cyclic voltammetry will be utilized to monitor phasic dopamine release in combination with brain-region specific pharmacological manipulations in rats performing operant tasks that assess motivation. During the mentored phase of the award, the candidate will examine how the stress-released neuropeptide corticotropin-releasing factor (CRF) acts in the VTA to affect motivated behavior and phasic dopamine release in the nucleus accumbens to reward-related stimuli for natural (Aim 1) and drug (Aim 2a) reinforcers. Because drug exposure induces synaptic changes within the dopamine system, including how CRF interacts with dopamine neurons, the candidate will next assess how prior drug intake influences CRF's effect on motivated behavior for natural reinforcers (Aim 2b). With this foundation of how a stress-related neuropeptide affects phasic dopamine release and behavior, subsequent experiments during the independent phase of the award will directly examine how stress (escapable and inescapable) and stress-associated cues affect behavior and phasic dopamine release in the nucleus accumbens (Aim 3a). Emerging evidence suggests that catecholamine (dopamine and norepinephrine) release in the prefrontal cortex and amygdala are also involved with mediating the response to stress, so the candidate will also address how phasic catecholamine release in these brain regions is affected by stress and stress-associated cues (Aim 3b). The findings from the proposed work will not only be of great importance to addiction research by yielding valuable findings on the interaction between stress, motivation, and phasic catecholamine release, but will also lay a foundation for future experimentation. The research designed in this project is a logical extension and synergistic amalgamation of the candidate's previous (cellular level analysis of CRF modulating dopamine neuron firing rate) and current work (examining phasic catecholamine release during motivated behavior). The candidate will become proficent in performing drug self-administration studies under the advising of his mentor Dr. Paul Phillips, and consulting with Dr. Jeansok Kim will add to the candidate's experimental repitoire by incorporating voltammetry recordings during stress manipulations. The proposed career development plan is designed to afford the candidate the best opportunity of achieving his long-term goal of becoming an independent tenure-track investigator conducting neuroscience research focused on examining the role of catecholamines during behavior. Specifically, the candidate will strive toward this long-term goal by performing the proposed research, attending various scientific seminars at the University of Washington, presenting at scientific conferences, giving lectures to graduate level classes about drug abuse and addiction, and taking classes to enhance his scientific intellect. The candidate will receive career development advising and will be evaluated on his progress in his monthly joint meetings with his primary mentor, Dr. Phillips and co-mentor, Dr. Charles Chavkin. Dr. Phillips pioneered voltammetry recordings using chronically implanted electrodes that remain viable for months, and as such provides an excellent enviroment to perform these experiments. Furthermore, the atmosphere at the University of Washington and through the Center for Drug Addiction Research is conducive for developing young scientists, as evidenced by the recent awardees of the K99/R00 whom have transitioned to independent scientific careers.
Treatment for individuals suffering from drug addiction is difficult due to the high incidence of relapse, which often is precipitated by exposure to stressful events. Therefore, it is critical to characterize the neural mechanisms mediating how stress influences motivated behavior. Thus, the goal of this research is to use rodent models to examine how stress and stress-related compounds affect motivation and the release of neurotransmitters involved with facilitating motivated behavior.
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