Tod Kippin - US grants

[unreadable] DESCRIPTION (provided by applicant): Sex differences have been previously reported in preclinical and clinical studies of cocaine abuse. While relapse to cocaine use following abstinence is the most significant impediment in the treatment of dependence, limited attention has been given as to whether sex differences exist in relapse to cocaine seeking after prolonged abstinence. Consistent with clinical evidence, laboratory animal studies have demonstrated that there are sex differences in cocaine self-administration and in the reinstatement of cocaine-seeking behavior. Relative to males, females have been reported to exhibit higher levels of responding for cocaine, higher levels of extinction responding, higher levels of reinstatement following reexposure to small amounts of cocaine but either the same or lower levels reinstatement following exposure to cues associated with cocaine intake. Further, females show higher levels of initial and sensitized cocaine-induced locomotion than do males. Recent research has increasingly focused on time-dependent changes in the nervous system following demonstrations that cocaine-seeking increases during drug abstinence. This "incubation of craving" effect has also been observed in clinical populations and is thought to precipitate relapse to drug taking. Given the sex differences in other animal models of relapse vulnerability, it is likely that sex differences contribute to the neuroadaptations underlying the incubation of drug craving. Accordingly, the proposed project will investigate the time course of cocaine-seeking during abstinence from cocaine self-administration in male and female rats. It is predicted that females will exhibit enhanced incubation. These findings will further our understanding of the relation between sex differences and behavioral plasticity involved in drug addiction. These initial experiments will form the bases of subsequent studies examining the organizational and activational effects of gonadal hormones and the neuroendocrine bases of sex differences in time-dependent neuroadaptations. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): A hallmark of addiction is excessive drug-seeking behavior which is believed to be mediated by pathological changes in a number of brain structures, including the prefrontal cortex, involving drug-induced alterations in gene expression. Chromatin remodeling or epigenetic regulation is a key determinant of gene expression that has recently been implicated in drug-induced neuroplasticity. The present project will develop a collaborative effort been the Principal Investigator (Kippin), whose expertise is in behavioral neuroscience, and the co-Principal Investigator (Sun), whose expertise is in epigenetics, to explore chromatin remodeling produced during a rat cocaine self-administration model of addiction. Specifically, this study is based on a rat model of cocaine self-administration (via a i.v. catheter) with either short or prolonged daily access with the latter condition leading to a time-dependent escalation of cocaine intake and subsequent relapse vulnerability which is similar to the pattern observed in cocaine addiction. Based on the results of a high-throughput, genome-wide analysis of DNA methylation using a MeDIP-CHIP assay in the dorsal medial prefrontal cortex produced by prolonged access to cocaine self- administration, the present application will verify methylation in genes of interest, determine the consequences for expression of those genes (at mRNA and protein levels), determine changes in the epigenetic machinery produced by cocaine exposure, and determine the enduring nature of these changes across 2 months of cocaine withdrawal. The long-term goals of this project are to establish the utility of high-throughput DNA methylation and other techniques to identify molecular targets involved in addiction as well as establish a collaboration between our laboratories to map changes in chromatin remodeling (both DNA methylation and histone modifications) in neural circuits mediating motivational and cognitive processes that are disrupted in addiction. These studies will provide a more detailed understanding of the role of chromatin remodeling to the brain pathology associated with the addiction process. PUBLIC HEALTH RELEVANCE: Changes in gene expression are widely implicated in the pathological function of brain structures during the addiction processes. The present project will determine the contribution of chromatin remodeling, specifically DNA methylation, to gene expression changes within the prefrontal cortex that are produced in a rat model of excessive cocaine intake. These experiments will establish a framework for studying the long-term changes in genetic function at the chromatin modification level in addiction through the employment of high-throughput molecular techniques combined with diseases relevant behavioral models in order to inform our understanding of addiction-related brain pathology.

