To date, there are no effective therapeutic treatments for cocaine craving and relapse, which can be precipitated in abstinent human addicts by re-exposure to environmental stimuli that were previously associated with drug taking. This cue-induced drug craving in humans progressively increases during early drug withdrawal and remains high throughout extended periods of drug abstinence. This phenomenon was modeled in rats using a self-administration/reinstatement paradigm in which responsiveness to cues previously paired with cocaine was shown to progressively increase (or """"""""incubate"""""""") over the first two months of forced drug abstinence. Brain-derived neurotrophic factor (BDNF) protein expression also was increased in mesocorticolimbic nuclei according to a similar time course as the incubation of cocaine craving (ICC), which suggests that BDNF may potentiate the ongoing expression of ICC. However, the precise molecular mechanisms that regulate time-dependent changes in BDNF expression during ICC remain to be determined. Preliminary data from our lab indicate for the first time that mesolimbic BDNF mRNA expression also is increased during cocaine abstinence according to a similar time course to the expression of ICC. The goal of the proposed Research and Training Plans is to acquire molecular neuroscience techniques through supervised hands-on training and didactic coursework in order to incorporate molecular/epigenetic methods into Specific Aims focused on elucidating the mechanisms that regulate BDNF expression during ICC. The main hypothesis of this K01 application is that altered BDNF mRNA expression during ICC is mediated by chromatin remodeling within BDNF promoters.
Aim 1 will require training in Western blot, ELISA, and real-time PCR methods in order to determine the precise time course that BDNF mRNA and protein expression is regulated within mesocorticolimbic nuclei during the development and expression of ICC.
Aim 2 will require proficiency in ChIP techniques in order to examine chromatin remodeling (i.e. histone acetylation and/or methylation) at BDNF promoters associated with increased BDNF mRNA expression during ICC. In order to identify the enzymes that regulate chromatin structure at BDNF promoters, ChIP methods also will be used in Aim 2 to isolate transcription factors [TFs] bound to BDNF promoters. Further training in molecular biology, will be required in Aim 3 in order to use viral-mediated delivery of siRNAs to knock-down TFs that bind to BDNF promoters during ICC. Expression of ICC as well as altered histone acetylation and/or methylation will be examined following viral-mediated TF knock-down in order to demonstrate a causal association between DNA- protein interactions, chromatin remodeling, enhanced BDNF expression and ICC. Understanding how chromatin remodeling alters BDNF expression during ICC will contribute important insights into the emerging field of epigenetic addiction research and may provide novel drug targets aimed at reducing cocaine craving and relapse in human addicts.
These proposed experiments will investigate the molecular mechanisms (i.e., epigenetic/chromatin remodeling) that regulate mesolimbic brain-derived neurotrophic factor (BDNF) expression during the incubation of cocaine craving, an animal model of drug craving and relapse in human addicts. This proposal aims to identify the molecular substrates that regulate chromatin structure and transcription of BDNF promoter regions during the incubation of cocaine craving. Therefore, this proposal will provide insight into the epigenetic mechanisms underlying cocaine addiction as well as identify novel targets for treating drug craving and relapse.
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