DESCRIPTION (provided by applicant): Cocaine addiction is a complex phenotype resulting from an interaction from genetic and environmental factors. The overall-arching rationale for this proposal is that specific polygenetic backgrounds interact with specific experiences to determine cocaine responsiveness making an individual more or less vulnerable to cocaine addiction. Our goal is to elucidate genetic factors that modulate the ability of early environmental experiences to alter adult responsiveness to cocaine. Extensive research has focused on delineating specific early (as well as adult) environmental conditions that increase cocaine responsiveness. Epidemiological data indicates broad-spectrum increases in neuropsychiatric disease for that are in utero during natural and man- made disaster. In animal studies, prenatal stress produces an adult phenotype comprising increased sensitivity to psychomotor stimulant effects of cocaine, greater cocaine intake during cocaine self-administration, and higher cocaine-seeking during extinction and reinstatement procedures suggesting that a history of early life stress produce greater vulnerability to cocaine addiction. Conversely, extensive research has also focused on determining which gene variants increase cocaine responsiveness. Clinical and familial studies indicate a substantial inheritance to cocaine addiction with minimal estimates indicating genetic variability can account for 30% of variability in addiction vulnerability across individuals. In animal studies, substantial differences between mouse strains have been observed in the behavioral and physiological effects of cocaine. Further, the mapping of the mouse genome along with the construction recombinant inbred mouse strain panels now allows quantitative analyses of the contribution of specific genetic loci to cocaine responsiveness. Conversely there is emerging evidence for gene-environment interactions in determining cocaine responsiveness, and, currently, a major impediment to our ability to predict individual cocaine responsiveness is the lack of systematic investigation of the interactions between genes and environment and determination of these factors will facilitate a priori determination of individuals at risk for cocaine addiction. Thus, it is now time to extend quantitative trait loci analyses by incorporating systematic investigation of gene-environment interactions, for e.g. determination of the specific genetic loci genes that facilitate or impede early environmental modulation of cocaine responsiveness. The overall goal of the present proposal is to provide an analysis of the early environmental modulation of genetic predisposition to addiction vulnerability employing a mouse model. Aim 1 will assess prenatal stress (PNS)-induced differences in cocaine responsiveness between two mouse strains that show distinct cocaine responsiveness (C57BL/6 and DABA/2J) and their F1 progeny. This will include assessment of strain x PNS shifts in the dose-response curve for not only the psychostimulant, but also the rewarding, properties of cocaine as well as responsiveness to mild psychological and physical stressors and neuroadaptations in these responses with repeated exposures. In order to more directly investigate the interaction between specific genetic factors (at the chromosomal loci level) and early environmental stress, Aim 2 will examine the impact of PNS on cocaine responsiveness in across a panel of recombinant inbred strains derived from C57BL/6 and DBA/2 parental lines followed by quantitative trait loci (QTL) analyses to allow determination which specific chromosomal loci are associated with PNS-induced changes in cocaine responsiveness. In addition, control data for these responses will be utilized to replicate and extend previous RI-QTL studies. Finally, multivariant analyses will be performed on the genetic and phenotypic variables in order to determine inter-relatedness of these variables in attempt to define cluster factors that control cocaine responsiveness. These studies will provide novel analyses of gene-environment interactions by determining the specific genetic mediators of PNS-induced changes in cocaine responsiveness. PUBLIC HEALTH RELEVANCE: There are marked individual differences in vulnerability to drug addiction which result from complex genetic and environmental interactions, however, there is limited research examining such interactions. The proposed research will examine the interaction between two model systems that examine the contribution of genetic variation (recombinant inbred mouse lines) and the contribution of adverse early environmental conditions (prenatal stress). The goal of this project is to identify genetic factors, at the level of specific chromosomal loci, that predispose individuals to the dramatic developmental changes produced by early stress resulting in high addiction vulnerability and these findings will set the foundation for a detailed understanding of the intricate interactions between genome and environment in determination of this phenotype.

Summary. While the established electrochemical and microdialysis-based techniques for measuring drugs and neurotransmitters in the brain have unimpeachably contributed to our understanding of brain function, they are not without limitations. For example, when the same dose of cocaine is infused over 5 s versus 90 s the behavioral, metabolic, and even genetic outcomes vary dramatically, suggesting that the 2 min resolution of the most highly resolved of prior in-brain cocaine measurements are poorly matched to timescale of the drug's psychobiology. More generally, no drugs and only a small number of neurotransmitters have been measured to date in the brain with the most behaviorally relevant seconds time resolution. In response, our vision is to adapt electrochemical aptamer-based (E-AB) sensors, an in-vivo measurement platform that does not rely on the chemical or enzymatic reactivity of its targets (thus ensuring generality), to the problem of simultaneously monitoring drugs of abuse and the neurotransmitters they modulate in situ in the brains of freely moving, normally behaving rodents. To this end, we have already demonstrated feasibility by performing the high frequency, multi-hour measurement of more than a half dozen molecules in the blood and brains of live rats. Leveraging these preliminary results we propose here the adaptation of E-AB sensors to the problem of studying of brain chemistry. If successful, the proposed work will greatly expand the number of neurochemically relevant molecules that can be measured in real time and with second resolution in the living brain, thus creating a new window into brain chemistry that provides unique capabilities for closed-loop study and intervention.